Transmitter-specific retrograde labeling in the striato-nigral and raphe-nigral pathways

Striatal structure and function in mood disorders: a comprehensive review

OBJECTIVES

  A large and diverse literature has implicated abnormalities of striatal structure and function in both unipolar and bipolar disorder. Recent functional imaging studies have greatly expanded this body of research. The aim of this review is to provide a comprehensive and critical appraisal of the relevant literature.

METHODS

  A total of 331 relevant articles were reviewed to develop an integrated overview of striatal function in mood disorders.

RESULTS

  There is compelling evidence from multiple studies that functional abnormalities of the striatum and greater corticostriatal circuitry exist in at least some forms of affective illness. The literature does not yet provide data to determine whether these aberrations represent primary pathology or they contribute directly to symptom expression. Finally, there is considerable evidence that bipolar disorder may be associated with striatal hyperactivity and some suggestion that unipolar illness may be associated with hypoactivation.

CONCLUSIONS

  Additional research investigating striatal function in affective disorders will be critical to the development of comprehensive models of the neurobiology of these conditions.

Distribution of GABA immunoreactive systems in the forebrain and midbrain of the chameleon

An immunocytochemical method, using glutaraldehyde fixation and an antiserum developed against a GABA-glutaraldehyde protein conjugate, permitted direct visualization of GABAergic structures in the brain of a reptile (chameleon). GABA immunoreactive cell bodies and nerve terminals were observed to be evenly distributed throughout the forebrain and midbrain. In the forebrain, GABA-positive perikarya were shown in all cortical areas, the septal area, the striatum, the dorsal ventricular ridge, and in the nucleus accumbens. In the midbrain, the optic tectum contained a dense and laminar distribution of GABA neurons. These neurons were also observed in the lateral geniculate nucleus, nucleus profundus mesencephali, nucleus opticus tegmenti and substantia nigra. Immunoreactive nerve fibers and terminals were observed in the same structures and, additionally, in the tractus septo-hypothalamicus, habenula complex, median eminence, intermediate lobe of the pituitary, basal part of the subcommissural organ, torus semicircularis and nucleus reticularis isthmi. These results provide a framework for a further electron microscopic analysis of the GABAergic innervation of some encephalic areas involved in physiological regulations particular to this species especially the visual system.

Tracing specific transmitter pathways in the rat CNS: combination of [3H]serotonin retrograde labelling with immunocytochemical detection of endogenous transmitters

Selective retrograde labelling with [3H]serotonin ([3H]5-HT) can be used to identify serotonergic cell bodies after specific [3H]5-HT uptake by the corresponding nerve terminals. In the present study, we demonstrate that autoradiography of this [3H]5-HT radiolabelling can be combined with immunocytochemical detection of endogenous serotonin, GABA or substance P on the same tissue section. The midbrain raphe serotonergic projections to the olfactory bulb and the spinal projections of medullary serotonergic nuclei were investigated. The specificity of retrograde labelling with [3H]5-HT was confirmed by immunoreactivity of the radiolabelled cells for serotonin, using an antiserum specific for formaldehyde-fixed serotonin. After spinal injections of [3H]5-HT, many retrogradely labelled cells in the medullary raphe were immunopositive for substance P, and a few for GABA. These results are in agreement with the available information on the co-existence of putative transmitters in the spinal projections of caudal raphe neurons. Therefore, autoradiography of [3H]5-HT retrograde labelling combined with immunocytochemistry offers a possibility to test the specificity of transmitter-selective retrograde labelling, to identify transmitter-defined neuronal interactions and to investigate the projection fields of multitransmitter containing neurons.

Schizophrenia: a disease of interhemispheric processes at forebrain and brainstem levels?

The evidence is convincing that each human cerebral hemisphere is capable of human mental activity. This being so, every normal human thought and action demands either a consensus between the two hemispheres, or a dominance of one over the other, in any event integrated into a unity of conscious mentation. How this is achieved remains wholly mysterious, but anatomical and behavioral data suggest that the two hemispheres, and their respective bilateral, anatomical-functional components, maintain a dynamic equilibrium through neural competition. While the forebrain commissures must contribute substantially to this competitive process, it is emphasized in this review that the serotonergic raphé nuclei of pons and mesencephalon are also participants in interhemispheric events. Each side of the raphé projects heavily to both sides of the forebrain, and each is in receipt of bilateral input from the forebrain and the habenulo-interpeduncular system. A multifarious loop thus exists between the two hemispheres, comprised of both forebrain commissural and brainstem paths. There are many reasons for believing that perturbation of this loop, by a variety of pathogenic agents or processes, probably including severe mental stress in susceptible individuals, underlies the extraordinarily diverse symptomatology of schizophrenia. Abnormality of features reflecting interhemispheric processes is common in schizophrenic patients; and the 'first rank' symptoms of delusions or hallucinations are prototypical of what might be expected were the two hemispheres unable to integrate their potentially independent thoughts. Furthermore, additional evidence suggests that the disorder lies within, or is focused primarily through, the raphé serotonergic system, that plays such a fundamental role in consciousness, in dreaming, in response to psychotomimetic drugs, and probably in movement, and even the trophic state of the neocortex. This system is also well situated to control the dopaminergic neurons of the ventral tegmental area, thus relating to the prominence of dopaminergic features in schizophrenia; and the lipofuscin loading and intimate relation with blood vessels and ependyma may make neurons of the raphé uniquely vulnerable to deleterious agents.

Serotonin in involuntary movement disorders

Several recent studies have emphasized that serotonergic pathways in the CNS are intimately involved in the modulation of motor behavior, and in the pathophysiology of human involuntary movement disorders. These observations are supported by recent reports demonstrating large serotonergic innervation of the striatum and substantia nigra, and a close interaction between the activity of serotonergic neurons with the dopamine system in the striatum and nigra. In the following communication we summarize evidence demonstrating defective serotonergic functions in a number of human movement disorders and discuss their management with serotonergic drugs.

