Enhanced expression of AMPA receptor protein at perforated axospinous synapses

Odontacarus khanjani Goff & Saboori (Leeuwenhoekiidae) and Neotrombicula iranensis Goff & Saboori (Trombiculidae) were described as new. Both species were collected as unengorged larvae on alfalfa plants, Medicago sativa, in western Iran.     

Differential localization of delta glutamate receptors in the rat cerebellum: coexpression with AMPA receptors in parallel fiber-spine synapses and absence from climbing fiber-spine synapses

The delta 2 glutamate receptors are prominently expressed in Purkinje cells and are thought to play a key role in the induction of cerebellar long-term depression. The synaptic and subsynaptic localization of delta receptors in rat cerebellar cortex was investigated with sensitive and high-resolution immunogold procedures. After postembedding incubation with an antibody raised to a C-terminal peptide of delta 2, high gold particle densities occurred in all parallel fiber synapses with Purkinje cell dendritic spines, whereas other synapses were consistently devoid of labeling. Among the types of immunonegative synapse were climbing fiber synapses with spines and parallel fiber synapses with dendritic stems of interneurons. At the parallel fiber-spine synapse, gold particles signaling delta receptors were restricted to the postsynaptic specialization. By the use of double labeling with two different gold particle sizes, it was shown that delta and AMPA GluR2/3 receptors were colocalized along the entire extent of the postsynaptic specialization without forming separate domains. The distribution of gold particles representing delta receptors was consistent with a cytoplasmic localization of the C terminus and an absence of a significant presynaptic pool of receptor molecules. The present data suggest that the delta 2 receptors are targeted selectively to a subset of Purkinje cell spines and that they are coexpressed with ionotropic receptors in the postsynaptic specialization. This arrangement could allow for a direct interaction between the two classes of receptor.     

Fertility in anovulatory patients after primary cesarean section

We report a successful surgical treatment of an infective thoracic aortic aneurysm ruptured to the left lung. A 63-year-old man who had been suffering from fever and cough showed twice of hemoptysis. Chest CT revealed a descending thoracic aortic aneurysm ruptured to the left lung. A semiemergent operation was performed. At operation, aneurysm of descending thoracic aorta was found adherent to the left lung. Aneurysmectomy with left pneumonectomy was carried out. The postoperative course of the patient was uneventful. Conceivably, in order to avoid massive intraoperative bleeding during division of dense adhesion and postoperative graft infection, concomitant lung resection is necessary.     

Opioid-activated postsynaptic, inward rectifying potassium currents in whole cell recordings in substantia gelatinosa neurons

Opioid-activated postsynaptic, inward rectifying potassium currents in whole cell recordings in substantia gelatinosa neurons. J. Neurophysiol. 80: 2954-2962, 1998. Using tight-seal, whole cell recordings from isolated transverse slices of hamster and rat spinal cord, we investigated the effects of the mu-opioid agonist (-Ala2, N-Me-Phe4,Gly5-ol)-enkephalin (DAMGO) on the membrane potential and conductance of substantia gelatinosa (SG) neurons. We observed that bath application of 1-5 microM DAMGO caused a robust and repeatable hyperpolarization in membrane potential (Vm) and decrease in neuronal input resistance (RN) in 60% (27/45) of hamster neurons and 39% (9/23) of rat neurons, but significantly only when ATP (2 mM) and guanosine 5'-triphosphate (GTP; 100 microM) were included in the patch pipette internal solution. An ED50 of 50 nM was observed for the hyperpolarization in rat SG neurons. Because G-protein mediation of opioid effects has been shown in other systems, we tested if the nucleotide requirement for opioid hyperpolarization in SG neurons was due to G-protein activation. GTP was replaced with the nonhydrolyzable GTP analogue guanosine-5'-O-(3-thiotriphosphate) (GTP-gamma-S; 100 microM), which enabled DAMGO to activate a nonreversible membrane hyperpolarization. Further, intracellular application of guanosine-5'-O-(2-thiodiphosphate) (GDP-beta-S; 500 microM), which blocks G-protein activation, abolished the effects of DAMGO. We conclude that spinal SG neurons are particularly susceptible to dialysis of GTP by whole cell recording techniques. Moreover, the depletion of GTP leads to the inactivation of G-proteins that mediate mu-opioid activation of an inward-rectifying, potassium conductance in these neurons. These results explain the discrepancy between the opioid-activated hyperpolarization in SG neurons observed in previous sharp electrode experiments and the more recent failures to observe these effects with whole cell patch techniques.     

