Differential expression of Fos protein after transection of the rat infraorbital nerve in the trigeminal nucleus caudalis

To determine the effects of nerve injury on Fos expression, temporal and spatial distributions of Fos-positive neurons in the trigeminal nucleus caudalis were examined after tissue injury for isolation of the infraorbital nerve as controls and transection of this nerve as well as noxious chemical stimulation by formalin injection in adult rats. Fos immunoreactivity was markedly elevated in laminae I and II of the only ipsilateral nucleus caudalis 2 h after these surgical procedures and noxious chemical stimulation. The distributions of Fos-positive neurons were restricted rostro-caudally following formalin injection and tissue injury compared to transection of the infraorbital nerve. One day after tissue injury and nerve transection, however, Fos-positive neurons were distributed bilaterally in laminae III and IV extending rostro-caudally and medio-laterally in this nucleus, and this persisted over the 2-week study period. The number of Fos-positive neurons in the side ipsilateral to nerve transection was markedly less than that in the contralateral side whereas positive neurons in the tissue injured rats were distributed symmetrically along the rostro-caudal axis. There was no difference in the contralateral sides between nerve transection and tissue injury groups. The rostro-caudal level showing reduction in Fos expression corresponded roughly to the sites of central termination of the injured nerve in this nucleus, suggesting a role for the primary afferents in the reduction of Fos expression in laminae III and IV neurons of the ipsilateral nucleus caudalis.     

Morphine administered in the substantia gelatinosa of the spinal trigeminal nucleus caudalis inhibits nociceptive activities in the spinal trigeminal nucleus oralis

The present study investigates the effects of morphine microinjection into the spinal trigeminal nucleus caudalis (Sp5C) or the spinal trigeminal nucleus oralis (Sp5O) on C-fiber-evoked activities of Sp5O convergent neurons, after supramaximal percutaneous electrical stimulation in halothane-anesthetized rats. When it was microinjected into the Sp5O, morphine (2.5 microg in 0. 25 microl) never depressed the C-fiber-evoked responses of Sp5O convergent neurons (n = 13), whereas these neurons were responsive to the inhibitory effects of systemic morphine (6 mg/kg, i.v.) in a naloxone-reversible manner. On the contrary, morphine microinjected into the Sp5C produced a naloxone-reversible inhibition of the C-fiber-evoked responses of Sp5O neurons (n = 14). The magnitude and the time course of this effect varied according to the location of the injection sites. After microinjection into the superficial laminae (n = 7), a strong depressive effect of morphine (7 +/- 5% of control) on the C-fiber-evoked responses was apparent as soon as 5 min after the injection and could always be reversed by naloxone, administered either intravenously (0.4 mg/kg) or locally (2.5 microg in 0.6 microl) at the same site as morphine. After microinjection into deeper laminae (V-VI), a significant depressive effect (34 +/- 5% of control) of morphine could be detected only 20 min after the injection and was reversed only by intravenous administration of naloxone. These results suggest that morphine exerts its antinociceptive action on Sp5O convergent neurons by blocking the C-fiber inputs that relay in the Sp5C substantia gelatinosa. The mechanisms that underlie the activation of Sp5O convergent neurons by C-fibers and the inhibition of C-fiber-evoked responses of Sp5O convergent neurons by morphine microinjected into the Sp5C are discussed.     

Attenuation of Fos-like immunoreactivity in the trigeminal nucleus caudalis following trigeminovascular activation in the anaesthetised guinea-pig