Topographical organization of efferent projections from the cat substantia nigra pars reticulata

The topographical organization of the efferent projections from the cat substantia nigra (SN) to the thalamus and the superior colliculus was examined using the anterograde transport of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) and of labelled proteins. HRP-WGA or a mixture of [14C]amino acids was injected into various areas of the SN and the transported material visualized on coronal brain sections by histochemistry or autoradiography, respectively. The retrograde transport of [14C]gamma-aminobutyric acid ([14C]GABA) injected into thalamic nuclei was used also to determine the identity of the nigrothalamic projections. Identical results were found using either the anterograde transport of HRP-WGA or of labelled proteins. In the thalamus, dense nigral projections were observed in the nucleus ventralis medialis (VM) and in the rostromedioventral part of the nucleus ventralis lateralis (VL) whilst more limited projections were seen in the nuclei centralis lateralis (CL) and paracentralis (PC) as well as in the paralamellar zone of the nucleus medialis dorsalis (MD-Il). In addition, a patchy distribution of HRP-WGA or of radioactivity was found in the intermediate layer of the superior colliculus. More precisely, labelling of the VM was dense following injection of [14C]amino acids into the intermediate part of the SN pars reticulata (SNR) regardless of the depth of the injection site, whilst the intralaminar nuclei were labelled preferentially following injections made into the dorsal part of the intermediate SNR. Nigral projections to the intermediate layer of the superior colliculus were visualized over the whole mediocaudal and laterorostral extent when [14C]amino acids were injected into the rostral part of the SNR. Labelling of the superior colliculus was also seen following injection of [14C]amino acids into the intermediate part of the SNR but, in this case, ventral injections led to a more intense labelling than dorsal ones. Both the SNR and the SN pars compacta (SNC) were labelled when [14C]GABA was injected into the VM nucleus of the thalamus, confirming that the nigro VM projection is GABAergic and showing that recurrent collaterals of these GABAergic cells innervating the SNC also contained the transported radioactive material. In this condition ([14C]GABA injection into the VM), the thalamic reticularis nucleus also exhibited a dense labelling.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of GABA-like immunoreactivity in the pigeon brain

The distribution of GABA-like immunoreactivity in glutaraldehyde-fixed pigeon brains was studied by means of a monoclonal antibody. GABA-like immunoreactivity was observed in neuronal perikarya of different sizes as well as in neuropil and in certain fiber tracts. Certain staining patterns indicated the existence of several GABAergic projection systems in the pigeon brain. Indeed, a high density of immunostained perikarya and a low density of labeled terminal-like elements was the prominent pattern in the nuclei subpretectalis and posteroventralis, while an absence of perikaryal GABA-like immunoreactivity and accumulations of immunoreactive dots were observed in the isthmo-optic nucleus, amongst others. In the optic tectum, stained cell bodies with radially oriented processes in layer IIi (10) and with horizontally oriented processes in layer IId (5) were seen and were reminiscent of autoradiographic labeling patterns obtained previously following tectal injection of tritiated GABA. In the cerebellum, GABA-like immunoreactivity involved all types of neurons with the exception of granule cells. Purkinje cells showed regionally different intensities of immunostaining. In addition, in folium X no stained basket-like elements were observed. Although there is no evidence as yet about the function of GABA in most of the structures, the present results indicate an important role for this neurotransmitter in the pigeon brain.

Glycine: an alternative transmitter candidate of the pallidosubthalamic projection neurons in the rat

Autoradiographic retrograde tracing techniques with radioactive transmitters were used to analyse the identity of a putative transmitter in the rat pallidosubthalamic (GP-STN) pathway. One to 2 hours after the stereotaxic injection of 3H-glycine restricted to the STN, a large number of neuronal somata were radiolabeled in the GP. No comparable labeling was observed following the injection of 3H-gamma-aminobutyric acid (3H-GABA) into the same nucleus even with survival times as long as 6 hours. Specifically, no significant somatic labeling was detected either in the GP or in the caudoputamen (CPU). Only when 3H-GABA was injected into the substantia nigra did CPU and GP neurons become labeled. On the contrary, STN neuronal somata were invariably labeled 6 hours after the intrapallidal injection of 3H-GABA, whereas no perikaryal labeling was observed in the STN after 3H-glycine injection into the GP. The perikaryal labeling was prevented in all cases by intraventricular administration of colchicine 1 day before the isotope injections. The observations suggest that 3H-glycine was preferentially transported retrogradely through the GP-STN pathway, and 3H-GABA through the STN-GP projection. In view of the recent controversy on the role of GABA as a putative transmitter of the GP-STN projection, we now propose glycine as an alternative transmitter candidate of these critically situated neurons in the basal ganglia.

Evidence that serotonergic projections to the substantia nigra in the rat arise in the dorsal, but not the median, raphe nucleus

Following microinjections of the fluorescent retrograde tracer Fast blue into the substantia nigra, large numbers of retrogradely labeled cells were observed in the dorsal raphe nucleus. Using immunocytochemical techniques it could be demonstrated that the majority of these cells contained serotonin-like-immunoreactivity. In contrast, careful examination of the region of the median raphe nucleus revealed no suggestion of a significant projection from the median raphe to the substantia nigra.

Glutamate decarboxylase-like immunoreactive neurons in the rat caudate putamen

GAD-IR neurons were roughly divided into those with medium sized perikarya and large perikarya. The medium-sized GAD-IR neurons accounted for about 85% of the GAD-IR neurons. The medium-sized perikarya were further divided into two, those with a smooth nuclear membrane and those with an indented nucleus. The former were very similar to medium-sized spiny neurons and the latter corresponded to medium-sized aspiny neurons. The GAD-IR large cells that were identified by light microscopy, had nuclear indentations and were divided into two classes based on their ultrastructural features, type 1 large cells received few synaptic inputs and type 2 large cells received many synaptic contacts from non-immunoreactive or immunoreactive boutons. The former resembles Type I large cells and the latter Type II large cells identified recently by Chang and Kitai; the latter are also similar to the second type of projecting neurons identified by Bolam et al.

