Central projections of intracellularly labeled auditory nerve fibers in cats: morphometric correlations with physiological properties.

The central arborizations and endings of type I spiral ganglion neurons were labeled with intracellular injections of horseradish peroxidase (HRP) after their characteristic frequency (CF) and spontaneous discharge rate (SR) were physiologically determined. A fiber-by-fiber analysis was conducted and the morphological data compared with the fiber's response properties. The total number of branch points was correlated with total fiber length, a relationship that remained relatively constant when analyzing the ascending and descending branches together or separately. On the other hand, the ascending branches of four out of five fibers having CFs below 0.5 kHz bifurcated and gave rise to a pair of terminal endbulbs of Held. Low- and medium-SR fibers gave rise to more endings than did high-SR fibers, especially on the ascending branch. This difference was accounted for by small endings, a category composed of terminal boutons, string endings, and small complex endings. The categories of modified endbulbs, and endbulbs of Held did not vary in number with respect to fiber SR. The mean area of each ending type within the small ending category was statistically smaller for low- and medium-SR fibers than for high-SR fibers, whereas the mean area of modified endbulbs and endbulbs of Held was not correlated with fiber SR. Total ending area per fiber appeared independent of either CF or SR. These results are discussed in relation to issues of conservation of axon arborizations and terminals, and convergence of input from the different SR groups.

Tryptamine concentrations in areas of 5-hydroxytryptamine terminal innervation after electrolytic lesions of midbrain raphe nuclei.

The possible existence of tryptamine-containing neurons originating in the midbrain raphe is suggested by several reports of tryptamine-mediated responses to electrical stimulation of the raphe nuclei. To assess this hypothesis, we have investigated the effects of electrolytic lesions of the median and dorsal raphe nuclei on striatal, hypothalamic, and hippocampal concentrations of tryptamine, 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid. In addition, the rat striatal tryptophan concentrations were also determined. No changes in the concentrations of tryptamine were observed at 1 or 2 weeks after lesioning the dorsal and median raphe nuclei, at which time the other 5-hydroxyindoles were markedly reduced; furthermore, no reductions were observed in tryptamine concentrations in the striatum, hypothalamus, or hippocampus of rats pretreated with a monoamine oxidase inhibitor. The only change observed in these rats was a limited increase in striatal tryptamine and tryptophan observed at 1 day after lesioning. The results indicate that tryptamine concentration is independent of the integrity of 5-HT-containing neurons of the midbrain raphe nuclei. Furthermore, if tryptamine-containing neurons that have terminal projections to the striatum, hypothalamus, and hippocampus exist, their cell bodies are located in regions outside the dorsal and median raphe nuclei. Another possibility could be that tryptamine is located in glial cells.

Ontogeny of neuropeptidergic systems: luteinizing hormone releasing hormone (LHRH); somatostatin (SRIF) and neurophysin (NF) in the hypothalamus of the domestic pig by immunocytochemistry.

The ontogenic development of some hypothalamic neuropeptides: luteinizing hormone releasing hormone (LHRH); somatostatin (SRIF) and neurophysin (NF) and their localization in the hypothalamus of fetuses in different stages of the fetal life were studied by immunoperoxidase method. It was found that differentiation of the neurons which produce the examined hormones begins in the midstage of pregnancy. LHRH is stored in the nerve terminals of the median eminence (ME) and organum vasculosum of the lamina terminalis (OVLT) since 72 day of gestation and its amount gradually increases with the development of the embryo. In this stage a few immunoreactive (ir) LHRH perikarya appear but they are most numerous in the last days of pregnancy (110 day). They are localized in the most anterior periventricular parts of the hypothalamus, area preoptica, diagonal band of Broca and very rare in the medial-basal hypothalamus. Somatostatin is produced in the separate neuronal system and appears in the last days of fetal life. Neurophysin is present in both magnocellular nuclei in 72 day-old fetuses, but at the end of gestation it is seen also in some preoptico-septal region.

The luteinizing hormone releasing hormone-containing pathways and their co-termination with tanycyte processes in and around the median eminence and in the pituitary stalk of the rat.

The origin, course and termination of two luteinizing hormone releasing hormone (LH-RH)-containing pathways were studied in the brain of rats by immunohistochemistry. In addition, the joint termination of LH-RH-containing nerve terminals and tanycyte processes over a rostro-caudally elongated belt surrounding the median eminence (ME) is described. The preoptico-infundibular tract originates from neurons confined to a pyramid-shaped area between the anterior commissure, the organum vasculosum laminae terminalis (OVLT) and the most caudal level of the suprachiasmatic nucleus (SCH). The axons of these neurons form three fascicles. Fibres of the median fascicle run in caudal direction on the dorsal and ventral surfaces of the optic chiasma. Fibres of the medial fascicle run along the lateral border of the SCH towards the retrochiasmatic area. Fibres of the lateral fascicle course laterally in close contact with the concave dorsomedial surface of the optic tract. These latter fibres gradually turn in medial direction and reach the lateral margin of the ME. The caudal LH-RH fibre tract was characterized only partially because the perikarya giving rise to these fibres were not identified. The fibres run rostrally among the ependymal cells of the mesencephalic aqueduct and form two fascicles. The fibres of the mammillary fascicle enter, and seem to terminate, in the medial mammillary nucleus, while the fibres of the tuberal fascicle course rostrally and join the fibres of the preoptico-infundibular tract. The surface areas of the brain along which LH-RH fibres terminate (retrochiasmatic area, inframammillary region, lateral margin of the ME) were found to display a special surface covering formed by tanycyte processes. The course of LH-RH fibre tracts described here is in good agreement with earlier experimental results on the localization of neural pathways controlling ovulation and the secretion of pituitary gonadotropic hormones. The significance of the joint termination of LH-RH fibres and tanycyte processes, especially in areas where portal capillaries are absent, remains unclear.

