Calcium/Diacylglycerol-Dependent Protein Kinase and Its Major 87-Kilodalton Protein Substrate Are Differentially Distributed in Rat Basal Ganglia

When brain tissue is subjected to subcellular fractionation, both calcium/diacylglycerol-dependent protein kinase (protein kinase C) and an 87-kilodalton (kDa) protein substrate for this enzyme are enriched in the crude nerve terminal fraction. The present study, using chemical and surgical lesions of neurons in the rat neostriatum and substantia nigra, has examined whether the 87-kDa protein is colocalized with protein kinase C in identified neurons and nerve terminals. Our results show that, in the basal ganglia, protein kinase C is highly enriched in local striatal neurons and the striatonigral fibers and terminals. In contrast, the 87-kDa protein appears to be widely and evenly distributed in both neuronal and nonneuronal cells. The 87-kDa protein may therefore mediate functions of protein kinase C not restricted to nerve terminals.     

Ibotenic acid-induced lesions of striatal target and projection neurons: ultrastructural manifestations in dopaminergic and non-dopaminergic neurons and in glia

The cytological changes elicited by central microinjections of the excitotoxin, ibotenic acid (IBO) were examined in the adult rat striatonigral system using electron microscopic immunocytochemistry. The chemical markers included tyrosine hydroxylase (TH), a biosynthetic enzyme in dopaminergic neurons, and glial fibrillary acidic protein (GFAP). Both short (1-7 day) and long (30-60 days) term effects were evaluated at the site of IBO-injections in the striatum and more distally in the substantia nigra, which both contributes afferents and receives efferents from the striatum. In the neostriatum at every survival period examined, TH-labeled axonal processes appeared equally numerous in the control and IBO-injected hemispheres. However, the TH-labeled axons in the striatum ipsilateral to the IBO-injection were slightly enlarged, and generally lacked synaptic densities. In the early period the remaining neuropil showed signs of edema and contained perikarya and dendrites with vacuolar or dense cytoplasm as well as intact, unlabeled terminals. Numerous astrocytes, and apparently demyelinated axons were more commonly seen at the 7 day period. At 30 and 60 days, bundles of myelinated axons, unlabeled axon terminals, and astrocytes containing a variety of cytosomes and other cytoplasmic inclusions were in close apposition to TH-labeled axon terminals. These results suggest that the dopaminergic terminals may serve neuromodulatory functions with respect to glia or other afferent axons remaining after IBO-injections in the striatum. In the substantia nigra, homolateral to the injection, a dense type of degeneration was seen in a few perikarya and dendrites at 7 days of survival. At this stage, electron dense anterograde degeneration also was seen in terminals contacting both TH-labeled and unlabeled dendrites. The secondary long term changes in nuclear groups located distal to the primary lesion are characteristic of certain types of progressive human neuropathological disorders.     

Ultrastructural changes in the gracile nucleus of the spontaneously diabetic BB rat.

The present study describes the structural changes in the gracile nucleus of the spontaneously diabetic BB rat. At 3-7 days post-diabetes, axons, axon terminals and dendrites showed electron-dense degeneration. Degenerating axons were characterized by swollen mitochondria, vacuolation, accumulation of glycogen granules, tubulovesicular elements, neurofilaments and dense lamellar bodies. Degenerating axon terminals consisted of an electron-dense cytoplasm containing swollen mitochondria, vacuoles and clustering of synaptic vesicles. These axon terminals made synaptic contacts with cell somata, dendrites and other axon terminals. Degenerating dendrites were postsynaptic to normal as well as degenerating axon terminals. At 1-3 months post-diabetes, degenerating electron-dense axons, axon terminals and dendrites were widely scattered in the neuropil. Macrophages containing degenerating electron-dense debris were also present. At 6 months post-diabetes, the freshly degenerating neuronal elements encountered were similar to those observed at 3-7 days. However, there were more degenerating profiles at 6 months post-diabetes compared to the earlier time intervals. Terminally degenerating axons were vacuolated and their axoplasm appeared amorphous. It is concluded that degenerative changes occur in the gracile nucleus of the spontaneously diabetic BB rat.     