Distribution of GABA-immunoreactive neurons in the basal ganglia of the squirrel monkey (Saimiri sciureus)

The distribution of GABA-immunoreactive neurons was visualized in the basal ganglia of the squirrel monkey (Saimiri sciureus), by using a highly specific antiserum raised against GABA-glutaraldehyde-lysyl-protein conjugate and revealed by the indirect peroxidase-antiperoxidase immunohistochemical method. In the dorsal striatum, GABA-immunoreactive nerve cell bodies were small to medium in size (sectional area ranging from 90 to 125 microns2), but some larger ones (500-600 microns2) were also found. These cells displayed no obvious clustering but were significantly more numerous in the caudate nucleus than in the putamen; their number was also markedly greater at caudal than at rostral striatal levels. A moderate number of evenly distributed positive axon terminals were visible in both the caudate nucleus and the putamen. In the ventral striatum, GABA-immunoreactive nerve cell bodies and axon terminals were seen in fair number within the nucleus accumbens and in the deep layers of the olfactory tubercle. Many positive terminals but no somata were found in the islands of Calleja. In the globus pallidus, virtually all nerve cell bodies were GABA-immunoreactive and the neuropil exhibited a multitude of positive terminals. In the substantia innominata, clusters of small, globular GABA-immunoreactive somata were scattered among aggregates of larger, nonimmunoreactive neurons belonging to the nucleus basalis, and the whole region showed a low to moderate number of evenly spread GABA-positive terminals. In the subthalamic nucleus, nerve cell bodies were generally surrounded by several GABA-positive terminals but were not themselves immunoreactive. The substantia nigra showed many GABA-immunoreactive somata, which predominated in the pars lateralis and diminished progressively in number along the lateromedial axis of the pars reticulata. These cells formed a rather pleomorphic group comprising round, fusiform, or polygonal elements of relatively large size (sectional area ranging from 200 to 800 microns2). In the pars compacta and ventral tegmental area, a few GABA-immunoreactive neurons of small size were dispersed among larger, unreactive neurons. In both pars lateralis and pars reticulata of the substantia nigra, the number of GABA-positive terminals was high and their distribution was rather uniform; a smaller number were visible in the pars compacta of the substantia nigra and in the ventral tegmental area. The present results demonstrate that GABA-containing neurons are widely and heterogeneously distributed in the various components of the squirrel monkey's basal ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)

Dopaminergic axons directly make synapses with GABAergic neurons in the rat neostriatum

We examined with an electron microscopic 'mirror technique' whether glutamic acid decarboxylase-immunoreactive (GAD-IR) neurons are in direct synaptic contact with tyrosine hydroxylase-immunoreactive (TH-IR) axons in the rat neostriatum. Three types of GAD-IR neurons were identified in the nucleus caudatus putamen based upon their size and ultrastructural characteristics. These were medium spiny, medium aspiny and large cells. All types of GAD-IR neurons made synaptic contact with TH-IR axonal boutons at least on perikarya and proximal dendrites. This provides ultrastructural evidence for catecholaminergic, presumably, nigrostriatal dopaminergic inputs to both long- and short-axon neurons most probably containing GABA.

A comparative radioautographic study of the bidirectional axonal and transcellular transport of different amino acids and sugars in the lamprey visual system

Following recent radioautographic evidence for the bidirectional axonal transport of [3H]proline from the eye of Lampetra fluviatilis, the present study examined the anterograde and/or retrograde labeling properties of 11 other amino acids and two sugars after intraocular injections of these tritiated substances in the lamprey. The intraocular injections of aspartic acid, glutamic acid, gamma-aminobutyric acid, arginine, phenylalanine, fucose and acetyl glucosamine resulted in a weak labeling of the primary visual centers: there was no evidence of either the transcellular transport of these tracers or the retrograde labeling of the retinopetal neurons. The primary visual system was found to be heavily labeled 24 h after eye injections of alanine, leucine, glycine, lysine, serine and valine. Among the latter only glycine produced a retrograde somatic labeling of retinopetal neurons. With a longer survival period (7 days), a specific transneuronal labeling was also noted after glycine injections. The significance of the differential uptake and transport of these different tracers in the lamprey visual system and possible mechanisms involved in the axonal retrograde transport of [3H]glycine and [3H]proline in the centrifugal pathways are discussed.

Immunohistochemical demonstration of differential substance P-, met-enkephalin-, and glutamic-acid-decarboxylase-containing cell body and axon distributions in the corpus striatum of the cat

The immunohistochemical localization of neuronal cell bodies and axons reactive for substance P (SP) and methionine-enkephalin (ME) was investigated in the corpus striatum of the adult cat brain and compared with that of glutamate decarboxylase (GAD), synthetic enzyme for gamma-aminobutyric acid. Striatal cell bodies reactive for ME could be identified only in colchicine treated cats, are medium size, ovoid striatal cells, and are found in large numbers in a more or less even distribution throughout the caudate nucleus, putamen, and nucleus accumbens. The striatal region most densely occupied by ME-immunoreactive cells is the ventral and central part of the caudate head. Modest numbers of larger ME-reactive neurons are dispersed throughout the entopeduncular nucleus and the pars reticulata of the substantia nigra. Striatal cells of medium size reactive for SP could be identified, with or without colchicine, in largest numbers in the medial half of the caudal three-fourths of the putamen and in clusters of irregular size and shape in the head of the caudate nucleus. Cells reactive for SP are also common in layer II and the islands of Calleja of the olfactory tubercle. We could not reliably visualize GAD-positive cell bodies in the striatum, even with colchicine treatment; however, they could be seen readily in all pallidal structures such as the globus pallidus, ventral pallidum, entopeduncular nucleus, and substantia nigra. Axons reactive for ME are found mainly in the globus pallidus where they form a dense and even network throughout the nucleus. The globus pallidus is almost devoid of SP reactivity except near its extreme caudal pole. Conversely, SP-immunoreactive axons form dense meshworks in the entopeduncular nucleus and substantia nigra where ME immunoreactivity is minimal. Fewer, but still ample numbers, of SP-reactive axons are present also in the ventral tegmental and retrorubral areas of the midbrain tegmentum and in the ventral pallidum of the basal forebrain, but only sparse ME-reactive axons are present in these areas. This differential distribution of SP- and ME-containing axons in the pallidal and nigral structures stands in contrast to the relatively homogeneous and dense distribution of GAD-containing axons throughout the dorsal and ventral pallidum, entopeduncular nucleus, and substantia nigra.(ABSTRACT TRUNCATED AT 400 WORDS)

Retrograde transport of [3H]GABA in the striatotegmental system of the pigeon

The method of retrograde transport of gamma-aminobutyric acid (GABA) injected into the nigral complex of the pigeon was used to determine the transmitter-specificity of the striatotegmental projection system in this species. The results indicate that descending GABAergic projections are derived from the nucleus accumbens (Ac), ventral lobus parolfactorius (LPO) and the ventral paleostriatum (VP). In birds VP is considered comparable to the mammalian ventral pallidum/substantia innominata area. These results are interpreted in terms of the similarities and differences of striatal organization in birds, reptiles and mammals.