The location of LH-RH neurons in the rat hypothalamus and their pathways to the median eminence. Experimental immunohistochemistry and radioimmunoassay.

The location of the perikarya of LH-RH neurons in the rat hypothalamus and their pathways to the median eminence were studied by immunohistochemistry and radioimmunoassay after placing stereotaxic electrolytic lesions in several parts of the hypothalamus. The principal location of the cell somata was found to be in the ventral part of the medial preoptic area; their pathways were classified into a main baso-lateral pathway and an accessory descending pathway branching off from the former. The main pathway was found to cross in the vicinity of the corresponding neuronal perikarya. The central median eminence and the dorsal and ventral walls of the tubero-infundibular sulcus of the caudal part of the median eminence are innervated mainly by the baso-lateral pathway. On the other hand, the rostral and most caudal protions of the median eminence are innervated principally by the descending pathway and have a subsidiary dual innervation. The projection of LH-RH neurons to the OVLT is believed to originate from perikarya adjacent to this circumventricular organ.

Direct projection from the medial preoptic area to the median eminence of the cat.

The projection from the medial preoptic area to the median eminence of the cat was clarified by electron microscopy. After placing the electrolytic lesion in the preoptic area several kinds of degenerating neuronal processes and terminals were observed in the external layer of the median eminence. The one was dark shrunk terminals containing dense cored vesicles, the other was the dark ones containing myeline figure-like structure. The relationship between catecholamine-containing nerve endings and RH/IH-containing endings in the external layer of the median eminence was discussed.

Morphological organization of catecholamine terminals in the diencephalon of the rhesus monkey.

The hypothalamus and thalamus of the rhesus monkey were investigated using the fluorescence histochemical method of Falck and Hillarp. The hypothalamus was found to be richly supplied with catecholamine fluorescent nerve terminals with many thick and a few varicosities, whereas nerve terminals with fine varicosities were found to be distributed over the thalamus except for the midline and medial nuclei which were innervated by nerve terminals with thicker and more intense fluorescent varicosities. The morphological characteristics and distribution pattern of catecholamine terminals were similar between the rhesus monkey and the rat. However, some species differences were noted in the suprachiasmatic nucleus, arcuate nucleus and internal layer of infundibulum in the hypothalamus. The pulvinar, which was nonexistent in the rat, had fine terminals.

[Distribution of catecholamine containing nerve endings in the hypothalamus of the rhesus monkey].

Using the Falck-Hillarp method, the distribution of catecholamine nerve terminals in the rhesus monkey hypothalamus was studied. The distribution pattern was fundamentally similar to that in the rat, cat and human fetus; abundunt catecholamine varicosities (presumed noradrenaline nerve terminals) were observed in the dorsomedial nucleus, supraoptic nucleus, paraventricular nucleus, medial forebrain bundle, periventricular layer and internal layer of the infundibulum, while little were in the mamillary nucleus, ventromedial nucleus and anterior hypothalamic area. A band of diffuse green fluorescence (dopamine nerve terminals) was observed around the capillary loops in the external layer of the infundibulum. the discrepancy with the rat was noted in the abundunt noradrenaline nerve terminals in the suprachiasmatic nucleus and denser innervation of them in the arcuate nucleus and internal layer of the infundibulum. In addition to the noradrenaline nerve fibers from the peripheral sympathetic NA nerve, the noradrenaline nerve terminals of central origin closely approximated to the small intracerebral vessels.

Distribution of monoamine-containing terminals and fibers in the central nervous system of the chicken.

In the mesencephalon of the chicken, the two large groups of CA terminals and fibers appeared to correspond to the dorsal and ventral bundles of the CA containing fibers in the rat. These ran rostrally in the medial forebrain bundle and appeared to terminate within the thalamus, hypothalamus, preoptic region and corpus striatum. 5-HT containing terminals and fibers also were observed in the mesencephalon and appeared to run rostrally in the medial part of the medial forebrain bundle. In comparison with the CA terminals, however, 5-HT terminals were for the greater part, difficult to observe in many areas of the brain. Based on the observation concerning postnatal ontogeny of monoamine-containing neurons, the chicken brain appears to acquire behavioral and functional maturity at an earlier stage after birth than does that of the rat. Effect of reserpine, nialnmide, L-Dopa and 5-HTP on the monoamine-containing terminals and fibers are briefly discussed.