The neuroanatomical basis of comparative neuroendocrinology

The distribution of vasotocin and mesotocin immunoreactivity in the brain of the snake, Bothrops jararaca

Polyclonal antibodies against vasotocin (AVT) and mesotocin (MST) were used to explore the distribution of these peptides in the brain of the snake Bothrops jararaca. Magnocellular AVT- and MST-immunoreactive (ir) perikarya were observed in the supraoptic nucleus (SON), being AVT-ir neurons more numerous. A portion of the SON, in the lateroventral margin of the diencephalon ventrally to optic tract, showed only AVT-ir perikarya and fibers. However, the caudal most portion displayed only mesotocinergic perikarya. Parvocellular and magnocellular AVT- and MST-ir perikarya were present in the paraventricular nucleus (PVN) being AVT-ir fibers more abundant than MST-ir. Vasotocinergic perikarya were also found in a dorsolateral aggregation (DLA) far from the PVN. Mesotocinergic perikarya were also present in the recessus infundibular nucleus and ependyma near to paraventricular organ. Nerve fibers emerging from supraoptic and paraventricular nuclei run along the diencephalic floor, internal zone of the median eminence (ME) to end in the neural lobe. Also a dense network of AVT- and MST-ir fibers was present in the external zone of the ME, close to the vessels of the hypophysial portal system. As a rule, all regions having vasotocinergic and mesotocinergic perikarya also showed immunoreactive fibers. Vasotocinergic and mesotocinergic fibers but not perikarya were found in the lamina terminalis (LT). Moreover AVT-ir fibers were present in the nucleus accumbens and MST-ir fibers in the septum. In mesencephalon and rhombencephalon MST-ir fibers were more numerous than AVT-ir fibers. Vasotocinergic and mesotocinergic fibers in extrahypothalamic areas suggest that these peptides could function as neurotransmitters and/or neuromodulators in the snake B. jararaca.

Ultrastructural characterization of the sexually dimorphic medial preoptic nucleus of male Japanese quail

The medial preoptic nucleus is a sexually dimorphic structure whose cytoarchitecture, afferent and efferent connections, and functions have been previously described. No detailed ultrastructural study has, however, been performed to date. Here we describe the ultrastructural organization of this important preoptic structure of the male quail. Neuronal cell bodies of the medial preoptic nucleus generally show extensive development of protein-synthesis-related organelles (rough endoplasmic reticulum, polysomes), and of secretory structures (Golgi complexes, secretory vesicles, dense bodies). Previous morphometrical studies at the light-microscopical level have demonstrated the presence of a medial and a lateral neuronal population distinguished by the size of their cell bodies (the medial neurons are smaller than the lateral neurons). The present ultrastructural investigation confirms the difference in size, but no difference has been observed in the ultrastructural organization of the neurons. In both the medial and the lateral part, the nucleus is characterized by a large variety of cell bodies, including some that, on the basis of their ultrastructure, can be considered as putative peptidergic neurons. Close contacts are frequently observed between adjacent cell bodies that are normally arranged in clusters. Various types of synaptic endings are also present, suggesting a rich supply of nerve fibers. A few glial cells are scattered within the nucleus. In view of the crucial role of this region in regulating quail sexual behavior, the large heterogeneity of neurons and of afferent nervous fibers suggest that this region might have an important role in the integration of information arriving from different brain regions.

Vasoactive intestinal peptide-immunoreactive cerebrospinal fluid-contacting neurons in the reptilian lateral septum/nucleus accumbens

By means of immunocytochemical demonstration of vasoactive intestinal peptide (VIP) an accumulation of cerebrospinal fluid (CSF)-contacting neurons was found in a circumscribed region of the nucleus accumbens/lateral septum of eleven reptilian (chelonian, lacertilian, ophidian, crocodilian) species. Basal processes of these cells contribute to a subependymal plexus whose density displays considerable interspecific variation. VIP-immunoreactive nerve fibers occur also in the lateral septum and the nucleus accumbens where they encompass immunonegative cells in a basket-like pattern. The CSF-contacting neurons are surrounded by columnar ependymocytes frequently arranged in a pseudostratified manner. These specialized arrays of ependymal cells, however, occupy a more extended area than the VIP-immunoreactive CSF-contacting neurons and can be traced from the rostro-ventral pole of the lateral ventricle to the interventricular foramen. These observations suggest the existence of a telencephalic site of CSF-contacting neurons which may be more widespread than hitherto thought and which may participate in a circumventricular system of the lateral ventricle. Previous studies mainly performed with birds indicate that the VIP-immunoreactive CSF-contacting neurons of the nucleus accumbens might form a part of the "encephalic" (extraretinal and extrapineal) photoreceptor. However, further experiments are required to test this supposition since the VIP-immunoreactive neurons of the nucleus accumbens remained unlabeled by antibodies against bovine rodopsin and chicken cone-opsin in all eleven species analysed in this investigation.

