Selective blockade of substance P or neurokinin A receptors reduces the expression of c-fos in trigeminal subnucleus caudalis after corneal stimulation in the rat

Stimulation of the cornea activates neurons in two distinct regions of the spinal trigeminal nucleus: at the transition between trigeminal subnucleus interpolaris and subnucleus caudalis and at the transition between trigeminal subnucleus caudalis and the upper cervical spinal cord as estimated by expression of the immediate early gene, c-fos. To determine if receptors for substance P or neurokinin A, neurokinin 1 and neurokinin 2 receptors, respectively, contribute to the production of Fos-positive neurons in these brainstem regions, receptor-selective antagonists were given intracerebroventricularly 15 min prior to stimulation of the cornea in anesthetized rats. The number of Fos-positive neurons produced in superficial laminae at the trigeminal subnucleus caudalis/cervical cord transition by application of the selective small fiber excitant, mustard oil, to the corneal surface was reduced by the neurokinin 1 receptor antagonist, CP99,994 (5-100 nmol, i.c.v.) and the neurokinin 2 receptor antagonist, MEN10,376 (0.01-1.0 nmol, i.c.v.). Combined pretreatment with CP99,994 and the competitive N-methyl-D-aspartate receptor antagonist, CPP, caused a greater reduction in c-fos expression at the subnucleus caudalis/cervical cord transition than after either drug alone suggesting interaction between receptors for glutamate and substance P. Tachykinin receptor antagonists did not reduce the number of Fos-positive neurons produced at the subnucleus interpolaris/subnucleus caudalis transition. The elevation in plasma concentration of adrenocorticotropin, but not the increases in arterial pressure or heart rate, evoked by corneal stimulation was prevented by pretreatment with CP99,994 or MEN10,376 at doses lower than those needed to reduce c-fos expression. The results indicate that receptors for substance P and neurokinin A contribute to the transmission of sensory input from corneal nociceptors to brainstem neurons in trigeminal subnucleus caudalis and to increased activity of the hypothalamo-pituitary axis that accompanies acute stimulation of the cornea.     

Activation of spinal N-methyl-D-aspartate or neurokinin receptors induces long-term potentiation of spinal C-fibre-evoked potentials

The use-dependent increase in synaptic strength between primary afferent C-fibres and second-order neurons in superficial spinal dorsal horn may be an important cellular mechanism underlying central hyperalgesia. This long-term potentiation can be blocked by antagonists of the N-methyl-D-aspartate subtype of glutamate receptor, the neurokinin 1 or the neurokinin 2 receptor. We have tested here whether activation of these receptors by superfusion of the spinal cord with corresponding agonists in the absence of presynaptic activity is sufficient to induce long-term potentiation. In urethane anaesthetized rats C-fibre-evoked field potentials were elicited in superficial laminae of lumbar spinal cord by electrical stimulation of the sciatic nerve. In rats with intact spinal cord, controlled superfusion of the spinal cord at recording segments for 60 min with N-methyl-D-aspartate, substance P or neurokinin A never induced long-term potentiation. Spinal superfusion with a mixture of N-methyl-D-aspartate, substance P and neurokinin A also failed to induce long-term potentiation in four rats tested. In spinalized rats, however, long-term potentiation was induced by either N-methyl-D-aspartate (at 10 microM, to 173 +/- 16% of control) substance P (at 10 microM, to 176 +/- 13% of control) or by neurokinin A (at 1 microM, to 198 +/- .20% of control). The induction of long-term potentiation by N-methyl-D-aspartate, substance P or neurokinin A was blocked by intravenous application of the receptor antagonists dizocilpine maleate (0.5 mg/kg), RP67580 (2 mg/kg) or SR48968 (0.2 mg/kg), respectively. Thus, activation of N-methyl-D-aspartate or neurokinin receptors may induce long-lasting plastic changes in synaptic transmission in afferent C-fibres and this effect may be prevented by tonic descending inhibition.     