Sprouting of primary afferent fibers after spinal cord transection in the rat

After spinal cord injury, hyper-reflexia can lead to episodic hypertension, muscle spasticity and urinary bladder dyssynergia. This condition may be caused by primary afferent fiber sprouting providing new input to partially denervated spinal interneurons, autonomic neurons and motor neurons. However, conflicting reports concerning afferent neurite sprouting after cord injury do not provide adequate information to associate sprouting with hyper-reflexia. Therefore, we studied the effect of mid-thoracic spinal cord transection on central projections of sensory neurons, quantified by area measurements. The area of myelinated afferent arbors, immunolabeled by cholera toxin B, was greater in laminae I-V in lumbar, but not thoracic cord, by one week after cord transection. Changes in small sensory neurons and their unmyelinated fibers, immunolabeled for calcitonin gene-related peptide, were assessed in the cord and in dorsal root ganglia. The area of calcitonin gene-related peptide-immunoreactive fibers in laminae III-V increased in all cord segments at two weeks after cord transection, but not at one week. Numbers of sensory neurons immunoreactive for calcitonin gene-related peptide were unchanged, suggesting that the increased area of immunoreactivity reflected sprouting rather than peptide up-regulation. Immunoreactive fibers in the lateral horn increased only above the lesion and in lumbar segments at two weeks after cord transection. They were not continuous with dorsal horn fibers, suggesting that they were not primary afferent fibers. Using the fluorescent tracer DiI to label afferent fibers, an increase in area could be seen in Clarke's nucleus caudal to the injury two weeks after transection. In conclusion, site- and time-dependent sprouting of myelinated and unmyelinated primary afferent fibers, and possibly interneurons, occurred after spinal cord transection. Afferent fiber sprouting did not reach autonomic or motor neurons directly, but may cause hyper-reflexia by increasing inputs to interneurons.     

Muscarine receptor activation in the substantia gelatinosa of the spinal trigeminal nucleus of the guinea pig

1. Intracellular recordings were made from slices of guinea pig spinal trigeminal nucleus pars caudalis (SG). 2. Muscarine [0.3-30 microM; half maximally effective concentration (EC50) = 2.9 microM] hyperpolarized 61% of SG neurons. The effect was mimicked by carbachol (0.3-30 microM; EC50 = 3.9 microM) and antagonized by pirenzepine (1 microM). Thirty-four percent of the neurons were depolarized by muscarine and carbachol (1-30 microM: EC50 = 5.7 microM), and the effect was antagonized by pirenzepine (100 nM). 3. In approximately 80% of recordings, muscarine (10-30 microM) evoked repetitive spontaneous inhibitory postsynaptic potentials (IPSPs) that were sensitive to bicuculline (10 microM). 4. Muscarine (1-30 microM; EC50 = 3 microM) decreased the amplitude of the majority of evoked excitatory postsynaptic potentials (EPSPs), and the effect was mimicked by carbachol and antagonized by pirenzepine (100 nM). 5. These results indicate that there are at least three mechanisms by which muscarine inhibits SG neurons: 1) hyperpolarization through activation of non-M1 receptors; 2) activation of gamma-amino-butyric acid-containing interneurons that mediate IPSPs in a subset of neurons; and 3) a decrease in evoked EPSP amplitude. Muscarine can also activate SG neurons via interaction with an M1-type receptor.     

Glycine uptake governs glycine site occupancy at NMDA receptors of excitatory synapses

Glycine uptake governs glycine site occupancy at NMDA receptors of excitatory synapses. J. Neurophysiol. 80: 3336-3340, 1998. At central synapses occupation of glycine binding sites of N-methyl--aspartate receptors (NMDA-Rs) is a necessary prerequisite for the excitatory neurotransmitter glutamate to activate these receptors. There is conflicting evidence as to whether glycine binding sites normally are saturated. If they are not, then alterations in local glycine concentration could modulate excitatory synaptic transmission. By using an in vitro brain stem slice preparation we investigated whether the glycine site is saturated for synaptically activated NMDA-Rs in neonatal rat hypoglossal motoneurons. We found that the NMDA-R-mediated component of spontaneous miniature excitatory postsynaptic currents could be potentiated by exogenously applied glycine as well as by -serine. The effects of glycine were observed only at concentrations (100 microM or more) two orders of magnitude above the apparent dissociation constant of glycine from NMDA receptors. In contrast, -serine, a nontransported NMDA-R glycine site agonist, was effective in the low micromolar range, i.e., at concentrations similar to those found to be effective on isolated cells or on outside-out patches. We conclude that at these synapses the glycine concentration around synaptic NMDA-Rs is set below the concentration required to saturate their glycine site and is likely to be stabilized by a powerful glycine transport mechanism.     

