Muscarinic receptors in the central nervous system of the rat. IV. A comparison of the effects of axotomy and deafferentation on the binding of [3H]propylbenzilylcholine mustard and associated synaptic changes in the hypoglossal and pontine nuclei

Vesicular acetylcholine transporter–immunoreactive axon terminals enriched in the pontine nuclei of the mouse

Information to the cerebellum enters via many afferent sources collectively known as precerebellar nuclei. We investigated the distribution of cholinergic terminal-like structures in the mouse precerebellar nuclei by immunohistochemistry for vesicular acetylcholine transporter (VAChT). VAChT is involved in acetylcholine transport into synaptic vesicles and is regarded as a reliable marker for cholinergic terminals and preterminal axons. In adult male mice, brains were perfusion-fixed. Polyclonal antibodies for VAChT, immunoglobulin G-peroxidase and diaminobenzidine were used for immunostaining. In the mouse brain, immunoreactivity was seen in almost all major cholinergic cell groups including brainstem motoneurons. In precerebellar nuclei, the signal could be detected as diffusely beaded terminal-like structures. It was seen heaviest in the pontine nuclei and moderate in the pontine reticulotegmental nucleus; however, it was seen less in the medial solitary nucleus, red nucleus, lateral reticular nucleus, inferior olivary nucleus, external cuneate nucleus and vestibular nuclear complex. In particular, VAChT-immunoreactive varicose fibers were so dense in the pontine nuclei that detailed distribution was studied using three-dimensional reconstruction of the pontine nuclei. VAChT-like immunoreactivity clustered predominantly in the medial and ventral regions suggesting a unique regional difference of the cholinergic input. Electron microscopic observation in the pontine nuclei disclosed ultrastructural features of VAChT-immunoreactive varicosities. The labeled bouton makes a symmetrical synapse with unlabeled dendrites and contains pleomorphic synaptic vesicles. To clarify the neurons of origin of VAChT-immunoreactive terminals, VAChT immunostaining combined with wheat germ agglutinin-conjugated horseradish peroxidase retrograde labeling was conducted by injecting a retrograde tracer into the right pontine nuclei. Double-labeled neurons were seen bilaterally in the laterodorsal tegmental nucleus and pedunculopontine tegmental nucleus. It is assumed that mesopontine cholinergic neurons negatively regulate neocortico-ponto-cerebellar projections at the level of pontine nuclei.

La réparation nerveuse périphérique : 30 siècles de recherche

INTRODUCTION

Nerve injury compromises sensory and motor functions. Techniques of peripheral nerve repair are based on our knowledge regarding regeneration. Microsurgical techniques introduced in the late 1950s and widely developed for the past 20 years have improved repairs. However, functional recovery following a peripheral mixed nerve injury is still incomplete.

STATE OF ART

Good motor and sensory function after nerve injury depends on the reinnervation of the motor end plates and sensory receptors. Nerve regeneration does not begin if the cell body has not survived the initial injury or if it is unable to initiate regeneration. The regenerated axons must reach and reinnervate the appropriate target end-organs in a timely fashion. Recovery of motor function requires a critical number of motor axons reinnervating the muscle fibers. Sensory recovery is possible if the delay in reinnervation is short. Many additional factors influence the success of nerve repair or reconstruction. The timing of the repair, the level of injury, the extent of the zone of injury, the technical skill of the surgeon, and the method of repair and reconstruction contribute to the functional outcome after nerve injury.

CONCLUSION

This review presents the recent advances in understanding of neural regeneration and their application to the management of primary repairs and nerve gaps.

Methyl parathion increases neuronal activities in the rat locus coeruleus

Exposure to organophosphate insecticides induces undesirable behavioral changes in humans, including anxiety and irritability, depression, cognitive disturbances and sleep disorders. Little information currently exists concerning the neural mechanisms underlying such behavioral changes. The brain stem locus coeruleus (LC) could be a mediator of organophosphate insecticide-induced behavioral toxicities since it contains high levels of acetylcholinesterase and is involved in the regulation of the sleep-wake cycle, attention, arousal, memory, and pathological processes, including anxiety and depression. In the present study, using a multi-wire recording technique, we examined the effects of methyl parathion, a commonly used organophosphate insecticide, on the firing patterns of LC neurons in rats. Systemic administration of a single dose of methyl parathion (1 mg/kg, i.v.) increased the spontaneous firing rates of LC neurons by 240% but did not change the temporal relationships among the activities of multiple LC neurons. This dose of methyl parathion induced a 50% decrease in blood acetylcholinesterase activity and a 48% decrease in LC acetylcholinesterase activity. The methyl parathion-induced excitation of LC neurons was reversed by administration of atropine sulfate, a muscarinic receptor antagonist, indicating an involvement of muscarinic receptors. The methyl parathion-induced increase in LC neuronal activity returned to normal within 30 min while the blood acetylcholinesterase activity remained inhibited for over 1 h. These data indicate that methyl parathion treatment can elicit excitation of LC neurons. Such excitation could contribute to the neuronal basis of organophosphate insecticide-induced behavioral changes in human.

Modulation of GABA(A) receptor subunit mRNA levels in olivocerebellar neurons of purkinje cell degeneration and weaver mutant mice

In olivocerebellar circuits, changes in the subunit composition of GABA(A) receptors occur at a time of extensive synaptic remodeling. In the deep cerebellar nuclei, GABA(A) receptor alpha1, beta2, and gamma2 subunit mRNA expression increases throughout neonatal development, whereas in the inferior olivary complex, the perinatal combination of alpha3, alpha5, beta3, and gamma2 mRNAs switches to the adult combination of alpha2, alpha4, beta3 and gamma1 during postnatal week 2. In situ hybridization was used to examine changes in subunit expression in the olivocerebellar nuclei of Purkinje cell degeneration and weaver mutant mice. In Purkinje cell degeneration, subunit transcripts decreased below control levels in olivary neurons; however, alpha1, beta2, and gamma2 transcript levels were slightly increased in the medial nucleus of the deep cerebellar nuclei. In weaver olivary neurons, although the switch from early- to late-onset subunit mRNAs occurred as in normal mice, transcript levels were differentially modulated by the mutation. Our studies indicate that major alterations in synaptic connectivity do not prevent developmentally programmed switches in GABA(A) receptor gene expression but can modulate the timing and level of transcript expression in afferent and efferent neurons.