The present study has examined the involvement of sensory neurotransmitters in activating neurones in the trigeminal nucleus caudalis following stimulation of the trigeminovascular system in anaesthetised guinea-pigs. Electrical stimulation of the right trigeminal ganglion produced a unilateral expression of Fos-like immunoreactivity (Fos-LI) in the trigeminal nucleus caudalis. The tachykinin NK1 receptor antagonist, GR205171 (100 micrograms/kg i.v.) and the N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 (1 mg/kg i.v.) each inhibited expression of Fos-LI following electrical stimulation. The calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP8-37 (1.3 mg/kg i.v.), administered following rostral intracarotid infusion of mannitol to disrupt the blood-brain barrier, tended to reduce Fos-LI evoked by electrical stimulation, although this failed to reach statistical significance. Capsaicin (10 nmol in 0.1 ml), administered intracisternally, produced a bilateral expression of Fos-LI in the trigeminal nucleus caudalis. This expression was unaffected by the peripherally acting NK1 receptor antagonist, GR82334 (0.2 mg/kg i.v.) or CGRP8-37 (1.3 mg/kg i.v.). The centrally penetrant NK1 receptor antagonist, GR205171 (100 micrograms/kg i.v.), inhibited significantly Fos-LI evoked by intracisternal capsaicin administration. It is concluded that the sensory neurotransmitters, substance P and glutamate are released centrally following activation of the trigeminovascular system and that each may be involved in activation of cells in the trigeminal nucleus caudalis.     

The time-course of abeta-evoked c-fos expression in neurons of the dorsal horn and gracile nucleus after peripheral nerve injury

We have examined the mechanisms underlying Abeta-evoked c-fos expression in the dorsal horn and gracile nucleus following either sciatic nerve section or crush injury. The results indicate that in the spinal cord Abeta-evoked c-fos does not depend on primary afferent sprouting but is associated with the disconnection from the peripheral target since its expression in the dorsal horn reverts to normal after crush injury when regeneration occurs but persists after cut and ligation where regeneration is prevented. In contrast, however, Abeta-evoked c-fos expression in the gracile nucleus may be under some other control since its expression appears independent of peripheral nerve regeneration.     

Morphologic characteristics of physiologically defined neurons in the cat trigeminal nucleus principalis

Although the principalis nucleus (Vp) contains trigeminothalamic and internuclear tract cells, the functional and morphologic differences between the two kinds of neurons have remained unsettled. The present study was aimed to address these problems by using the intracellular horseradish peroxidase injection technique in the cat. Of 20 neurons stained, 7 and 13 were located in the dorsomedial subnucleus (Vpd) and ventrolateral subnucleus (Vpv) of Vp, respectively. The Vpd neurons received input from the intraoral structures only but the Vpv neurons from the intraoral or facial structures. Nineteen neurons could be divided as class I and class II, based on the branching pattern of their stem axons. Class I (eight neurons) had an ascending stem axon without branching. Class II was divided into two subclasses (IIa and IIb). Class IIa (eight neurons) had an ascending stem axon from which branches were given off. Their branches formed a local-circuit restricted to the lower brainstem. Class IIb (three neurons) had a stem axon that formed the local-circuit only. The dendritic morphology was indistinguishable between different classes of neurons and between the subdivisions. Although the dendritic arborization pattern was governed by the location of the somata, it was suggested to be also important elements for determining primary afferent arborizations. In the brainstem nuclei, the jaw-closing motor nucleus received the highest density of projections from class II neurons with the receptive field involving the periodontal ligaments. The present study provides new findings that Vp neurons could be divided into three distinct populations and suggests that each population exerts a distinct function with respect to sensory discrimination, sensorimotor reflexes, or both.     

Acetylcholinesterase activity of synaptic structures in the spinal trigeminal nucleus

The electron microscope has been used to study the localization of acetylcholinesterase (AChE) activity in the spinal trigeminal nucleus of normal cats with special emphasis on the distribution near synaptic structures. Reaction product is found around both round and flattened synaptic vesicle-containing axon terminals, particularly in synaptic clefts and often specifically associated with the presynaptic, or less frequently the postsynaptic membrane. The presence of reaction product at these specific sites suggests that these are areas of high AChE activity and that acetylcholine may be important in neurotransmission in these regions.     

Effects of 5-hydroxytryptamine and bradykinin in cat dorsal horn neurones activated by noxious stimuli

The levels of homovarillic acid and 3,4-dihydroxyphenylacetic acid in rat c. striatum after acute and 10 day administration of clozapine (30 and 100 mg/kg p.o.), thioridazine (100 mg/kg p.o.), haloperidol (1 mg/kg p.o.), and chlorpromazine (30 mg/kg p.o.), were estimated. With clozapine and haloperidol, the mesolimbic area was also investigated. With all these neuroleptics, the levels of both dopamine metabolites were reduced after a 10 day treatment as compared to acute administration, sometimes almost to control values. With clozapine, however, such a reduction occurred only with the higher dose of 100 mg/kg p.o., acting for a period longer than 24 h. This tolerance phenomenon was also observed with clozapine and haloperidol in the mesolimbic area. We conclude that clozapine is not qualitatively different from classical neuroleptics with respect to development of biochemical tolerance.     