Tachykinins alter inositol phosphate formation, but not cyclic AMP levels, in primary cultures of neonatal rat spinal neurons through activation of neurokinin receptors

The naturally occurring tachykinins, substance P, neurokinin A and neurokinin B, induce the formation of inositol phosphates or cAMP in a variety of tissues but their effects on neurons have not been resolved. We used primary cultures of neonatal rat spinal cord to determine whether neurokinin receptors mediate changes in these second messengers in spinal neurons. We found that substance P, neurokinin A and neurokinin B induced the formation of inositol phosphates in a concentration-dependent manner with similar potencies (EC50S: 3.6, 5.7 and 21.3 nM, respectively), but at concentrations tested (0.1-1.0 microM) these peptides had no effect on cAMP levels. All three tachykinins induced the formation of inositol phosphates predominately by activation of neurokinin1 receptors. CP-96,345 and WIN 51,708, neurokinin1 receptor antagonists, attenuated the response to substance P, neurokinin A and neurokinin B. GR 103,537, a neurokinin2 receptor antagonist, had no effect on the responses induced by any of the tachykinins. Furthermore, the selective neurokinin1 receptor agonist, GR-73632, induced the formation of inositol phosphates in a concentration-dependent manner, whereas the selective neurokinin2 receptor agonist, GR-64349, generated inositol phosphates only at the highest concentration tested (10 microM). Senktide, a neurokinin3 receptor agonist, did not induce the formation of inositol phosphates at any of the concentrations tested (0.01-10 microM). Inositol phosphate formation appeared to be due to a direct effect of the tachykinins on neuronal neurokinin1 receptors. These results suggest that biological responses in spinal neurons following activation of neurokinin1 receptors are mediated mainly by the hydrolysis of phosphoinositol 4,5-bisphosphate to form inositol 1,4,5-trisphosphate and diacylglycerol. It remains to be determined which of these second messengers mediates the increased neuronal excitability and depolarization that occurs in response to substance P.     

Release of immunoreactive substance P in the trigeminal brain stem nuclear complex evoked by chemical stimulation of the nasal mucosa and the dura mater encephali--a study with antibody microprobes

In order to study a possible involvement of substance P in the processing of chemonociceptive input from the nasal mucosa and the dura mater encephali in the spinal trigeminal, the release of immunoreactive substance P was measured in the trigeminal brain stem nuclear complex in anaesthetized rats. Microprobes coated with antibody to substance P were inserted into the lateral area of the brain stem up to 1 mm posterior to the obex corresponding to the trigeminal subnucleus caudalis. When the nasal mucosa was stimulated by topical administration of mustard oil (1% and 5%) into the nostrils, immunoreactive substance P was mainly detected in the dorsal region of the trigeminal brain stem nuclear complex with a maximum in the superficial gray matter. When the dura mater encephali was stimulated by topical administration of Tyrode's solution (pH 6.2), immunoreactive substance P was mainly released in the ventral region of the trigeminal brain stem nuclear complex; with pH 5.5 the release was more diffuse extending from the ventral to the dorsal part of the spinal trigeminal nucleus. Release was maximal rather after than during the administration of the stimuli, and it considerably outlasted the stimulation periods. These data suggest that substance P plays an important role in the processing of chemonociceptive inputs from the nasal mucosa and the dura mater encephali in the trigeminal brain stem nuclear complex. Substance P may be important, therefore, in the generation of those headaches that are caused by affections of the nasal mucosa and the dura mater encephali. Since enhanced levels of immunoreactive substance P were present for considerable time periods beyond the administration of the stimuli, substance P and neurokinin-1 receptors may be involved in long-lasting neuronal events following noxious stimulation.     

The effects of GnRH and adrenergic agents on PRL and beta-endorphin secretion by porcine pituitary cells in vitro