Uncoupling of cerebral blood flow and glucose utilization in the regenerating facial nucleus after axotomy

Axotomy is known to activate various metabolic processes including protein synthesis and glucose utilization in the motor nucleus. Although it is generally assumed that the local cerebral blood flow (CBF) fluctuates in response to the axonal reaction, there has been no direct evidence for changes in CBF in the motor nucleus following axotomy. In this study, the CBF in the facial nuclei was measured after axotomy of the facial nerve employing the [14C]iodoantipyrine method to evaluate the relation between the CBF and axonal reaction. Following unilateral facial nerve axotomy in neonates, which induced neuronal degeneration in the facial nucleus, the CBF and glucose uptake was significantly decreased on the operated nucleus, suggesting that CBF and glucose metabolism are coupled in the degenerating nucleus. In contrast, after axotomy in adults, which induced regeneration of neurons and glial reactions, glucose uptake was increased on the operated nucleus, while the CBF did not differ significantly between the operated and unoperated nucleus. These findings imply that glucose metabolism and CBF are uncoupled in the regenerating nucleus, suggesting that the relation between CBF and metabolism in the regenerating nucleus following axotomy may clearly contradict the classical concept of a tight coupling between CBF and metabolism.

Glutamate receptors in spinal motoneurons after sciatic nerve transection

Severing the axon of a neuron triggers profound changes in its soma, beginning within a few days and becoming maximal within a few weeks. Unravelling these changes bears directly on our understanding of degeneration and regeneration after injury. Classically described chromatolysis arises from reorganization of rough endoplasmic reticulum, associated with biosynthetic changes in response to injury. Since motoneurons, in contrast with other central neurons, are able to regenerate their axons, their response to axotomy is of special interest. For successful regeneration, a neuron must shift its cellular machinery from "operational" (e.g., integration of synaptic currents, conduction of action potentials, release of transmitter) to "regenerative" (e.g., repair of membrane and axoplasm, remyelination, growth cone guidance). Motoneurons become unresponsive to synaptic input after axotomy, and the conduction velocity of the proximal stump is reduced. The loss of synaptic contacts on to axotomized neurons has been suggested to underlie this lost responsiveness. Here, we demonstrate rapid, selective and dramatic changes in immunostaining for ionotropic glutamate receptors in axotomized motoneurons and in supporting cells, suggesting that altered expression of glutamate receptors underlies the changed reflex responsivity.

Mechanism of synapse disassembly at the developing neuromuscular junction

Throughout the developing nervous system of higher vertebrates, synaptic connections are concurrently being established and eliminated. The consequence of this synaptic remodeling is that axons strengthen their connections with some targets while completely disconnecting from other postsynaptic cells. The transition from multiple to single axonal innervation of skeletal muscle fibers is the most accessible example of this developmental reorganization. In muscle, the elimination of axonal input appears to be driven by a protracted competition between different axons co-innervating the same junction, with the muscle fiber as intermediary. Asynchronous synaptic activity may be the factor that differentiates the competing inputs. In some circumstances, synapses can also be lost in ways that are independent of activity. Similarities between activity-dependent and activity-independent synapse elimination provide insights into mechanisms underlying developmental synaptic reorganization.

Differential expression of alpha-CGRP and beta-CGRP genes within hypoglossal motoneurons in response to axotomy

In this study we have analysed, by in situ hybridization, the expression of the genes for both alpha-CGRP and beta-CGRP in hypoglossal motor nuclei following transection of the left hypoglossal nerve. Our results show that the gene for alpha-CGRP displays a peculiar sequence of regulation (a successive up-down-up-recovery sequence) within ipsilateral hypoglossal motoneurons in response to axotomy. It is initially up-regulated, then down-regulated (displaying mRNA levels below basal), and later again up-regulated before recovery. By contrast, the gene for beta-CGRP displays a successive and distinct up-down-recovery sequence of regulation (it does not display a second increase in mRNA production). The first up-regulation of the alpha-CGRP gene occurs just during the early period of perineuronal glial reaction and the second up-regulation just during the period of delayed astrocyte reaction and muscle reinnervation. Because alpha-CGRP is a neuron-derived factor for many types of cells, including astrocytes and skeletal myocytes, our results suggest that the pleiotropic alpha-CGRP may be a motoneuron-derived trophic signal for both glial and skeletal muscle cells in order to maintain the motoneuron itself and, in consequence, might be of therapeutic interest in treating degenerative disease of motoneurons. beta-CGRP might be redundant within the hypoglossal motoneurons.

The progression of deafferentation as a retrograde reaction to hypoglossal nerve injury

This study examined the fate of axon terminals of one of the major sources of hypoglossal afferents, the spinal V nucleus, after XIIth nerve resection in adult Sprague-Dawley rats. In order to anterogradely label trigemino-hypoglossal projections, small quantities of horse radish peroxidase were pressure-injected into the ipsilateral dorsal (mandibular) portion of the spinal V nucleus two days before the animals were killed. Survival periods ranged from 5 to 33 days after nerve injury (dpo). Axonal injury produced relative changes in the association of labelled axon terminals to structures in the hypoglossal nucleus on the injured side. The proportion of horse radish peroxidase-labelled spinal V nucleus terminals with spherical vesicles (S-terminals) that were unapposed to hypoglossal somata or dendrites increased rapidly and reached maximal levels by 11 dpo. By contrast, the isolation of labelled terminals with pleomorphic/flattened vesicles (P/F-terminals) from postsynaptic structures began later, advanced at a slower rate and did not attain maximal levels until 20 dpo. S-terminals not apposed to neuronal cell parts increased at a rate of 2.2 times greater than unapposed P/F-terminals. In addition, at peak levels, the proportion of labelled S-terminals that were detached from somata and dendrites was significantly greater than unapposed, labelled P/F-terminals. Axotomy did not alter the caliber of the labelled axon terminals. However, by 29 days after axotomy, the average diameter of dendrites remaining in contact with SPVN terminals was 1/3 the diameter of dendrites of uninjured neurons apposed to labelled axon terminals. These findings provide the morphological correlate for physiological and pharmacological evidence that the effectiveness of excitatory and inhibitory synapses are down-regulated in a coordinated manner after hypoglossal nerve injury.