C-PON immunoreactive neurons in the neostriatum of the hedgehog (Erinaceus europaeus): a correlated light- and electron-microscopic study

The present study provides light- and electronmicroscopic immunocytochemical data on the presence of neurons that are immunoreactive to the C-terminal flanking peptide of neuropeptide Y, C-PON, in the neostriatum of the hedgehog (Erinaceus europaeus). Positive neurons have mostly fusiform or round perikarya from which two to four poorly branched processes arise. Immunostained fibers and puncta are also evenly distributed throughout the neostriatum. Ultrastructurally, each neuron exhibits a deeply invaginated nucleus surrounded by abundant cytoplasm with a well-developed rought endoplasmic reticulum and Golgi apparatus. Positive neurons receive symmetric and asymmetric synapses from unlabeled terminals. The results of this study can be correlated with previous findings, as the C-PON-positive neurons of the hedgehog resemble medium-sized neostriatal neurons that are known to be local circuit neurons exhibiting C-PON in the rat. Thus, a high degree of C-PON neuronal system phylogenetic conservation and function can be postulated for the neostriatum of mammals.     

鸽丘脑听觉中继核团传出神经投射的研究

应用神经示踪物生物素标记的葡聚糖对环鸽丘脑听觉中继核团的传出神经投射进行了研究。结果发现：（１）丘脑卵圆核的传出纤维投射至端脑新纹状体内侧的Ｌ２听区;（２）卵圆核壳的传出纤维投射至Ｌ１、Ｌ３和部分Ｌ２听区,在Ｌ区周围亦存在许多标记终末;（３）尾侧卵圆核壳的传出投射参与了卵圆核壳的形成并发出二束纤维分别投射至下丘脑腹内侧核和端脑新纹状体Ｌ区外侧的旁听区。本实验结果首次揭示在鸟类丘脑听中继核团、端脑新     

Cholinergic Surface Antigen Chol-1 Is Present in a Subclass of VIP-Containing Rat Cortical Synaptosomes

The colocalization of vasoactive intestinal polypeptide (VIP) with the cholinergic specific surface antigen Chol-1 was investigated in synaptosomes derived from the rat cerebral cortex. Immunoaffinity purification of cortical synaptosomes using antisera to Chol-1 resulted in the copurification of VIP and cholinergic nerve terminals. VIP was purified with a yield of 75% of that of choline acetyltransferase (ChAT). These results suggest that approximately 53% of the cortical cholinergic terminals contain VIP, whereas 75% of the cortical VIP content is present in these cholinergic terminals. Both hypotonic lysis and depolarization of the nerve terminals resulted in the differential release of VIP and acetylcholine (ACh), indicating the different compartmentalization in the same nerve terminal. Complement-mediated lysis of cholinergic nerve terminals, using antisera to Chol-1, resulted in the release of 64% of the ChAT, 71% of ACh, and 27% of the VIP. The application of our method enables quantifying and mapping, with a fast, efficient, and specific technique, the coexisting peptides in cholinergic neurons of distinct brain areas.     

The overlapping in the striatum of the projection areas of corticofugal fibers from the somatosensory and motor regions of the rat cerebral cortex]

The Fink-Heimer techniques were used to determine the neostriatal projections from cortical M1 and S1 physiologically identified representations of the forepaw. While corticostriatal fibres from S1 enter dorso-lateral parts of the neostriatum fibres from M1 penetrate the dorsal part of the neostriatum more rostrally. Both fibre groups pass in rostrocaudal direction to the globus pallidum, forming terminals on their way. Most of the fibre terminals of M1 projection are located laterally overlapping the zone of distribution of S1 fibre terminals in the neostriatum. Overlapping terminals of the corticofugal fibres of S1 and M1 in the lateral neostriatum can form a basis for interaction of somatosensory and motor impulses. It may be suggested that the role of the neostriatum in sensory integration is associated with certain features of the corticofugal fibre terminals distribution in it at all levels of development of the central nervous system.     

