Tyrosine hydroxylase-like immunoreactive synaptic boutons in the inferior colliculus of the cat.

The data on the distribution of catecholaminergic cells and fibers in such a significant subcortical relay auditory center as the inferior colliculus (IC) are both few and controversial, and ultrastructural data are lacking. Young adult mongrel cats of both sexes were used. Following routine preparation procedures, the ultrathin sections were prepared for the ultrastructural examination of tyrosine hydroxylase (TH)-like immunoreactivity. TH-positive neuronal perikarya were not detected in the IC. On the other hand, an appreciable number of TH-immunoreactive unmyelinated axons and synaptic boutons were found in all subdivisions of the IC, most often in the nucleus externus, followed by the nucleus pericentralis, and a few were seen in the dorsomedial part of the central nucleus. The boutons measured 0.5-1.8 microns, contained pleomorphic synaptic vesicles, and established symmetrical synaptic contacts almost exclusively with dendrites of small caliber.

Topographical distribution of NADPH-diaphorase positive neurons in the cat's inferior colliculus.

By using a histochemical procedure NADPH-diaphorase the topographical distribution of neurons and fibers containing NADPH-diaphorase activity in the cat's inferior colliculus is examined. Neurons and fibers positive for NADPH-diaphorase are observed throughout the rostro-caudal extent of the inferior colliculus, located in its three main subdivisions: nucleus centralis, nucleus pericentralis and nucleus externus. According to the size of the perikarya, dendritic and axonal morphology the positive neurons are classified as follows: large, medium-sized and small. The morphological differences could contribute to the different functions of these cells. The results support the hypothesis that large and medium-sized NADPH-diaphorase positive neurons represent the projections neurons while the small NADPH-diaphorase positive neurons have morphological characteristics that corresponds to the interneurons. Finally, results demonstrating existence of dense network of NADPH-diaphorase positive fibers and fragments suggest that they are dendrites and axons of NADPH-diaphorase positive neurons distinguished in inferior colliculus.

Cholecystokinin-like immunoreactivity in cat inferior colliculus. Light and ultrastructural study.

Cholecystokinin-like immunoreactive (CCK-LI) neurons are observed in the pericentral nucleus, the external nucleus and the dorsomedial part of the central nucleus of the cat's inferior colliculus. The largest number of CCK-LI cell bodies is observed in the caudal part of the pericentral nucleus. Using the electronmicroscopical examination we distinguish two different types of CCK-LI neurons. The first type CCK-LI neurons is characterized by a relatively large nucleus, surrounded by a dark rim of cytoplasm containing single cisterns of granular endoplasmic reticulum, few mitochondria and lysosomes. The second type CCK-LI neurons are smaller than the neurons of the first type. The nucleus is relatively larger while the cytoplasmic rim is quite thin. The CCK-LI immunoreactivity is also found in the large, medium-sized and small dendrites as well as in the dendritic spines. The CCK-LI axon terminals contain small round or pleomorphic vesicles. Sometimes they show a mixed population of clear and dense core vesicles. The immunoreactive terminal boutons establish typical asymmetrical synaptic contacts with dendritic spines, small or medium-sized dendrites. More rarely, the immunoreactive axon terminals perform symmetrical or intermediate synaptic contacts with proximal dendritic trunks or perikarya.

Neurotensin immunoreactivity in the colliculus inferior of cat: light and electron microscopic investigations.

Neuronal perikarya with neurotensin-like immunoreactivity (NT-LI) are found in the pericentral and external nuclei and the dorsomedial part of the central nucleus of the inferior colliculus. On electron-microscopic examination, these neurons are characterized by a relatively large nucleus, a small amount of cytoplasm and paucity of organelles. NT-LI is observed in large and small dendrites and dendritic spines as well as in axon terminals which contain small round or elongated clear vesicles and/or dense core vesicles. The immunoreactive terminal boutons make asymmetrical axodendritic and symmetrical axo-somatic synapses mainly on non-immunoreactive elements.

The fine structure of the inferior colliculus in the cat. II. Synaptic organization.