Developmental changes in the expression of gamma-aminobutyric acidA/benzodiazepine receptor subunit mRNAs in the murine inferior olivary complex

The pharmacological and physiological properties of ligand-gated ion channels are dependent on their subunit composition; spontaneously occurring changes in subunit composition during neuronal development may result in dramatic functional differences between embryonic and adult forms of the receptor complex. In the present study, in situ hybridization with antisense cRNA probes was used to examine the subunit composition of the gamma-aminobutyric acidA/benzodiazepine (GABAA/BZ) receptor in the developing inferior olivary complex. This receptor is thought to be a pentameric chloride channel comprised of selected alpha, beta, gamma, delta, and rho subunits, the majority of which have several isoforms: alpha 1-6, beta 1-4, gamma 1-4, and rho 1,2. Among the 13 subunit variants present in the mammalian central nervous system, alpha 2-5, beta 3, and gamma 1,2 mRNAs are expressed at significant levels in the inferior olivary complex. Two clearly different temporal patterns of GABAA/BZ receptor subunit mRNA expression were observed: The expression of alpha 3, alpha 5, beta 3, and gamma 2 mRNAs was at a peak during embryonic and early postnatal development followed by rapid down-regulation thereafter. Conversely, alpha 2, alpha 4, and gamma 1 mRNA expression was very low or absent during early development, and a pronounced increase was observed at the end of postnatal week 1. These studies suggest that there are developmental changes in the subunit composition of the GABAA/BZ receptor in inferior olivary neurons. These changes in subunit expression, which occur during a period of major alterations in afferent and efferent synaptic connections, may subserve a change in the role of GABA from its function as a neurotrophic factor to that of an inhibitory neurotransmitter.

Ontogeny of GABAA/benzodiazepine receptor subunit mRNAs in the murine inferior olive: transient appearance of beta 3 subunit mRNA and [3H]muscimol binding sites

The GABAA/benzodiazepine receptor consists of at least four subunits, alpha, beta, gamma and delta, each comprised of several variants. The developmental expression of the alpha 1, beta 1-3, gamma 2 and delta subunits was studied in the murine inferior olivary nucleus by in situ hybridization with antisense cRNA probes. The postnatal appearance and distribution of [3H]flunitrazepam and [3H]muscimol binding sites, alpha and beta subunit-specific ligands respectively, were also studied autoradiographically. The beta 3 subunit was transiently expressed in each of the subnuclei of the inferior olive: The signal was strong at birth, increased throughout postnatal week 1 and rapidly declined thereafter to low adult levels. A similar pattern of labeling was observed with [3H]muscimol. Detectable levels of alpha 1 subunit mRNA hybridization signal and [3H]flunitrazepam binding sites were also present in the inferior olive at birth, decreasing thereafter. Low to moderate levels of beta 1, beta 2, and gamma 2 subunit mRNAs were present in olivary neurons throughout postnatal development, while delta mRNAs were largely absent. It has been reported previously that, during the 2nd postnatal week, the ratio of climbing fiber terminals to Purkinje cells is reduced from 3:1, as observed in neonates, to the 1:1 relationship observed in the adult cerebellar cortex. Our results raise the possibility that the subunit composition of the GABAA/benzodiazepine receptor in inferior olivary neurons undergoes changes during development, and that this process may be related to the elimination of multiple climbing fiber innervation of cerebellar Purkinje cells.

Changes in expression of peptides in rat facial motoneurons after facial nerve crushing and resection

In situ hybridization histochemistry was used to study changes in mRNAs coding neuropeptides such as alpha-calcitonin gene-related peptide (CGRP), beta-CGRP, cholecystokinin (CCK) and galanin, in rat facial motoneurons following axotomy of the facial nerve. In control rats, 38%, 55% and 7% of the facial motoneurons expressed alpha-CGRP, beta-CGRP and CCK mRNAs, respectively. No galanin mRNA-containing motoneurons were observed in these animals. The levels of mRNA for alpha-CGRP, CCK and galanin were increased while the beta-CGRP mRNA level was decreased after axotomy. The levels of mRNAs for these peptides returned to the control values by 2-4 weeks after nerve crush, whereas nerve resection had more prolonged effects. Within 3-4 weeks after injury, nerve resection had greater effects on beta-CGRP, CCK and galanin mRNAs than did nerve crush. Thus, there appear to be differences in the regulation of mRNA expression of these peptides in axotomized motoneurons.

Expression of choline acetyltransferase and nerve growth factor receptor within hypoglossal motoneurons following nerve injury

In the present study we employed light microscopic immunocytochemical techniques in order to investigate the temporal response of choline acetyltransferase (ChAT) and nerve growth factor receptor (NGFr) within hypoglossal motoneurons following unilateral transection or crushing of the XII nerve or after intraneural injections of ricin into the nerve. In control rats (i.e., sham operated) virtually all the motoneurons of the XII nucleus displayed intense immunolabeling for ChAT and were devoid of NGFr immunoreactivity. As early as 3 days post-operative the intensity and the number of ChAT-labeled neurons were reduced on the axotomized side compared to the non-lesioned side. This decrease was maximal approximately two weeks post-operative when virtually no ChAT-labeled cells were present on the lesioned side. In contrast, no loss of hypoglossal neurons was found using Nissl stains. This absence of ChAT immunolabeling persisted for several days, yet by 30 days many of the motoneurons had begun to re-express the enzyme. In contrast to the decrease in ChAT immunoreactivity, transection of the XII nerve also resulted in the expression of NGFr immunoreactivity within the lesioned motoneurons. This response was detected as early as one day post-operatively and continued throughout all time points thus far examined including times after many of the motoneurons had begun to re-express ChAT. Crushing of the XII nerve effected the expression of ChAT and NGFr in a manner comparable to, yet less intense than, that observed following transection. Ricin injected directly into the XII nerve resulted in the loss of hypoglossal motoneurons as demonstrated both in immunohistochemical and Nissl-stained tissue preparations. The cell loss was readily apparent 3 days post-operatively, and ChAT immunoreactivity permanently disappeared. NGFr immunolabeling was seen only in scattered surviving neurons but not in ricin poisoned cells. The possible mechanisms underlying the differential expression of ChAT and NGFr are discussed.

