Expression of c-Fos protein in medial septum/diagonal band of Broca and CA3 region, associated with the temporary inactivation of the supramammillary area.

The supramammillary (SuM) area is part of the diencephalic nuclei comprising the mammillary bodies, and is a key structure in the memory and spatial learning processes. It is a critical region in the modulation/generation of hippocampal theta rhythm. In addition, many papers have recently shown a clear involvement of this structure in the processes of spatial learning and memory in animal models, although it is still not known how it modulates spatial navigation and response emotional. The aim of the present research was to study the effect of the temporary inactivation of the SuM area on synaptic plasticity of crucial structures in the formation of spatial memory and emotional response. Sprague-Dawley rats were asigned in three groups: a control group where the animals were not subjected to any treatment, and two groups where the rats received microinjections of tetrodotoxin (TTX) in the SuM area (5ng diluted in 0.5µl of saline) or saline (0.5µl). The microinjections were administered 90min before the perfusion. Later, cellular activity in medial septum/diagonal band of Broca (MS/DBB) and CA3 region of the dorsal hippocampus was assessed, by measuring the immediate early gene c-fos. The results show a clear hiperactivity cellular in medial septum/diagonal band of Broca and a clear hypoactivity cellular in the CA3 region of the hippocampus when there was a functional inactivation of the SuM area. It suggests that the SuM area seems to be part of the connection and information input pathways to CA3 region of the hippocampal formation, key for proper functioning in spatial memory and emotional response.

Autonomic and neuroendocrine actions of adrenomedullin in the brain: mechanisms for homeostasis.

In addition to its role as a potent vasodilator, adrenomedullin (ADM) affects an animal's physiological status through its effects in the brain. We have shown that circulating ADM activates neurons, including nitric oxide (NO)-producing neurons, in autonomic centers of the brain such as the hypothalamic paraventricular nucleus (PVN). Systemic ADM gains access to the brain through the area postrema (AP), a brainstem circumventricular organ, and the PVN is a major target of these ADM-sensitive AP neurons. Neurons expressing the preproADM (ppADM) gene are distributed throughout the brain, with high levels in autonomic centers. Lipopolysaccharide (LPS, immune stress), restraint (psychological stress), and 24 h dehydration all down-regulate ppADM gene expression in different subsets of autonomic centers. Receptor-activity-modifying protein (RAMP) 2 and RAMP3, ADM receptor subunits, are expressed in autonomic centers including the PVN and supraoptic nucleus. Intracerebroventricular injections of ADM increase arterial pressure, heart rate, tyrosine hydroxylase mRNA levels in the locus coeruleus, plasma levels of ACTH, and NO production in the hypothalamus. ADM excites putative GABAergic and cholinergic neurons in dissociated cells from a basal forebrain integrative center, the diagonal band of Broca. These results demonstrate that the signalling components necessary for ADM to influence physiological systems are present in the brain and that ADM is an important transmitter of brain autonomic pathways which are involved in regulating homeostatic balance.

Cholinergic neurons expressing neuromedin K receptor (NK3) in the basal forebrain of the rat: a double immunofluorescence study.

By using a double immunofluorescence method we have examined the distribution of cholinergic neurons expressing neuromedin K receptor (NK3) in the rat brain and spinal cord. The distribution of neuromedin K receptor-like immunoreactive neurons completely overlapped with that of choline acetyltransferase-positive neurons in certain regions of the basal forebrain, e.g. the medial septal nucleus, nucleus of the diagonal band of Broca, magnocellular preoptic nucleus and substantia innominata. Partially overlapping distributions of neuromedin K receptor-like immunoreactive and choline acetyltransferase-positive neurons were found in the basal nucleus of Meynert, globus pallidus, ventral pallidum of the forebrain, tegmental nuclei of the pons and dorsal motor nucleus of the vagus. Neurons showing both neuromedin K receptor-like and choline acetyltransferase immunoreactivities, however, were found predominantly in the medial septal nucleus, nucleus of the diagonal band of Broca and magnocellular preoptic nucleus of the basal forebrain: 66-80% of these choline acetyltransferase-positive neurons displayed neuromedin K receptor-like immunoreactivity. Neurons showing both neuromedin K receptor-like and choline acetyltransferase immunoreactivities were hardly detected in other aforementioned regions of the forebrain, brainstem and spinal cord. The present study has provided morphological evidence for direct physiological modulation or regulation of cholinergic neurons by tachykinins through the neuromedin K receptor in the basal forebrain of rats.

Thalamic distribution of zinc-rich terminal fields and neurons of origin in the rat.

Several cortico-cortical and limbic-related circuits are enriched in zinc, which is considered as an important modulator of glutamatergic transmission. While heavy metals have been detected in the thalamus, the specific presence of zinc has not been examined in this region. We have used two highly sensitive variations of the Timm method to study the zinc-rich innervation in the rat thalamus, which was compared to the distribution of acetylcholinesterase activity. The origin of some of these zinc-rich projections was also investigated by means of retrograde transport after intracerebral infusions of sodium selenium (Na2SeO3). The overall zinc staining in the thalamus was much lower than in the neocortex, striatum or basal forebrain; however, densely stained terminal fields were observed in the dorsal tip of the reticular thalamic nucleus, the anterodorsal and lateral dorsal thalamic nuclei and the zona incerta. In addition, moderately stained zinc-rich terminal fields were found in the rostral intralaminar nuclei, nucleus reuniens and lateral habenula. Intracerebral infusions of Na2SeO3 in the lateral dorsal nucleus resulted in retrogradely labeled neurons that were located in the postsubiculum, and also in the pre- and parasubiculum. These results are the first to establish the existence of a zinc-rich subicular-thalamic projection. Similar infusions in either the intralaminar nuclei or the zona incerta resulted in labeling of neurons in several brainstem structures related to the reticular formation. Our results provide morphological evidence for zinc modulation of glutamatergic inputs to highly selective thalamic nuclei, arising differentially from either cortical limbic areas or from brainstem ascending activation systems.