Response classes in the dorsal cochlear nucleus and its output tract in the chloralose-anesthetized cat

Neurons in the dorsal cochlear nucleus (DCN) can be classified into three major physiological classes on the basis of responses to pure tone and broadband noise stimuli. A circuit diagram that associates these classes with different cell types has been proposed. According to this proposal, type II cells are inhibitory interneurons that respond well to tones and poorly to broadband noise, type IV cells are projection neurons with the opposite behavior, and type III cells are an inhomogeneous class with intermediate properties. To test the associations proposed, I compared the response type distribution in the DCN with its output tract, the dorsal acoustic stria (DAS), in chloralose-anesthetized cats. Axonal recordings in the DAS showed type III and IV responses as in DCN, but no type II responses. Compared with reports in decerebrate animals, fewer type IV neurons were encountered having sustained inhibition that generated strongly nonmonotonic responses to tones in both DCN and DAS. The presence of type II responses in the nucleus, but not in the output tract, offers strong support for the proposed association with DCN interneurons. On the other hand, the distinction between type III and IV responses needs refinement because the differences are only graded and because both types of responses occur in DAS, which shows that they are both associated with projection neurons.     

Facilitation of acoustic responses of cartwheel neurons of the cat dorsal cochlear nucleus

Responses to clicks were increased in cartwheel cells of the dorsal cochlear nucleus of cats after pairing presentations of the clicks with local iontophoretic delivery of glutamate. The cells were identified by bursting discharges, and were recorded intracellularly in vivo. The findings indicate that inhibitory interneurons such as cartwheel cells can participate in complex adaptive acoustic signal processing. Each cell displayed doublet discharges of > 800 Hz. In 70% of the cells, some of the doublet discharges reached rates > 1000 Hz.     

Somatotopic redistribution of c-fos expressing neurons in the superficial dorsal horn after peripheral nerve injury

The functional somatotopic reorganization of the lumbar spinal cord dorsal horn after nerve injury was studied in the rat by mapping the stimulus-evoked distribution of neurons expressing proto-oncogene c-fos. In three different nerve injury paradigms, the saphenous nerve was electrically stimulated at C-fibre strength at survival times ranging from 40 h to more than six months: 1) Saphenous nerve stimulation from three weeks onwards after ipsilateral sciatic nerve transection resulted in an increase in the number of Fos-immunoreactive neurons within the dorsal horn saphenous territory in laminae I-II, and an expansion of the saphenous territory into the denervated sciatic territory until 14 weeks postinjury. 2) Saphenous nerve stimulation from five days onwards after ipsilateral sciatic nerve section combined with saphenous nerve crush resulted in an increase in the number of Fos-immunoreactive neurons within the dorsal horn saphenous nerve territory, and an expansion of the saphenous nerve territory into the denervated sciatic nerve territory. 3) Stimulation of the crushed nerve (without previous adjacent nerve section) at five days, but not at eight months resulted in a temporary increase in the number of Fos-immunoreactive neurons within the territory of the injured nerve, and no change in area at either survival time. The results indicate that nerve injury results in an increased capacity of afferents in an adjacent uninjured, or regenerating nerve, to excite neurons both in its own and in the territory of the permanently injured nerve in the dorsal horn. The onset and duration of the increased postsynaptic excitability and expansion depends on the types of nerve injuries involved. These findings indicate the complexity of the central changes that follows in nerve injuries that contain a mixture of uninjured, regenerating and permanently destroyed afferents.     

Increased response to sural nerve input in the dorsal horn following chronic spinal cord hemisection

Monosynaptic input from sural nerve afferents to dorsal horn neurons was mapped bilaterally using electrical stimulation in normal cats and cats with spinal cord hemisections. Animals hemisected 6 h-5 days previously did not differ significantly from normals and the sides of the cord did not differ in either group. In animals hemisected 88-182 days previously there were significantly more sites responsive to sural nerve input ipsilateral to the hemisection, than contralateral to it.     