The direct effects of alpha- and beta-adrenergic agents on PRL and beta-endorphin (beta-END) secretion in vitro by porcine pituitary cells have been investigated. Pituitary glands were obtained from mature gilts, which were ovariectomised (OVX) one month before slaughter. Ovariectomised gilts, assigned to four groups, were primed with: (1) vehicle (OVX); (2) and (3) oestradiol benzoate (EB; 2.5 mg/100 kg b.w.) at 30-36 h (OVX+EB I) and 60-66 h (OVX+EB II) before slaughter, respectively; and (4) progesterone (P4; 120 mg/100 kg b.w.) for 5 consecutive days before slaughter (OVX+P4). Isolated anterior pituitary cells were submitted to 3.5 h incubation in the presence of GnRH, alpha- and beta-adrenergic agonists [phenylephrine (PHEN) and isoproterenol (ISOP), respectively], or alpha- and beta-adrenergic blockers [phentolamine (PHENT) and propranolol (PROP), respectively]. The culture media were assayed for PRL (exp. I) and beta-endorphin-like immunoreactivity (beta-END-LI) (experiment II). In experiment I, GnRH did not influence PRL release by pituitary cells in all experimental groups. Some of tested doses of adrenergic agonists, PHEN and ISOP, increased PRL release from pituitary cells of OVX gilts, but not from those of OVX+EB I animals. In the OVX+EB II group, PHEN alone, but ISOP with PROP, potentiated PRL secretion by the cells. In OVX+P4 animals, PHEN alone or in combination with PHENT and also ISOP alone or with PROP enhanced PRL output from the cells. In experiment II, addition of GnRH increased beta-END-LI release from pituitary cells only in the OVX+EB II group. PHEN and PHENT potentiated beta-END-LI secretion by pituitary cells in OVX+EB II and OVX+P4 groups, while ISOP and PROP increased beta-END-LI secretion by the cells of OVX and OVX+EB II animals. In turn, in the OVX+EB I group, effect of PHENT and PROP on PRL secretion by pituitary cells was inhibitory. In conclusion, our results suggest that adrenergic agents can modulate PRL and beta-END secretion by porcine pituitary cells in a manner dependent on the hormonal status of gilts.     

Accuracy of automated finger blood pressure devices

Substance P and glial fibrillary acidic protein (GFAP) immunohistochemistry was applied to the medulla of neonatal infants who died of sudden infant death syndrome (SIDS). A quantitative analysis of cells demonstrating immunoreactivity to GFAP and substance P in 15 neonatal SIDS cases revealed increased GFAP immunoreactivity in the reticular formation, the dorsal vagal nucleus, and the solitary nucleus and an increase in substance P immunoreactivity in the spinal trigeminal nucleus and the solitary nucleus as compared with that in age-matched controls. GFAP immunopositivity suggests astrogliosis which implies a pathologic insult to neurons in the area of astrogliosis. The failure of neurons in these sites to show enhanced substance P immunopositivity may indirectly indicate altered neurons. Further study of prenatal events may be of importance in clarifying the pathogenesis of neonatal SIDS.     

Short-term regulation of gonadotropin subunit mRNA levels by estrogen: studies in the hypothalamo-pituitary intact and hypothalamo-pituitary disconnected ewe

In this study the levels of mRNA for the pituitary gonadotropin hormone subunits luteinizing hormone beta (LHbeta), follicle stimulating hormone beta (FSHbeta) and the common alpha-subunit were assessed during the acute feedback stages of estradiol benzoate (EB) action in ovariectomized (OVX) ewes with and without hypothalamo-pituitary disconnection (HPD). In OVX/HPD ewes maintained on hourly pulses of 250 micrograms of gonadotropin-releasing hormone (GnRH) a single i.m. injection of EB in oil caused a biphasic (decrease and then increase) change in plasma LH levels and a monophasic decrease in FSH levels. There was a decrease in pituitary alpha-subunit and FSHbeta mRNA levels during the acute negative (8 h post EB) and through the positive feedback (20 h post EB) stages of the response. No significant change was seen in LHbeta mRNA levels following treatment with EB. In hypothalamic-pituitary intact OVX ewes the same EB treatment as above caused a biphasic change in LH secretion with the positive feedback component being much greater than in GnRH-pulsed OVX-HPD ewes. The levels of mRNA for all three gonadotropin subunits were reduced by 8 h after EB injections and remained low throughout the positive feedback period. These data suggest that the LH surge in this experimental model does not require an increase in LHB mRNA levels. Furthermore, the fall in LHbeta subunit mRNA seen after estrogen injection of OVX ewes is most likely due to an effect of estrogen to decrease GnRH secretion, since pulsatile GnRH replacement prevents this effect. These data also show that estrogen feedback can effect rapid alterations in pituitary gonadotropin subunit mRNA levels. Short-term changes in FSHbeta mRNA are reflected in changes in FSH secretion; the same is not true for LH.     