Selective retrograde axonal transport of free glycine in identified neurons of Aplysia

The specific retrograde axonal transport of free glycine within the identified neurons R3-14 of Aplysia californica was studied. The soma of the R3-14 neurons are located in the parietovisceral ganglion and their axons project down the branchial nerve to end in a large peripheral field. Using a double-chambered apparatus, the peripheral tissue was incubated in medium containing a 3H-amino acid for 4-48 hr, while the nerve and ganglion were isolated and perfused with plain or chemically altered medium. The nerve and ganglion were then either rapidly frozen for scintillation counting or fixed for autoradiography. When 3H-glycine was used, radioactivity entered the nerve rapidly, reached the ganglion in 3 hr, and was transported largely (greater than 80%) in the free amino acid form [trichloroacetic acid (TCA) soluble]. The right parietovisceral hemiganglion accumulated up to nine times more radioactivity than the left hemiganglion, reflecting the presence of the R3-14 axons and soma. Two phases of radioactivity were observed, a fast component moving at about 3 mm/hr and a slower (but larger) component moving at about 0.4 mm/hr. Light microscope autoradiography on nerves containing 3H-glycine revealed that the R3-14 axons accounted for more than 30% of the total label in the nerve but occupied less than 7% of the total cross-sectional area of the axonal core. Electron microscope autoradiography showed a close association of silver grains and dense core vesicles in the R3-14 axons. Retrograde axonal transport of free glycine was inhibited by (in decreasing order of effectiveness) mercuric chloride, vinblastine, colchicine, Nocodazole, and 2,4-dinitrophenol (2,4-DNP). Comparative studies of other amino acids [3H-leucine, 3H-serine, 3H-glutamic acid, 3H-gamma-aminobutyric acid (3H-GABA), and 3H-alanine] showed that 3H-glycine is the only amino acid that is rapidly axonally transported in large quantities within the R3-14 axons. This work demonstrates, for the first time, that a free amino acid, glycine, is transported in the retrograde direction within a select group of axons. The significance of this transport of glycine is discussed in relation to its use as a neural messenger by neurons R3-14.

Selective retrograde labeling of neurons of the cat vestibular ganglion with [3H]D-aspartate

D-[2,3-3H]Aspartate [( 3H]D-Asp) was injected in the cat vestibular nuclei. Labeling patterns resulting from retrograde axonal transport by the vestibular nerve fibers were observed in the vestibular ganglion neurons and also in the nerve fibers. The selectivity of such labeling, related to the neurotransmitter's specificity, is strongly indicated.

Retrograde axonal transport of beta-adrenoreceptors in rat brain: effect of reserpine

Retrograde axonal transport of beta-adrenoreceptors was assessed by measuring the accumulation of binding sites for the beta-receptor ligand [125I]iodocyanopindolol [( 125I]ICP) distal to a unilateral 6-hydroxydopamine (6-OHDA) lesion placed in the ascending noradrenergic axons of the locus coeruleus. Accumulation of binding sites was linear over a 3 day period and was blocked by intracerebroventricular 6-OHDA given 1 day prior to sacrifice. A single dose of reserpine (5 mg/kg, i.p.) caused a long lasting (6-8 week) biphasic depletion of frontal cortex norepinephrine (NE) associated with increased frontal cortex binding of another beta-receptor ligand, [3H]dihydroalprenolol [( 3H]DHA), at 7-14 days, and again at 28 days post-reserpine. Unlike the changes in cortical beta-receptors, retrograde transport of [125I]ICP in presynaptic noradrenergic neurons was decreased or blocked completely at 7-14 days and at 6 weeks, and was increased to 470% and 240% of control at 21 days and 8 weeks after reserpine. Anterograde transport of [3H]DHA binding sites was measured by accumulation proximal to a 6-OHDA lesion in this pathway. This transport varied in a pattern similar to that seen for retrograde transport of [125I]ICP binding sites. These data and others suggest that presynaptic beta-receptors are regulated independently of frontal cortex beta-receptors, which appear to be located primarily on postsynaptic cells. On the other hand, the regulation of both anterograde and retrograde transport appears to be interrelated since both types of transport were altered in a similar way in the face of long-term NE depletion by reserpine.

Uptake of D-aspartate and L-glutamate in excitatory axon terminals in hippocampus: autoradiographic and biochemical comparison with gamma-aminobutyrate and other amino acids in normal rats and in rats with lesions

High affinity uptake sites for 3H-labelled amino acids were studied in synaptosome-containing homogenates processed biochemically or in surface autoradiograms of incubated slices of hippocampus. D-aspartate and L-glutamate had apparently identical distributions. In normal rat hippocampus the highest uptake was in the terminal fields of axons from the pyramidal cells of regio inferior and hilus fasciae dentatae, while there was a moderate uptake in the terminal fields of the medial and lateral perforant paths, slight uptake in the mossy fibre layer and no uptake in the terminal fields of the basket cells. Uptake sites for gamma-aminobutyrate were concentrated in the latter fields, and in the most superficial cortical layers. The present method shows no uptake in cell bodies. The uptake activities were strongly inhibited by recognized blockers of (neuronal) high affinity uptake of glutamate or gamma-aminobutyrate. Autoradiographically, several other amino acids showed negligible uptake. The uptake of D-aspartate was reduced by 80% in stratum oriens and stratum radiatum of regio superior 4-14 days (70% at 3 days) after transection of the afferent pyramidal cell axons from the ipsi-and contralateral regio inferior. The reduction was in the number of uptake sites, not in their affinity. Uptake of gamma-aminobutyrate was not reduced. Lesions affecting regio superior caused a loss of D-aspartate uptake in subiculum at a site known to receive hippocampal afferents. Autoradiographically, the uptake of D-aspartate was strongly reduced in the inner zone (i.e. the target zone), but increased in the middle zone of the dentate molecular layer after lesions of the hilus fasciae dentatae. At 4 days and longer after transection of the entorhinal afferents, there was a conspicuous reduction of D-aspartate and L-glutamate uptake in the target zones of both the medial and lateral contingent of these fibres. In the same animals, the terminal zone of afferents from hilus fasciae dentatae had an increased radioactivity and was slightly wider than normally. Concomitantly, the gamma-aminobutyrate uptake was increased in the target zones of the degenerating perforant path fibres. The results demonstrate that uptake sites for D-aspartate and L-glutamate are highly localized in axon terminals of regio inferior pyramidal cells and in perforant path afferents. The latter category of terminals has a lower density of acidic amino acid uptake sites than the former. Uptake sites for gamma-aminobutyrate are localized in terminals of intrinsic neurones, including the axosomatic terminals of basket cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Failure to demonstrate retrograde labelling of cerebellar Purkinje cells after injection of [3H]GABA in Deiters' nucleus

