GABA innervation in adult rat oculomotor nucleus: a radioautographic and immunocytochemical study.

GABA innervation in the adult rat oculomotor nucleus (n.III) was investigated using two complementary approaches: radioautography after incubation of brain slices with tritiated GABA ([3H]GABA) along with local in vivo microinjections of the tracer, and GABA immunocytochemical procedures involving antibodies directed against a GABA-glutaraldehyde-protein conjugate. As determined by radioautography after in vitro or in vivo labelling, the [3H]GABA uptake sites in the n.III mainly involved axon terminals. These were distributed throughout the neuropil and were often closely apposed to unlabelled motoneuron somata. A small number of glial cells also showed preferential accumulation of the tracer. The GABA-immunostaining likewise involved axon terminals throughout the nucleus, but no glial cells were immunopositive. In the dorsal region of the structure, occasional GABA-immunostained internuclear neurons were observed among unstained motoneuron cell bodies. Electron microscopic examination of [3H]GABA-labelled or GABA-immunostained profiles in n.III revealed axon terminals of around 1 micron in diameter, always filled with small, round synaptic vesicles homogeneously distributed throughout the axoplasm. These boutons frequently contained mitochondria and one or more large granular vesicles. In single thin sections, 35% of [3H]GABA-labelled, and 19% of GABA-immunostained varicose profiles exhibited a synaptic differentiation, suggesting the existence of a predominantly if not entirely junctional innervation. These synapses mostly involved dendritic trunks or dendritic branches and were usually of the symmetrical type. A few, which were always symmetrical, were also observed on large somata of motoneurons. Some of the dendrites synaptically contacted by GABA-immunostained axon terminals were themselves GABA immunoreactive. These data substantiate the idea that GABA is involved in the control of motoneuron activity in n.III, and provide a structural basis for the inhibitory role of this transmitter in oculomotor function.

The medial division of the medial geniculate body of the cat: implications for thalamic organization.

The structure of neurons and axons was studied in the medial division of the medial geniculate body of the cat with the Golgi methods. The results show that the medial division consists of morphologically heterogeneous neurons. The main types, in descending order of frequency, are medium-sized neurons with (1) radiate, (2) tufted, or (3) elongate dendrites; (4) small stellate or radiate neurons, including Golgi type II cells with a locally arborizing, sparsely branching axon collateral system; (5) large neurons, which are weakly tufted. A variety of afferent axons impose a reticulate appearance on the fiber architecture of the medial division. The dominant element in the neuropil consists of axons terminating in the medial division as well as a collateral system of fibers traveling to the adjacent ventral and dorsal divisions of the medial geniculate body. Four types of extrinsic axons are described, including two kinds of thin axons with collateral systems, thick fibers with restricted branches, and large axons with elaborate, serpentine collaterals. Compared to the dorsal and ventral divisions of the medial geniculate body, where, respectively, radiate and tufted neurons are more frequent, the medial division is intermediate in a sense-not that the degree of radiate or tufted dendritic branching is less well developed, but neither type of cell predominates. Moreover, all of the cell types are overlapping in distribution, although the large ones tend to be more common rostrally in the medial division. Likewise, there is no clear-cut regional segregation of axonal types. The ascending projections to the medial division originate in many different structures, involving purely auditory tracts from the inferior colliculus, spinal inputs, and pathways from polysensory regions, such as the midbrain tegmentum and deep layers of the superior colliculus. The spinothalamic tract projects most heavily to the rostromedial region of the medial division bordering the ventrobasal complex. The auditory input from the central nucleus of the inferior colliculus tends to project more heavily to the caudolateral region next to the ventral nucleus of the medial geniculate body. However, these inputs overlap in the medial division. Moreover, the pathways from the tegmentum and the superior colliculus have a broad distribution in the medial division. Still other inputs are known, not to mention those from the cerebral cortex and a widespread and complicated pattern of thalamocortical projections.(ABSTRACT TRUNCATED AT 400 WORDS)

Location of interganglionic neurons in the stomatogastric system of the spiny lobster.

The stomatogastric ganglion produces distinct and complex patterned output driving the mastication and filtration of food. It does so with a small number of neurons whose properties and interconnections have been extensively examined. The motor patterns are subject to modulation and integration by neurons of other ganglia. This paper reports a search for interneurons of the four interconnecting ganglia of this system, using cobalt chloride backfilling techniques. It was determined that only a small number of neurons may interconnect these ganglia: (1) In the stomatogastric ganglion there are two to three small neurons and six large neurons with neurites projecting anteriorly towards the other ganglia. (2) In the two commissural ganglia there are one to three small neurons whose neurites project to the primary input nerve of the stomatogastric ganglion. (3) In the oesophageal ganglion there are three small neurons whose location would allow them to play a co-ordinating role in the output of all four ganglia.

Tectal efferents in the branded water snake, Natrix sipedon.

