P. D. Prasada Rao

Differential brain distribution of gonadotropin-releasing hormone receptors in the goldfish.

The present study describes the differential distributions in the brain of the two goldfish gonadotropin-releasing hormone (GnRH) receptors, using both immunohistochemistry and in situ hybridization approaches. The goldfish GnRH GfA and GfB receptors are variant forms of the same receptor subtype, although with distinct differences in ligand binding characteristics, and differential distributions in the pituitary and body tissues [Proc. Natl. Acad. Sci. USA 96 (1999) 2526]. The goldfish GnRH GfA receptor was found to be widespread throughout the brain, with neurons showing immunoreactivity in the olfactory bulbs, telencephalon, preoptic region, ventro-basal hypothalamus, thalamus, midbrain, motor neurons of the fifth, seventh, and tenth cranial nerves, reticular formation, cerebellum, and motor zone of the vagal lobes. The tracts in the posterior commissure, optic tectum, and motor zone of the vagal lobes also demonstrated immunoreactivity. While the brain was not systematically surveyed for in situ hybridization, hybridization was found in similar locations in the telencephalon, preoptic region, ventro-basal hypothalamus, cerebellum, and optic tectum. Hybridization was additionally found in the medial hypothalamus. The goldfish GnRH GfB receptor was found to have a more restricted distribution in the brain, with neurons showing immunoreactivity in the telencephalon, preoptic region, and ventro-basal hypothalamus. In situ hybridization demonstrated a somewhat wider distribution of expression of the receptor, with hybridization occurring in the preoptic region, ventro-basal and medial hypothalamus, as well as in the thalamus, epithalamus, and optic tectum. The widespread distribution of GnRH GfA receptor, and in particular its localization in the midbrain tegmentum in the region of the GnRH-II neurons, suggests that this receptor may be involved in the behavioral actions of GnRH peptides in the goldfish.

A cytoarchitectonic study of the hypothalamus of the lizard, Calotes versicolor.

SummaryThe hypothalamic nuclei of the lizard, Calotes versicolor, can be broadly divided into ‘AF-positive’ Selectively stainable with paraldehyde fuchsin and other dyes of the Gomori type and ‘AF-negative’. The AF-positive cell complexes include the nucleus supraopticus, nucleus paraventricularis, and a few interconnecting bridge cells. In addition, some AF-positive neurones are also observed in the median eminence. As many as 15 AF-negative nuclei-like accumulations of nerve cells can be identified in the hypothalamus. The nucleus periventricularis hypothalami of earlier authors is subdivided into eight circumscribed neuronal complexes. In addition, a few AF-negative nuclei, e.g. nucleus subfornicalis, nucleus ventralis tuberis, nucleus med. recessus infundibuli, nucleus lat. recessus infundibuli and nucleus praemamillaris, are regarded for the first time as anatomical entities. The distribution of the hypothalamic nuclei and their cytoarchitectonic features are described at the light microscopical level. An attempt has been made to interprete the nuclei identified in the present study on a comparative and phylogenetic basis.

Effect of Electrical Stimulation of the Optic Nerve on the Nucleus preopticus and Nucleus lateralis tuberis of the Catfish, Clarias batrachus (Linn.)

The changes in the nucleus preopticus (NPO) and nucleus lateralis tuberis (NLT) of the catfish, Clarias batrachus, were studied after electrical stimulation of the optic nerve. The aldehyde fuchsin (AF)-positive neurosecretory material from the entire NPO was depleted after a 10-min stimulation as revealed from the bulk-stained preparations and tissue sections. However, a 3-min stimulation was sufficient to cause significant hypertrophic changes in the neuronal nuclei (p less than 0.005 in the ventral neurons; p less than 0.01 in the dorsal neurons). In order to evoke significant stimulatory changes in the cell nuclei of the NLT, a longer period of stimulation than that for the NPO was essential. Similarly, stimulations of different durations were required to induce significant hypertrophic changes in the pars anterior and pars posterior of the NLT. Based on these observations, the possible existence of an afferent pathway from the optic nerve to the hypothalamic neurosecretory nuclei is suggested.

Cytoarchitectonic pattern of the hypothalamus in the turtle, Lissemys punctata granosa

SummaryIn the hypothalamus of the turtle, Lissemys punctata granosa, two magnocellular and 23 parvocellular neuronal complexes can be distinguished. The magnocellular complexes include the nucleus supraopticus and the nucleus paraventricularis; paraventricular neurons are partly arranged in rows parallel to the third ventricle. Most infundibular parvocellular nuclei display neurons disposed in rows parallel to the ventricular surface. In the preoptic region, the prominent parvocellular neuronal complexes encompass the nucleus periventricularis anterior, lateral preoptic area, the nucleus of the anterior commissure and the nucleus suprachiasmaticus. The prominent nucleus periventricularis posterior extends caudad and shows neurons arranged in vertical rows parallel to the third ventricle. Other parvocellular nuclei of the rostral hypothalamus are composed of clustered subunits. The nucleus arcuatus is a fairly large nuclear entity extending from the level marked dorsally by the nucleus paraventricularis to the area occupied by the nucleus of the paraventricular organ. A well-developed ventromedial nucleus is located ventrolateral to the paraventricular organ. The prominent paraventricular organ consists of tightly arranged neurons, some of which possess apical projections into the third ventricle; it is surrounded by the nucleus of the paraventricular organ. Nucleus hypothalamicus medialis et lateralis, nucleus hypothalamicus posterior and the nuclei recessus infundibuli are further nuclear units of the tuberal region. The caudal end of the hypothalamus is marked by the nucleus mamillaris; its neurons are scattered among the fibers of the retroinfundibular commissure. The median eminence is well developed and shows a large medial and two lateral protrusions into the infundibular recess.