Analysis of molecular determinants in native AMPA receptors

For this study, 194 respondents completed a biographical data sheet, the Templer (1970) Death Anxiety Scale and the Constantinople (1973) Inventory of Psychosocial Development to help assess the relationship among death anxiety, age, and psychosocial maturity. Findings showed that psychosocial maturity was a better predictor of death anxiety than age was. However, both variables were significantly negatively correlated with death anxiety, revealing that as psychosocial maturity and age increase, death anxiety decreases.     

Increased spike-frequency adaptation and tea sensitivity in dorsal root fibers after sciatic nerve injury

Excitability of rat dorsal root axons were studied 3 weeks after injury to the sciatic nerve. Whole nerve recordings were obtained from injured and control nerves in a sucrose gap chamber. Constant current depolarization pulses (30-200 ms) applied approximately 50% above the stimulus strength required for maximal amplitude compound action potentials (CAPs) evoked a burst of action potentials in the dorsal root which displayed spike adaptation. The depolarization-induced burst response of the dorsal roots was greatly reduced after crush or transection of the sciatic nerve. However, application of the potassium channel blocker, tetraethylammonium (TEA), restored the burst discharge in injured dorsal root axons. Brief tetanic stimulation of the dorsal root also induced an afterhyperpolarization (AHP) that was twice as large in the transection group as compared to the control group, and which was blocked by TEA. There were no changes seen in the amplitude of the compound action potential, frequency-following characteristics, refractory properties, or 4-AP sensitivity in the dorsal roots after peripheral nerve injury. These results suggest that there is enhanced spike adaptation that occurs at the same time as an increase in the sensitivity to the potassium channel blocker, TEA, in axon regions proximal to the site of nerve injury and have implications for the pathophysiology of nerve injury.     

GABA-dependent firing of glutamate-evoked action potentials at AMPA/kainate receptors in developing hypothalamic neurons

Although it plays a major inhibitory role in the adult mammalian CNS, gamma-aminobutyric acid (GABA) may have an excitatory function in developing neurons. The present study focuses on the dependence of glutamate on GABA to generate action potentials in developing hypothalamic neurons. Under conditions where glutamate by itself could not evoke an action potential, GABA facilitated glutamate-mediated depolarization to fire action potentials. This facilitation had a broad time window during the decaying phase of the GABA-mediated depolarization in developing neurons in culture. The glutamate-mediated depolarization was shunted only during the peak of GABA-mediated depolarization, but was facilitated after that. Similar results were obtained in the presence of 2-amino-5-phosphonopentanoic acid (AP5), indicating that GABA can facilitate glutamate responses independent of relief of the Mg2+ block of the N-methyl-D-aspartate (NMDA) receptor. This novel interaction between GABA- and glutamate-mediated excitation could play a role in strengthening neuronal circuits during early development and would exert a maximal effect if GABA and glutamate receptors were activated after a slight temporal delay.     

Recovery of semicircular canal primary afferent activity in the pigeon after streptomycin ototoxicity