Synaptology of three peptidergic neuron types in the central nucleus of the rat amygdala

The synaptology of neurotensin (NT)-, somatostatin (SS)- and vasoactive intestinal polypeptide (VIP)-immunoreactive neurons was studied in the central nucleus of the rat amygdala (CNA). Three types of axon terminals formed synaptic contacts with peptide-immunoreactive neurons in the CNA: Type A terminals containing many round or oval vesicles; Type B terminals containing many pleomorphic vesicles; and Type C terminals containing fewer, pleomorphic vesicles. Peptide-immunoreactive terminals were type A. All three types of terminals formed symmetrical axosomatic and asymmetrical axodendritic contacts. However, type B and peptide-immunoreactive terminals frequently formed symmetrical axodendritic synaptic contacts. VIP-immunoreactive terminals also formed asymmetrical axodendritic contacts. SS- and NT-immunoreactive terminals commonly formed symmetrical contacts on SS- and NT-immunoreactive cell bodies, respectively. VIP-immunoreactive axon terminals were postsynaptic to nonreactive terminals. Type B terminals appeared more frequently on VIP neurons than on NT or SS neurons.     

The Intrinsic Organization of the Ventroposterolateral Nucleus and Related Reticular Thalamic Nucleus of the Rat: A Double-Labeling Ultrastructural Investigation with γ-Aminobutyric Acid Immunogold Staining and Lectin-Conjugated Horseradish Peroxidase

An electron-microscopic investigation of the synaptic organization of the rat's ventroposterolateral nucleus (VPL) and of a reticular thalamic nucleus (RTN) area related to somatosensory thalamic nucleus was performed. In a group of 11 rats, wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) was injected either in the first somatosensory area of cortex (SI) or in the dorsal column nuclei (DCN). The retrogradely and/or anterogradely transported enzyme was visualized using paraphenylenediamine-pyrocatechol (PPD-PC) as substrate. In a second series of six experiments, an immunocytochemical procedure using a specific anti-γ-aminobutyric acid (anti-GABA) was employed. Postembedding localization of GABA was performed for ultrastructural observation by means of the colloidal gold immunostaining procedure. Thin sections of recognized VPL and RTN areas from WGA:HRP-injected animals were further processed for immunocytochemistry in order to localize simultaneously, at the electron-microscopic level, the transported enzyme and GABA.

The results obtained with this procedure demonstrated that HRP-labeled terminals from DCN contacted the soma and proximal dendrites of VPL neurons, while the terminals labeled after SI cortical injections were predominantly localized to the distal portion of the dendrites. The same cortical injection also determined the presence of labeled synaptic boutons contacting the soma, and both proximal and distal dendrites of RTN neurons. GABA-immunolabeled terminals were observed in VPL in a number larger than those observed with other methods, since not only typical F terminals were labeled but also terminals containing round and/or pleomorphic vesicles. GABA-ergic terminals contacted the soma and the proximal and distal dendrites of VPL neurons, while in RTN cells they made synaptic contact mainly with the soma and proximal dendrites. In the double-labeling experiments, terminals containing both HRP and specific immunogold GABA staining were never observed.

The present data provide a direct demonstration of the presence of a strong inhibitory input from RTN upon VPL neurons and of the existence of autoinhibition within RTN neurons.     

Septal afferents to the area dentata terminate on vasoactive intestinal polypeptide (VIP)-like immunoreactive,non-pyramidal neurons

Summary Thermic lesions in the medial septum of adult rats result in dark degeneration of terminal boutons in the stratum moleculare and hilus of the area dentata. While most of the degenerating terminals are in synaptic contact with non-reactive cells, part of them end on dendrites of VIP-like immunoreactive neurons.     