Effect of neonatal capsaicin and infraorbital nerve section on whisker-related patterns in the rat trigeminal nucleus

In the present study, we investigated the effect of neonatally administered capsaicin on whisker-related pattern formation in the rat trigeminal complex. Both normal whisker-related patterns of barrelettes and the modified patterns seen after neonatal section of the infraorbital nerve were assessed. Capsaicin caused no change in the pattern or size of cytochrome oxidase (CO) barrelettes in the principal trigeminal nucleus (Vp) or trigeminal nucleus interpolaris (Vi) or caudalis (Vc). Injections of horseradish peroxidase (HRP) or wheatgerm agglutinin conjugated to HRP (WGA-HRP) into the posteroorbital (PO) whisker follicle in vehicle-treated animals showed that WGA labelled a larger number of trigeminal ganglion cells than HRP (203 +/- 23; cf. 158 +/- 19), with an increased labelling of small-diameter neurons (HRP: 25.9 +/- 7.7 microm; WGA: 23.2 +/- 7.2 pm). Capsaicin caused a loss of smaller diameter cells but had no effect on the location, cross-sectional area, or rostrocaudal extent of the transganglionically labelled HRP terminations in Vp, Vi, Vc, and cervical dorsal horn. WGA-HRP labelling revealed similar, but less dense, central terminal areas as HRP and an additional area of superficial terminals in the caudal medulla; these were also unaffected by capsaicin treatment. After infraorbital nerve section, CO patches and transganglionically labelled afferent terminations, corresponding to innervated nonmystacial whiskers, were approximately doubled in size. Capsaicin had no effect on the increased size of these spared whisker patches or their afferent terminal areas. These results suggest that barrelette formation is not dependent on unmyelinated afferents and that the changes in response properties seen after capsaicin, such as increased receptive fields, reflect functional changes rather than anatomical expansion of afferent terminal areas.     

Stimulation of the spinal trigeminal nucleus supports classical conditioning of the rabbit's nictitating membrane response.

Acquisition, extinction, and differential conditioning of the rabbit's nictitating membrane response to a tone conditioned stimulus were supported by electrical stimulation of the spatial trigeminal nucleus. Stimulation of the accessory abducens nucleus, the abducens nucleus, and the reticular formation at the level of the spinal trigeminal nucleus supported lower, transient levels of conditioning. The results are discussed in terms of stimulation of sensory inputs to the brainstem and cerebellum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quantitative analysis of substance P-immunoreactive boutons on physiologically characterized dorsal horn neurons in the cat lumbar spinal cord

A quantitative analysis of substance P (SP)-immunoreactive (IR) terminals contacting physiologically characterized dorsal horn neurons was performed. Three types of neuron were studied: nociceptive specific (NS) from lamina I (n = 3), wide dynamic range (WDR) from laminae II-IV (n = 3), and nonnociceptive (NN) from lamina IV (n = 3). The nociceptive response of focus was a slow, prolonged depolarization to noxious stimuli, because this response was previously shown to be blocked by selective neurokinin-1 (NK-1) receptor antagonists. Ultrastructural immunocytochemistry was used to quantify the relative number of SP-IR boutons apposed to the intracellularly labeled cell per unit of length (density). Densities of the total population (SP immunoreactive+nonimmunoreactive) of apposed boutons were similar in all three regions (cell body, proximal and distal dendrites) for the three functional types of neuron. NS neurons received a significantly higher density of appositions from SP-IR boutons than NN cells in all three regions. However, compared to WDR cells, NS cells possessed a significantly higher density of appositions from SP-IR boutons only in the cell body and proximal dendrites. WDR cells had a higher density of appositions from SP-IR boutons than NN cells, but only in the proximal and distal dendrites. On average, 33.5% of the SP-IR boutons apposed to the cells displayed a synaptic contact. Finally, 30-45% of the SP-IR boutons apposed to the cells colocalized calcitonin gene-related protein (CGRP) immunoreactivity, indicating their primary sensory origin. The data indicate a direct correlation between the amount of SP-IR input and the nociceptive nature of the cells and suggest that SP acts on NK-1 receptors at a short distance from its release site.     