After microinjections of [3H]GABA into the dorsal part of the Deiters' nucleus no retrograde labelling could be observed in the cerebellar Purkinje cells projecting to this nucleus. Tentatively, this failure to demonstrate transmitter specific retrograde labelling is attributed to lack of high affinity uptake mechanisms in the GABAergic Purkinje axon terminals. These observations indicate a very important role of terminal uptake mechanisms in initiation of transmitter specific retrograde labelling. Anterograde axonal labelling was observed along several tracts originating in the injected area, but was not limited to connections with GABA as likely transmitter candidate.

Quantitative autoradiographic studies of 5-HT-accumulating neurones in the nodose ganglia of the cat after perikaryal or terminal uptake

The distributions of ganglionar cell bodies, specifically labeled with 3H-5-HT, were studied in light microscope autoradiographs of the cat nodose ganglion. The size, number and localization of labeled cells were examined under different experimental conditions: after in vitro incubation of the ganglion with 3H-5-HT and after retrograde transport of 3H-5-HT injected into the nucleus of the solitary tract (NST) which receives primary visceral sensory projections from nodose ganglia cells of the vagal nerve. Following incubation of the nodose ganglia with a low concentration of 3H-5-HT (10(-6) M), some ganglionar cell bodies took up and retained the tracer. In both the right and left ganglia, they were significantly smaller in size than the unreactive neurones. The mean diameter of their perikaryon was 36.97 +/- 0.52 microns, compared with 45.76 +/- 0.87 microns in unreactive neurones. About 600 labeled cell bodies were counted in each ganglion, corresponding to 2-3% of the total nodose ganglion cell population. These reactive neurones were not localized in one particular area of the ganglia, but scattered throughout both of them. Following bilateral or unilateral microinjections of 3H-5-HT in the NST, retrogradely labeled cell bodies were observed, 24 h later, in the nodose ganglia. Their mean diameter was estimated to be 36.14 +/- 0.69 microns and they represented approximately 2% of the total ganglion cell population. As in in vitro experiments, the labeled cells were not grouped in any particular region of the ganglion. These experiments show that the distribution of both populations of labeled cells, observed under these conditions, are comparable. On an anatomical and quantitative basis one may reasonably suppose that the perikaryal or terminal uptakes concern the same neuronal population.

The section-Golgi impregnation procedure. 2. Immunocytochemical demonstration of glutamate decarboxylase in Golgi-impregnated neurons and in their afferent synaptic boutons in the visual cortex of the cat

Sections of the cat's visual cortex were stained by an antiserum to glutamate decarboxylase using the peroxidase-antiperoxidase method; they were then impregnated by the section Golgi procedure and finally the Golgi deposit was replaced by gold. Neurons containing glutamate decarboxylase immunoreactivity were found in all layers of the visual cortex, without any obvious pattern of distribution. Fifteen immunoreactive neurons were also Golgi-impregnated and gold-toned, which enabled us to study the morphology and synaptic input of identified GABAergic neurons. These neurons were found to be heterogeneous both with respect to the sizes and shapes of their perikarya and the branching patterns of their dendrites. All the immunoreactive, Golgi-impregnated neurons had smooth dendrites, with only occasional protrusions. The synaptic input of glutamate decarboxylase-immunoreactive neurons was studied in the electron microscope. Immunoreactive neurons received immunoreactive boutons forming symmetrical synapses on their cell bodies. The Golgi-impregnation made it possible to study the input along the dendrites of immunoreactive neurons. One of the large neurons in layer III whose soma was immunoreactive was also Golgi-impregnated: it received numerous non-immunoreactive asymmetrical synaptic contacts along its dendrites and occasional ones on its soma. The same neuron also received a few boutons forming symmetrical synaptic contacts along its Golgi-impregnated dendrites; most of these boutons were immunoreactive for glutamate decarboxylase. Glutamate decarboxylase-immunoreactive boutons were also found in symmetrical synaptic contact with non-immunoreactive neurons that were Golgi-impregnated. A small pyramidal cell in layer III was shown to receive several such boutons along its somatic membrane. It is concluded that the combination of immunoperoxidase staining and Golgi impregnation is technically feasible and that it can provide new information. The present study has shown that there are many morphologically distinct kinds of aspiny GABAergic neurons in the visual cortex; that the predominant type of synaptic input to the dendrites of such neurons is from boutons forming asymmetrical synapses, but that some of the GABAergic neurons also receive a dense symmetrical synaptic input on their cell bodies, and occasional synapses along their dendrites, from the boutons of other GABAergic neurons. These findings provide a morphological basis, firstly, for a presumed powerful excitatory input to GABAergic interneurons and, secondly, for the disinhibition which has been postulated from electrophysiological studies to occur in the cat's visual cortex.

Retrograde transport of gamma-amino[3H]butyric acid reveals specific interlaminar connections in the striate cortex of monkey

Several lines of evidence suggest that gamma-aminobutyric acid is an inhibitory neurotransmitter in the cerebral cortex. To study the intracortical projection of neurons that selectively accumulate this amino acid, we injected radioactive gamma-aminobutyric acid into the upper layers of the striate cortex of monkeys along tracks at an oblique angle to the pia. Sections from the injected area were then processed by a combination of autoradiography and Golgi impregnation to reveal the distribution of labeled neurons and their morphological characteristics. Labeled neurons always occurred around the injection site in each layer. In addition, a consistent radial pattern of perikaryal labeling was observed in layers IVc-VI below the injection track in layers I-IVa. The closer the injection track was to the pia the deeper the peak density of labeled cells appeared. After injection in layers IVa and the lower part of III, the highest number of labeled neurons was in layer IVc; after injection in the upper part of layer III, most labeled neurons were in layer V; and, after injection in layers I and II, the proportion of labeled neurons increased in the lower part of layer V and in layer VI. All these neurons in the infragranular layers are presumably labeled by retrograde axonal transport via the labeled fiber bundles that extended from upper to lower layers. Thirty-four Golgi-stained neurons of various types were also examined for retrograde labeling. Two were labeled, and both were aspiny stellate cells in layer V. The arrangement of these putative GABAergic neurones, with axons that ascend from lower to upper layers in a regular pattern and arborize locally, would enable them to mediate inhibition within cortical columns and between neighboring columns.