Kinetic Parameters and Lactate Dehydrogenase Isozyme Activities Support Possible Lactate Utilization by Neurons

Lactate is potentially a major energy source in brain, particularly following hypoxia/ischemia; however, the regulation of brain lactate metabolism is not well understood. Lactate dehydrogenase (LDH) isozymes in cytosol from primary cultures of neurons and astrocytes, and freshly isolated synaptic terminals (synaptosomes) from adult rat brain were separated by electrophoresis, visualized with an activity-based stain, and quantified. The activity and kinetics of LDH were determined in the same preparations. In synaptosomes, the forward reaction (pyruvate + NADH + H⁺ → lactate + NAD⁺), which had a V _max of 1,163 μmol/min/mg protein was 62% of the rate in astrocyte cytoplasm. In contrast, the reverse reaction (lactate + NAD⁺ → pyruvate + NADH + H⁺), which had a V _max of 268 μmol/min/mg protein was 237% of the rate in astrocytes. Although the relative distribution was different, all five isozymes of LDH were present in synaptosomes and primary cultures of cortical neurons and astrocytes from rat brain. LDH1 was 14.1% of the isozyme in synaptic terminals, but only 2.6% and 2.4% in neurons and astrocytes, respectively. LDH5 was considerably lower in synaptic terminals than in neurons and astrocytes, representing 20.4%, 37.3% and 34.8% of the isozyme in these preparations, respectively. The distribution of LDH isozymes in primary cultures of cortical neurons does not directly reflect the kinetics of LDH and the capacity for lactate oxidation. However, the kinetics of LDH in brain are consistent with the possible release of lactate by astrocytes and oxidative use of lactate for energy in synaptic terminals. Special issue dedicated to John P. Blass.     

Axons containing neuropeptide Y innervate arginine vasopressin-containing neurons in the rat paraventricular nucleus

Summary Synaptic connections between neurons immunoreactive for arginine vasopressin (AVP) and axon terminals immunoreactive for neuropeptide Y (NPY) were found in the magnocellular part of the paraventricular nucleus (PVN) in the rat hypothalamus. In pre-embedding double immunolabeling, NPY axon terminals labeled with diamin-obenzidine (DAB) reaction product established synaptic junctions on the perikarya and neuronal processes of AVP neurons labeled with silver-gold particles. Ultrastructural morphology of the neurons was more suitably preserved by a combination of pre- and post-embedding procedures. The presynaptic NPY terminals contained many small clear vesicles and a few cored vesicles, and DAB chromogen (immunoreaction product) was located on the surface of the vesicular profiles and on the core. The postsynaptic AVP neurons possessed many large secretory granules labeled with gold particles. At the synaptic junctions, small clear vesicles were accumulated at the presynaptic membrane, and the postsynaptic membrane was coated with a dense accumulation of fine electron dense particles. The perikarya also received synapses made by immuno-negative axon terminals containing many small clear vesicles and a few cored vesicles. These terminals were found more frequently than those containing NPY.     

Histochemical demonstration of transmitter release from noradrenaline,dopamine and 5-hydroxytryptamine nerve terminals in field stimulated rat brain slices

