Annual reproductive phase-related profile of sex steroids and their carrier, SHBG, in the Indian major carp, Labeo rohita.

This study reports annual cyclic changes in the plasma levels of sex hormone binding globulin (SHBG), sex steroids (E(2), estradiol; T, testosterone; P, progesterone) and protein (PRT) in correlation with reproductive phases in both sexes of an Indian major carp, Labeo rohita. Plasma SHBG, E(2), T and PRT levels in females and SHBG and T levels in males showed steady increases (p<0.005) in parallel with the gonadosomatic index (GSI) escalation in the preparatory and prespawning phases attaining peak levels before spawning. During the late spawning and early postspawning phases, E(2), T and SHBG levels revealed an abrupt and significant descent coincident with the GSI in both the sexes. The plasma P levels in females, attaining measurable quantities only in prespawning phase, underwent a rapid increase followed by a quick decline to undetectable levels in the spawning phase. This occurrence of P for a short duration suggests a limited role in ovarian function. During the resting phase, the E(2), T and SHBG levels in both sexes declined to minimum in conjunction with a decrease in the GSI, while PRT showed an increase. These data suggest that a significant increase in SHBG (p<0.005) prior to spawning enhances its binding capacity with sex steroids in both sexes synchronizing the reproductive activity. The significant increase of PRT in females during early spawning reflects its role in oocyte function, while PRT and E(2) in males may not significantly affect the testicular activity.

Oxytocin and vasopressin immunoreactivity within the forebrain and limbic-related areas in the mustached bat, Pteronotus parnellii.

The nonapeptides, oxytocin and arginine vasopressin, play an important role in mammalian social and reproductive behavior. Using immunocytochemical procedures, we identified oxytocin-immunoreactive neurons in the frontal and auditory cortices, limbic areas such as the medial septal nucleus, horizontal limb of the diagonal band and the amygdala. Only arginine vasopressin neurons were present in the bed nucleus of the stria terminalis. In limbic-related areas, the hypothalamic paraventricular and supraoptic nuclei and the nucleus centralis contained both oxytocin and arginine vasopressin neurons. The medial preoptic area showed a positive reaction for several arginine vasopressin fibers, but not oxytocin fibers, except in one female bat sacrificed during the breeding season. Arginine vasopressin fibers were observed in another limbic-related area, the periaqueductal gray. Furthermore, oxytocin was predominantly localized within sensory (e.g., auditory) and frontal cortex and limbic areas, whereas arginine vasopressin was restricted largely to known audiovocal regions of the periaqueductal gray. Classical neurosecretory nuclei in the hypothalamus contain both peptides. Oxytocin-immunoreactive neurons were also found in other structures such as the olfactory bulb, olfactory tubercle, primary and secondary motor cortex, fronto-parietal cortex, piriform cortex and the nucleus of the internal capsule. Both oxytocin and arginine vasopressin immunoreactivity was present in the suprachiasmatic nucleus, median eminence, neural lobe of the hypophysis and the pineal gland. Together with previous studies, the presence of these peptides within auditory areas of the cortex (sensory and frontal), and limbic as well as limbic-related regions provides anatomical evidence supporting their proposed role in social vocal behaviors and probably in auditory processing.

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.

Gonadotropin-releasing hormone-immunoreactive neurons and associated nicotinamide adenine dinucleotide phosphate-diaphorase-positive neurons in the brain of a teleost, Rhodeus amarus.

Using combined nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHd) histochemistry and salmon gonadotropin-releasing hormone (sGnRH) immunocytochemistry, it is reported for the first time that possible potential contacts occur between the nitric oxide (NO)- and the GnRH-containing neurons in the brain of a freshwater teleost, Rhodeus amarus. GnRH-immunoreactive (ir) neurons were observed in the olfactory nerve (OLN), olfactory bulb (OB), medial olfactory tract (MOT), ventral telencephalon (VT), nucleus preopticus periventricularis (NPP), nucleus lateralis tuberis (NLT), and midbrain tegmentum (MT). Although NADPHd neurons were widely distributed in the brain, only those having an association with GnRH-ir neurons are described. Based on the nature of the association between the GnRH and the NADPHd neurons, the former were classified into three types. The Type I GnRH neurons were characterized by the presence of NADPHd-positive granules in the perikarya and processes and occurred in the OLN, OB, MOT, and VT. The Type II GnRH neurons, having soma-soma or soma-process contacts with the NADPHd neurons, were restricted to the MT; the long processes of NADPHd cells crossed over either the perikarya or the thick processes of GnRH cells. However, the Type III GnRH neurons, found in the NPP and NLT, did not show direct contact, but a few NADPHd fibers were present in the vicinity. The terminal-soma contacts in the olfactory system and the VT and the soma-soma contacts in the MT represent the sites of possible potential contacts indicating a direct NO involvement in GnRH function, although NO action by diffusion remains possible. NO may influence the NPP and NLT GnRH cells by diffusion only, since a direct contact was not observed.