Selective retrograde labelling of vestibular efferent neurons with [3H]choline

Following administration of [3H]choline in the lateral semicircular canal of the cat labyrinth, bidirectional axoplasmic transport [3H]choline and its derivatives was shown by radioautography in the vestibular system. Light-microscopic radioautographs exhibited various patterns of radioautographic labelling. First, a diffuse reaction was observed in vestibular nuclei representing anterograde-labelled, vestibular nerve endings. Second, a heavy labelling limited to perikarya was detected in efferent vestibular neurons and corresponded to retrograde transport. The anterograde migration of [3H]choline is known to be non-selective and is related to synthesis of phospholipids, non-diffusable molecules. In contrast, the retrograde perikaryal labelling seems highly selective and related to the cholinergic specificity of the transmitter. The selectivity of such labelling offers a further possibility of identifying cholinergic neurons and is additional evidence that cholinergic mechanisms are involved in the efferent vestibular control.

Gamma-aminobutyric acid interneurons in the rat hippocampal region studied by retrograde transport of glutamic acid decarboxylase antibody after in vivo injections

The retrograde axonal labeling of hippocampal GABA-ergic neurons was studied after in vivo injections of a characterized antibody against glutamic acid decarboxylase (GAD) into different parts of the hippocampal region. Small injections (50 nl) of undiluted GAD antibody into the area dentata (AD) labelled fusiform and dentate pyramidal basket cells within the AD and fusiform and multipolar cells in subfields CA2/CA3 (a and b) of Ammon's horn. The labeled cells were characterized by intense immunoreactivity of the soma and proximal parts of the dendrites, while the nucleus contained little or none. The morphological appearance and laminar positions of these cells corresponded to hippocampal GAD-positive neurons, as shown previously (Ribak et al. 1978) with immunocytochemistry. Injections of anti-GAD into the medial entorhinal area, subiculum, and CA1 region labeled cells in strata oriens, pyramidale and radiatum of CA2 and CA3a, but injections of the antibody into these latter areas failed to label cells in the medial CA1 and subiculum, thus suggesting a preferential organization of hippocampal GABA neuronal projections in a lateral to medial direction. Injections of preimmune sera or antiserum preabsorbed with the pure enzyme antigen GAD failed to label cells in a manner similar to that described for the anti-GAD injections. These observations, taken together with the finding that injections of anti-GAD into the terminal field of non-GABA-ergic pathways never resulted in retrograde axonal transport of the antibody-antigen complex, suggest that the in vivo injection of GAD antibody is a useful method to study the organization of hippocampal GABA-ergic neurons and their projections.

Selective retrograde transport of 3H-serotonin in vagal afferents

A new serotonergic afferent vagal component has been demonstrated in the cat by radioautography. Twenty-four hours after a bilateral injection of tritiated serotonin (3H-5-HT) into the area of the nucleus of the solitary tract (NST), heavily and lightly labelled cell bodies were observed in the nodose ganglia. After unilateral injections of 3H-5-HT into the same area, labelled ganglionar cell bodies were found in the ipsilateral nodose ganglion. Some were also found in the contralateral one, suggesting a serotonergic crossed fibers component. Dense clusters of silver grains, depicting typical labelling of neuronal varicosities, were observed in the NST. After destruction of the serotonergic terminals with 5,7-dihydroxytryptamine, followed by injection of 3H-5-HT, the number of labelled cell bodies decreased dramatically in the ipsilateral nodose ganglia and the clusters of silver grains disappeared in the NST. After ligature or section of the supranodose vagal nerve, following injection of 3H-5-HT into the NST, no radioautographic reaction was observed in the homolateral nodose ganglia. The present study demonstrates the existence of a peripheral serotonergic system in vagal afferents. The physiological implications of this new serotonergic visceral pathway remain to be studied.

Neurotransmitter receptor ligand binding and enzyme regional distribution in the pigeon visual system

The relative importance of acetylcholine, dopamine, endogenous opiates, gamma-aminobutyric acid (GABA), glutamate, glycine, noradrenaline, and serotonin as transmitters in the pigeon visual system was estimated by measuring the activity of choline acetyltransferase (ChAT), glutamic acid decarboxylase (GAD), and aromatic amino acid decarboxylase (AAD) as well as the binding of dihydroalprenolol, etorphine, kainic acid, muscimol, serotonin, spiroperidol, strychnine, and quinuclidinyl benzilate (QNB) in the tectum opticum, nucleus rotundus, ectostriatum, dorsolateral thalamus, and hyperstriatum (Wulst). As a nonvisual reference structure, the paleostriatal complex was included in the examination. The regional distribution of most of these parameters was very similar to data reported in the mammalian CNS supporting the hypothesis that the avian tectofugal and thalamofugal visual systems are homologous to the mammalian tecto-thalamo-cortical and retino-geniculo-striate pathways, respectively. On the basis of the low values of their parameters, some transmitters can be excluded as significant contributors in a number of structures. As a hypothesis for further investigations, the presence of cholinergic and serotoninergic systems in the Wulst, possibly originating in the dorsolateral thalamus and nucleus raphe, respectively, and of glycinergic and dopaminergic terminals in the paleostriatal complex is proposed.