Summary The effect of electrical field stimulation on noradrenaline (NA), dopamine (DA) and 5-hydroxytryptamine (5-HT) nerve terminals in rat brain slicesin vitro was investigated. Slices prepared from the cerebral cortex or the neostriatum were incubated in physiologic buffer for 30 min and then superfused by buffer and stimulated by an electrical field (biphasic pulses, 10 Hz, 12 mA, 2 ms) for various time periods. The effect of the stimulation was studied at the cellular level with the histochemical fluorescence technique of Falck and Hillarp. The transmitter overflow into the superfusing buffer caused by the stimulation was studied with isotope technique. Cerebral Cortex NA Nerve Terminals. Stimulation caused release of NA from cortical NA nerve terminals. Already after 2 min stimulation a slight decrease of the fluorescence intensity of the nerve terminals could be found. Stimulation for 15 to 30 min greatly reduced the fluorescence intensity. In slices preincubated with³H-NA the stimulation-induced overflow of tritium during 2 min stimulation was about 15% (i.e. 15% of the tissue tritium content was overflowing into the superfusing buffer in response to stimulation for 2 min). During prolonged stimulation there was a considerable decline of the tritium efflux. Cerebral Cortex 5-HT Nerve Terminals. The 5-HT-analogue 6-hydroxytryptamine (6-HT) which is readily taken up into 5-HT nerve terminals was used to permit good visualization of these nerve terminals. Uptake of 6-HT into cortical NA nerve terminals was prevented by preincubation with 6-hydroxydopamine (6-OH-DA) or protriptyline. Stimulation for 15 to 30 min reduced the fluorescence intensity of the 5-HT nerve terminals. In slices preincubated with³H-5-HT the stimulation-induced overflow of tritium during 2 min stimulation was about 5%. The tritium efflux slowly decreased during continuous stimulation. Neostriatal DA Nerve Terminals. In slices frozen directly after preparation an intense diffuse fluorescence could be seen. After incubation in drug-free buffer at 37° C the fluorescence was localized in the varicosities of the DA nerve terminals. The central parts of the slices almost completely lacked specific fluorescence, while the outer zones were brightly fluorescent. No clear reduction of the fluorescence intensity of the DA nerve terminals in the outer zone could be observed after stimulation for 30 min. In slices preincubated with³H-DA the stimulation-induced overflow of tritium during 2 min stimulation was about 2%. The tritium efflux slowly decreased during continuous stimulation.It is suggested that the differences in release between the various nerve terminal systems foundin vitro reflect differences in transmitter release occurringin vivo. The comparably high release of NA per impulse from the cortical NA nerve terminals implicate that the discharge rate of these neuronsin vivo is very low.This investigation has been supported by grants from the Swedish Medical Research Council (B72-14X-2330-05A) and Magnus Bergwall's Foundation.The author is greatly indebted to Mrs. Annika Hamberger for her skillful technical assistance. For generous supplies of drugs thanks are due to Hässle, Göteborg, Sweden, through Dr. H. Corrodi (6-HT, 6-OH-DA and H44/68).     

Involvement of Different Types of Voltage-Sensitive Calcium Channels in the Presynaptic Regulation of Noradrenaline Release in Rat Brain Cortex and Hippocampus

Abstract: Transmitter release at the nerve terminal is mediated by the influx of Ca²⁺ through voltage-sensitive calcium channels (VSCCs). Many types of VSCCs have been found in neurons (T, N, L, and P), but uncertainty remains about which ones are involved in neuronal excitation-secretion coupling. Specific ligands for the L- and N-type VSCCs were used to determine which of these subtypes might be involved in the K⁺-evoked [³H]noradrenaline release from superfused rat brain cortical and hippocampal synaptosomes. In cortical presynaptic terminals the 1,4-dihydropyridine agonist Bay K 8644 enhanced the K⁺ (15 m M )-evoked [³H]noradrenaline release. This effect was reversed by the 1,4-dihydropyridine antagonists nimodipine and nitrendipine. The L-type VSCC ligands had no effect on hippocampal synaptosomes. In contrast, the N-type VSCC blocker ω-conotoxin markedly reduced the K⁺-evoked [³H]noradrenaline release in nerve terminals from both regions. Inhibition was greater in hippocampal synaptosomes. When applied together the inhibitory actions of nimodipine and ω-conotoxin were approximately additive. These findings indicate that both L- and N-type VSCCs participate in noradrenaline release in rat brain cortex and suggest that noradrenergic terminals in the two regions examined may have distinct populations of VSCCs: L type in cortex and N type in hippocampus.     

