No abstract

The distribution of angiotensin II (AII)-immunoreactive cells and fibers was examined in adult male Sprague-Dawley rats with and without colchicine pretreatment. As seems to be the case for a number of other neuropeptides, AII is preferentially found in brain stem, hypothalamic, and limbic structures involved in the control of homeostatic functions. AII-stained cell bodies were most prominent in magnocellular parts of the paraventricular and supraoptic nuclei, and cells were also found in parvocellular parts of the former. Other hypothalamic nuclei containing cell bodies include the suprachiasmatic nucleus, the medial preoptic area, and perifornical parts of the lateral hypothalamic area. Of considerable interest was robust staining in several of the circumventricular organs, in particular the subfornical organ, where both cells and fibers were found. The results of water deprivation and nephrectomy suggest that this staining does not represent uptake of circulating peptide, but instead, represents AII-containing neural connections. In the thalamus, AII-stained cells were found in the paraventricular nucleus, the central medial nucleus, the nucleus reuniens, and rostral parts of the zona incerta. Two cell groups in the basal telencephalon, in the dorsal part of the bed nucleus of the stria teminalis and in the medial nucleus of the amygdala, lay at either end of an AII-stained pathway coursing through the stria terminalis. In the midbrain, immunoreactive cells were found in the interpeduncular and peripeduncular nuclei, and one pontine cell group was detected in the most lateral part of the lateral parabrachial nucleus. The only AII-stained cells in the medulla were in the nucleus of the solitary tract, near the margin of the area postrema. Fibers were found at all levels of the central nervous system, from the olfactory bulbs to the spinal cord, where terminal fields were observed in the substantia gelatinosa and in the intermediolateral cell column. Longitudinally oriented fibers were present throughout the periventricular fiber system and in the medial forebrain bundle, including its caudal extension in ventrolateral parts of the brain stem. It is suggested that, at many different levels, AIIserves as both a hormone and neurotransmitter for fluid balance.

The normal morphology of the rat preoptic region has been briefly described on the basis of Nissl- and silver-stained preparations and its efferent connections have been studied autoradiographically in over 50 rat brains with single small injections of 3H-proline, or various mixtures of 3H-proline, 3H-leucine, and 3H-lysine. Injections in the anteroventral part of the lateral preoptic area labeled fibers projecting through, and perhaps to, the anterior and lateral hypothalamic areas and ending in the supramammillary region, and ventral fiber lamina of the mammillary complex; other labeled fibers ended in the periventricular hypothalamic gray and the internal lamina of the median eminence. The posteromedial lateral preoptic area projects to the same regions, as well as to the medial septal-diagonal band complex, and to the lateral habenula through the stria medullaris. Injections of the posterolateral lateral preoptic area labeled each of the above fiber systems as well as fibers to the main olfactory bulb, anterior olfactory nucleus and taenia tecta. Other fibers coursed over the genu of the corpus callosum, through the stria terminalis and ansa peduncularis to the medial, cortical and basal amygdaloid nuclei and the anterior amygdaloid area, and through the medial forebrain bundle to the substantia nigra. The transition region between the lateral preoptic and lateral hypothalamic areas at the level of the supraoptic nucleus has widespread connections as a whole (a) with the medial septal-diagonal band complex, lateral septum and bed nucleus of the stria terminalis, (b) through or to most of the hypothalamus, the substantia nigra, central tegmental field, central gray, superior central nucleus, and the locus coeruleus, (c) through the stria medullaris to the lateral habenula (bilaterally), parataenial, paraventricular, and mediodorsal nuclei of the thalamus, (d) through the stria terminalis and ansa peduncularis to the central, medial and cortical nuclei of the amygdala, and (e) to the main olfactory bulb, anterior olfactory nucleus, cingulate bundle, olfactory tubercle, medial septal-diagonal band complex and the lateral septum.

The anterior pituitary gland provides a model for investigating the molecular basis for the appearance of phenotypically distinct cell types, within an organ, a central question in development. The rat prolactin and growth hormone genes are selectively expressed in distinct cell types (lactotrophs and somatotrophs) of the anterior pituitary gland, which reflect differential mechanisms of gene activation or restriction because of interactions of multiple factors binding to these genes. We find that the pituitary-specific 33,000 dalton transcription factor, Pit-1, normally expressed in somatotrophs, lactotrophs, and thyrotrophs, can bind to and activate both growth hormone and prolactin promoters in vitro at levels even tenfold lower than those normally present in pituitary cells. In the case of the prolactin gene, high levels of expression in transgenic animals required two cis-active regions; a distal enhancer (-1.8 to -1.5 kb) and a proximal region (-422 to +33 bp). Each of these regions alone can direct low levels of fusion gene expression to prolactin-producing cell types in transgenic mice, but a synergistic interaction between these regions is necessary for high levels of expression. The initial appearance of the prolactin transgene expression closely follows the appearance of high levels of Pit-1, but later increases in expression coincident with appearance of mature lactotrophs suggest the operation of additional, critical positive factor(s). Unexpectedly, transgenes containing the distal enhancer removed from its normal context are expressed in both the prolactin-producing lactotrophs and the TSH-producing thyrotrophs, thereby suggesting that sequences flanking this enhancer are necessary to restrict expression to the correct cell type within the pituitary. These data indicate that distinct processes of gene activation and restriction are necessary for the fidelity of cell-type specific expression within an organ. Consistent with this model, we find that lactotroph cell lines that cannot express the growth hormone gene contain high levels of functional Pit-1. We suggest a large, highly related POU-domain gene family, potentially exceeding 100 members, has been conserved and expanded in evolution to meet the increasing requirements for more intricate patterns of cell phenotypes. The POU-domain subgroup of the homeodomain gene family, in concert with other homeodomain proteins and with other classes of transcription factors, is likely to contribute to the establishment of the mammalian neuroendocrine system.

Preproenkephalin mRNA production by efferent neurons projecting to the gerbil inner ear was assessed using combined in situ hybridization and retrograde labeling with fluorescent tracers. Virtually all vestibular efferent neurons were positive for preproenkephalin mRNA. Of the cochlear efferents, one-half of the medial olivocochlear neurons were positive for enkephalin. All lateral olivocochlear neurons were negative for enkephalin. The results suggest that there are two, biochemically distinct subpopulations of medial olivocochlear efferents in the gerbil.