Involvement of a central dopaminergic system in 5-methoxy-N,N-dimethyltryptamine-induced turning behaviour in rats with lesions of the dorsal raphé nuclei

The turning behaviour induced by 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) has been investigated in rats with lesions of the dorsal raphé nucleus (DRN). 5-MeODMT caused a dose-related contralateral turning in rats with 5,7-dihydroxytryptamine (5,7-DHT) lesions of the substantia nigra and a similar effect was observed in DRN-lesioned rats. In contrast, a dose-related ipsilateral turning was observed when 5-MeODMT was injected into rats with 5,7-DHT lesions of the striatum. These results suggest that the effects of 5-MeODMT in DRN-Lesioned rats are mediated via the substantia nigra. The contralateral turning induced by 5-MeODMT in rats with a 5,7-DHT lesion of the DRN was significantly reduced when a second 5-hydroxydopamine lesion was placed in the striatum, but not when it was placed in the nucleus accumbens. Thus the nigrostriatal dopaminergic system seems to be involved in 5-MeODMT-induced turning. The release of tritium from slices of substantia nigra previously labelled with [3H]-dopamine was inhibited by 5-MeODMT (10(-7) to 10(-5) M) and this effect was blocked by methysergide in a concentration-related manner. Tetrodotoxin (10(-7) M) failed to antagonise 5-MeODMT. These results suggest that 5-MeODMT can inhibit dopamine release from nigral dendrites, which could in turn enhance nigrostriatal activity by reducing the auto-inhibitory actions of dopamine, thereby causing contralateral turning in DRN-lesioned rats.

Bilateral serotonergic projections to the dorsal hippocampus of the rat: simultaneous localization of 3H-5HT and HRP after retrograde transport

Horseradish peroxidase (HRP, Sigma VI, 30-70 nl of a 10-15% solution in saline) or 3H-5HT (30 Ci/mmole, 2.5 X 10 -3 M containing 3.3 X 10(-3) M norepinephrine in saline, 50-100 nl) was injected unilaterally into the dorsal hippocampus in separate groups of rats. HRP-labeled cells were seen in the hippocampus, medial septal nucleus, nucleus of the diagonal band, supramammilary nucleus, median raphe nucleus, interfascicular portion of the dorsal raphe nucleus, and the locus coeruleus. In contrast, 3H-5HT-labeled cells were largely restricted to the raphe nuclei. In this nucleus an equal number of ipsilateral and bilateral cells were found. Occasionally, these labeled cells stretched across the midline (bridge pattern). In another series, the 3H-5HT and HRP were injected into the same hippocampus either as a mixture or sequentially. This resulted in double labeling of the median and dorsal raphe neurons. A final group of rats received injections of 3H-5HT and HRP into opposing hippocampi. Double-labeled cells accounted for 10% of the neurons labeled. In addition, closely paired neurons composed of an HRP- and 3H-5HT-containing cell were found. In summary, the serotonergic fibers may play a key role in harmonizing the electrical activity of the hippocampi by use of bilateral projections, paired neurons with differential projections, and bridging neurons stretching across the midline but with unilateral projections.

Localization of axonally transported [3H]glycine in vesicles of identified neurons

A specific association of axonally transported, free [3H]glycine with vesicles in the identified neurons R3-R15 of Aplysia is demonstrated by high resolution autoradiography. The association of glycine with vesicles, the first such finding in any animal for a neuroactive amino acid, adds to evidence that glycine may be utilized as a neuro-chemical messenger by R3-R14.

Visual claustrum: topography and receptive field properties in the cat

A region containing visually responsive cells was found in the dorsocaudal claustrum. This area contains a single orderly map of the contralateral visual field. Like cortical cells, most claustral cells are selective for stimulus orientation. They are binocular, and they respond to either direction of movement and to a broad range of velocities. Their most striking property is a marked preference for very long stimuli.

Unilateral 5,7-dihydroxytryptamine lesions of the dorsal raphe nucleus (DRN) and rat rotational behaviour

A unilateral lesion in the dorsal raphe nucleus (DRN) resulted in a decreased concentration of 5-hydroxytryptamine (5-HT) in the ipsilateral striatum (CS), anterior cortex and substantia nigra (SN), a loss of [3H]5-HT uptake sites in the cortex and striatum and a selective reduction in 5-HT turnover in the substantia nigra. The directly acting 5-HT agonist 5-methoxy-N,N-dimethyltryptamine induced contralateral turning behaviour in the lesioned animals, whilst the 5-HT releasing agent, p-chloroamphetamine, induced ipsilateral rotation. All rotational behaviour was blocked by haloperidol and the turning behaviour in response to 5-MeODMT was blocked by methysergide. The data presented suggest that the DRN innervates the SN and CS differentially and that nigral 5-HT receptors become supersensitive after denervation of the DRN-SN pathway.

Aspartate and glutamate as possible neurotransmitters of cells in layer 6 of the visual cortex

Earlier work has suggested that aspartate, glutamate and gamma-aminobutyric acid (GABA) act as transmitters in the cerebral cortex. There is reasonable evidence for the identity of the cell population responsible for GABA release but until now there has been little evidence concerning the sources for release of aspartate and glutamate. Here we have used two approaches to identify possible neurotransmitters used by cells in the visual cortex: measurement of the efflux of endogenous compounds in conditions of synaptic release and localization of these compounds to particular cell classes using neurotransmitter-specific histochemical techniques. Our results suggest that the acidic amino acids aspartate and glutamate may be cortical neurotransmitters, as shown by calcium-dependent release from endogenous stores and by uptake specific to pyramidal cells in layer 6 of the cortex. These substances may therefore have a role in the function of layer 6 cells, which are responsible for the recurrent projection from the cortex to the lateral geniculate nucleus and for the projection within the cortex from layer 6 to layer 4.

Radioautographic evidence for both orthograde and retrograde axonal transport of labeled compounds after intraocular injection of [3H]proline in the lamprey (Lampetra fluviatilis)

[3H] Proline injected intraocularly in lampreys has been shown to be bidirectionally transported: 24--96 h after the injection, retinofugal fibers and terminals as well as nerve cell bodies at the origin of the retinopetal system were intensely labeled. These results are at variance with the generally held belief that [3H]proline is taken up only by cell bodies and transported by the anterograde flow. The significance of the retrograde axonal transport of [3H]proline in the lamprey retinopetal system is discussed.

Uptake of [3H]glycine and [3H]GABA by amacrine cells in the cat retina

After intravitreal injection, [3H]glycine accumulates in 3 distinct subpopulations of amacrine cells in the cat retina whereas [3H]GABA accumulates in 4 different subpopulations. Each labeled cell type can be distinguished on the basis of size and cytologic features. The density of label associated with each subpopulation serves as an additional distinguishing characteristic. [3H]Glycine is concentrated within the outer two-thirds of the inner plexiform layer (IPL). [3H]GABA is localized in two narrow bands in the outer half of the IPL and in a wider band adjacent to the ganglion cell layer.