Effects of advancing age on the central response of rat facial neurons to axotomy: light microscope morphometry

Following axotomy, the regrowth of peripheral axons takes longer in older individuals than in young ones. The present study compares central responses of facial motor neurons to a crush injury of the facial nerve in 3-month-old and 15-month-old male rats sampled through 28 days post-crush (dpc). Neuronal somata, nuclei, and nucleoli were measured in 30 microns brain stem sections within subdivisions of the facial nucleus that contain the cell bodies responsible for the movement of the vibrissae. The temporal patterns of change in the size of the three structures were interpreted with reference to the re-establishment of functional connections, i.e., the return of voluntary vibrissae activity, which is delayed by 4 days in the older animals relative to the younger ones. There was no age-related difference in the pattern of somal swelling and recovery, nor was there an age-related difference in the response of nuclei and nucleoli to axotomy through 4 dpc. Both nuclei and nucleoli increased in size in animals of both age groups, but after 4 dpc in the older animals nuclear enlargement was prolonged and the nucleolar increases were less robust compared to the younger animals. The greatest age difference appeared with the re-establishment of functional connections. In the 3-month-old animals, the resumption of whisker activity coincided with vigorous transient increases in the sizes of nuclei and nucleoli; in the 15-month-old animals, there was little nuclear response to functional recovery and a comparatively small increase in nuclear sizes.(ABSTRACT TRUNCATED AT 250 WORDS)

RNA levels of neuronal nicotinic acetylcholine receptor subunits are differentially regulated in axotomized facial motoneurons: an in situ hybridization study

In situ hybridization histochemistry using complementary RNA probes revealed that alpha 3 and beta 2 neuronal nicotinic acetylcholine receptor subunit mRNAs were expressed in 12% and 40% of facial motoneurons of the rat, respectively. The alpha 3 subunit mRNA signals disappeared in response to axotomy, whereas the beta 2 subunit mRNA signal was remarkably enhanced, suggesting that mRNA levels of receptor subunits are differentially regulated in axotomized motoneurons.

GABA and benzodiazepine receptors in the cat motor thalamus after lesioning of nigro- and pallidothalamic pathways

Binding parameters of [3H]muscimol ([3H]MUS) and [3H]flunitrazepam ([ 3H]FLU) were determined in the thalamic area of overlap of nigro- and pallidothalamic pathways at short- (1-10 weeks) and long-term (6-11 months) survival times after kainic acid lesioning of substantia nigra pairs reticularis (SNr) and/or entopeduncular nucleus (EPN). No statistically significant lesion-induced changes in Kd could be established in any of the lesioned groups. Bmax values for both binding sites, when corrected for nerve cell densities, revealed some changes in all but one instance (no statistically significant changes in the number of [3H]MUS binding sites were detected after SNr lesions). Significant bilateral increase in the number of [3H]MUS binding sites was found after unilateral EPN and combined EPN + SNr lesions. In the first group the changes were transient; in the second, the number of binding sites appeared to be still on the rise at 8 months postlesion. The latter increase was interpreted as resulting from plasticity type changes in GABAergic local circuit neurons in response to massive deafferentation from extrinsic inhibitory inputs. Changes in [3H]FLU binding sites were of different character and of extremely low magnitude compared to changes in [3H]MUS binding sites. Subtle, but statistically significant, ipsilateral increase in the number of [3H]FLU binding sites as a function of time postlesion was found in the SNr lesioned group. In two other lesioned groups small magnitude increase occurred bilaterally, although in the EPN lesioned group it was more pronounced on the operated side. The results are consistent with earlier suggestion that [3H]MUS and [3H]FLU binding sites in the motor thalamus appear to be associated with different types of GABAergic synapses with none of them being directly associated with the basal ganglia thalamic pathways.

Incorporation of plasma [14C]palmitate into the hypoglossal nucleus following unilateral axotomy of the hypoglossal nerve in adult rat, with and without regeneration

Incorporation of plasma [14C]palmitate into the hypoglossal nucleus of the rat following transection, with and without regeneration of the hypoglossal nerve, was studied using quantitative autoradiography. The left hypoglossal nerve of 3-month-old, male Fischer-344 rats was transected using either: (1) an R-operation, which allowed nerve regeneration; or (2) a D-operation, in which regeneration was prevented. One to 84 days after axotomy, [14C]palmitate was injected intravenously and its rates of incorporation into stable structures of the left and right hypoglossal nuclei were measured at 4 h after injection. Following the R-operation, incorporation into the left hypoglossal nucleus was increased during and following axonal regeneration (up to 23% compared to control side), whereas incorporation was decreased 6-7% in the absence of regeneration, using the D-operation. The time courses of incorporation in both cases corresponded to histological changes, especially cell membrane changes following axotomy and suggest that [14C]palmitate incorporation reflects regenerative and degenerative neuronal changes associated with changes in lipid synthesis.

The localization of GABAA receptors in mice with mutations affecting the structure and connectivity of the cerebellum

The distribution of cerebellar [3H]muscimol binding sites was studied autoradiographically in normal C57BL/6J mice and in the weaver, reeler, Purkinje cell degeneration and staggerer mutant mice. In the normal 79-day-old mouse cerebellum, the highest concentration of [3H]muscimol binding sites was observed in the granule cell layer. A much lower grain density was present over the Purkinje cell and molecular layers and negligible numbers of binding sites were seen over the deep cerebellar nuclei and white matter. A significant decrease in [3H]muscimol labeling was observed over the cerebellar cortex of the 81-86-day-old weaver mutant; this was most pronounced in the vermis where granule cell loss was the greatest. Over the hemispheres, where fewer granule cells degenerate, a higher density of binding sites remained. In the 27-29-old reeler cerebellum, where Purkinje cells are malpositioned, no labeling was seen over the deep Purkinje cell masses. In the quasi-normal superficial cortex, labeling density over the surviving granule cell layer was only slightly decreased. In the 54-57-day-old Purkinje cell degeneration mutant, where essentially all Purkinje cells have disappeared by day 45, a 29% decrease in grain density over the granule cell layer was observed, while labeling was still present in the molecular layer. Virtually no [3H]muscimol labeling was detected over any part of the cerebellar cortex of the 25-27-day-old staggerer mutant (which lacks parallel fiber-Purkinje cell synapses), although clusters of surviving granule cells were present in significant numbers in the lateral aspects of the cortex. Our autoradiographic data indicate that GABAA receptors are associated with granule cells in both the molecular and granule cell layers. Furthermore, our results raise the possibility that the maintenance of receptor levels may be dependent upon synaptic contacts between the granule cell and its main postsynaptic target, the Purkinje cell.

