A light and electron microscopic study of GAT-1-positive cells in the cerebral cortex of man and monkey

Summary Specimens of human cerebral cortex were obtained during neurosurgical operations and studied by immunocytochemistry and electron microscopy, using antibodies to the GABA transporter GAT-1. Cortical material from macaque monkeys was prepared similarly. Large numbers of GAT-1-positive non-pyramidal neurons were observed in layers I, II, V, and VI of the cortex. Electron microscopy also showed that the GAT-1-positive axon terminals formed symmetrical and not asymmetrical synapses, suggesting that they were the terminals of non-pyramidal neurons. Processes of cells in the walls of blood vessels were also labelled. We conclude that GAT-1 is present in cell bodies and axon terminals of non-pyramidal neurons, and a population of mural cells in blood vessels, in the primate cerebral cortex.     

A light and electron microscopic study of the GABA transporter GAT-3 in the monkey basal ganglia and brainstem

The present study aimed to elucidate the distribution of the GABA transporter GAT-3 in the monkey basal ganglia and brainstem. Very dense GAT-3 immunoreactivity was observed in the medial septum, diagonal band, basal nucleus of Meynert, thalamus, globus pallidus, and substantia nigra. Moderate levels were observed in the subthalamic nucleus, periaqueductal grey, spinal trigeminal and vestibular nuclei. A general light level of staining was observed in the remainder of the brainstem regions, and very light staining was observed in the caudate nucleus and putamen. Electron microscopy showed that GAT-3 immunoreactivity was present in cell bodies with light cytoplasm and dense bundles of glial filaments, and features of astrocytes. Large numbers of astrocytic processes were also labeled in the neuropil. The cell bodies and processes of neurons were unlabeled. Further study is necessary to elucidate GAT-3 expression in neurological conditions, including hyperalgesia and Parkinson's disease.     

GAT-1 regulates both tonic and phasic GABA(A) receptor-mediated inhibition in the cerebral cortex

γ-Aminobutyric acid 1 (GAT-1) is the most copiously expressed GABA transporter; we studied its role in phasic and tonic inhibition in the neocortex using GAT-1 knockout (KO) mice. Immunoblotting and immunocytochemical studies showed that GAT-2 and GAT-3 levels in KOs were unchanged and that GAT-3 was not redistributed in KOs. Moreover, the expression of GAD65/67 was increased, whereas that of GABA or VGAT was unchanged. Microdialysis studies showed that in KOs spontaneous extracellular release of GABA and glutamate was comparable in WT and KO mice, whereas KCl-evoked output of GABA, but not of glutamate, was significantly increased in KOs. Recordings from layer II/III pyramids revealed a significant increase in GABA_AR-mediated tonic conductance in KO mice. The frequency, amplitude and kinetics of spontaneous inhibitory post-synaptic currents (IPSCs) were unchanged, whereas the decay time of evoked IPSCs was significantly prolonged in KO mice. In KO mice, high frequency stimulation of GABAergic terminals induced large GABA_AR-mediated inward currents associated with a reduction in amplitude and decay time of IPSCs evoked immediately after the train. The recovery process was slower in KO than in WT mice. These studies show that in the cerebral cortex of GAT-1 KO mice GAT-3 is not redistributed and GADs are adaptively changed and indicate that GAT-1 has a prominent role in both tonic and phasic GABA_AR-mediated inhibition, in particular during sustained neuronal activity.     

Expression of GABA transporters,GAT-1 and GAT-3, in the cerebral cortex and thalamus of the rat during postnatal development

The cellular and subcellular localization of two GABA transporters, GAT-1 and GAT-3, was investigated using immunocytochemical methods in the rat cerebral cortex and thalamus during postnatal development. The distribution of the transporters is compared with that of the neuronal marker GABA, and with that of vimentin and of glial fibrillary acidic protein, which identify immature and mature astrocytes, respectively. Our observations show that the two transporters are already expressed at birth in both brain areas with the same cellular localization as in adult rats, as GAT-1 is present in growth cones and terminals only in the cortex, whereas both transporters are expressed in astrocytes in the cortex and thalamus. The distribution of GAT-1 and GAT-3 undergoes postnatal changes reflecting in general the neurogenetic events of the neocortex and thalamus and, more specifically, the maturation of GABAergic innervation. The adult-like pattern of expression is achieved in the third postnatal week in the cortex and in the second postnatal week in the thalamus. The early expression of GAT-1 in GABAergic terminals confirms previous studies showing the existence of neuronal mechanisms of GABA uptake from the embryonic stages. As for the glial localization, the precocious existence of two astrocytic GABA transporters suggests that they operate through different functional mechanisms from birth, whereas their exclusively glial expression in the thalamus indicates that the astroglia plays a major role in the transport, recycling and metabolism of thalamic GABA.     