Ascending spinal projections to the optic tectum, facial and vagal lobes in the goldfish, Carassius auratus.

Using biotinylated dextran-amines as tracer, we observed prominent ascending spinal projections to three unreported areas in the gold fish brain viz. the optic tectum (OT), facial (FL) and vagal (VL) lobes. From the lateral spinal lemniscus (LSL), some fiber tracts separated off and extended mediodorsally, fanned out and innervated the FL. The VL was clearly laminated and showed three layers-the inner primary motor neuron and fiber layer (PMNF), outer secondary neuron layer (SN) and middle primary and secondary fiber layer (PSF). The PMNF received maximal innervation. Besides several fibers extending directly into the SN from the LSL, a few fibers extended dorsolaterally from the PMNF and innervated the SN. Several ascending fibers extended into the torus semicircularis, thalamic and pretectal areas and innervated the OT. The possible functional significance of the spinal innervation of these brain areas has been discussed.

Distribution of NADPH-diaphorase activity in the hypothalamo-hypophysial system of the frog, Rana esculenta.

Using nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase (ND) histochemistry, this study reports a wide distribution of ND activity in the hypothalamus, and for the first time in the median eminence (ME), the neural lobe (NL) and in the pars distalis (PD) of the frog, Rana esculenta. Perikarya are ND-active within the nucleus preopticus (NPO), the nucleus preopticus periventricularis (NPP), located around the preoptic recess (PR), the suprachiasmatic nucleus (SCN) and within five infundibular nuclei. Several ND-positive neurons of the nucleus infundibularis ventralis are cerebrospinal fluid-contacting in nature, while a few occupy a subependymal region. The infundibulum shows a thick sheet-like fiber plexus which receives fibers not only from its ND-active neurons, but also from the anterior and central thalamic nuclei. The ME, NL and most cells of the posterodorsal PD are ND-positive. The pituitary function may be mediated by nitric oxide through modulating the secretion of hormone-releasing factors of the hypothalamus. Possible functional significance of the ND-stained hypothalamic areas is discussed.

Descending projection neurons to the spinal cord of the goldfish, Carassius auratus.

The sources of descending spinal tracts in the goldfish, Carassius auratus, were visualized by retrograde transport of horseradish peroxidase (HRP) administered to the hemisected spinal cord. In the diencephalon, HRP-positive neurons were identified in the nucleus preopticus magnocellularis pars magnocellularis and ventromedial nucleus of the thalamus of the ipsilateral side. In the mesencephalic tegmentum, a few somata of the contralateral nucleus ruber and several ipsilateral neurons of the nucleus of the median longitudinal fasciculus were labeled. The reticular formation of the rhombencephalon was the major source of descending afferents to the spinal cord. A larger number of neurons were retrogradely labeled in the ipsilateral superior, middle, and inferior nuclei than in the contralateral nuclei. A few raphe neurons and the contralateral Mauthner neuron were also HRP-positive. The octaval area showed retrogradely labeled neurons in the anterior, magnocellular, descending, and posterior octaval nuclei of the ipsilateral side. A large number of neurons in the facial lobe and a few somata located adjacent to the descending trigeminal tract were labeled on the ipsilateral side. The pattern of descending spinal projections in goldfish is comparable to that of tetrapods and suggests that the spinal tracts have originated quite early in the course of vertebrate evolution.

Asymmetry of the olfactory system in the brain of the winter flounder, Pseudopleuronectes americanus.

Adult flatfishes exhibit grossly asymmetric external morphology. Even the olfactory apparatus is asymmetric, being larger on the upward-facing side. We undertook the present study on the winter flounder, Pseudopleuronectes americanus, to examine whether the asymmetry of the peripheral olfactory system is maintained in its central organization. In winter flounder, the right olfactory organ, nerve, and bulb are larger than the contralateral counterparts. In addition, the right telencephalon is about 8% larger than the left. Horseradish peroxidase (HRP) and degeneration techniques were used to trace the central connections of the olfactory bulbs. Neurons afferent to the olfactory bulb occur bilaterally in the telencephalon and mesencephalic tegmentum. Afferent neurons are also present at the junction between the posterodorsal bulb and telencephalon, in the basal preoptic region, nucleus of the posterior tuber, locus coeruleus, raphe nucleus, and the contralateral bulb. Each olfactory bulb projects bilaterally to several restricted areas of the telencephalon, the posterodorsal neurons of the nucleus preopticus and the tuberal region, with ipsilateral connections being heavier in all areas. Corresponding to the differences in the peripheral olfactory apparatus, the central olfactory projections were also asymmetric. The right olfactory bulb projects to 2.6% of the ipsilateral telencephalon and 1.99% of the contralateral telencephalon. The left bulb projects to 1.8% of the ipsilateral and 0.6% of the contralateral telencephalic hemisphere. Thus the left telencephalon receives roughly equal olfactory input from the two sides, while the right telencephalon receives vastly more input from the right olfactory system. The asymmetry in the projections of the right and left bulbs may be due to differential postmetamorphic growth of the olfactory system on the two sides.