Visual information reaches the dorsal thalamus by two distrinct routes in most reptiles. Retinal efferents terminate directly in the dorsal lateral geniculate nucleus (DLGN). Retinal information is also channeled indirectly through the tectum to nucleus rotundus. Retinal projections to DLGN and tectum are also well established in snakes, but the status of the tecto-rotundal link of the indirect visual pathway is uncertain. Thus, tectal efferents were studied with Fink-Heimer methods in banded water snakes (Natrix sipedon). The tectum gives rise to crossed and uncorssed projections to the brainstem reticular formation. Commissural connections are effected with the contralateral tectum via the tectal and posterior commissures. Tectum projects densely to the ipsilateral basal optic nucleus. Bilateral ascending projections reach the pretectal area, nucleus lentiformis mescencephali, lateral habenular nuclei, and posterodorsal nuclei. Ascending projections reach the ventral lateral geniculate and suprapeduncular nuclei. There is a diffuse projection to the central part of the caudal thalamus and a dense, bilateral projection to the DLGN. These results indicate that the relation of the tectum to the dorsal thalamus is different in snakes than in other reptiles. Nucleus rotundus is either absent or poorly differentiated and there is a strong convergence of the direct and indirect visual pathways at DLGN.

[Catecholaminergic axons in the human cerebral cortex. Observation by histofluorescence of cerebral biopsies in 2 cases of Alzheimer's disease]. / Axones catécholaminergiques du cortex cérébral humain. Observation, en histofluorescence, de biopsies cérébrales dont 2 cas de maladie d'Alzheimer

Catecholamine axons have been visualized in human cerebral cortex obtained during routine neurosurgical operations. The fluorescence histochemical method of Lindvall et al. was used, slightly modified (calcium-deprived buffer, glyoxylic acid fixation followed by formaldehyde vapours exposition). The frontal cortex was more richely provided with catecholamine terminals than the parietal cortex. Two general types of axon morphology are evident. The most frequent is thin and sinous, sometimes forming clews, or loose basket-like arrangement around presumed nerve cells. The other one is moniliform and demonstrates spherical evenly-spaced varicosities. They look like, respectively, the well characterized dopaminergic and noradrenergic axons of the rat cerebral cortex. In two cases of Alzheimer's disease, noradrenergic-like fibers were missing and voluminous green-fluorescent varicosities, sometimes in obvious connection with typical axons, were observed in the proximity of senile plaques.

Immunoreactive LRF neurosecretory pathways in mammals.

Using antisera to synthetic luteinizing hormone-releasing factor (LRF) and antisera labeled with fluorescein isothiocyanate or peroxidase, it was possible in various physiological and experimental conditions to determine the topography of the LRF secretory cells in the guinea pig. The axons of these cells form a preoptico-infundibular LRF pathway, which controls the prehypophyseal gonadotropic secretion, and various "extrahypophyseal pathways". These latter suggest that LRF, in addition to its prehypophysiotropic action, may have a neuromodulator function.

Association of calcium with membranes of squid giant axon: ultrastructure and microprobe analysis.

Giant axons from the squid, Loligo pealei, were fixed in glutaraldehyde and postfixed in osmium tetroxide. Calcium chloride (5 mM/liter) was added to all aqueous solutions used for tissue processing. Electron-opaque deposits were found along the axonal plasma membranes, within mitochondria, and along the basal plasma membranes of Schwann cells. X-ray microprobe analysis (EMMA-4) yielded signals for calcium and phosphorus when deposits were probed, whereas these elements were not detected in the axoplasm.

Turnover of transmitter and synaptic vesicles at the frog neuromuscular junction.

Curarized cutaneous pectoris nerve-muscle preparations from frogs were stimulated at 10/s or at 2/s for periods ranging from 20 min to 4 h. End plate potential were recorded intracellularly and used to estimate the quantity of transmitter secreted during the period of stimulation. At the ends of the periods of stimulation the preparations were either fixed for electron microscopy or treated with black widow spider venom to determine the quantities of transmitter remainind in the terminal. Horseradish peroxidase or dextran was added to the bathing solution and used as a tracer to detect the formation of vesicles from the axolemma. During 4 h of stimulation at 2/s many new vesicles were formed from the axolemma and the quantity of transmitter secreted was several times greater than the quantity in the initial store. After this period of stimulation, the terminals were severely depleted of transmitter, but not of vesicles, and their general morphological organization was normal. During 20 min of stimulation at 10/s the nerve terminals swelled and were severely depleted both of vesicles and of transmitter. During a subsequent hour of rest the changes in morphology were largely reversed, many new vesicles were formed from the axolemma and the stores of transmitter were partially replenished. These results suggest (a) that synaptic vesicles fuse with, and re-form from, the membrane of the nerve terminal during and after stimulation and (b), that the re-formed vesicles can store and release transmitter.

Cerebellar alterations in the weaver mouse.

The fine structure of the cerebellum of weaver mouse was examined and the paucity of granule cells and their axons, the parallel fibers, was confirmed. Unexpectedly, however, the dendritic spines of the Purkinje cells which, in normal animals, are the postsynaptic mates of the parallel fibers, were present. Furthermore, their essential morphology and their staining reactions were indistinguishable from those of the Purkinje cell dendritic spines in normal animals. Possible mechanisms of development are discussed.