The synaptic organization of the central nucleus of the inferior colliculus (ICc) of the cat has been investigated by means of electron microscopy. On the basis of the following criteria: the size and the shape of the synaptic vesicles, the distribution and density of the vesicular population, the size and the shape of the synaptic boutons, their origin, and the characteristics of the active synaptic zones, several types of synaptic boutons in the ICc have been discriminated: LR1, LR2, SR, SSB, F1, F2, P, DCV-terminals, and "d"-profiles. The LR1, LR2, SR and SSB bouton types contain clear, round or slightly oval synaptic vesicles and form asymmetrical synapses mainly with middle sized and small dendrites and dendritic spines. LR2-terminals not rarely contact also the neuronal perikarya, whilst the SR-boutons form exclusively axodendritic and axospinous synapses. The P, F1 and F2-boutons contain a pleomorphic vesicular population (P-boutons), with an increased degree of vesicle flattening (F1 and F2-boutons) and form symmetrical axosomatic, axodendritic and axospinous contacts. Especially often the F1-boutons form axosomatic synapses, whilst the F2-terminals end mainly on dendrites. The DCV-boutons contain a mixed population of clear round synaptic vesicles and large dense core vesicles. The DCV-boutons terminate mainly on spines and small distal dendrites by means of asymmetrical synaptic specializations. The "d"-profiles originate from dendrites, and are identical to the thalamic "d"-profiles but are far more rarely observed in the ICc. The "d"-profiles are postsynaptic mainly to the LR-types, and are presynaptic to conventional dendrites, thus participating in synaptic triads. The axonal hillocks and the initial axonal segments of the larger perikarya in the ICc are substantially innervated mainly by LR and P-boutons. Glomerulus-like formations are fairly often, especially around the LR1-terminals, contacting several small postsynaptic targets. True synaptic glomeruli are only rarely observed. Branching myelinated axons are found mainly within the fibrodendritic laminae, whilst unmyelinated collaterals, emitted by myelinated axons are especially often encountered outside the laminae. Various types of myelinated axons form nodal synapses.

Projections to the inferior colliculus from the dorsal column nuclei. An experimental electron microscopic study in the cat.

The projections from the dorsal column nuclei (DCN) to the inferior colliculus (IC) were investigated in cats by means of electron microscopy. The DCN were destroyed unilaterally by electrocoagulation and the animals survived 3 or 4 days. A variable number of degenerating synaptic boutons were observed bilaterally in the IC-external nucleus and in the intercollicular area. The greatest number of degenerating terminals was encountered in the rostral portions of the IC-external nucleus and in the intercollicular area contralateral to the DCN lesion. In these regions some series of ultrathin sections the degenerating boutons comprised 6-13% of the entire synaptic bouton population of the examined area. In the caudal portion of the contralateral IC-external nucleus the number of degenerating boutons greatly diminished and the latter showed a patchy distribution. Ipsilateral to the DCN lesion the number of degenerating terminals was low, and a more substantial number was found only in the rostroventral portion of the IC-external nucleus and in the intercollicular area. The degenerating synaptic boutons displayed markedly diverse patterns of alterations. Most often was the dark (electron-dense) degeneration pattern, followed by the filamentous degeneration. More rare were the light (electron-lucent) degenerating boutons, and a very limited number of terminals displayed pinocytotic degeneration changes. The DCN boutons contained round and oval synaptic vesicles and terminated mainly on proximal dendritic trunks, followed by the perikarya of the efferent neurons, and smaller, distal dendrites. Rarely the degenerating terminals contacted dendritic spines, and no contacts were found with the small (interneuronal) perikarya and with other vesicle containing profiles. The axodendritic contacts were asymmetrical and the axosomatic--from the intermediate type. In agreement with previous light microscopic data, the present findings demonstrate the existence of substantial excitatory projection from the DCN to the polysensory nuclei of the IC that integrate converging auditory and tactile information, and are involved in acoustico-motor behavior.

Ultrastructure of Golgi-impregnated and gold-toned neurons in the central nucleus of the inferior colliculus in the cat.

The combined Golgi/electron microscope technique was used to analyse the cytoarchitecture and the fine structure of the central nucleus of the inferior colliculus in the cat. The analysis of Golgi-impregnated sections discriminates three major neuronal types, according to somato-dendritic morphology, and to presence or absence of dendritic spines. Two major types (spiny and aspiny) might be further subdivided into large, medium-large, medium-small and small, whilst the third ("mixed") type is subdivided into large and medium-large types. The large, medium-large and medium-small cells of the major types appear to be efferent (relay) neurons, whilst the small spiny, and especially the small aspiny cells are interneurons. In agreement with previous data, the subdivision of the relay neurons in disc-shaped and stellate cells is confirmed but the disc-shaped neurons are further subdivided in typical and atypical. The dendritic fields of the latter neurons correspond greatly but not exclusively to the fibrodendritic laminae of the central nucleus. In addition to the axonal ramification of the local circuit neurons, the axons of most (if not all) types of relay cells emit a moderate to scant, rarely--a substantial number of collaterals. The collaterals of the large spiny neurons (atypical disc-shaped cells) occasionally innervate also the cell of origin. Parallel to the light microscopic discriminations of the different neuronal types, the electron microscopic observations confirm that the ultrastructural characteristics might be very distinct. Especially evident are the differences between the large neuronal types, concerning the amount and arrangement of the granular endoplasmic reticulum, and the mode of the perikaryal, dendritic, and axonal innervation by various synaptic bouton types. Along with the unequivocal discrimination of the neurons in the central nucleus of the inferior colliculus according to the dendritic orientation, we suggest also a more detailed classification of the neuronal types according to the perikaryal size, fine dendritic morphology, and ultrastructural characteristics. Further hodological experiments, combined with the presently explored technique, will help to clarify the complicated synaptic events in the central nucleus of the inferior colliculus.