Subcortical projections of the visual cortex in the adult albino rat and during postnatal development

We have investigated the subcortical projections of the rat striate cortex by using the silver-degeneration method and the HRP-technique too. Cortical lesions were made in 60 young animals (1, 4, 5, 6, 7, 10 and 14 days old) and in 6 adult rats. The terminal regions of projection occurred only ipsilateral to the lesions. After passing the internal capsule the degenerating pathway divides into 2 bundles. In the dorsal thalamus one of them runs in caudal direction. The other bundle turns ventrally, reaches the cerebral peduncle and terminates in the pons. The first fibre bundle terminates in the following structures: Nc. reticularis thalami, Nc. lateralis thalami, Nc. lateralis posterior thalami, Corpus geniculatum laterale, pars dorsalis (Cgld), Corpus geniculatum laterale, pars ventralis (Cglv), Nc. praetectalis anterior et posterior and Colliculus superior. The fibers of the second bundle innervate the Nc. lateralis pontis. Fibers from this bundle terminate probably in the Cglv and in the Zona incerta too. By using the HRP-technique it could be demonstrated that the axons terminating in the Cgld originate in layer VI of the area 17. In contrast, the projection to Cglv, Nc. lateralis posterior, Colliculus superior and Nc. lateralis pontis originates from pyramidal cells in layer V. The development of the projection in young animals indicates: Like in adults rats, terminal degeneration is present in all subcortical projection regions at postnatal day (PD) 10. At PD 4-7 we can observe heavily degenerating axons but the terminal degeneration is different. It is remarkable in the "visual" part of the reticular nucleus and iln the Cgld (decreasing from inside to outside). Only a weak terminal degeneration is visible in the pretectal region and in the superior colliculus. At PD 1 the trajectory of degenerating fibres is clearly visible. Signs of terminal degeneration can only be found in the reticular nucleus. It is discussed whether the date of generation of the cortical neurons and the time of the differentiation of the cortical layers is of importance for the time of innervation of the subcortical projection fields. The question when the axons arrive at their terminal region and form there synaptic contacts has not yet been exactly answered. To solve this problem electronmicroscopic investigations are necessary.     

DARPP-32 and Phosphatase Inhibitor-1, Two Structurally Related Inhibitors of Protein Phosphatase-1, Are Both Present in Striatonigral Neurons

DARPP-32 (dopamine- and cyclic AMP-regulated phosphoprotein of Mr = 32,000) and phosphatase inhibitor-1, two previously characterized inhibitors of protein phosphatase-1, were identified in both the neostriatum and the substantia nigra. Phosphatase inhibitor-1 was partially purified from bovine caudate nucleus and found to be distinct from DARPP-32 in some of its biochemical properties. The neuronal localization of DARPP-32 and phosphatase inhibitor-1 within the rat neostriatum and substantia nigra was investigated by studying the effects of kainic acid. Injection into the neostriatum of kainic acid, which destroys striatonigral neurons and striatonigral fibers, decreased the amounts of DARPP-32 and phosphatase inhibitor-1 to the same extent, both in the lesioned neostriatum and in the ipsilateral substantia nigra. The specific activity of protein phosphatase-1 in the neostriatum was unaffected by kainic acid. The results indicate that, in rat brain, DARPP-32 and phosphatase inhibitor-1 are both present in striatal neurons and in striatonigral fibers, and that they probably coexist in at least a subpopulation of striatonigral neurons. In contrast, protein phosphatase-1 does not appear to be enriched in any specific neuronal subpopulation in the neostriatum.     