Retrograde axonal transport following injection of [3H]serotonin in the olfactory bulb. I. Biochemical study

A retrograde axonal transport from the serotonergic nerve terminals in the olfactory bulb (OB) to their parent cell bodies in the midbrain raphe nuclei has been demonstrated after stereotaxic injection of [2H]5-HT into the OB of rats pretreated with a monoamine oxidase (MAO) inhibitor: at various time intervals thereafter (4-92 h) there was a preferential accumulation of radioactivity mainly in the raphe dorsalis nucleus (RDN). Maximal accumulation occurred at 24 h. Of this radioactivity, 30-50% was recovered as 5-HT. The accumulation was estimated to take place at two rates: a fast one (48 mm/day) and a slower one (16 mm/day). Under the same experimental conditions there was no clear evidence for a retrograde accumulation of [3H]norepinephrine in the RDN. A passive diffusion mechanism could be excluded since the diffuson of tracer towards the cerebrospinal fluid was prevented by prior mechanical obstruction of the olfactory diverticle of the lateral ventricle. Furthermore, colchicine strongly reduced (by 80%) the radioactive accumulatin in the RDN. Destruction of serotonergic nerve terminals by 5,6-dihydroxytryptamine or inhibiton of 5-HT uptake by fluoxetine decreased this retrograde accumulation whereas destruction of catecholaminergic nerve terminals by 6-hydroxydopamine was without effect. Pretreatment with reserpine decreased the amount of radioactivity transported to the RDN by 40%. In the absence of MAO inhibition pretreatment, animals still presentd 35% of the tracer transported to the RDN. Intrabulbar injection of MAO inhibitor did not affect the accumulation rates when compared with animals which received the inhibitor by the intraperitoneal route. In conclusion, the retrograde axonal transport following [3H]5-HT injection in the serotonergic RDN-OB system occurs via an active process which depends on a colchicine-sensitive mechanism and is partially linked to a reserp ine-sensitive structure. During its transport, the amine seems to be relatively protected from metabolic inactivation.

Cellular synthesis and axonal transport of gamma-aminobutyric acid in a photoreceptor cell of the barnacle

1. [3H]glutamate or [3H]gamma-aminobutyric acid (GABA) was injected into the photoreceptor cell of the lateral ocellus of Balanus eburneus, in order to study the transmitter substance of the cell. 2. The photoreceptor cell synthesized [3H]GABA from injected [3H]glutamate. 3. The newly formed [3H]GABA moved inside the photoreceptor axon towards the axon terminal with a velocity of about 0.9 mm/hr. Injected [3H]GABA moved at 0.9 mm/hr and also at 0.4 mm/hr. 4. Axonally transported [3H]GABA reached the axon terminal within several hours following the injection. It did not accumulate at the terminal, but gradually disappeared. 5. Light-microscope and electron-microscope autoradiography following the injection of [3H]GABA revealed that [3H]-reacted silver grains were present in a certain type of axon terminal. The terminal thus identified as that of a photoreceptor cell contains many clear, polymorphic synaptic vesicles about 300-500 A in diameter, some dense-cored vesicles 700-1300 A in diameter, and glycogen granules. The terminal forms many synapses, and each synapse has a synaptic dense body. The terminal always faces two post-synaptic elements at the synapse, forming a triad with a gap distance of about 160-200 A. 6. A GABA analogue, [3H]di-aminobutyric acid, was selectively taken up into the terminals previously identified as those of photoreceptors. 7. These results support the notion that the transmitter substance of the photoreceptor cell of the barnacle is GABA.

Selective retrograde labeling indicating the transmitter of neuronal pathways

A number of tritiated transmitter related compounds-amino acids and biogenic amines-were injected into the rat caudoputamen or substantia nigra in order to test (1) for the occurence of autoradiographic perikaryal labeling, (2) for a selectivity of perikaryal labeling relating certain compounds to certain pathways, and (3) for the relation of perikaryal labeling to known transmitter specificitites of the systems involved. Perikaryal labeling was observed after injection of some but not all of the substances used and was best explained by retrograde labeling in pathways projecting to the injection sites. Six hours after injection of high concentrations of tritiated transmitter into the terminal area, perikaryal labeling was observed: (A) in substantial nigra compacta (A9), A10 (rostral) and A8 (all heavy), and in n. raphe dorsalis (light) after [3H]-dopamine and [3H]-norepinephrine injection into caudoputamen; (B) same pattern as in A, but heavy in n. raphe dorsalis after [3H]-serotonin injection into caudoputamen; perikaryal labeling absent in cortex and thalamus after injection of substances mentioned in A and B; (C) only in substantia nigra compacta (minimally) after [3H]-GABA injection into caudoputamen; (D) in cerebral cortex and thalamus but not in substantia nigra, A10, A8, nor in n. raphe dorsalis after injection of [3H]-D-aspartate into caudoputamen; (E) in the rat caudoputamen but not in n. raphe dorsalis after [3H]-GABA injection into substantia nigra; (F) in n. raphe dorsalis but not in caudoputamen after [3H]-serotonin into substantia nigra. These results indicated, indeed, a certain selectivity-partly related to transmitter specificity-for perikaryal labeling patterns. As a method, transmitter specific retrograde tracing could be useful in pathways with dopamine-, serotonin-, and GABA-mediated synaptic transmission.

Transmitter-related retrograde labeling in the pigeon optic lobe: a high resolution autoradiographic study

High resolution light microscopic and electron microscopic autoradiography in a restricted area of the pigeon subtectal nucleus isthmi, pars parvocellularis (Ipc) 30 min after onset of a tectal [3H]glycine injection shows labeling mainly of the following elements: neuronal perikarya, initial axon segments and dendrites. Rapid labeling of such intrinsic Ipc elements and not of synaptic terminals possibly of tectal origin strongly suggests a fast retrograde migration of radioactivity within Ipc-tectal neurons. Fixation experiments indicate a soluble nature of this radioactive material. This type of retrograde labeling in the glycinergic Ipc-tectal pathway seems to be related to the transmitter specificity of the system.