Evidence for the existence of a projection from the dorsal column nuclei to the substantia nigra in the cat.

Discrete injections of horseradish peroxidase in the substantia nigra of cats resulted in moderate to scant retrograde neuronal labeling of the contralateral dorsal column nuclei (nucleus gracilis and nucleus cuneatus). A moderate number of degenerating synaptic boutons emanating from the axons of stereotaxically lesioned dorsal column nuclei were identified by electron microscopy in the neuropil of the contralateral substantia nigra zona compacta and its dorsal division-nucleus parabrachialis pigmentosus. The present findings furnish evidence for a moderate, entirely crossed afferent projection of the dopaminergic neurons of the mesencephalic tegmentum, arising in the dorsal column nuclei.

Suprachiasmatic nuclei lesions eliminate light/dark variations in short-term feeding responses to deprivation or insulin treatment in rats.

Short-term (1-h, 4-h and 12-h) and long-term (24-h) feeding responses to 24-h food deprivation (FD) or insulin treatment (IT) (8 mU/kg IP) were studied in male rats under a 12/12-h light/dark (L/D) cycle. The 24-h FD or the IT began either at onset (Dawn) or offset (Dusk) of the lights. In sham-operated rats (Shams) both protocols elicited greater short-term feeding responses at Dusk (p less than 0.05 or less). In suprachiasmatic nuclei (SCN)-lesioned rats the L/D variations in short-term responses were absent. In both SCN and Shams the 24-h feeding responses did not depend on stimuli time-schedule. We conclude that the regulation of short-term (circadian), but not long-term, feeding responses to metabolic stimuli is dependent on SCN integrity in the rat.

The fine structure of the inferior colliculus in the cat. I. Neuronal perikarya in the central nucleus.

The fine structure of the neurons in the ventrolateral and the dorsomedial parts of the central nucleus of the inferior colliculus has been studied. 318 neurons, followed in serial ultrathin sections were examined. On the basis of the cell size, four major types of neuronal perikarya were identified: large (greater than 22 microns), medium-large (18-22 microns), medium-small (12-18 microns), and small (less than 12 microns). According to the shape of the perikarya, the ultrastructural features of their organelles, the occurrence and number of axosomatic synaptic contacts, the main neuronal types were subdivided in more discrete varieties. The large neurons have three varieties (oval, irregular, and fusiform). The nucleocytoplasmic ratio of these cells is usually above 1:1.8. They possess voluminous cytoplasm, that is rich in organelles. The granular endoplasmic reticulum is organized in NISSL bodies. Extremely numerous axosomatic synapses are present. These neurons represent the large stellate and disc-shaped projection (efferent) neurons, described in GOLGI studies. The medium-large neurons have two varieties. The nucleocytoplasmic ratio is 1:1.6-1:1.3. They possess a lesser amount of cytoplasm. Only the first variety possess discrete NISSL bodies. These cells are moderately afferented. The medium-small neurons display distinct differences in the number and pattern of cell organelles, and might be splitted in four varieties. The nucleocytoplasmic ratio is 1:1.4-1:1.1. Some of the medium-small neurons (especially--the first and the second variety) are probably projection cells, whilst others (especially--the third variety) might be interneurons. The small neurons display relatively large nucleus, small amount of cytoplasm (nucleocytoplasmic ratio approx. 1:1.2), general paucity of organelles, and extremely few axosomatic synapses. The both varieties of the small neurons, in all probability, represent local circuit neurons. From the total number of 318 neurons, 250 cells were followed in long rows of serial sections, that allowed distinct discrimination. From the latter, 18.4% were classified as large, 27.2%-medium-large, 44.4%-medium-small, and 10.0%-small neurons. The remaining 68 perikarya do not offer reliable electron microscopic criteria that could allow an unequivocal identification. The description of the cell somata in the central nucleus of the inferior colliculus, and its synaptic organization (to be published) will provide a basis for future studies on the connectivity, synaptic events, and neurotransmitter interactions in the relay nuclei of the auditory system.

Reciprocal connections between the claustrum and the auditory cortical fields in the cat. An experimental study using light- and electron microscopic anterograde degeneration methods, and the horseradish peroxidase retrograde axonal transport.