Vestibular nucleus projections to nucleus tractus solitarius and the dorsal motor nucleus of the vagus nerve: potential substrates for vestibulo-autonomic interactions

Autonomic effects of vestibular stimulation are important components of phenomena as diverse as acute vestibular dysfunction and motion sickness. However, the organization of neural circuits mediating these responses is poorly understood. This study presents evidence for direct vestibular nucleus projections to brain stem regions that mediate autonomic function. One group of albino rabbits received injections of Phaseolus vulgaris leucoagglutinin into the vestibular nuclei. The tracer was visualized immunocytochemically with standard techniques. Anterogradely labeled axons from the caudal medial vestibular nucleus (cMVN) and inferior vestibular nucleus (IVN) could be traced bilaterally to nucleus tractus solitarius (NTS). Fewer axons ended near the somata of neurons in the dorsal motor nucleus of the vagus nerve (DMX). A second group of rabbits received pressure or iontophoretic injections of cholera toxin B-HRP or Fluoro-Gold into a region including NTS and DMX. Retrogradely labeled neurons were observed bilaterally in the caudal half of cMVN and ipsilaterally in IVN. The labeled somata were small and they tended to occupy the center of cMVN in transverse sections. These previously unreported vestibular nucleus projections to NTS and DMX are a potential substrate for vestibular influences on autonomic function. In particular, they may contribute to both cardiovascular control during head movements (e.g., orthostatic reflexes) and autonomic manifestions of vestibular dysfunction, motion sickness and exposure to altered gravitational environments.     

Effect of nitrous oxide on spinal dorsal horn WDR neuronal activity in cats

The effects of nitrous oxide (75%) on the spinal dorsal born wide dynamic range (WDR) neuronal activity were studied in either spinal cord intact or spinal cord-transected cats. Extracellular activity was recorded in the dorsal horn from single WDR neurons responding to noxious and non-noxious stimuli applied to the cutaneous receptive fields on the left bind foot pads of intact or decerebrate, spinal cord-transected (L 1-2) cats. The experiment was divided into four sections as follows: (1) When 10 micrograms of bradykinin (BK) was injected into the femoral artery ipsilateral to the recording site as the noxious test stimulus in the spinal cord-transected cat, all of 6 WDR neurons gave excitatory responses which were not depressed by 75% nitrous oxide. (2) When the injection of 10 micrograms of BK into the femoral artery ipsilateral to the recording site was used in the spinal cord-intact cat, 6 of 15 WDR neurons (40%) gave excitatory responses, which were significantly depressed by 75% nitrous oxide, and 9 of 15 WDR neurons (60%) gave inhibitory responses, which were not affected by 75% nitrous oxide. (3) When 10 micrograms of bradykinin (BK) was injected into the femoral artery contralateral to the recording site as the noxious test stimulus in the spinal cord transected cat, 6 of 12 WDR neurons gave excitatory reasons, which were not depressed by 75% nitrous oxide. (4) When the injection of 10 micrograms of BK into the femoral artery contralateral to the recording site was used in the spinal cord-intact cat, 6 of 6 WDR neurons (100%) gave responses, which were affected by 75% nitrous oxide. We have observed that nitrous oxide reduces the excitation and inhibition of dorsal born WDR neuronal activities induced by BK injection in spinal cord-intact cats, but does not reduce the excitation of those in spinal cord-transected cats. This finding confirmed that the antinociceptive effect of nitrous oxide might be modulated by supraspinal descending inhibitory control systems. In addition our result showed that the supraspinal effect of nitrous oxide was mediated not only by an increase but also a decrease in a supraspinal descending inhibition.     