The ipsilateral retinotectal projection in normal and albino channel catfish.

The retinal projection to the ipsilateral optic tectum was examined first in normal channel catfish. After unilateral optic nerve section and horseradish peroxidase (HRP) application, a sparse retinal projection was seen in the ipsilateral optic tectum. When HRP was applied to the ipsilateral rostral tectum, labeled ganglion cells were observed in the ventrotemporal quadrant of the ipsilateral eye. Electrophysiological mapping of the ipsilateral projection confirmed that cells in the temporal retina projected to the rostral tectum. When albino catfish were examined using these techniques, the ipsilateral retinotectal projection was found to be much sparser than the ipsilateral projection of normal catfish.

Retinofugal pathways in juvenile and adult channel catfish, Ictalurus (Ameiurus) punctatus: an HRP and autoradiographic study.

The retinal projections of the juvenile and adult channel catfish, Ictalurus (Ameiurus) punctatus, were studied by using horseradish peroxidase (HRP) and autoradiography. The contralateral optic tract sends fibers to the suprachiasmatic nucleus (SCN) and divides into lateral (LOT) and medial optic tracts (MOT). In the adult fish, the former is thicker than the latter, whereas in the juvenile form, the reverse is true. The MOT curves laterally and divides into eight to 15 medial fascicles of the optic tract (MFOT). The contralateral optic fibers project to the nucleus opticus dorsolateralis, nucleus of the posterior commissure, nucleus geniculatus lateralis, pretectal nuclear complex, nucleus corticalis, stratum fibrosum et griseum superficiale (SFGS), and a few optic fibers extend into the stratum griseum centrale. The tractus opticus accessorius arises from the posterodorsal margin of the LOT and extends ventromedially to project to the nucleus opticus accessorius. At the optic chiasm a few fibers do not decussate, and these fibers project to almost all ipsilateral sites similar to those of the contralateral side, including the optic tectum. The autoradiographic observations substantiated the analysis of optic fiber projections provided by the HRP technique.

Changes in formaldehyde-induced fluorescence of the hypothalamus and pars intermedia in the frog, Rana temporaria, following background adaptation.

Adaptation of the frog, Rana temporaria, to a white background for 12 hr has resulted in an intense formaldehyde-induced fluorescence (FIF) in the neurons of the preoptic recess organ (PRO), paraventricular organ (PVO), nucleus infundibularis dorsalis (NID) and their basal processes permitting visualization of the PRO- and PVO-hypophysial tracts that extend into the median eminence (ME) and pars intermedia (PI); the FIF is reduced in all the structures by 3 days. In frogs adapted to a black background, for 12 hr and 3 days, there was a general reduction in the FIF of the PRO neurons and PRO-hypophysial tract. By 12 hr black background adaptation, the PVO/NID neurons and only their adjacent basal processes show FIF which was sharply reduced by 3 days, making the PVO-hypophysial tract undetectable. In the PI fibers the fluorescence was more intense in black-adapted frogs than in white-adapted ones at both the intervals studied. The simultaneous changes in the FIF of the hypothalamic nuclei, tracts and PI suggest that the PRO and PVO/NID neurons participate in PI control through release of neurotransmitter(s) at the axonal ends.

Seasonal changes in the corpuscles of Stannius and the gonads of the catfish, Heteropneustes fossilis (Bloch).

The seasonal changes in the corpuscles of Stannius (CS) and the gonads of the catfish, Heteropneustes fossilis were studied. The annual sex cycle of the fish has been divided into 4 phases on the basis of the variations in the gonosomatic index and histocytological features displayed by the testes and ovaries. There is a rise in the percentage of aldehyde fuchsin (AF)-positive cells in the CS and an increase in the nuclear diameter, at the beginning of preparatory period (February). In the prespawning period (May--June) the AF-positive cells undergo degranulation. A slight regranulation and rise in the percentage of AF-positive cells occurs during early spawing period (July). During the postspawning phase (September--January) the corpuscles remain predominated by AF-negative cells and show histolytical changes; the nuclear indices are reduced. In view of the concomitant changes occurring in the CS and the gonads the possibility of some direct or indirect relationship between the two has been discussed, although it is difficult to ascertain whether the changes in the corpuscles are cause or consequence of the gonadal cycle.

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

The hypothalamic nuclei of the lizard, Calotes versicolor, can be broadly divided into "AF-positive" 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.