Preferential synaptic relationships between substance P-immunoreactive boutons and neurokinin 1 receptor sites in the rat spinal cord

Substance P plays an important role in the transmission of pain-related information in the dorsal horn of the spinal cord. Recent immunocytochemical studies have shown a mismatch between the distribution of substance P and its receptor in the superficial laminae of the dorsal horn. Because such a mismatch was not observed by using classical radioligand binding studies, we decided to investigate further the issue of the relationship between substance P and its receptor by using an antibody raised against a portion of the carboxyl terminal of the neurokinin 1 receptor and a bispecific monoclonal antibodies against substance P and horseradish peroxidase. Light microscopy revealed a good correlation between the distributions of substance P and the neurokinin 1 receptor, both being localized with highest densities in lamina I and outer lamina II of the spinal dorsal horn. An ultrastructural double-labeling study, combining preembedding immunogold with enzyme-based immunocytochemistry, showed that most neurokinin 1 receptor immunoreactive dendrites were apposed by substance P containing boutons. A detailed quantitative analysis revealed that neurokinin 1 receptor immunoreactive dendrites received more appositions and synapses from substance P immunoreactive terminals than those not expressing the neurokinin 1 receptor. Such preferential innervation by substance P occurred in all superficial dorsal horn laminae even though neurokinin 1 receptor immunoreactive dendrites were a minority of the total number of dendritic profiles in the above laminae. These results suggest that, contrary to the belief that neuropeptides act in a diffuse manner at a considerable distance from their sites of release, substance P should act on profiles expressing the neurokinin 1 receptor at a short distance from its site of release.     

Hypothalamus-pituitary-ovarian axis in cyclic rats lacking progesterone actions

Antagonizing diestrous progesterone actions in cyclic rats by s.c. injections of the antiprogesterone RU486 (2 mg twice a day from metestrus through proestrus) increased LH and decreased FSH basal serum concentrations. Ovariectomy at metestrus (0800 h) increased serum levels of both gonadotropins in controls and reversed the RU486-induced dissociation of basal gonadotropin secretion. RU486-dissociated gonadotropin secretion is also dependent upon LHRH, since treatment (s.c.) with 1 mg GnRH antagonist (ORG 30276) twice a day on metestrus and diestrus completely prevented both the RU486-induced increase in LH and the decrease in FSH serum concentrations. The LHRH content in the medial basal hypothalamus and median eminence increased on proestrous morning in RU486-treated rats. The LH pituitary response to an exogenous i.v. bolus of 25 ng LHRH (Peninsula 7201; Peninsula Laboratory, Inc., Merseyside, UK) at 1700 h on diestrus was enhanced in rats treated with RU486. No differences in pituitary FSH response were noted with respect to oil-injected rats. The pituitary content of both gonadotropins decreased in RU486-treated rats on proestrous morning. All these effects due to RU486 in cyclic rats were reversed by ovariectomy. Testosterone serum levels increased significantly from diestrus onward, and the estradiol concentration increased on proestrous morning in RU486-treated rats. Ovariectomy as well as LHRH antagonist treatment eliminated the effects of RU486 on ovarian steroid production. Moreover, antiestrogen tamoxifen treatment reversed RU486-dissociated gonadotropin secretion, while antiandrogen flutamide treatment had no effect. The results of this experiment have confirmed previous findings that RU486 treatment dissociates basal gonadotropin secretion in cyclic rats. In addition, the present results show that: (1) this effect of RU486 is not due to a direct effect of this compound or to the blockade of progesterone action at a central level; (2) the effect of RU486 on pituitary gonadotropin secretion depends on ovarian substances other than progesterone and LHRH, since it is reversed by ovariectomy and completely abolished by LHRH antagonist treatment; (3) the reduction in FSH serum levels in rats treated with RU486 seems to be exerted by inhibin and estradiol at the pituitary level by reducing FSH synthesis and secretion; and (4) the hypersecretion of LH in rats treated with RU486, as compared to that resulting from ovariectomy, seems to be the consequence of, first, a lack of progesterone inhibitory action on LH secretion, and, second, an inappropriate feedback system involving increased hypothalamic LHRH activity and pituitary sensitivity to LHRH of moderately high levels of estradiol in the presence of abnormally high levels of testosterone.     