Retinal projections in the catfish, Mystus vittatus (Bloch) as revealed by tracer studies with horseradish peroxidase

SummaryThe retinal efferents of the catfish, Mystus vittatus, were investigated with the use of the horseradish peroxidase (HRP) technique. Most retinal fibres extended contralateral to the eye that had received HRP label, while a few fascicles projected to the ipsilateral side without decussation in the optic chiasma. The contralateral fibres projected to the suprachiasmatic nucleus, the nucleus opticus dorsolateralis, the nucleus of the posterior commissure, the nucleus geniculatus lateralis, pretectal nuclear complex, and to two layers of the optic tectum, i.e., stratum fibrosum et griseum superficiale and stratum griseum centrale. The accessory optic tract arose from the inner area of the optic tract and extended ventromedially to the accessory optic nucleus. The ipsilateral fascicles projected to almost all the above mentioned nuclei, but these projections were comparatively sparse. The ipsilateral retinal projection was restricted to the rostral tectum.

Effects of some corticosteroids and metopirone on the corpuscles of Stannius and interrenal gland of the catfish, Heteropneustes fossilis (Bloch)

Abstract The histological changes in the corpuscles of Stannius (CS) and interrenal gland (IG) after administration of two corticosteroids, viz. hydrocortisone acetate and deoxycorticosterone acetate, and metopirone (Ciba) have been studied in the catfish, Heteropneustes fossilis (Bloch). After the injections of the above steroid hormones there is a significant nuclear hypertrophy in the CS accompanied by an initial accumulation of granules. This is followed by a subsequent degranulation, thus indicating distinct stimulatory changes. On the other hand, administration of the steroid hormones resulted in a reduction of the nuclear size of the interrenal cells indicating an inhibition of their activity. After metopirone treatment there is a marked degranulation of the CS cells and a significant nuclear hypertrophy in the cells of the CS as well as the IG. Based on these concomitant changes in the CS and IG after administration of steroid hormones and metopirone, the possible existence of adrenocortical-corpuscular axis is discussed.

Cytoarchitectonic pattern of the hypothalamus in the crocodile, Gavialis gangeticus

SummaryThe hypothalamus of the crocodile, Gavialis gangeticus, was investigated to reveal the organization of various nuclear complexes and to suggest homologies. The hypothalamic nuclei of G. gangeticus are composed of magnocellular and parvocellular neuronal entities. In the magnocellular system the nucleus supraopticus is well developed, whereas the nucleus paraventricularis and nucleus retrochiasmaticus are represented by scattered somata. Application of cytoarchitectonic criteria permits the delineation of 24 distinct parvocellular nuclear complexes extending rostrocaudally from the anterior commissure to the level indicated by the median eminence and nucleus mamillaris; some are further divisible into subgroups. The nucleus of the preoptic recess appears to be a unique property of the crocodilian hypothalamus. The nucleus suprachiasmaticus possesses a wing-like ventrolateral expansion that protrudes along the lateral aspect of the optic nerve. The tuberal region displays an elaborate pattern of nuclei segregated by regional specializations of the neuropil. The nucleus hypothalamicus posterior occupies the periventricular zone, flanked laterally by the nucleus hypothalamicus dorsomedialis and nucleus arcuatus. Further laterally, extended subdivisions of the nucleus hypothalamicus lateralis contain neurons rich in Nissl substance; the specializations shown by these subdivisions, in comparison to the lateral cell groups in lizards and snakes, are suggestive of enhanced integrative functions. The conspicuous paraventricular organ is encircled by dorsal and ventral divisions of the nucleus of the paraventricular organ. The neurons of the nucleus subfornicalis and nucleus hypothalamicus medialis are few in number, but large in size. The general organization of the hypothalamus of G. gangeticus reveals a mosaic-like pattern with the constituent groups appearing as clusters of small and large neurons, arranged medially and laterally in a definitive manner and accompanied by extensive zones of neuropil in the subependymal and lateral zones of the hypothalamus. The median eminence is divisible into an anterior and a posterior region. The nuclear pattern in the crocodilian hypothalamus reveals a higher state of morphologic organization compared to the situation in lizards or snakes, and thus reflects an evolutionary trend in the avian direction.

Effect of some antithyroid drugs on the corpuscles of Stannius and thyroid gland of the catfish, Heteropneustes fossilis (Bloch)

Abstract The histological changes in the corpuscles of Stannius (CS) and the thyroid gland were studied after administration of two antithyroid drugs, viz., thiourea and thiouracil in the catfish, Heteropneustes fossilis (Bloch). Injections of thiourea resulted in hypertrophy, hyperplasia, and hyperaemia of the thyroid follicles, whereas thiouracil treatment produced stimulatory changes in the thyroid gland up to 30 days only. After a prolonged immersion in thiourea solution the hypertrophied thyroid follicles underwent atrophic changes. Despite pronounced alterations in the thyroidal activity no significant changes could be discerned either in the granularity or in the cell and nuclear diameters of the CS. It, therefore, seems that a lack of thyroid hormone has no apparent effect on the CS of the catfish.