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Messenger RNAs occur within the axons of magnocellular hypothalamic neurons known to secrete oxytocin and vasopressin. In Brattleboro rats, which have a genetic mutation that renders them incapable of vasopressin expression and secretion and thus causes diabetes insipidus, injection into the hypothalamus of purified mRNAs from normal rat hypothalami or of synthetic copies of the vasopressin mRNA leads to selective uptake, retrograde transport, and expression of vasopressin exclusively in the magnocellular neurons. Temporary reversal of their diabetes insipidus (for up to 5 days) can be observed within hours of the injection. Intra-axonal mRNAs may represent an additional category of chemical signals for neurons.

Neuronal mRNA is thought to be restricted to perikaryal and dendritic compartments containing rough endoplasmic reticulum. We have used both in situ hybridization and DNA polymerase chain reaction methods to determine the precise intracellular distribution of oxytocin mRNA. Using light-and electron-microscopic detection of in situ hybridization with 5'-bromo-2'-deoxyuridine-labeled oligonucleotide probes, we found oxytocin mRNA in axons and Herring bodies in the lateral and ventral hypothalamus, the median eminence, and the posterior lobe of the pituitary in postpartum lactating rats. Southern blot analysis of the amplification products confirmed the presence of oxytocin mRNA in all three tissue samples. The present findings indicate that oxytocin mRNA can be transported axonally. Such transport could reflect an adventitious compartmentalization or a functional storage in Herring bodies for subsequent secretion. In the mammalian brain, specific intradendritic mRNAs are seen consistently (1,8,9). On the other hand, Guitteny and Bloch (10), using autoradiographic detection of vasopressin mRNA hybridization by both light and electron microscopy, reported that hybridization was restricted to perinuclear cytoplasm. Nevertheless, the micrographs presented in this study do not exclude the possibility that vasopressin mRNA is present in more distal neuronal processes. McCabe et al. (11) reported the presence of vasopressin mRNA in extracts of the posterior lobe by using solution hybridization. Although they did not directly determine the cellular origin of this mRNA, they suggested that it might arise from pituicytes (11), the major cell type in the posterior pituitary other than the vascular elements.We recently developed an immunocytochemical method for in situ hybridization with BrdUrd-labeled oligonucleotide probes (12). This sensitive nonradioactive method also provides resolution of hybridization sites by electron microscopy. In a recent light microscopy study, we found that oxytocin mRNA hybridization was present in neuronal processes at some distance from neuronal perikarya (13). Therefore, we initiated these studies to apply this method to an evaluation of possible intraaxonal localization of the mRNA for oxytocin in the posterior pituitary. The neurohypophysial magnocellular system is ideal for analysis ofthe intraneuronal compartmentalization of neuropeptide mRNAs as its cell bodies are concentrated within the hypothalamus, while the axons of these neurons are concentrated in neuron-free sites in the median eminence and neurophypophysis. Early lactating animals were chosen for these experiments to take advantage of their high rates of oxytocin synthesis (14) accompanied by high levels of oxytocin mRNA (15). Our results indicate that in this physiological state, the oxytocin mRNA can indeed be detected in the axons of oxytocincontaining neurons in the median eminence and the posterior pituitary by both light microscopy and ultrastructural in situ hybridization as well as in RNA samples from the poste...

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We used immunocytochemistry to obtain a complete cellular and subcellular mapping of the 1,25-dihydroxyvitamin D3 receptor protein (VDR) in the rat limbic system. We observed specific VDR immunostaining in the nucleus as well as in the perinuclear cytoplasm of neuronal cells. The limbic system consists of a variety of neuronal structures, and is known to have influence on memory, behavior, emotions and reproduction. In the hippocampal formation, we found strong nuclear staining as well as less distinguished cytoplasmic VDR staining in CA1, CA3 and CA4. The CA2 area showed a unique cytoplasmic predominance of VDR. The amygdala was found to exhibit specific patterns of VDR distribution in the various regions of the nucleus. We observed distinct differences of VDR localization within the limbic preoptic areas of the hypothalamus. Further parts of the brain we analyzed included the mammillary bodies, the indusium griseum and the cingulate cortex. The subcellular distribution of VDR in regions of the limbic system suggests a specific functional role of the receptor protein and indicates a role for calcitriol as a neuroactive steroid.

Serial brain sections of female rats at late pregnancy, parturition or early lactation were immunostained for oxytocin. Immunoreactive perikarya were visible in the magnocellular nuclei in all experimental animals as well as in ovariectomized, nulliparous controls. During late pregnancy and at parturition additional immunostaining appeared in groups of perivascular neurons in the preoptic region, the lateral subcommissural nucleus, the perifornical region and scattered throughout the ventral portion of the hypothalamus. Immunostaining of almost all of these perivascular neurons disappeared by day two postpartum, while another population of oxytocin neurons, without association with blood vessels, appeared in these brain regions after parturition. Immunostaining of processes from oxytocinergic neurons in the periventricular nucleus increased markedly near parturition. Many of these processes projected toward the third ventricle. Oxytocinergic neuronal systems that are activated in late pregnancy and early postpartum may contribute to several physiological changes associated with parturition and lactation including the onset of maternal behavior.

New and more active concepts of steroid binding globulin action are emerging from recent research. As a result, examination of steroid levels in aging humans and the role of steroid binding globulins need to be re-visited. This review will discuss the possibility that sex hormone binding globulin (SHBG) plays an active role in the aging process. It will discuss the changes in blood levels of SHBG in aging humans in association with sexual activity, prostate hypertrophy and cancer, uterine leiomyoma, breast cancer, obesity and particularly the relationship between SHBG and HDL-cholesterol, Alzheimer's disease, osteoporosis, and cardiovascular disease. Starting with the idea that SHBG is an active participant in steroid action demands a re-evaluation of data demonstrating a primary change in blood SHBG levels in association with various pathologies. Here we discuss the postulate that SHBG may act at its own receptor at the plasma membrane level to influence other receptors such as scavenger receptors and HDL-cholesterol receptors. We will also suggest that SHBG is a critical marker for mating and thus may be an important physiological molecule in control of aging.

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