Margaret M. Moga

Organization of neural inputs to the suprachiasmatic nucleus in the rat

The circadian timing of the suprachiasmatic nucleus (SCN) is modulated by its neural inputs. In the present study, we examine the organization of the neural inputs to the rat SCN using both retrograde and anterograde tracing methods. After Fluoro‐Gold injections into the SCN, retrogradely labeled neurons are present in a number of brain areas, including the infralimbic cortex, the lateral septum, the medial preoptic area, the subfornical organ, the paraventricular thalamus, the subparaventricular zone, the ventromedial hypothalamic nucleus, the posterior hypothalamic area, the intergeniculate leaflet, the olivary pretectal nucleus, the ventral subiculum, and the median raphe nuclei. In the anterograde tracing experiments, we observe three patterns of afferent termination within the SCN that correspond to the photic/raphe, limbic/hypothalamic, and thalamic inputs. The median raphe projection to the SCN terminates densely within the ventral subdivision and sparsely within the dorsal subdivision. Similarly, areas that receive photic input, such as the retina, the intergeniculate leaflet, and the pretectal area, densely innervate the ventral SCN but provide only minor innervation of the dorsal SCN. A complementary pattern of axonal labeling, with labeled fibers concentrated in the dorsal SCN, is observed after anterograde tracer injections into the hypothalamus and into limbic areas, such as the ventral subiculum and infralimbic cortex. A third, less common pattern of labeling, exemplified by the paraventricular thalamic afferents, consists of diffuse axonal labeling throughout the SCN. Our results show that the SCN afferent connections are topographically organized. These hodological differences may reflect a functional heterogeneity within the SCN. J. Comp. Neurol. 389:508–534, 1997.

Brain natriuretic peptides: differential localization of a new family of neuropeptides.

Brain natriuretic peptide (BNP) is a recently discovered neuropeptide, isolated from the porcine brain, that is highly homologous to atriopeptin (AP), the atrial natriuretic peptide. We used a set of highly selective antisera against the two peptides to map their differential distribution immunohistochemically in the rat central nervous system. BNP immunoreactivity has a distinct distribution, involving many central autonomic and endocrine control structures that contain little if any AP immunoreactivity. AP and BNP belong to a family of neuropeptides that may be important in central cardiovascular control.

Efferent projections of the intergeniculate leaflet and the ventral lateral geniculate nucleus in the rat.

The intergeniculate leaflet (IGL) and the ventral lateral geniculate nucleus (VLG) are ventral thalamic derivatives within the lateral geniculate complex. In this study, IGL and VLG efferent projections were compared by using anterograde transport of Phaseolus vulgaris‐leucoagglutinin and retrograde transport of FluoroGold. Projections from the IGL and VLG leave the geniculate in four pathways. A dorsal pathway innervates the thalamic lateral dorsal nucleus (VLG), the reuniens and rhomboid nuclei (VLG and IGL), and the paraventricular nucleus (IGL). A ventral pathway runs through the geniculohypothalamic tract to the suprachiasmatic nucleus and the anterior hypothalamus (IGL). A medial pathway innervates the zona incerta and dorsal hypothalamus (VLG and IGL); the lateral hypothalamus and perifornical area (VLG); and the retrochiasmatic area (RCA), dorsomedial hypothalamic nucleus, and subparaventricular zone (IGL). A caudal pathway projects medially to the posterior hypothalamic area and periaqueductal gray and caudally along the brachium of the superior colliculus to the medial pretectal area and the nucleus of the optic tract (IGL and VLG). Caudal IGL axons also terminate in the olivary pretectal nucleus, the superficial gray of the superior colliculus, and the lateral and dorsal terminal nuclei of the accessory optic system. Caudal VLG projections innervate the lateral posterior nucleus, the anterior pretectal nucleus, the intermediate and deep gray of the superior colliculus, the dorsal terminal nucleus, the midbrain lateral tegmental field, the interpeduncular nucleus, the ventral pontine reticular formation, the medial and lateral pontine gray, the parabrachial region, and the accessory inferior olive. This pattern of IGL and VLG projections is consistent with our understanding of the distinct functions of each of these ventral thalamic derivatives. J. Comp. Neurol. 420:398–418, 2000.