Trigeminal nuclear complex of the ferret: anatomical and immunohistochemical studies

In order to establish the ferret as an animal model for studies of trigeminal pain, we describe the cytoarchitecture and neurochemistry of the trigeminal nuclear complex in the ferret and compare them to those of the cat and rat. The complex was divided as previously described, but the ferret differed in the extent of the nuclear boundaries. The neuroanatomical istribution of substance P-, calcitonin gene-related peptide-, galanin-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and neurotensin-immunoreactivity was determined throughout the rostrocaudal extent of the complex. In subnucleus caudalis, substance P-, calcitonin gene-related peptide-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and galanin-immunoreactivity was densest in laminae I and II. In subnucleus interpolaris, immunoreactivity for all the above neurochemicals was most dense along the lateral border and the ventral third of the caudal part of the subnucleus. Enkephalin-immunoreactive cell bodies were present in subnucleus caudalis and interpolaris. In subnucleus oralis, labelling for substance P, calcitonin gene-related peptide, galanin, enkephalin, and serotonin was most prominent in the dorsomedial part of the subnucleus. Somatostatin-immunoreactive cell bodies were distributed throughout the spinal nucleus. Labelling of serotonin, substance P, calcitonin gene-related peptide, galanin, enkephalin, and somatostatin was present in the main sensory nucleus. The motor nucleus contained fibers immunoreactive for substance P, enkephalin, serotonin and neuropeptide Y, and cell bodies immunoreactive for calcitonin gene-related peptide. The majority of neurotensin-immunoreactivity was found at the level of subnucleus caudalis, where it was densest in the trigeminal extension of the lateral cervical nucleus. The distribution of peptides in this species throughout the spinal nucleus is consistent with the notion that all the subnuclei may be involved in the processing of nociceptive inputs.     

Distribution of trigeminohypothalamic and spinohypothalamic tract neurons displaying substance P receptor-like immunoreactivity in the rat

Primary afferent neurons containing substance P (SP) are apparently implicated in the transmission of noxious information from the periphery to the central nervous system, and SP released from primary afferent neurons acts on second-order neurons with the SP receptor (SPR). In the rat, nociceptive information reached the hypothalamus not only through indirect pathways but also directly through trigeminohypothalamic and spinohypothalamic pathways. Thus, in the present study, the distribution pattern of trigeminohypothalamic and spinohypothalamic tract neurons showing SPR-like immunoreactivity (SPR-LI) was examined in the rat by a retrograde tract-tracing method combined with immunofluorescence histochemistry for SPR. A substantial number of trigeminal and spinal neurons with SPR-LI were retrogradely labeled with Fluoro-Gold (FG) injected into the hypothalamic regions. These neurons were distributed mainly in lamina I of the medullary and spinal dorsal horns, lateral spinal nucleus, regions around the central canal of the spinal cord, and the lateral aspect of the deep part of the spinal dorsal horn. A number of SPR-LI neurons in the spinal parasympathetic nucleus were labeled with FG injected into the area around the paraventricular hypothalamic nucleus. Some SPR-LI neurons in the lateral spinal nucleus and the lateral aspect of the deep part of the spinal dorsal horn were also labeled with FG injected into the septal region. On the basis of the distribution areas of SPR-LI trigeminal and spinal neurons projecting to the hypothalamic and septal regions, it is likely that these neurons are involved in the transmission of somatic and/or visceral noxious information.     

Mechanism of LH release with synthetic LH-RH (author's transl)