Brain-derived neurotrophic factor (BDNF) enhances GABA transport by modulating the trafficking of GABA transporter-1 (GAT-1) from the plasma membrane of rat cortical astrocytes

The γ-aminobutyric acid (GABA) transporters (GATs) are located in the plasma membrane of neurons and astrocytes and are responsible for termination of GABAergic transmission. It has previously been shown that brain derived neurotrophic factor (BDNF) modulates GAT-1-mediated GABA transport in nerve terminals and neuronal cultures. We now report that BDNF enhances GAT-1-mediated GABA transport in cultured astrocytes, an effect mostly due to an increase in the V(max) kinetic constant. This action involves the truncated form of the TrkB receptor (TrkB-t) coupled to a non-classic PLC-γ/PKC-δ and ERK/MAPK pathway and requires active adenosine A(2A) receptors. Transport through GAT-3 is not affected by BDNF. To elucidate if BDNF affects trafficking of GAT-1 in astrocytes, we generated and infected astrocytes with a functional mutant of the rat GAT-1 (rGAT-1) in which the hemagglutinin (HA) epitope was incorporated into the second extracellular loop. An increase in plasma membrane of HA-rGAT-1 as well as of rGAT-1 was observed when both HA-GAT-1-transduced astrocytes and rGAT-1-overexpressing astrocytes were treated with BDNF. The effect of BDNF results from inhibition of dynamin/clathrin-dependent constitutive internalization of GAT-1 rather than from facilitation of the monensin-sensitive recycling of GAT-1 molecules back to the plasma membrane. We therefore conclude that BDNF enhances the time span of GAT-1 molecules at the plasma membrane of astrocytes. BDNF may thus play an active role in the clearance of GABA from synaptic and extrasynaptic sites and in this way influence neuronal excitability.     

GABA-immunohistological observations, at the electron-microscopical level, of the neurons of isthmic nuclei in chicken, Gallus domesticus

Following a demonstration of Golgi-impregnated neurons and their terminal axon arborization in the optic tectum, the neurons of the nucleus parvocellularis and magnocellularis isthmi were studied by means of postembedded electron-microscopical (EM) γ-aminobutyric acid (GABA)-immunogold staining. In the parvocellular nucleus, none of the neuronal cell bodies or dendrites displayed GABA-like immunoreactivity in EM preparations stained by postembedded GABA-immunogold. However, numerous GABA-like immunoreactive and also unlabeled terminals established synapses with GABA-negative neurons. GABA-like immunoreactive terminals were usually found at the dendritic origin. Around the dendritic profiles, isolated synapses of both GABA-like immunoreactive and immunonegative terminals established glomerulus-like structures enclosed by glial processes. All giant and large neurons of the magnocellular nucleus of the isthmi displayed GABA-like immunoreactivity. Their cell surface was completely covered by GABA-like immunoreactive and unlabeled terminals that established synapses with the neurons. These neurons are thought to send axon collaterals to the parvocellular nucleus; their axons enter the tectum opticum. The morphological characteristics of neurons of both isthmic nuclei are like those of interneurons, because of their numerous axosomatic synapses with both asymmetrical and symmetrical features. These neurons are not located among their target neurons and exert their modulatory effect on optic transmission in the optic tectum at a distance.     

GABA immunoreactivity in the human cerebellar cortex: a light and electron microscopical study

The distribution of gamma-aminobutyric acid (GABA) in surgical samples of human cerebellar cortex was studied by light and electron microscope immunocytochemistry using a polyclonal antibody generated in rabbit against GABA coupled to bovine serum albumin with glutaraldehyde. Observations by light microscopy revealed immunostained neuronal bodies and processes as well as axon terminals in all layers of the cerebellar cortex. Perikarya of stellate, basket and Golgi neurons showed evident GABA immunoreactivity. In contrast, perikarya of Purkinje neurons appeared to be negative or weakly positive. Immunoreactive tracts of longitudinally- or obliquely-sectioned neuronal processes and punctate elements, corresponding to axon terminals or cross-sectioned neuronal processes, showed a layer-specific pattern of distribution and were seen on the surface of neuronal bodies, in the neuropil and at microvessel walls. Electron microscope observations mainly focussed on the analysis of GABA-labelled axon terminals and of their relationships with neurons and microvessels. GABA-labelled terminals contained gold particles associated with pleomorphic vesicles and mitochondria and established symmetric synapses with neuronal bodies and dendrites in all cortex layers. GABA-labelled terminals associated with capillaries were seen to contact the perivascular glial processes, basal lamina and endothelial cells and to establish synapses with subendothelial unlabelled axons.     