Recovery of semicircular canal primary afferent activity in the pigeon after streptomycin ototoxicity. J. Neurophysiol. 80: 3297-3311, 1998. The electrophysiological activity of horizontal semicircular canal primary afferents (HSCPA) was investigated in vivo in the barbiturate-anesthetized pigeon by means of extracellular single-fiber vestibular nerve action potential recordings. The spontaneous and driven discharges to pulse (step/trapezoid waveform, peak velocity = 120 degrees/s) and sum-of-sines (0.03, 0.09, 0.21, 0.39, 0.93, 1.83 Hz, peak velocity = 30 degrees/s for each frequency) rotations were measured both in normal control animals and a group of animals at 30, 40, 50, 60, 71, and 150 days postinjection sequence (PIS) of streptomycin sulfate. Prior to 30 days PIS, the activity in the nerve was not appropriately modulated during and after rotation. At 30 days PIS and thereafter, the responses resembled those observed in control animals but with systematic changes in parameters of fitted pulse responses and fitted Bode plots as days PIS increased. The return of parameters characterizing the neural dynamics of the semicircular canals were monotonic and could be best described by either linear or exponential functions. After 30 days PIS, the mechanical cupula-endolymph system, the function of which can be inferred from the cupula long time constant (tauL) following step velocity, did not change systematically (tauL = 6.92 +/- 3.96, 8.64 +/- 5.52, 8.35 +/- 4.21, 10.00 +/- 2.79, 9.05 +/- 3.67, 7.05 +/- 2.72; means +/- SD). However, the mean gain (G) of the HSCPA response to pulse rotation nearly doubled between 30 and 150 days PIS (from 1.31 +/- 0. 39 to 2.40 +/- 1.04) and returned linearly to control values (G = 2. 39 +/- 0.77) over this time period [G = 1.33 + 0.009(PIS-30), R2 = 0. 92, P < 0.05]. Meanwhile, neural adaptation as quantitated using a fractional operator, k, decayed exponentially (single exponential) to an asymptote. The time constant of this exponential was approximately 55 days [k = 0.034 + 0.33e-(PIS-30)/55.4, R2 = 0.99, P < 0.01]. Features of the spontaneous discharge previously shown to be correlated with k changed appropriately. That is, the coefficient of variation (CV) and frequency of firing (FF) decayed and grew asymptotically, respectively. These parameters also exhibited an exponential time course of return to control values from 30 to 150 days PIS [CV = 0.44 + 0.65e-(PIS-30)/21.5, R2 = 0.96, P < 0.01, and FF = 39.97 + 101.42(1 - e-(PIS-30)/32.6), R2 = 0.97, P < 0.01]. The trends of recovery for G, k, and tauL derived from analysis of the pulse response were confirmed by strong positive correlations with best fitted parameters obtained from analysis of the sum-of-sines frequency domain response of HSCPAs. There were statistically significant correlations (r = 0.90, P < 0.05 and r = 0.93, P < 0.05) between parameters (G, k) derived from pulse responses and those (G', k') from sum-of-sines responses, respectively. The cupula time constant based on sum-of-sines' data (tau'L) showed no statistically significant change between 30 and 150 days PIS (P > 0.05, analysis of variance). Thus the results in present study indicate that both the spontaneous discharge and the driven response to rotation of pigeon HSCPAs recovered their normal physiological status between 30 and 150 days PIS after hair cell death due to aminoglycoside ototoxicity. The recovery was systematic for the parameters chosen to be tested with the exception of the cupula long time constant, tauL. The mechanisms (changes in ciliary dynamics, changes in hair cell ionic currents, changes in bouton terminals, etc.) underlying these changes await further morphophysiological studies.     

Blockade of M2-like muscarinic receptors enhances long-term potentiation at corticostriatal synapses

Cortical glutamatergic fibres and cholinergic inputs arising from large aspiny interneurons converge on striatal spiny neurons and play a major role in the control of motor activity. We have investigated the interaction between excitatory amino acids and acetylcholine (ACh) on striatal spiny neurons by utilizing intracellular recordings, both in current- and in voltage-clamp mode in rat brain slices. Muscarine (0.3-10 microM) produced a reversible and dose-dependent increase in the membrane depolarizations/inward currents induced by brief applications of N-methyl-D-aspartate (NMDA), while it did not affect the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-induced responses. These concentrations of muscarine did not alter the membrane potential and the current-voltage relationship of the recorded cells. Neostigmine (0.3-10 microM), an ACh-esterase inhibitor, mimicked this facilitatory effect. The facilitatory effects of muscarine and neostigmine were antagonized either by scopolamine (3 microM) or by pirenzepine (10-100 nM), an antagonist of M1-like muscarinic receptors, but not by methoctramine (300 nM), an antagonist of M2-like muscarinic receptor. Accordingly, these facilitatory effects were mimicked by McN-A-343 (1-10 microM), an agonist of M1-like muscarinic receptors, but not by oxotremorine (300 nM), an agonist of M2-like receptors. Tetrodotoxin (TTX) did not block the facilitatory effect produced by the activation of muscarinic receptors suggesting that this effect is postsynaptically mediated. The action of neostigmine was prevented either by the intracellular calcium (Ca2+) chelator BAPTA (200 mM) or by preincubating the slices with inhibitors of protein kinase C (PKC) (staurosporine 100 nM or calphostin C 1 microM). McN-A-343 did not alter the excitatory post synaptic potentials (EPSPs) evoked by corticostriatal stimulation in the presence of physiological concentration of magnesium (Mg2+ 1.2 mM), while it enhanced the duration of these EPSPs recorded in the absence of external magnesium. Our data show that endogenous striatal ACh exerts a positive modulatory action on NMDA responses via M1-like muscarinic receptors and PKC activation.     