The purpose of this study is to examine the effect of LH-RH on LH release in the baboon. Fifteen female baboons having the normal menstrual cycle were used for this study. On hundred mug of synthetic LH-RH was injected subcutaneously in both the early follicular phase and the early luteal phase. For control purposes, 1 ml of saline was injected subcutaneously in the luteal phase. Blood samples were collected by femoral vein puncture with light anesthesia under prearranged schedule and were assayed for LH-RH, LH, estrogen and progestin. The plasma level of LH-RH reached a maximum within 4 minutes after s.c. injection of 100 mug LH-RH, decreased sharply at first, and then slowly later. Fast and slow disappearance components (t1/2 = 4.7 min., 37.1 min. respectively) were observed. In the baboon given LH-RH during the luteal phase, peaks in plasma levels of LH were observed within 30 minutes and within 90 to 150 minutes after injection. A lesser pituitary response to LH-RH for LH release occurred during the follicular phase. The first peak of LH was well-correlated with the peak of plasma LH-RH but the later elevations of LH (observed within 90 to 150 minutes after LH-RH injection) were not necessarily related to the plasma level of immunoassayable LH-RH. Elevation of plasma levels of estrogen and progestin was observed wtihin 45 minutes after LH-RH injection. In saline control, the plasma level of LH was not elevated; however, plasma levels of estrogen and progestin were increased within 45 minutes after saline injection. Later elevation of plasma LH observed between 90 and 150 minutes after LH-RH injection may be due to administered LH-RH in cooperation with elevated levels of plasma estrogen and progestin. To pursue this problem, injections of estrogen and/or progesterone were performed during the early follicular phase. Injection of 600 mug of estrodiol benzoate (EB) for 3 days caused an elevation of plasma level of LH and enhanced pituitary LH responsiveness to LH-RH for LH release; however, injection of 100 mug EB for 3 days showed less effect on LH release. Injection of 10 mg of progesterone for 3 days also caused an elevation of plasma level of LH and enhanced the pituitary responsiveness to LH-RH release. Injection of both 600 mug EB and 10 mg progesterone for 3 days did not elevate plasma level of LH and showed no significant effect of LH-RH on LH release as compared to control. These results suggest that elevated levels of circulating estrogen and progestin may determine LH release and exposure of the pituitary to LH-RH is necessary for LH release. In dose and time schedule used in this study, it is inferred that estrogen and progesterone may exert their direct effect to hypothalamus on endogenous LH-RH secretion and also may exert their effect on pituitary gonadotrophs to change the sensitivity to LH-RH, i.e. these steroid hormones may be major factors in the control of gonadotropin release in the baboon.     

Tachykinins, sensory nerves, and asthma--an overview

Tachykinin peptides, substance P (SP) and neurokinin A (NKA), are released from airway sensory nerves upon exposure to irritant chemicals and endogenous agents including bradykinin, prostaglandins, histamine, and protons, The released neuropeptides are potent inducers of a cascade of responses, including vasodilatation, mucus secretion, plasma protein extravasation, leukocyte adhesion--activation, and bronchoconstriction. Neurokinin 1 receptors (preferably activated by SP) seem to be most important for inflammatory actions, while neurokinin 2 receptors (preferably activated by NKA) mediate bronchoconstriction. Species differences exist whereby rat and guinea-pig have a more developed neurogenic inflammation response than normal human airways. However, disease states such as inflammation or viral infections lead to enhanced peptide synthesis and (or) increased sensory nerve excitability. Together with increased neurokinin 1 receptor synthesis and loss of major tachykinin-degrading enzymes such as neutral endopeptidase in airway inflammation, this suggests that recently developed, orally active nonpeptide neurokinin receptor antagonists could have a therapeutic potential in asthmatic patients.     

An acid sensing ion channel (ASIC) localizes to small primary afferent neurons in rats

The acid sensing ion channel (ASIC) identified in rat brain and spinal cord is potentially involved in the transmission of acid-induced nociception. We have developed polyclonal antisera against ASIC, and used them to screen rat brain and spinal cord using immunocytochemistry. ASIC-immunoreactivity (-ir) is present in but not limited to the superficial dorsal horn, the dorsal root ganglia (DRG) and the spinal trigeminal nucleus, as well as peripheral nerve fibers. These observations, combined with the disappearance of ASIC-ir following dorsal rhizotomy, suggest localization of ASIC to primary afferents. DRG ASIC-ir co-localizes with substance P (SP) and calcitonin gene-related peptide (CGRP)-ir in small capsaicin-sensitive cell bodies, suggesting that ASIC is poised to play a role in the transduction of noxious stimuli.     

Descending projections from the spinal and mesencephalic nuclei of the trigeminal nerve to the spinal cord in the cat. A study with the horseradish peroxidase technique