Neural activity in the regenerating optic nerve of the goldfish

1. Retinal ganglion cells of one eye were axotomized in goldfish either by sectioning the contralateral optic tract or by ablating the contralateral lobe of the optic tectum. Between 2 and 40 days later, multiunit activity in response to diffuse light flashes was recorded from the axotomized and normal optic nerves, and from the optic tectum. 2. Two days after tract section, the amplitude of the integrated multiunit response of the axotomized nerve was normal. By 16 days it had fallen to 15% of control values, at which time visual responses carried by the regenerating tract were first recorded in tectum. Activity in the axotomized nerve then recovered gradually. 3. After ablation of one tectal lobe, multiunit responses in the axotomized nerve had not recovered by 40 days. 4. Integrated spontaneous activity in the axotomized nerve was depressed with a similar time course to the depression of light-evoked activity, both after tract section and tectal ablation. 5. Retinal ganglion cell nuclear size, a morphological indicator of the cell body reaction, varied inversely with evoked activity, whether axotomy was by tract section or by tectal ablation. 6. Electrically evoked compound action potentials of normal amplitude could be recorded from an axotomized nerve despite depressed responses to light flashes. 7. It is concluded that optic nerve axotomy in goldfish reduces the number of optic fibres carrying impulses and/or the frequency of their discharge. The effect is closely linked to morphological changes occurring in the retinal ganglion cell bodies. Recovery of impulse activity and morphology depends upon the regenerating optic fibres innervating an appropriate target.

Autoradiographic localization of M1 and M2 muscarine receptors in the rat brain

The distribution of M1 and M2 muscarine receptors in the rat brain was investigated by in vitro autoradiography. Muscarine receptors were visualized after complete receptor uncoupling in ethylenediaminetetraacetic acid buffer containing 1 mM N-ethyl maleimide and saturation with the ligand [3H]quinuclidinyl benzilate. Pirenzepine, an M1-selective antagonist, was used in our assays as a counter ligand to occlude M1 sites, allowing the primary ligand, [3H]quinuclidinyl benzilate, to label the remaining M2 muscarine receptors. In adjacent section, M1 muscarine receptors were labelled with [3H]quinuclidinyl benzilate in the presence of sufficient carbachol, and M2-selective agonist, to inhibit the binding to M2 sites. Our results reveal a heterogeneous distribution of M1 and M2 receptors. Increased densities of carbachol-resistant and pirenzepine-sensitive sites (M1 receptor subtype) were apparent over many forebrain structures including the olfactory tubercle, caudate-putamen, nucleus accumbens, hippocampus, amygdala and cerebral cortex. In contrast, pirenzepine-resistant and carbachol-sensitive sites (M2 receptor subtype) were distributed throughout the brain with increased densities apparent over regions known to contain large numbers of cholinergic cell bodies. M2 receptor localization patterns were largely coincident with the regional distribution and intensity of acetylcholinesterase positive sites. Since the M2 receptor pattern appears to parallel regional innervation densities, we conclude that the M2 receptor may serve as a marker for cholinergic pathways. The findings also suggest that M1 muscarine receptors are involved in the presumptive postsynaptic actions of acetylcholine in many forebrain structures.

Effects of spinal cord lesions and rhizotomies on cholinergic and opiate receptor binding sites in rat spinal cord

Changes in the distribution of [3H]quinuclidinylbenzilate ([3H]QNB), [3H] alpha-bungaro-toxin ([3H]alpha-Btx) and [3H]etorphine binding sites were studied autoradiographically, and cholinacetyltransferase (ChAT) activity radioenzymatically, in the C6-7 segments of rats 1-20 days after combined dorsal and ventral C3-8 rhizotomies and spinal cord lesions at C3. After dorsal and ventral rhizotomies the number of [3H]QNB, [3H]alpha-Btx and [3H]etorphine binding sites were reduced ipsilaterally in the dorsal horn and those of [3H]QNB and [3H]alpha-Btx in the ventral horn. In the ventral horn ChAT activity was significantly reduced. After a unilateral spinal cord lesion at C3, ChAT activity was reduced in the ipsilateral ventral horn at C6-7 caudal to the lesions, whereas no change in receptor binding sites was observed.

Chemoarchitectonic zonation of the monkey cerebellum

The modular organization of the monkey cerebellum is revealed in normal material by histochemical methods for demonstrating the presence of the enzymes acetylcholinesterase (AChE) and cytochrome oxidase (CO). In the cerebellar white matter, AChE- and CO-rich fibers are distributed in longitudinal compartments, which are aligned with AChE- and CO-rich bands in the granule cell layer, and with narrower AChE-rich strips in the molecular layer. The number and disposition of zones demonstrated histochemically are consistent with, and extend, the basic scheme of cerebellar zonation established by Voogd and Voogd and Bigaré.

Effect of vagotomy on cholinergic parameters in nuclei of rat medulla oblongata

Cholinergic enzymes and muscarinic receptors in nuclei of rat medulla oblongata were examined after unilateral vagotomy to determine their association with efferent vagal neurons. Vagotomy caused an ipsilateral depletion of acetylcholinesterase from the dorsal motor nucleus of the vagus (DNV) and the nucleus ambiguus (NA). Choline acetyltransferase activity was reduced in ipsilateral DNV, nucleus tractus solitarius and rostral NA. Muscarinic receptor localization by autoradiography with [3H]quinuclidinyl benzilate (QNB) revealed marked intranuclear variations in receptor density. Vagotomy had no effect on the QNB binding pattern. Loss of cholinergic enzymes is a consistent response of motor and preganglionic autonomic neurons to axotomy. Depletion of muscarinic receptors is an additional component of axon reaction in brain stem motoneurons. Accordingly, previous studies have shown a decrease in neurotransmitter-related proteins after axotomy of motoneurons. In the present study, cholinergic enzymes were depleted from axotomized vagal neurons but receptors were not. It is concluded that muscarinic receptors in the DNV and NA are not associated with vagal efferent neurons.