Differential expression of galanin immunoreactivities in the primary sensory neurons following partial and complete sciatic nerve injuries

Neuropeptide expression in primary sensory neurons is highly plastic in response to peripheral nerve axotomy. While neuropeptide changes following complete sciatic nerve injury have been extensively studied, much less is known about the effects of partial sciatic nerve injuries on neuropeptide plasticity. Galanin. a possible endogenous analgesic peptide, was up-regulated in primary sensory neurons following complete sciatic nerve injury. We investigated the effects of partial sciatic nerve injuries on galanin expression in primary sensory neurons, and compared this effect with that after complete sciatic nerve injury. Complete transection, partial transection and chronic constriction injury were made, respectively, on the sciatic nerves of three groups of rats at high thigh level. Animals were allowed to survive for four and 14 days before being killed. L4 and L5 dorsal root ganglia, L4 5 spinal cord and lower brainstem were processed for galanin immunocytochemical staining. After all three types of sciatic nerve injuries, galanin-immunoreactive neurons were significantly increased in the ipsilateral dorsal root ganglia, and galanin-immunoreactive axonal fibres were dramatically increased in the superficial laminae of the dorsal horn and the gracile nuclei, compared to the contralateral side. However, in partial injury models, the percentages of galanin-immunoreactive dorsal root ganglion neurons were significantly higher than in complete nerve transection. Size frequency distribution analysis detected that more medium- and large-size galanin-immunoreactive dorsal root ganglion neurons were present after partial nerve transection and constriction injury than after complete nerve transection. Using a combined approach of retrograde tracing of flurorescent dyes and galanin immunostaining, we found that a partial transection increased the proportions of galanin-immunoreactive neurons among both axotomized and non-axotomized neurons. Galanin-immunoreactive axonal fibres were not only detected in the superficial laminae, but also in the deeper laminae of the dorsal horn of partial injury animals. Furthermore, more galanin-immunoreactive axonal fibres were observed in the ipsilateral gracile nuclei of partially injured rats than in completely injured rats. We conclude that partial sciatic nerve injuries induced greater galanin up-regulation in medium- and large-size dorsal root ganglion neurons than complete sciatic nerve injury. Galanin expression in primary sensory neurons seems to be differentially regulated following partial and complete sciatic nerve injuries.     

Motoneuronal death without expression of NADPH-diaphorase activity after sciatic nerve cut in 5-day-old mice

In BALB/c mice, the number of sciatic motoneurons lost was statistically insignificant whether the nerve was cut at one (P1) or five days (P5) of age. Although the motoneurons showed intense NADPH-d staining after sciatic nerve cut at P1, they were NADPH-d negative when the nerve was cut at P5. The present study casts doubt on a neurodestructive role of NO in the sciatic motoneurons after axotomy at P1.     

Neuregulin receptors, erbB3 and erbB4, are localized at neuromuscular synapses

Neuregulin (NRG) is concentrated at synaptic sites and stimulates expression of acetylcholine receptor (AChR) genes in muscle cells grown in cell culture. These results raise the possibility that NRG is a synaptic signal that activates AChR gene expression in synaptic nuclei. Stimulation of NRG receptors, erbB3 and erbB4 initiates oligomerization between these receptors or between these receptors and other members of the epidermal growth factor (EGF) receptor family, resulting in stimulation of their associated tyrosine kinase activities. To determine which erbBs might mediate synapse-specific gene expression, we used antibodies against each erbB to study their expression in rodent skeletal muscle by immunohistochemistry. We show that erbB2, erbB3 and erbB4 are concentrated at synaptic sites in adult skeletal muscle. ErbB3 and erbB4 remain concentrated at synaptic sites following denervation, indicating that erbB3 and erbB4 are expressed in the postsynaptic membrane. In addition, we show that expression of NRG and erbBs, like AChR gene expression, increases at synaptic sites during postnatal development. The localization of erbB3 and erbB4 at synaptic sites is consistent with the idea that a NRG-stimulated signaling pathway is important for synapse-specific gene expression.     

LTP of spinal A beta and C-fibre evoked responses after electrical sciatic nerve stimulation

Plasticity in the central nervous system may play an important role in clinical pain. The present study shows that long-term potentiation (LTP) may be induced in single wide dynamic range (WDR) neurons in the dorsal horn after high-frequency stimulation of the sciatic nerve in intact urethane anaesthetized rats. Extracellular recordings of firing responses after single pulse stimuli were made. The high-frequency conditioning stimulus increased the A beta- and C-fibre-mediated firing responses to single pulse stimuli by 60 and 130%, respectively, for more than 6 h. This finding supports a role for WDR neurons in 'nociceptive memory' in the dorsal horn. The model presented here may be an important tool for further investigations of mechanisms of plasticity within the dorsal horn.