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FERREIRA, J.G.P. Organization of the ventral tegmental area projections to the VTAnigral complex and to the hypothalamus in the rat and VTA neurons projecting to the accumbens express insulin receptor substrates. PhD thesis (Physiology) Biomedical Sciences Institute, the University of São Paulo, São Paulo, 2009. The ventral tegmental area (VTA) is involved in reward mechanisms and, more recently, has been identified as an additional center detecting peripheral metabolic signals. In the first part of this work, the projections from the VTA to the VTA-substantia nigra complex were investigated using the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). The results suggest that the dorsolateral VTA projects to itself and to the dorsal portion of the substantia nigra compacta and retrorubral nucleus. The ventrolateral VTA innervates mainly the interfascicular nucleus. The components of the caudomedial VTA (interfascicular, caudal linear and paranigral nuclei) are interconnected. The caudal pole of the VTA sends robust and bilateral projections to almost the entire VTA-substantia nigra complex, ending in both the dorsal and ventral tiers of the substantia nigra compacta. Appositions between PHA-L immunoreactive varicosities and neurons immunoreactive to tyrosine hydroxylase (TH+) were often observed. In the second part of this work, the VTA projections to the hypothalamus were investigated. The importance of dopaminergic mechanisms in the lateral hypothalamus has long been acknowledged, they are involved in food intake, conditioned place preference, acquisition of appetitive conditioned responses and locomotor activity. The present results suggest that: 1) the VTA projects mainly to the lateral preoptic area and lateral hypothalamic area, the posterior subfornical region as well as to the dorsomedial and posterior hypothalamic nuclei. The lateral hypothalamic area is more densely innervated at rostral levels than at tuberal or caudal levels. The VTA also provides modest inputs to the medial preoptic area, the perifornical area and to the supramammillary region; 2) VTA projections to the hypothalamus display some topographical organization. In particular, projections to the dorsomedial nucleus and posterior subfornical region originate primarily from the caudomedial VTA, whereas the rostrodorsal VTA avoids these hypothalamic districts; 3) Appositions between PHA-L immunoreactive varicosities and neurons immunoreactive to orexin or melanin-concentrating hormone were observed, but they are uncommon; and 4) In double labeling experiments with injections of anterograde biotin dextran amine into the accumbens and PHA-L into the VTA, an extensive overlap of these projections was observed in the lateral preoptic area and anterior part of the lateral hypothalamic area. In the third part of this work, we have investigated the co-localization of the insulin receptor substrate type I (IRS-1), IRS-1 phosphorylated and phosphatidylinositol-3 kinase (PI3K) with TH or cholera toxin B subunit (CTb) injected into either the accumbens or the caudate-putamen. Our data suggest that: 1) The vast majority of dopaminergic neurons of the VTA-substantia nigra complex express IRS-1; 2) Injections into the shell or core of the accumbens resulted in a similar percentage of double-labeled cells for CTb/IRS-1. A significant number of cells were double-labeled for CTb/PI3K and 3) Injections in the dorsal striatum resulted in cells that were double-labeled for CTb/PI3K and CTb/IRS-1 phosphorylated, 4) The IRS-1 immunolabeling was localized in the nucleus of cells, unlike the cytosolic labeling observed by Folli and colleagues (J. Neurosci. 14: 6412-6422, 1994).

Organização das projeções da área tegmental ventral para o complexo VTA-substância negra e para o hipotálamo no rato e estudo da expressão dos substratos do receptor de insulina em neurônios da VTA que se projetam para o estriado