Efferent projections from the lateral septal nucleus to the anterior hypothalamus in the rat: a study combining Phaseolus vulgaris-leucoagglutinin tracing with vasopressin immunocytochemistry

The tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected into the lateral septum of the rat at different rostrocaudal locations to study the efferent septal projections to the anterior hypothalamus. For spatial correlation of these septofugal elements with the vasopressinergic system a dual immunocytochemical technique was used (i) to demonstrate nerve fibers and their corresponding bouton-like structures labeled with the tracer, and (ii) to identify vasopressin in the same section. The hypothalamic paraventricular and supraoptic nuclei, the accessory hypothalamic magnocellular system, and the suprachiasmatic nucleus are recipients of PHA-L-labeled fibers from all parts of the lateral septum. Close appositions between (i) these axons and their varicosities, and (ii) vasopressin-immunoreactive perikarya and their processes, putatively indicating functional interrelationships, were observed in all these nuclear areas, especially in their neuropil formations.

Preliminary evidence for pineal-mediated extraretinal photoreception in relation to tail regeneration in the Gekkonid lizard, Hemidactylus flaviviridis

The tail of the Gekkonid lizard Hemidactylus flaviviridis was autotomized and the animals were subjected to eight different photoperiodic schedules during the process of tail regeneration. Our previous observation had shown that long-day photoperiods stimulate the regeneration process, whereas short-day photoperiods depress it. Furthermore, it has also been demonstrated that the lateral eyes, or retinae, do not participate in photoperiodically significant photoreception in H. flaviviridis, as blinded Hemidactylus regenerated their autotomized tails like their sighted counterparts exposed to similar experimental photoregimes. In a further attempt to localize the site(s) of photoreception in these animals, one group of lizards had their heads painted with a mixture of Indian ink and Nile blue sulphate (II-NBS) [NL (HP)] in order to prevent light from penetrating to the pineal gland, and another group had their pineal glands surgically removed (pinealectomy, Px); the regenerative potentials were compared with their normal (NL) counterparts. Our results showed that the initiation and onset of regeneration, the daily growth rate, the total new growth (regenerate) produced at the end of regeneration and the total percentage replacement of the lost (autotomized) tails were significantly retarded in Px and NL (HP) animals, compared with the NL (unoperated and nonpainted) ones. Since pinealectomy as well as light deprivation to the pineal abolished the stimulatory influence of long-length photoperiods, the pineal gland is discussed here as a major transmitter of photic stimulus in lacertilian tail regeneration. It is presumed that in the lizard, as in mammals and some birds, the pineal gland acts by way of the neuroendocrine complex and/or the hypothalamohypophyseal axis.

Immunocytochemical study of the hypothalamic magnocellular neurosecretory nuclei of the snake Natrix maura and the turtle Mauremys caspica

An immunocytochemical study of the magnocellular neurosecretory nuclei was performed in the snake Natrix maura and the turtle Mauremys caspica by use of antisera against: (1) a mixture of both bovine neurophysins, (2) bovine oxytocin-neurophysin, (3) arginine vasotocin, and (4) mesotocin. Arginine vasotocin- and mesotocin-immunoreactivities were localized in individual neurons of the supraoptic and paraventricular nuclei, with a distinct pattern of distribution in both species. The same cells appeared to be stained by the anti-oxytocin-neurophysin and antimesotocin sera. The supraoptic nucleus can be subdivided into rostral medial and caudal portions. In N. maura, but not in M. caspica, neurophysin-immunoreactive neurons were found in the retrochiasmatic nucleus. No immunoreactive elements were seen in the suprachiasmatic nucleus of both species after the use of any of the antisera. A dorsolateral aggregation of neurophysin-containing cells, localized over the lateral forebrain bundle, was present in both species. Magnocellular and parvocellular neurophysin-immunoreactive neurons were present in the paraventricular nucleus of both species. In the turtle, the paraventricular neurons were arranged into four distinct layers parallel to the ependyma; these neurons were bipolar with the major axis perpendicular to the ventricle, and many of them projected processes toward the cerebrospinal-fluid compartment. In N. maura a group of large neurons of the paraventricular nucleus was found in a very lateral position. The posterior lobe of the hypophysis and the external zone of the median eminence contained arginine vasotocin- and mesotocin-immunoreactive nerve fibers. The lamina termialis of both species was supplied with a dense bundle of fibers containing immunoreactive neurophysin. Neurophysin-immunoreactive fibers were also present in the septum, some telencephalic regions, including the cortex and the olfactory tubercule, in the paraventricular organ, and the periventricular and periaqueductal gray of the brainstem.