Effect of facial nerve transection on acetylcholinesterase, choline acetyltransferase and [3H]quinuclidinyl benzilate binding in rat facial nuclei

Choline acetyltransferase activity and localization of acetylcholinesterase and [3H]quinuclidinyl benzilate binding sites (muscarinic receptors) in rat facial nuclei were examined 2 weeks after right facial nerve transection or sham control surgery. Choline acetyltransferase activity in the right facial nucleus of nerve-transected rats was only one-third of that in the left nucleus. Histochemical observations revealed loss of acetylcholinesterase from most motoneurons and neuropil of the right facial nucleus after axotomy. Autoradiographic grains, marking muscarinic receptors, were likewise depleted substantially from this region. Facial nuclei of control animals were identical with respect to all of these neurochemical measures and undistinguishable from the left facial nucleus of nerve-transected rats. Cholinergic enzymes are known to be synthesized by motoneurons, but the source of muscarinic receptors in the facial nucleus is not known. Since all three proteins are depleted from the facial nucleus after axotomy of motoneurons, it is concluded that these cells produce cholinergic enzymes and muscarinic receptors. Synthesis of muscarinic receptors by facial motoneurons could indicate these neurons are cholinoceptive. Axotomy should be a useful tool for determining which other neurotransmitter receptors are produced by facial motoneurons and efferent neurons in other cranial nerve nuclei.

Suicide transport of ricin demonstrates the presence of substance P receptors on medullary somatic and autonomic motor neurons

Suicide transport of the toxic lectin, ricin, by hypoglossal and vagus neurons resulted in motor neuron loss in the associated nuclei, and reduced the binding of the 125I-Bolton-Hunter labeled substance P in the same nuclei. These data show that substance P receptors are located on the cell bodies of medullary somatic and preganglionic motor neurons of the hypoglossal and vagus nerves, and that suicide transport is a useful technique to determine the cellular localization of binding sites within a nucleus.

Cortically induced postsynaptic potentials in hypoglossal motoneurons after axotomy

Cortically induced postsynaptic potentials were studied in normal and axotomized cat hypoglossal motoneurons. In normal protruder motoneurons innervating tongue protruder muscles, we have demonstrated that stimulation of the orbital gyrus, at the point optimum for inducing lapping movements of the tongue by repetitive stimuli, produced inhibitory postsynaptic potentials or excitatory postsynaptic potentials followed by predominant inhibitory postsynaptic potentials. The cortically induced excitatory postsynaptic potential in normal protruder motoneurons was composed of only the short-latency component. In protruder motoneurons 30, 40, 60 and 80 days after axotomy, we have demonstrated that the number of protruder motoneurons responding with two components of excitatory postsynaptic potentials (the short- and the long-latency component) to cortical stimulation increased in correspondence with the lapse of days after axotomy and that the amplitude of cortically induced inhibitory postsynaptic potentials in axotomized protruder motoneurons was reduced in size as compared with normal protruder motoneurons.

Regulation of glycine receptor binding in the mouse hypoglossal nucleus in response to axotomy

Recent studies have shown that muscarinic receptors in brain hypoglossal nuclei exhibit a loss of specific ligand binding in response to axotomy of the hypoglossal nerve. The mouse hypoglossal nucleus contains a high level of receptors for the inhibitory neurotransmitter, glycine; the ligand [3H]strychnine binds to the glycine receptor with high affinity. In the present study [3H]strychnine binding in mouse hypoglossal nuclei was examined at 1 to 150 days after unilateral lesions of the hypoglossal nerve. Brains were sectioned on a cryostat, thaw-mounted onto microscope slides, incubated with [3H]strychnine and processed for light microscopic autoradiography. Receptor density was assessed by counting silver grains in photomicrographs of operated and control nuclei. During the first 25 days after axotomy grain density fell to 50 percent of that of the control nucleus. After this time grain density slowly increased, returning to control levels by 150 days post lesion. These data indicate that glycine receptors on the axotomized cells of the hypoglossal nucleus are lost when connection with the target muscles of the tongue is interrupted, and that the receptors reappear when the hypoglossal nerve regenerates. It is suggested that excitatory and inhibitory neurotransmitter receptor systems may be regulated in a coordinated fashion by the functional state of the motoneuron.

Distribution of muscarinic receptors on cultured myenteric neurons

The distribution of neurotransmitter receptors over the neuronal cell surface remains an outstanding question in neurobiology. In this study we have used autoradiographic procedures to localize muscarinic receptors on living cultures of enteric neurons, using the specific irreversible muscarinic ligand, [3H]propylbenzilylcholine mustard ([3H]PrBCM). Most of the label was associated with nerve processes surrounding the cell bodies and along the lengths of many of the neurites radiating from the cell bodies; a small proportion of the nerve cell bodies was also seen to be labeled. The distribution of autoradiograph silver grains along both varicose and non-varicose neurites demonstrated that muscarinic receptors were present on both pre-terminal and terminal regions of the nerve fibres.

Quantitative light microscopic autoradiographic localization of cholinergic muscarinic receptors in the human brain: brainstem

We have investigated the localization of muscarinic cholinergic receptors in the brainstem of eight patients free of neurological disease following quantitative autoradiography of microtome sections of postmortem tissue labeled in vitro with N-[3H]methyl scopolamine as a ligand. Receptor densities were quantified by microdensitometry with the aid of a computer assisted image analysis system. Our results reveal a heterogeneous distribution of receptor sites. High concentrations of muscarinic cholinergic receptor sites were associated with many nuclei and areas of the brainstem including the nucleus facialis (VII), hypoglossus (XII), ambiguus, the motor trigeminal nucleus (V), the nucleus solitarius, the nucleus of the lateral lemniscus, the superior and inferior colliculi, the sensory trigeminal nucleus (substantia gelatinosa), the pontine nuclei, the parabrachial nuclei, some tegmental nuclei and the periaqueductal gray matter. Very high concentrations of N-[3H]methyl scopolamine binding sites were also localized in the ventral tegmental area, the nucleus paranigralis and the nucleus ovalis. Receptor densities varied between individual brains although the relative distribution of the densities in the different nuclei was the same for all of the brains examined. Most of the brainstem nuclei containing muscarinic cholinergic receptors were enriched in high affinity agonist binding sites as shown by characteristic displacement of the ligand with carbachol. Exceptions were the substantia nigra, the nucleus olivaris inferior and the substantia gelatinosa of the fifth nerve. Receptor density values and pharmacological characteristics obtained in the cortex and basal ganglia in our cases are in good agreement with previously reported values in humans, using conventional biochemical methods. This indicates that procedures used in the autoradiographic technique are not detrimental to the pharmacological characteristics and densities of muscarinic cholinergic receptors. Our results thus clearly show the feasibility of using these techniques for the localization and quantification of muscarinic cholinergic receptors in human brain postmortem material. Furthermore, our findings indicate the potential involvement of the muscarinic cholinergic effect of acetylcholine in the normal function of many brainstem centers, including motor and sensory nuclei, visual and auditory relay nuclei and cardiovascular and respiratory-related nuclei.