Axons containing neuropeptide Y innervate arginine vasopressin-containing neurons in the rat paraventricular nucleus. Dual electron microscopic immunolabeling

Synaptic connections between neurons immunoreactive for arginine vasopressin (AVP) and axon terminals immunoreactive for neuropeptide Y (NPY) were found in the magnocellular part of the paraventricular nucleus (PVN) in the rat hypothalamus. In pre-embedding double immunolabeling, NPY axon terminals labeled with diaminobenzidine (DAB) reaction product established synaptic junctions on the perikarya and neuronal processes of AVP neurons labeled with silver-gold particles. Ultrastructural morphology of the neurons was more suitably preserved by a combination of pre- and post-embedding procedures. The presynaptic NPY terminals contained many small clear vesicles and a few cored vesicles, and DAB chromogen (immunoreaction product) was located on the surface of the vesicular profiles and on the core. The postsynaptic AVP neurons possessed many large secretory granules labeled with gold particles. At the synaptic junctions, small clear vesicles were accumulated at the presynaptic membrane, and the postsynaptic membrane was coated with a dense accumulation of fine electron dense particles. The perikarya also received synapses made by immuno-negative axon terminals containing many small clear vesicles and a few cored vesicles. These terminals were found more frequently than those containing NPY.     

人胚DA能神经元移植于帕金森氏病猴模型的TH免疫细胞化学的研究

为了对人胚黑质ＤＡ神经元移植治疗ＰＤ人的临床应用作出客观评估,将８－１２周人胚黑质细胞移植到用ＭＰＴＰ诱发的偏侧ＰＤ猴新纹状体内。实验动物分别存活２个月、５个月和１年后,用ＴＨ免疫细胞化学方法对被移植的人胚ＤＡ细胞的存活和与宿主间的突触联系进行检查。在光镜下可见被移植侧的新纹状体内有ＴＨ阳性细胞,它们成小群散在分布,每小群有３－１０个细胞。ＴＨ阳性细胞的轴突延伸到整个新纹状体,树突呈现出正常发育过     

Calcitonin Gene-Related Peptide (CGRP)-Positive Neurons and Fibers in the Cat Periaqueductal Grey Matter

The morphology and topographical distribution of neurons and terminals containing calcitonin gene-related peptide (CGRP) immunoreactivity in the cat periaqueductal grey (PAG) were studied using a rabbit antiserum raised against the C-terminal region of rat α-CGRP. In normal cats, numerous fibers, but rarely immunoreactive neurons, were observed in the PAG. CGRP-containing fibers showed bouton-like swellings along their length and expanded in terminal clusters of boutons. In many cases, CGRP-positive fibers were also observed in close association with small blood vessels. Immunoreactive fibers were particularly numerous at caudal PAG levels, mostly in its ventrolateral portion. In colchicine-treated cats, the pattern of CGRP-containing fibers was basically unchanged, despite a reduction of both the number of fibers and the intensity of fiber staining; in addition, numerous CGRP-positive neurons were found, mostly in the ventrolateral portion of the caudal PAG. These neurons were fusiform, spheroidal, and triangular in shape. The selective distribution of CGRP-positive elements in the PAG suggests a functional specialization of these neurons in the activation of pain-modulating mechanisms.     

Calcitonin gene-related peptide (CGRP)-positive neurons and fibers in the cat periaqueductal grey matter

The morphology and topographical distribution of neurons and terminals containing calcitonin gene-related peptide (CGRP) immunoreactivity in the cat periaqueductal grey (PAG) were studied using a rabbit antiserum raised against the C-terminal region of rat alpha-CGRP. In normal cats, numerous fibers, but rarely immunoreactive neurons, were observed in the PAG. CGRP-containing fibers showed bouton-like swellings along their length and expanded in terminal clusters of boutons. In many cases, CGRP-positive fibers were also observed in close association with small blood vessels. Immunoreactive fibers were particularly numerous at caudal PAG levels, mostly in its ventrolateral portion. In colchicine-treated cats, the pattern of CGRP-containing fibers was basically unchanged, despite a reduction of both the number of fibers and the intensity of fiber staining; in addition, numerous CGRP-positive neurons were found, mostly in the ventrolateral portion of the caudal PAG. These neurons were fusiform, spheroidal, and triangular in shape. The selective distribution of CGRP-positive elements in the PAG suggests a functional specialization of these neurons in the activation of pain-modulating mechanisms.