Neuronal organization of the avian paraventricular nucleus: intrinsic, afferent, and efferent connections

The heterogeneous paraventricular nucleus (PVN) of birds offers favorable conditions for the analysis of intrinsic, afferent, and efferent connections of neuroendocrine systems. Paraventricular neurons are successfully impregnated with the Golgi-technique. The findings indicate a direct influence of the cerebrospinal fluid (CSF) on the magnocellular neurons that, via their axon terminals in the neural lobe of the pituitary, are also exposed to the hemal milieu. The magnocellular neurons are intermingled with parvocellular elements which may represent local interneurons. A group of parvocellular nerve cells is identified as CSF-contacting neurons. This type of cell forms a basic morphologic component of the avian neuroendocrine apparatus. Immunocytochemical and ultrastructural studies further support the concept of neuronal interactions between parvocellular and magnocellular elements. Moreover, these findings speak in favor of the existence of recurrent collaterals of the magnocellular neurons. Nerve cells giving rise to afferent connections to the PVN are located in the limbic system and autonomic areas of the upper and lower brainstem. Further afferents may originate from the subfornical organ, the organon vasculosum laminae terminalis, the ventral tegmentum, and the area postrema. Via efferent projections, the PVN is connected to the nucleus accumbens, lateral septum, several hypothalamic nuclei, the neural lobe of the pituitary, the organon vasculosum laminae terminalis, the subfornical organ, the pineal organ, the area postrema, the lateral habenular complex, and various autonomic areas of the reticular formation in the upper and lower brainstem and the spinal cord. In conclusion, the PVN may be regarded as an integral component of the neuroendocrine apparatus reciprocally coupled to the limbic system, several circumventricular organs, and various autonomic centers of the brain.

Immunocytochemical identification of the mesotocin- and vasotocin-producing systems in the brain of temperate and desert lizard species and their modifications by cold exposure

Using immunofluorescent techniques, mesotocin (MT) and vasotocin (VT) neurosecretory systems were identified in the brain of different lizards: one temperate species living in southern France and three desert species coming from southern Algeria. In the four species, MT and VT were shown to be synthesized in specific neurons located in the anterior preoptic area (POA), the supraoptic (SON), paraventricular (PVN), and ventromedial (VMN) nuclei. The neurosecretory axons of the POA neurons terminated in the vicinity of the lamina terminalis; in the three desert species, several additional VT fibers extended more rostrally, going into the olfactory bulb. The axons originating in SON, PVN, and VMN ended either in the external zone of the rostral median eminence (ME) near the adenohypophyseal portal vessels, or in the neural lobe of the hypophysis. A short exposure to cold (4 degrees) in some specimens of Lacerta muralis induced a differential response in the dorsal and ventral parts of the PVN. Whereas the dorsal part remained unchanged, the ventral part instead appeared to be essentially composed of small neurons void of secretory granules. Cold exposure also led to a marked accumulation of both MT and VT in the internal zone of the ME, but of only VT in the external ME zone. On the other hand, a conspicuous amount of MT appeared in adenohypophyseal cells.

Intrinsic neurons and neural connections of the pineal organ of the house sparrow, Passer domesticus, as revealed by anterograde and retrograde transport of horseradish peroxidase

In Passer domesticus, intrapineal nerve cells were labeled by uptake of microiontophoretically administered horseradish peroxidase (HRP). Unipolar nerve cells with a dichotomously branching stem process are the main source of the dominant pinelaofugal component of the pineal tract, whereas multipolar and bipolar neurons appear to represent interneurons. HRP-Labeled nerve fibers are observed in the distal division (end-piece) of the pineal organ; they can be regarded either as processes of intrapineal neurons or projections of pinealopetal axons originating from central neurons. Furthermore, scattered labeled nerve fibers occur in different portions of the pineal stalk. Nerve fibers containing HRP were also demonstrated in the medial and lateral divisions of the habenular complex and in the periventricular layer of the hypothalamus; these axons apparently represent anterogradely labeled pinealofugal elements. On the other hand, retrogradely labeled neurons were found in the medial habenular complex and in the periventricular hypothalamic gray near the paraventricular nucleus, indicating that the pineal organ receives a pinealopetal innervation arising from the central nervous system. Ultrastructurally, the neuropil of the pineal organ of P. domesticus displays single basal processes of pinealocytes containing synaptic ribbons in association with clear synaptic vesicles. Occasionally, conventional synapses were observed the presynaptic terminals of which exhibit granular inclusions. The pineal tract consisting of four to six spatially separated fiber bundles comprises mainly unmyelinated elements accompanied by only few myelinated axons. The functional role of the neural apparatus revealed in the present study is discussed in context with the humoral (hormonal) control of circadian functions; the latter type of activity has been shown to exist in the pineal organ of P. domesticus (Zimmerman 1976).

On hypothalamic control of ovulation in the turkey

Small bilateral lesions of the ventromedial preoptic hypothalamus consistently blocked ovulation. Lesions that completely cut the supraoptico-hypophyseal tract or that were placed throughout the tuberal hypothalamus and median eminence had no effect on ovulation. Lesions placed in the posterodorsal, medial, and ventral parts of the infundibular nuclear complex and in the medial and posteria divisions of the median eminence resulted in slight to moderate atresia of rapidly growing follicles within 38 to 40 hr after surgery.

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.