A light and electron microscopic study of betaine/GABA transporter distribution in the monkey cerebral neocortex and hippocampus

The present study aimed to elucidate the distribution of betaine/γ-aminobutyric acid (GABA) transporter-1 (BGT-1) in the normal monkey cerebral neocortex and hippocampus by immunoperoxidase and Immunogold labelling. BGT-1 was observed in pyramidal neurons in the cerebral neocortex and the CA fields of the hippocampus. Large numbers of small diameter dendrites or dendritic spines were observed in the neuropil. These made asymmetrical synaptic contacts with unlabelled axon terminals containing small round vesicles, characteristic of glutamatergic terminals. BGT-1 label was observed in an extra-perisynaptic region, away from the post-synaptic density. Immunoreactivity was not observed in portions of dendrites that formed symmetrical synapses, axon terminals, or glial cells. The distribution of BGT-1 on dendritic spines, rather than at GABAergic axon terminals, suggests that the transporter is unlikely to play a major role in terminating the action of GABA at a synapse. Instead, the osmolyte betaine is more likely to be the physiological substrate of BGT-1 in the brain, and the presence of the transporter in pyramidal neurons suggests that these neurons utilize betaine to maintain osmolarity.     

Ultrastructural immunocytochemical localization of excitatory amino acids in the somatosensory system.

We studied the ultrastructure and the synaptic arrangement of glutamate-immunoreactive terminals in rats, in the superficial laminae of the spinal cord, the brainstem cuneate nucleus, and the thalamic ventroposterolateral nucleus, where a role for glutamate as neurotransmitter has been suggested by biochemical, physiological and pharmacological approaches. The antiserum employed was raised against glutaramate conjugated to keyhole limpet hemocyanin with glutaraldehyde, and was used for pre-embedding staining with an avidin-biotin-peroxidase method and for post-embedding staining with an immunogold procedure. Both methods yielded similar results, consisting of labeling of selected terminals in all the areas examined. Double immunogold labeling on the same thin section using antisera against gamma-amino-butyric acid (GABA) or substance P (SP), in combination with the anti-glutamate serum, showed that staining for glutamate and GABA was present in different terminals in all the regions examined; glutamate and SP were co-localized in a few terminals only in the superficial laminae of the spinal cord. By performing immunogold staining in combination with anterograde tracing, glutamate immunoreactivity could be localized in identified primary afferents to the dorsal spinal cord and cuneate nucleus, and in lemniscal afferents to the thalamus.     

GABAergic modulation of primary gustatory afferent synaptic efficacy

Modulation of synaptic transmission at the primary sensory afferent synapse is well documented for the somatosensory and olfactory systems. The present study was undertaken to test whether GABA impacts on transmission of gustatory information at the primary afferent synapse. In goldfish, the vagal gustatory input terminates in a laminated structure, the vagal lobes, whose sensory layers are homologous to the mammalian nucleus of the solitary tract. We relied on immunoreactivity for the GABA-transporter, GAT-1, to determine the distribution of GABAergic synapses in the vagal lobe. Immunocytochemistry showed dense, punctate GAT-1 immunoreactivity coincident with the layers of termination of primary afferent fibers. The laminar nature and polarized dendritic structure of the vagal lobe make it amenable to an in vitro slice preparation to study early synaptic events in the transmission of gustatory input. Electrical stimulation of the gustatory nerves in vitro produces synaptic field potentials (fEPSPs) predominantly mediated by ionotropic glutamate receptors. Bath application of either the GABA(A) receptor agonist muscimol or the GABA(B) receptor agonist baclofen caused a nearly complete suppression of the primary fEPSP. Coapplication of the appropriate GABA(A) or GABA(B) receptor antagonist bicuculline or CGP-55845 significantly reversed the effects of the agonists. These data indicate that GABAergic terminals situated in proximity to primary gustatory afferent terminals can modulate primary afferent input via both GABA(A) and GABA(B) receptors. The mechanism of action of GABA(B) receptors suggests a presynaptic locus of action for that receptor.     