Descending projections from the spinal (Vsp) and the mesencephalic nuclei (Vme) of the trigeminal nerve to the spinal cord were studied by means of the retrograde horseradish peroxidase technique in the cat. The number of labeled neurons was largest in the case of high cervical injections and decreased as the injections were placed caudally. Small laminae III and IV neurons of the nucleus caudalis (Vc) were labeled ipsilaterally following injections placed as caudally as the middle cervical segments (C4-C5). Lamina I (marginal) neurons of the Vc were labeled ipsilaterally after injections at the middle thoracic level (T6) but those of C1 were labeled after lumbar injections (L3). Lamina V neurons of C1 and the medullary counterparts were labeled bilaterally after injections placed caudally to thoracic segments. A few small neurons were labeled in the ipsilateral nucleus interpolaris (Vi) after injections placed as caudally as the middle cervical segments (C6). Among the subdivisions of the Vsp, the labeled neurons were most numerous in the nucleus oralis (Vo). They were medium-sized and large, and appeared bilaterally, with an ipsilateral predominance at the level of the superior olive. The great majority projected to the cervical segments but a few also projected to the lower cervical to the thoracic segments (C8-T9). Neurons of the Vme projected ipsilaterally to the upper cervical segments (C1-C3). No projections were found from the principal sensory nucleus. The present study suggests that the trigeminospinal projections of the Vsp and the Vme are composed of various cells of origin and thereby subserve not only the trigeminospinal reflex but other unknown functions.     

Inhibition of trigeminal neurons by intravenous administration of the serotonin (5HT)1B/D receptor agonist zolmitriptan (311C90): are brain stem sites therapeutic target in migraine?

Migraine is a common and debilitating condition. Its treatment has received considerable attention in recent times with the introduction into clinical use of the serotonin (5HT)1B/D-like agonist sumatriptan. It is known from human studies that the intracranial blood vessels and dura mater are important pain-sensitive structures since mechanical or electrical stimulation of these vessels, such as the superior sagittal sinus, causes pain. We have developed a model of craniovascular pain by stimulating the superior sagittal sinus and monitoring trigeminal neuronal activity using electrophysiological techniques. In this study we determined the effect of intravenous administration of the novel anti-migraine compound zolmitriptan (311C90) upon evoked neuronal activity in trigeminal neurons. Nine adult cats were anaesthetised with alpha-chloralose (60 mg/kg, i.p.; 20 mg/kg, i.v., 2-hourly) with all surgery being conducted under halothane (1-3%). The superior sagittal sinus was isolated for electrical stimulation. Recordings were made from caudal trigeminal neurons at the C2 level of the cervical spinal cord with tungsten-in-glass microelectrodes. Signals were amplified and analysed by a custom-written program that enabled software filtering and extraction of both evoked potential and single cell data. Data were collected before and after administration of zolmitriptan. Electrical stimulation of the superior sagittal sinus resulted in activation of neuronal elements within the trigeminal nucleus that could be monitored as single unit activity or as evoked potentials, the latter reflecting both primary afferent and trigeminal cell body activity. The evoked potential recorded from the trigeminal nucleus was 207 +/- 14 microV and was reduced by zolmitriptan (100 micrograms/kg, i.v.) to a mean of 98 +/- 17 microV. Similarly, the probability of firing for trigeminal neurons was reduced from a control level of 0.63 +/- 0.1 to 0.13 +/- 0.05 after a dose of 100 micrograms/kg intravenously. These effects were dose-dependent and were significantly different from the effect of vehicle (P < 0.05). These data demonstrate that systemically administered zolmitriptan can inhibit evoked trigeminovascular activity within the trigeminal nucleus. This inhibition of trigeminal activity may play a role in the anti-migraine actions of this compound and offers the prospect of a third pathophysiologically consistent target site for anti-migraine drug effects.     

Anxiolytic-like action of neurokinin substance P administered systemically or into the nucleus basalis magnocellularis region

There is evidence that the neurokinin substance P plays a role in neural mechanisms governing learning and reinforcement. Reinforcing and memory-promoting effects of substance P were found after it was injected into several parts of the brain and intraperitoneally. With regard to the close link between anxiety and memory processes for negative reinforcement learning, the aim of the present study was to gauge the effect of substance P on anxiety-related behaviors in the rat elevated plus-maze and social interaction test. Substance P was tested at injection sites where the neurokinin has been shown to promote learning and to serve as a reinforcer, namely in the periphery (after i.p. administration) and after injection into the nucleus basalis magnocellularis region. When administered i.p., substance P had a biphasic dose-response effect on behavior in the plus-maze with an anxiolytic-like action at 50 microg/kg and an anxiogenic-like one at 500 microg/kg. After unilateral microinjection into the nucleus basalis magnocellularis region, substance P (1 ng) was found to exert anxiolytic-like effects, because substance P-treated rats spent more time on the open arms of the plus-maze and showed an increase in time spent in social interaction. Furthermore, the anxiolytic effects of intrabasalis substance P were sequence-specific since injection of a compound with the inverse amino acid sequence of substance P (0.1 to 100 ng) did not influence anxiety parameters. These results show that substance P has anxiolytic-like properties in addition to its known promnestic and reinforcing effects, supporting the hypothesis of a close relationship between anxiety, memory and reinforcement processes.     