Androgen receptor-immunoreactivity in the forebrain of the Eastern Fence lizard (Sceloporus undulatus)

Androgen receptor (AR) distribution in the lizard forebrain and optic tectum was examined using PG21 immunohistochemistry. In the male Eastern Fence lizard, AR-immunoreactive (-ir) nuclei were observed in the medial preoptic area, ventromedial and arcuate hypothalamic nuclei, periventricular hypothalamus, premammillary nucleus, bed nucleus of the stria terminalis, and ventral posterior amygdala. Punctate immunostaining of neuronal processes (axons and/or dendrites) was concentrated in the cortex, hypothalamus, and optic tectum. AR-ir nuclei in the female brain were confined to the ventral posterior amygdala and ventromedial hypothalamic nucleus. The AR distribution in the lizard brain is similar to that reported for other vertebrate classes. Sex differences in AR-immunoreactivity may contribute to sex-specific behaviors in the Eastern Fence lizard.

Putative excitatory amino acid projections to the suprachiasmatic nucleus in the rat

Retrograde axonal transport of the select neuronal tracer [3H]D-aspartate was used to demonstrate possible sources of excitatory input to the suprachiasmatic nucleus (SCN) in the albino rat. Following injection of [3H]D-aspartate into the SCN, neurons were retrogradely labeled in the infralimbic cortex, the lateral septal nucleus, the paraventricular thalamic nucleus, the medial preoptic area, the ventromedial, dorsomedial and posterior hypothalamic nuclei, the zona incerta, the intergeniculate leaflet and the ventral subiculum. Retinal ganglion cells, which project to the SCN and use glutamate as a neurotransmitter, were not labeled in our [3H]D-aspartate experiments, demonstrating a limitation of this method (i.e., false negatives). Our results show that the [3H]D-aspartate neuronal tracer labels a subset of areas known to project to the SCN, indicating these areas as likely sources of excitatory input to the SCN.

p75 Neurotrophin receptor immunoreactivity in the aged human hypothalamus

Low-affinity p75 neurotrophin receptor (p75NTR) immunoreactivity in the aged human hypothalamus was examined in autopsied material. Numerous p75NTR-immunoreactive cells were found in the paraventricular and supraoptic hypothalamic nuclei. The suprachiasmatic nucleus was devoid of p75NTR-immunostaining. Many p75NTR-immunoreactive fibers extended laterally and ventrally from the paraventricular and supraoptic nuclei into the pituitary stalk and median eminence. Our results suggest that neurotrophins may be present within the human hypothalamo-hypophyseal system.

MAGNETOHYDRODYNAMIC WAVE RESONANCE AND THE EVOCATION OF EPILEPTIFORM ACTIVITY BY MILLITESLA DC MAGNETIC FIELDS

DC magnetic fields of low- to medium-flux density (nTesla to mTesla) affect a variety of brain activities. The cellular mechanism underlying these effects is unknown. A model involving magnetohydrodynamic waves and corresponding resonance phenomena is offered here as a solution. The model is discussed in relation to the evocation of epileptiform activity due to external DC magnetic fields in the mTesla range. The assumed existence of a resonance wave makes it possible to calculate the size of the involved area.

Delayed loss of p75 neurotrophin receptor-immunoreactivity in the rat suprachiasmatic nucleus and intergeniculate leaflet after binocular enucleation

The rat suprachiasmatic nucleus (SCN) contains a dense plexus of low-affinity p75 neurotrophin receptor (p75NTR)-immunoreactivity. Scattered patches of p75NTR immunoreactivity are present in the intergeniculate leaflet (IGL). Both SCN and IGL receive a direct retinal input. After binocular enucleation, there is a delayed loss of p75NTR-immunoreactivity in the SCN and IGL beginning at, respectively, 4 and 8 weeks post-enucleation, with complete loss occurring in both nuclei by week 12. This delayed loss may be due to an up-regulation of growth factor secretion by local cells in response to retinal axon degeneration.