The colocalization of neurotransmitters in the presynaptic boutons of inhibitory synapses in the lamprey spinal cord]

Using the electron microscopy immunocytochemistry, the GABA and glycine immunoreactivity was studied in presynaptic axon terminals of the spinal cord central gray in the lamprey Lampetra fluviatilis. All immunopositive presynaptic terminals contacting motoneurones or non-identified post-synaptic profiles were divided into only GABA- (44%), only glycine-immunopositive terminals (26%), and both GABA- and glycine-containing terminals (30%). The glycine-immunopositive axon terminals contained flattened synaptic vesicles. Large dense core vesicles were co-localised with conventional synaptic vesicles in 74% of GABA-containing presynaptic terminals.     

Adaptation-dependent plasticity of rod bipolar cell axon terminal morphology in the rat retina

We chose synaptic terminals of rat rod bipolar cells as a model system to study activity-related changes in the overall morphology and the fine structure of synaptic sites. Using confocal laser scanning microscopy in conjunction with three-dimensional reconstruction and electron microscopy, we examined the effect of light and dark adaptation on axon terminals identified by protein kinase C (PKC) immunoreactivity. Rod bipolar cell axon terminals consisted of 2–3 polymorphic boutons situated close to the ganglion cell layer and a single ovoid swelling located more distally. Both components of the terminal complex showed adaptation-dependent differences in the distribution of PKC immunoreactivity and in their morphology. In light-adapted rod bipolar cell axon terminals, PKC immunoreactivity was homogeneously distributed throughout the cytoplasm, whereas terminals from dark-adapted animals showed PKC immunoreactivity preferentially localised in the submembrane compartment and a reduced staining of the more central cytoplasm. In three-dimensional reconstructions of optical sections and at the ultrastructural level, the shape of light-adapted axon terminals was round and smooth and exhibited more convexly curved synaptic membranes. In contrast, dark-adapted terminals had irregular contours, numerous dimples and a concave synaptic curvature. No spinules of bipolar cell terminals were observed in dark-adapted material. These observations are discussed in the context of activity-related morphological plasticity of central nervous system synapses and of the functions of PKC in the cycle of vesicle fusion and retrieval at the tonically active ribbon synapses of the rod bipolar axon terminal. Received: 9 April 1998 / Accepted: 23 June 1998     

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.     

Differential expression of the GABA transporters GAT-1 and GAT-3 in brains of rats,cats, monkeys and humans

The homeostasis of GABA is critical to normal brain function. Extracellular levels of GABA are regulated mainly by plasmalemmal gamma-aminobutyric acid (GABA) transporters. Whereas the expression of GABA transporters has been extensively studied in rodents, validation of this data in other species, including humans, has been limited. As this information is crucial for our understanding of therapeutic options in human diseases such as epilepsy, we have compared, by immunocytochemistry, the distributions of the GABA transporters GAT-1 and GAT-3 in rats, cats, monkeys and humans. We demonstrate subtle differences between the results reported in the literature and our results, such as the predominance of GAT-1 labelling in neurons rather than astrocytes in the rat cortex. We note that the optimal localisation of GAT-1 in cats, monkeys and humans requires the use of an antibody against the human sequence carboxyl terminal region of GAT-1 rather than against the slightly different rat sequence. We demonstrate that GAT-3 is localised mainly to astrocytes in hindbrain and midbrain regions of rat brains. However, in species such as cats, monkeys and humans, additional strong immunolabelling of oligodendrocytes has also been observed. We suggest that differences in GAT distribution, especially the expression of GAT-3 by oligodendrocytes in humans, must be accommodated in extrapolating rodent models of GABA homeostasis to humans.Grant support was provided by the National Health and Medical Research Council (Australia) grant nos. 210127 and 102448, and a Senior Research Fellowship to David Pow.     