Deafferentation and axotomy of neurons in cat striate cortex: time course of changes in binocularity following corpus callosum transection

Single neurons were recorded in the callosal terminal and cell zones of area 17 in the cat to assess the time course of changes in the proportion of binocular neurons produced by corpus callosum transection. The callosal terminal zone contains all the degenerating terminals in area 17 after corpus callosum transection. The callosal cell zone contains all the cells in area 17 which contribute axons to the corpus callosum. The cell zone is larger than, and partially overlaps, the callosal terminal zone. After corpus callosum transection there was an initial change in ocular dominance of neurons in both callosal zones. This initial change was followed by a reduction in the proportion of binocular neurons in both zones. This reduction became maximal 2-4 weeks after transection. In the callosal terminal zone, binocularity did not recover even at the longest postoperative periods examined (31-42 weeks). In the part of the callosal cell zone outside of the callosal terminal zone, the proportion of binocular neurons began to recover after 5 weeks and was at normal levels at the longest survival periods studied. Corpus callosum transection deafferents and axotomizes cells in the callosal terminal zone and, since central neurons do not regenerate their long-ranging axons, the combined effects of deafferentation and axotomy in this zone are permanent. The callosal cell zone outside of the callosal terminal zone contains axotomized cells and no degenerating terminals following transection. The recovery of binocularity in this region may be attributed to the transient changes which axotomized cells undergo. The zone which contains no callosal cells or terminals is unaffected by transection of the corpus callosum.

Autoradiographic localization of substance P receptors in rat medulla: effect of vagotomy and nodose ganglionectomy

Light microscopic autoradiography of [125I]Bolton-Hunter substance P binding sites was used to study the localization and denervation-induced changes in substance P receptors in the medulla oblongata. Substance P binding sites were widely distributed. The highest density was in the rostral nucleus ambiguus, dorsal motor nucleus of the vagus, nucleus of the solitary tract, hypoglossal nucleus, spinal trigeminal nucleus and inferior olive. Moderate density was apparent in the commissural nucleus of the solitary tract, area postrema, parvocellular reticular nucleus, medial vestibular nucleus and facial nucleus. The remainder of the medullary nuclei contained few or no specific substance P binding sites. Specific binding was inhibited by the addition of unlabeled substance P (1 microM). The association of substance P binding sites with the spinal trigeminal nucleus and with several nuclei involved in autonomic function suggest a role for substance P receptor activation in nociceptive and autonomic regulation, respectively. To study the influence of afferent and efferent denervation, the substance P binding sites in the medulla of sham operated rats were compared with those of both unilateral nodose ganglionectomized and cervical vagotomized rats. Substance P binding was unilaterally reduced in the rostral nucleus ambiguus and the rostral dorsal motor nucleus of the vagus with either surgical procedure. No changes in substance P binding were detected in other medullary nuclei, including the nucleus of the solitary tract, the site of termination of afferent vagal fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Synaptic efficacy of inhibitory synapses in hypoglossal motoneurons after transection of the hypoglossal nerves

In cat hypoglossal motoneurons after axotomy the synaptic efficacy of inhibitory synapses made by the lingual nerve afferent fibers was studied. The amplitude of the short- and the long-lasting inhibitory postsynaptic potential produced in tongue protruder motoneurons 24 days after axotomy by stimulation of the lingual nerve was significantly reduced in size as compared with the control on the unoperated side. In most protruder motoneurons 40 days after axotomy a large excitatory postsynaptic potential and a spike was produced by stimulation of either the ipsilateral or the contralateral lingual nerve. We have demonstrated that the decline of synaptic efficacy of inhibitory synapses for the short-lasting inhibitory postsynaptic potential was more prominent than that for the long-lasting inhibitory potential in the motoneuron 24 days after axotomy. After the cut axons of protruder motoneurons were re-united to tongue muscles, we have demonstrated that the decline of synaptic efficacy of inhibitory synapses for the short-lasting inhibitory postsynaptic potential was less prominent than that in axotomized protruder motoneurons.

Pathways of decomposition of propylbenzilylcholine mustard in neutral and alkaline solution

High-voltage electrophoresis has been used to follow the decomposition of propylbenzilylcholine mustard (PrBCM) in aqueous solution. Dilute solutions of PrBCM in 10 mM phosphate buffer, pH 7.5, or Krebs-Henseleit solution allowed to stand for 1 h at room temperature (22-24 degrees C) contain mainly the aziridinium ion derivative. At pH 7.5 the concentration of this ion declines slowly, giving rise first to the N-hydroxyethyl derivative and then ultimately, following hydrolysis of the ester bond, to NN-bis(2-hydroxyethyl)propylamine and benzilic acid. In contrast, in 5 mM NaOH the ester bond undergoes rapid hydrolysis, so that the major species present after 15 min at room temperature is the N-hydroxyethylaziridinium ion. This ion then undergoes slow reaction with hydroxy ion to yield the same final decomposition product, NN-bis(2-hydroxyethyl)propylamine, as is observed at pH 7.5.

In vivo modulation of the number of muscarinic receptors in rat brain by cholinergic ligands

Administration of the muscarinic agonist oxotremorine led to a decrease in the number of muscarinic receptors, as determined by specific binding of [3H]quinuclidinyl benzilate ([3H]QNB), in several rat brain regions both during development and at maturity. In contrast, administration of the muscarinic antagonist scopolamine led to an increase in the number of [3H]QNB-binding sites in various brain regions. Scopolamine also prevented the decrease in the number of [3H]QNB-binding sites induced by administration of an organophosphorus drug. The results are compatible with the hypothesis that the number of brain muscarinic receptors, or at least of a sub-class of them, is regulated by their transmitter.