The gonadotropin-releasing hormone neurosecretory system of the jerboa (Jaculus orientalis) and its seasonal variations.

The distribution of cells expressing gonadotropin-releasing hormone (GnRH) immunoreactivity was examined in the brain of adult jerboa during two distinct periods of the reproductive cycle. During spring-summer, when the jerboa is sexually active, a high density of cell bodies and fibres immunoreactive (IR) for GnRH was observed at the level of separation of the frontal lobes, in the medial septal nucleus (MS) and in the diagonal band of Broca (DBB), in the preoptic area (POA), in the organum vasculosum laminae terminalis (OVLT), in the retrochiasmatic area and hypothalamus. In autumn, when the jerboa is sexually inactive, GnRH-immunoreactivity was less intense than during spring-summer. In the POA, we noted a 55% decrease in the number of GnRH containing cells with no change in cell numbers in the MS-DBB. Furthermore, a lower density of GnRH immunopositive axon fibres is observed in all the previously mentioned structures and the immunoreaction intensity was very weak particularly within the median eminence and OVLT. Independently of the season, the GnRH immunoreactivity within neurones and fibres was similar in jerboas living in captivity and in jerboas living in their natural biotope. The effects of photoperiod on the density of POA-GnRH and arcuate nucleus beta-endorphin-containing cells were studied in jerboas maintained in long day [(LD) 16-h light, 8-h dark] and short day [(SD) 8-h light, 16-h dark] for 8 weeks. In the POA, the GnRH-IR cell number was not significantly altered by the photoperiod. Similarly, in the mediobasal hypothalamus, the number of beta-endorphin-IR neurones was not affected by such a parameter. Consequently, the GnRH seasonal variations cannot be correlated to changes in the photoperiod alone.

Comparative analysis of FMRFamide-like immunoreactivity in caiman (Caiman crocodilus) and turtle (Trachemys scripta elegans) brains.

The distribution of FMRFamide (FMRFa)-like peptides in caiman (Caiman crocodilus) and turtle (Trachemys scripta elegans) brains was studied by immunohistochemistry. In both species, distinct groups of FMRFa-like immunoreactive (ir) perikarya were present in the medial septal nucleus, accumbens nucleus, nucleus of the diagonal band of Broca, suprachiasmatic area, lateral hypothalamic area, and periventricular hypothalamic nucleus. A few FMRFa-ir neurons in the hypothalamic area were located in the neuroepithelial cell lining of the third ventricle. FMRFa-ir fibers were scattered in all major areas of the brain, from the olfactory bulbs to the rhombencephalon. They formed dense aggregates in the medial septal area, basal telencephalon, median eminence, and infundibulum, and adjacent to the fourth ventricle. The most obvious difference between the FMRFa-ir systems in caimans and turtles concerned the number of nuclei that contained neurons with this immunoreactivity. Eight such clusters were present in the caiman brain, whereas thirteen clusters were found in the turtle brain. The turtle also displayed scattered FMRFa-ir somata in the anterior olfactory nucleus, striatum, lateral septal nucleus, medial and lateral cortex, medial forebrain bundle, lateral preoptic area, and lateral geniculate nucleus. In the caiman brain, a few FMRFa-ir neurons were noted in the ventrolateral area of the pallial commissure and an even smaller number of ir neurons was found dispersed in the optic tracts. Neither formed nuclear aggregates. The results are compared with those described for other vertebrates.

Relationship between neuropeptide Y and luteinizing-hormone-releasing hormone immunoreactivities in the hypothalamus and preoptic region.

The purpose of this study was to examine the anatomical relationships of perikarya and fibers containing neuropeptide Y (NPY) and luteinizing-hormone-releasing hormone (LHRH) in the hypothalamus and preoptic region of female rats. In view of our previous report of stimulatory effects of estrogen on LHRH and NPY levels in the median eminence, animals were bilaterally ovariectomized and subsequently implanted subcutaneously with capsules containing estradiol benzoate in oil or vehicle. Following intracerebroventricular injection of colchicine, rats were perfused with fixative and their brains sectioned and processed for immunohistochemical visualization of NPY and LHRH in the same section and in consecutive sections. Estrogen treatment had no discernible effect on the distribution or relationship of these peptides. NPY-immunoreactive fibers were intimately associated with LHRH-labeled primary dendrites and perikarya in the medial preoptic region and horizontal limb of the diagonal band of Broca. Fibers containing NPY or LHRH overlapped extensively in the lateral palisade region of the median eminence and also in the subependymal and internal zones. The external zone of the median eminence displayed relatively less overlap of these peptide systems. LHRH-immunoreactive axons coursed among NPY-labeled perikarya in the arcuate nucleus and appeared to contact these cells. These results suggest that NPY-containing axons may influence LHRH-positive neurons at the cell body and also at the site of axon termination in the median eminence. LHRH-containing axons appear to contact NPY-immunoreactive perikarya in the arcuate nucleus and may interact with terminals in the median eminence. This arrangement may provide a mechanism for communication between NPY and LHRH neurons and for the neuroendocrine coordination of hypothalamic NPY and LHRH secretion before ovulation.