Glutamatergic components of the retrosplenial granular cortex in the rat

The ultrastructural characteristics, distribution and synaptic relationships of identified, glutamate-enriched thalamocortical axon terminals and cell bodies in the retrosplenial granular cortex of adult rats is described and compared with GABA-containing terminals and cell bodies, using postembedding immunogold immunohistochemistry and transmission electron microscopy in animals with injections of cholera toxin- horseradish peroxidase (CT-HRP) into the anterior thalamic nuclei. Anterogradely labelled terminals, identified by semi-crystalline deposits of HRP reaction product, were approximately 1 μm in diameter, contained round, clear synaptic vesicles, and established asymmetric (Gray type I) synaptic contacts with dendritic spines and small dendrites, some containing HRP reaction product, identifying them as dendrites of corticothalamic projection neurons. The highest densities of immunogold particles following glutamate immunostaining were found over such axon terminals and over similar axon terminals devoid of HRP reaction product. In serial sections immunoreacted for GABA, these axon terminals were unlabelled, whereas other axon terminals, establishing symmetric (Gray type II) synapses were heavily labelled. Cell bodies of putative pyramidal neurons, containing retrograde HRP label, were numerous in layers V–VI; some were also present in layers I–III. Most were overlain by high densities of gold particles in glutamate but not in GABA immunoreacted sections. These findings provide evidence that the terminals of projection neurons make synaptic contact with dendrites and dendritic spines in the ipsilateral retrosplenial granular cortex and that their targets include the dendrites of presumptive glutamatergic corticothalamic projection neurons.     

Distribution of GABAergic perikarya and terminals in the centers of the higher auditory pathway of the chicken

Summary The distribution of presumed GABAergic neurons and axon terminals in nuclei of the higher auditory pathway of the chicken was investigated by immunocytochemical methods employing antisera to the rate-limiting enzyme of GABA synthesis, glutamic acid decarboxylase, and to GABA. In the mesencephalic auditory center (MLD) about 20% of the cells reveal immunoreactivity. In contrast, the thalamic relay station nucleus ovoidalis is devoid of immunostained somata. This nucleus contains a high density of punctate immunoreactive structures presumed to be GABAergic axon terminals. In the auditory forebrain center field L and the auditory portions of the hyperstriatum ventrale, up to 8% of the cells were immunopositive. These neurons were significantly smaller than estimated from measurements of the overall cell population in these nuclei. From the two-dimensional arrangement of immunopositive neurons it is suggested that the GABAergic system in the avian auditory telencephalon consists of two separate groups of neurons: one subgroup mediating local inhibitory interactions, the other responsible for lateral inhibition between different frequency representations.This work was supported by the Deutsche Forschungsgemeinschaft (SFB 45)     

Synaptic interactions between ghrelin- and neuropeptide Y-containing neurons in the rat arcuate nucleus

Morphological relationships between neuropeptide Y- (NPY) like and ghrelin-like immunoreactive neurons in the arcuate nucleus (ARC) were examined using light and electron microscopy techniques. At the light microscope level, both neuron types were found distributed in the ARC and could be observed making contact with each other. Using a preembedding double immunostaining technique, some NPY-immunoreactive axon terminals were observed at the electron microscope level to make synapses on ghrelin-immunoreactive cell bodies and dendrites. While the axo-somatic synapses were mostly symmetric in nature, the axo-dendritic synapses were both symmetric and asymmetric. In contrast, ghrelin-like immunoreactive (ghrelin-LI) axon terminals were found to make synapses on NPY-like immunoreactive (NPY-LI) dendrites although no NPY-like immunoreactive perikarya were identified receiving synapses from ghrelin-LI axon terminals. NPY-like axon terminals were also found making synapses on NPY-like neurons. Axo-axonic synapses were also identified between NPY- and ghrelin-like axon terminals. The present study shows that NPY- and ghrelin-LI neurons could influence each other by synaptic transmission through axo-somatic, axo-dendritic and even axo-axonic synapses, and suggests that they participate in a common effort to regulate the food-intake behavior through complex synaptic relationships.     

Identification of a lithium interaction site in the gamma-aminobutyric acid (GABA) transporter GAT-1