Descending neural projections to the spinal cord in the channel catfish, Ictalurus punctatus

Retrograde transport of horseradish peroxidase was used to determine the descending projections to the spinal cord in an otophysan fish, the channel catfish, Ictalurus punctatus. The majority of cells projecting to the spinal cord are located in the reticular formation, which is organized into rhombomeric segments. Vestibulospinal neurons are located in the descending, magnocellular, and tangential octaval nuclei, as well as in the medial octavolateralis nucleus of the lateral line system. Cells in the facial lobe project to the spinal cord. Additionally, axons of cells of the trigeminal system and the nucleus of the lateral lemniscus project caudally into the spinal cord. In the midbrain, descending spinal projections arise from cells of the medial longitudinal fasciculus and the red nucleus. More rostrally, cells of the ventrolateral thalamus, dorsal periventricular hypothalamus, central pretectal and magnocellular preoptic nuclei also project to the cord. The results of this study indicate that there are a number of homologies in the descending systems of bony fishes and other vertebrate taxa, including tetrapods. We also provide further evidence that a red nucleus is present in the brains of bony fishes and is therefore a primitive vertebrate character antedating the evolution of tetrapods.     

Cervical epidural steroid injection with intrinsic spinal cord damage. Two case reports

STUDY DESIGN: Intrinsic cervical spinal cord damage represents the serious and permanent complications that can occur if cervical epidural steroid injections are administered while the patient is sedated. Two case reports are presented. OBJECTIVES: To draw attention to the dangerous consequences that can arise from sedating a patient before administering a cervical epidural steroid injection. SUMMARY OF BACKGROUND DATA: Reported complications of cervical epidural steroid injections have been minor and infrequent. No reports of intrinsic cervical cord damage could be found in a comprehensive English language literature search. METHODS: Two case reports of permanent intrinsic cervical cord damage in patients who had been administered cervical epidural steroid injections while under intravenous sedation are presented. Magnetic resonance imaging was performed before and after the administration of cervical epidural steroid injections. Each patient had herniated nucleus pulposus before they received cervical epidural steroid injections and intrinsic cord damage on postinjection magnetic resonance images. RESULTS: Both patients developed increased pain and neurologic symptoms within 24 hours of injection. To date, these symptoms appear to be permanent. However, Patient 1 had pain relief in her right arm and shoulder after undergoing a microdiscectomy, but pain was still persistent in her left leg, and she has developed a positive Lhermitte's sign. CONCLUSION: These case reports indicate fluoroscopic guidance will not insure or prevent intrathecal perforation or spinal cord penetration during the administration of cervical epidural steroid injections. In addition, although intravenous sedations during cervical epidural steroid injections have been used numerous times without reported complications, it appears intravenous sedation in these two cases resulted in the inability of the patient to experience the expected pain and paresthesias at the time of spinal cord irritation. Therefore, the authors conclude that the patient should be fully awake during the administration of cervical epidural steroid injections, with only local anesthetic in the skin used for analgesia.     

Endomorphin-2 is an endogenous opioid in primary sensory afferent fibers

Evidence is presented that the recently discovered endogenous mu-selective agonist, endomorphin-2, is localized in primary sensory afferents. Endomorphin-2-like immunoreactivity was found to be colocalized in a subset of substance P- and mu opiate receptor-containing fibers in the superficial laminae of the spinal cord and spinal trigeminal nucleus. Disruption of primary sensory afferents by mechanical (deafferentation by dorsal rhizotomy) or chemical (exposure to the primary afferent neurotoxin, capsaicin) methods virtually abolished endomorphin-2-like immunoreactivity in the dorsal horn. These results indicate that endomorphin-2 is present in primary afferent fibers where it can serve as the endogenous ligand for pre- and postsynaptic mu receptors and as a major modulator of pain perception.