Regional distribution of cholinergic muscarinic receptors in spinal cord

Quinuclidinylbenzilate ([3H]QNB) binding sites are present in the rat spinal cord. The binding site are muscarinic in character based on displacement of [3H]QNB by cholinoceptive drugs. They are distributed rather uniformly along the cord, although the receptor density is greater in gray matters than in white matter. Binding to white matter may be associated with glial cells. Within the gray matter, the receptor density is higher in the ventral horn than in the dorsal horn. In the thoracic region receptor density is about equal in the intermediate zone and ventral horn. Mid-thoracic transection of the cord does not change the receptor density or the dissociation constant of [3H]QNB in the lumbar cord. In contrast, treatment with the neurotoxin, 6-aminonicotinamide, which produces lesions of the cord, loss of motor control and paralysis, reduces the receptor density and affinity of [3H]QNB for lumbar gray matter but not white matter. The presence of [3H]QNB binding sites thrughout the spinal cord as well as the documented presence of acetylcholine-containing neurons, suggest that muscarinic receptors play a role in all phases of spinal cord physiology.

Muscarinic receptors in the central nervous system of the rat. II. Distribution of binding of [3H]propylbenzilylcholine mustard in the midbrain and hindbrain

The distribution of muscarinic receptors has been studied in the rat midbrain and hindbrain by counting silver grains in light microscope autoradiographs of the specific (atropine-sensitive) binding of [3H]propylbenzilylcholine mustard in cryostat sections. Of the 78 areas studied 6 had grain counts between 6 and 9 times the nonspecific level ("high"), and a further 15 had counts 4-6 times non-specific ("intermediate"). The basilar pontine nuclei and the ventral nuclei of the lateral lemniscus had high counts. Among the cranial nerve motor nuclei the facial and hypoglossal nuclei had high counts and the motor trigeminal nucleus and nucleus ambiguus had medium counts. The interpeduncular nucleus as a whole had low counts but there were two bands of intense staining on each side around the entry zone of the bundles of afferent cholinergic fibres from the habenula. Intermediate levels of binding occurred over the inferior colliculus and the superficial and intermediate grey layers of the superior colliculus. The molecular layer of the vestibulocerebellar vermis was distinctly labelled.

Muscarinic receptors in the central nervous system of the rat. I. Technique for autoradiographic localization of the binding of [3H]propylbenzilylcholine mustard and its distribution in the forebrain

[3H]Propylbenzilylcholine mustard ([3H]PrBCM) is a synthetic, potent muscarinic antagonist, which binds specifically and irreversibly by means of a covalent linkage to muscarinic receptors. Ten micrometer coronal cryostat sections taken through unfixed rat brain at the level of the maximum extent of the caudate nucleus were mounted on glass slides and incubated with 2.4 nM [3H]PrBCM at 30 degrees C for 25 min. They showed a total binding of 3250 pmol/g protein, of which 2130 pmol/g protein was sensitive to pretreatment with 10-6 M atropine. The specific (atropine-sensitive) binding was saturable. Saturation was reached at 15 min, with a rate constant of 1.3 x 106 M-1 sec-1. Binding was unaffected by drugs acting at nicotinic receptors (D-tubocurarine, hexamethonium), or by physostigmine, but was inhibited by muscarinic drugs (pilocarpine, oxotremorine, 3-quinuclidinylbenzilate). Postfixation for 15 min in Carnoy's fixative reduced the specific binding by 10% and the non-specific by 50%. Prefixation (i.e. before incubation with [3H]PrBCM) with any fixatives containing formaldehyde largely prevented specific binding, but a range of concentrations of glutaraldehyde (2% to 0.05%) caused only small reductions in specific binding (e.g. 0.1% glutaraldehyde caused only a 6% reduction). Clear, regionally specific patterns of localization of specific label in light microscope autoradiographs could be obtained from cryostat sections prefixed with 0.1% glutaraldehyde, incubated with 2.4 nM [3H]PrBCM for 15 min at 30 degrees C, and postfixed for 15 min in Carnoy's solution. Of the 105 forebrain areas studied 12 had grain counts between 6 and 9 times the non-specific level and a further 30 had counts 4 to 6 times non-specific. The higher grain counts were in the external plexiform layer of the olfactory bulb, anterior olfactory nucleus, olfactory tubercle, pyriform cortex, stratum radiatum of the hippocampus, stratum moleculare of the dentate gyrus, lateral amygdaloid nucleus, cortico-amygdaloid transition zone, anteroventral thalamic nucleus, hypothalamic supraoptic nucleus, caudate-putamen, nucleus accumbens, and in laminae 3 and 6 of the neocortex (parietal region). There were high grain densities over the choroid plexus the lateral but not the third or fourth ventricles.

Muscarinic receptofs in the central nervous system of the rat. III. Postnatal development of binding of [3H]propylbenzilylcholine mustard

The postnatal development of muscarinic receptors has been studied in 7 selected areas from the brains of 1-17-day-old rats by counting silver grains in light microscope autoradiographs of the specific (atropine-sensitive) binding of [3H]propylbenzilylcholine mustard in cryostat sections. A major part of the adult receptor density is present at 1 day of age, a time when only a small fraction of the adult number of synapses has yet been formed. Of the areas studied the hypoglossal nucleus is the most precocious in muscarinic receptor development, and the dentate gyrus the latest (associated with the late development of the dentate granule cells). The pattern of receptor distribution changes with development. The caudate-putamen first develops receptor in patches, beginning at the lateral (ventricular) surface. The pontine nuclei develop receptor in a medial to lateral sequence. The maturation of the adult laminar pattern of the olfactory bulb depends on the alignment of cells (especially the mitral cells). The neocortex initially has uniform labelling throughout its depth, and later the labelling in layer 4 becomes relatively less dense (probably associated with the ingrowth of afferent fibres). The hippocampal formation first develops receptor evenly over the pyramidal cell dendrites; later receptor appears over the newly formed dentate stratum moleculare and becomes much reduced over the hippocampal stratum lucidum and stratum lacunosum-moleculare (probably associated with the ingrowth of afferent fibres from the dentate gyrus and entorhinal area). In the cerebellum muscarinic receptor is found only in the lobules which receive the primary vestibular afferents. In the neonate it is present in the granular layer, but this later disappears and is replaced by the adult pattern of labelling in the molecular layer.