Loss of nerve endings in the spinal dorsal horn after a peripheral nerve injury. An anatomical study in Macaca fascicularis monkeys

In patients, the long-term outcome of injuries to sensory nerves is poor. This is only partly due to mismatching of regenerating axons at the transection site. We found in the macaque monkey that 70% of the transganglionic labelling in the spinal dorsal horn was still significantly reduced 21 months after transection and suturing of the sensory radial nerve. The reduction was evenly distributed throughout the terminal field of nerve endings, which were labelled with a mixture of the intra-axonal nerve tracer wheat germ agglutinin-horseradish peroxidase conjugate and pure horseradish peroxidase.     

Vagal innervation of the gastrointestinal tract arises from dorsal motor nucleus while that of the heart largely from nucleus ambiguus in the cat

The origin of medullary cells that form the cardiac vagal branch and the vagal branches in the lower thorax innervating the gastrointestinal (GI) tract was studied using horseradish peroxidase (HRP), a retrograde transport tracer in the cat. The distributions of parasympathetic postganglionic neurons of the heart were studied with acetylcholinesterase histochemistry. Intracardiac ganglionic neurons were found mainly in the connective tissue surrounding the base of the pulmonary arteries and in an area in and dorsal to the interatrial septum. Following injection of HRP into the subepicardum where most of the cardiac postganglionic neurons reside, 91% of the labelled neurons were found bilaterally distributed in the nucleus ambiguus (NA). A small population of labelled neurons was found in the dorsal motor nucleus of the vagus (DMV) and an intermediate zone (IZ) between the two nuclei. When HRP was injected into the left or right cardiopulmonary vagus branch, labelled neurons were found exclusively in the ipsilateral NA, DMV and IZ with a predominance in the NA. In the thorax, after they course around the heart, the left and right thoracic vagus nerves divides into a left and a right branch, respectively. The left branch of the left thoracic vagus joins the left branch of the right thoracic vagus to form the anterior vagus nerve at 3 cm above the diaphragm. The right branch of the right thoracic vagus nerve joins the right branch of the left thoracic vagus to form the posterior vagus nerve. After application of HRP into the right or the left branch of the left thoracic vagus, HRP labelled cells were found in the left DMV. Similarly, after application of HRP into the left or the right branch of the right thoracic vagus, labelled cells were found in the right DMV. On the other hand, when HRP was injected into the anterior vagus, labelled neurons were found bilaterally in the DMV. This suggests that all rostral branches of the thoracic vagus have their origin in the ipsilateral DMV, and intermixing occurs only at the caudal level near the diaphragm. Findings of the present experiments suggest that parasympathetic preganglionic neurons innervating the GI tract are located exclusively in the DMV while those of the heart are located mainly in the NA. Within the DMV, GI vagal neurons were found medially from the level 0-2.5 mm rostral to the obex. In contrast, cardiac vagal neurons were found in the lateral edge of the DMV at the level 0-1 mm rostral to the obex.     

Light microscopic observations of the contacts made between two spindle afferent types and alpha-motoneurons in the cat trigeminal motor nucleus

Previous studies indicate that cat jaw-muscle spindle afferents can be divided into two types (type I and II) on the basis of their axonal trajectories. The present study examined the relationship between spindle afferent fibers and their target masseter alpha-motoneurons in the cat by using the intracellular horseradish peroxidase (HRP) injection technique, and provided several new findings on the synaptic organization generated between the two. Five type I afferent fiber-motoneuron pairs and nine type II afferent-motoneuron pairs were well stained with HRP. The following conclusions were drawn: 1) A motoneuron received contacts from only one collateral of any given spindle afferent. 2) The number of contacts made between an afferent and a motoneuron ranged from one to three. 3) The contacts made by a spindle afferent were on the same dendrite or dendrites branching from the same primary dendrite. 4) The vast majority of the contacts made by an afferent on a motoneuron were distributed in the dendritic tree within 600 microns from the soma, i.e., in the proximal three fourths of the dendritic tree. The differences observed between the two afferent types were as follows. First, type II afferent terminals made contacts on more distal dendrites of the motoneurons than did type I afferent terminals. Second, the contacts made between a type I afferent and a motoneuron were clustered together, but those made between a type II afferent and a motoneuron were widely dispersed. The present results provided the general rules of synaptic contacts between the spindle afferents and masseter alpha-motoneurons, and demonstrated that the spatial distribution of synaptic contacts on the dendritic tree was different between type I and type II afferents.