The reciprocal connections between the claustrum and the auditory cortical fields AI, AII and Ep were investigated by means of Nauta and Fink-Heimer selective silver impregnation procedures, electron microscopic identification of degenerated axons and synaptic boutons, and with the Mesulam horseradish peroxidase retrograde tracing technique. The course and termination of degenerating corticoclaustral axons were investigated following circumscript lesions of the AI, AII and Ep areas in 19 cats. The greatest amount of degeneration debris was observed following destruction of the AII area. The central third of the claustrum (stereotaxic level A13-A15) is filled with degenerating terminals (d. t.), with greatest concentration in the lateral wedge of the nucleus, and along its inferolateral border. Rostrally and caudally the density of degeneration diminishes but scattered d. t. were observed up to the rostral pole, and a moderate number - up to the caudal pole of the claustrum. Slightly lesser amount of d. t. was observed following Ep destruction. The caudal portion of the claustrum is filled with d. t. In the central third the degeneration field occupies mainly the ventrolateral zone of the nucleus. The rostral pole of the claustrum is free of degeneration. The projection from the AI field is considerably more moderate, and is diffusely organized. A substantial number of d. t. is encountered only in the lateral parts of the central claustral third. The crossed corticoclaustral connections mirror the ipsilateral ones but are far more modest. The AII area projects mainly to the central claustral third, the Ep area--to the caudal third. The projection of the AI area to the contralateral claustrum is very weak. The electron microscopic examination of the claustrum following auditory cortex destruction in 9 cats revealed an appreciable number of degenerating synaptic boutons. They undergo dark and more rarely light degenerative changes. The cortical terminals are classified in two types: "small round" (SR), comprising approximately 70 to 75% of the corticoclaustral boutons, and "large round" (LR)-25-30%, resp. The SR boutons measure 0.6-1.2 micron, contain tightly packed round synaptic vesicles (380-420 A), and form asymmetrical axodendritic contacts. The LR boutons measure 1-2.5 microns, contain round vesicles (400-500 A) and form asymmetrical axodendritic and (far more rarely) axosomatic contacts. The claustrocortical connection was investigated in 13 cats with selective injections of 30% HRP in the three subdivisions of the auditory cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Projections from the auditory cortex to the nucleus of the oculomotor nerve. Silver impregnation and radioautographical study.

A monosynaptic, bilateral connection, between morphophysiological auditory cortical areas and the nucleus of the oculomotor nerve was established by means of contemporary silver impregnation methods and radioautographical technique. Degenerating (resp.--labeled) axons enter the oculomotor nucleus neuropil diffusely from rostro-dorso-laterally, and proceed caudo-ventro-medially. The number of degenerating (resp.--labeled) preterminals and terminals is larger within the territory of the nucleus, located ipsilaterally to the cortical lesion (resp.--isotope injection). The presently described projection is relatively very modest, when compared with the substantial connections of the auditory cortex with the subcortical centers of the auditory system. However, the direct temporooculomotor pathway might serve as a rapid and effective mechanism for the vision-turning reflex after auditory stimulation.

Retinal innervation of the inferior colliculus in adult cats: electron microscopic observations.

A moderate number of degenerating synaptic boutons (DSB) in the pericentral nucleus of the inferior colliculus (IC) were identified electron microscopically following contralateral eye enucleation in adult cats. Most of the DSB measure 0.6-1 micron and a lower percent are larger (1-2.5 micron). Both types contain a slightly polymorph population of clear vesicles, mainly round and oval, and a very few are elongated. The DSB are involved in asymmetric axodendritic contacts. The present report provides evidence for a crossed retinofugal monosynaptic excitatory tract innervating the IC pericentral nucleus, a possible audio-visual integrative subcortical center.

Somatodendritic synapses in the central nucleus of colliculus inferior (CI) in the cat.

During the ultrastructural investigation of the central nucleus of cat's colliculus inferior (CI) neurons containing synaptic vesicles were encountered. Their perikarya form somatodendritic synapses and occupy presynaptic positions. These neurons were located in the dorsomedial portion of the central nucleus of the CI. On the basis of their electron microscopical appearance and synaptic relationships they might be discriminated as putative interneurons.

Modified Nauta and Fink-Heimer procedures with special reference to the demonstration of monoaminergic pathways in the central nervous system.

Modifications of the selective silver impregnation methods of Nauta and Fink-Heimer are described. Both procedures were tested in wide variety of species: from reptiles to carnivores, as well as in human autoptic cases. The modified Nauta procedure is recommended as a method of choice for tracing axonal trajectories due to an improved impregnation selectivity of the degenerating axoplasm. Its use for the demonstration of monoaminergic (NA, DA, 5-HT) pathways, however, remains limited. The modified Fink-Heimer procedure demonstrates successfully the degeneration of axons, and especially--the thin preterminal arborizations, as well as the terminal boutons in many fiber systems studied, including the nigrostriatal, raphe-nigral, and coerulocortical tracts. Both methods provide an additional cytoarchitectonic orientation due to a counterstain of nerve cell bodies with cresylechtviolett.