The sodium- and chloride-dependent electrogenic gamma-aminobutyric acid (GABA) transporter GAT-1, which transports two sodium ions together with GABA, is essential for synaptic transmission by this neurotransmitter. Although lithium by itself does not support GABA transport, it has been proposed that lithium can replace sodium at one of the binding sites but not at the other. To identify putative lithium selectivity determinants, we have mutated the five GAT-1 residues corresponding to those whose side chains participate in the sodium binding sites Na1 and Na2 of the bacterial leucine-transporting homologue LeuT(Aa). In GAT-1 and in most other neurotransmitter transporter family members, four of these residues are conserved, but aspartate 395 replaces the Na2 residue threonine 354. At varying extracellular sodium, lithium stimulated sodium-dependent transport currents as well as [3H]GABA uptake in wild type GAT-1. The extent of this stimulation was dependent on the GABA concentration. In mutants in which aspartate 395 was replaced by threonine or serine, the stimulation of transport by lithium was abolished. Moreover, these mutants were unable to mediate the lithium leak currents. This phenotype was not observed in mutants at the four other positions, although their transport properties were severely impacted. Thus at saturating GABA, the site corresponding to Na2 behaves as a low affinity sodium binding site where lithium can replace sodium. We propose that GABA participates in the other sodium binding site, just like leucine does in the Na1 site, and that at limiting GABA, this site determines the apparent sodium affinity of GABA transport.     

A light and electron microscopic study of glutamate receptors in the monkey subthalamic nucleus

The distribution of glutamate receptors in the monkey subthalamic nucleus was studied using affinity purified polyclonal antibodies to GluR1, phosphorylated GluR1, GluR2/3, NMDAR1, mGluR1a and mGluR5. Intense staining for both the unphosphorylated and the phosphorylated forms of the AMPA receptor subunit GluR1 was observed in the cell bodies and proximal dendrites of neurons in this nucleus. In comparison to GluR1, less intense staining for GluR2/3 was observed in the cell bodies and processes. NMDAR1 immunoreactivity was present in cell bodies and large numbers of small diameter dendrites. Light staining was observed in cell bodies with mGluR1a and no staining was observed on cell bodies with mGluR5. The neuropil, however, contained many processes that were labeled for mGluR1a or mGluR5. Electron microscopy showed that label was present in cytoplasmic locations in cell bodies and dendrites, in addition to components of the synaptic region, in sections stained for GluR1, GluR2/3 and NMDAR1. In contrast, very lightly labeled or unlabeled cell bodies but labeled dendrites and axon terminals, was observed in sections stained for mGluR1a and mGluR5. In addition to neural processes, occasional astrocytic processes were also labeled for mGluR5. Of the immunogold particles that were associated with components of the synaptic region, label for ionotropic glutamate receptors was mostly present on postsynaptic densities, whilst that for metabotropic glutamate receptors was mostly present in a perisynaptic location. The ratio of GluR1/GluR2 messenger RNAs has been reported to increase in the aged hippocampus (PAGLIUSI, S. R., GERRARD, P., ABDALLAH, M., TALABOT, D. & CATSICAS, S. (1994) Neuroscience 61, 429–433.), and it is possible that a similar change in the ratio of GluR1 and GluR2 may occur in neurons of the subthalamic nucleus with age. It is postulated that this could result an increase in calcium permeability via AMPA receptors, and an enhancement of excitatory transmission in this nucleus.     

大鼠孤束核内脑啡肽样免疫反应阳性结构及其轴突终末的突触联系

本文应用免疫细胞化学方法在光镜与电镜下观察了大鼠孤束核内脑啡肽样免疫反应（ＥＮＫ－ＬＩ）阳性结构的分布特征和ＥＮＫ－ＬＩ轴突终末的突触联系以及非突触性关系。结果表明：（１）经秋水仙素处理的大鼠,其孤束核内有许多ＥＮＫ－ＬＩ胞体的分布;而未经秋水仙素处理的大鼠,其孤束核内可见密集的ＥＮＫ－ＬＩ纤维与终末;ＥＮＫ－ＬＩ胞体、纤维和终末主要分布于锥体交叉平面至闩平面的孤束核内侧亚核与胶状质亚核。（２）ＥＮＫ－ＬＩ阳性产物主要定位于小圆形清亮囊泡外表面、大颗粒囊泡内和线粒体外表面等处。（３）ＥＮＫ－ＬＩ轴突终末主要与阴性树突形成轴－树突触。（４）阴性轴突终末终止于ＥＮＫ－ＬＩ轴突终末上,形成轴－轴突触。（５）ＥＮＫ－ＬＩ轴突终末与阴性轴突终末形成非突触性的轴－轴并靠。以上结果提示孤束核内的ＥＮＫ－ＬＩ神经成分主要通过突触后机制、也不排除突触前作用,参与孤束核中内脏信息的整合过程,而且这一作用又受到非ＥＮＫ－ＬＩ神经成分的调控。