[Show abstract][Hide abstract] ABSTRACT: In contrast to the restricted receptive field (RF) properties of the ventral posteromedial nucleus (VPM), neurons of the ventral thalamus zona incerta (ZI) have been shown to exhibit multiwhisker responses that vary from the ventral (ZIv) to the dorsal (ZId) subdivision. Differences in activity may arise from the trigeminal nuclear complex (TNC) and result from subnucleus specific inputs via certain cells of origin, axon distribution patterns, fiber densities, bouton sizes, or postsynaptic contact sites. We tested this hypothesis by assessing circuit relationships among TNC, ZI, and VPM. Results from tracer studies show that, 1) relative to ZId, the trigeminal projection to ZIv is denser and arises predominantly from the principalis (PrV) and interpolaris (SpVi) subdivisions; 2) the incertal projection from TNC subnuclei overlaps and covers most of ZIv; 3) two sets of PrV axons terminate in ZI: a major subtype, possessing bouton-like swellings, and a few fine fibers, with minimal specialization; 4) both PrV and SpVi terminals exhibit asymmetric endings and preferentially target dendrites of ZI neurons; 5) small and large neurons in PrV are labeled after retrograde injections into ZI; 6) small PrV cells with incertal projections form a population that is distinct from those projecting to VPM; and 7) approximately 30-50% of large cells in PrV send collaterals to ZI and VPM. These findings suggest that, 1) although information to ZI and VPM is essentially routed along separate TNC circuits, streams of somatosensory code converge in ZI to establish large RFs, and 2) subregional differences in ZI response profiles are attributable in part to TNC innervation density.
The Journal of Comparative Neurology 04/2008; 507(4):1521-41. DOI:10.1002/cne.21624 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A significant fraction of infants born to mothers taking selective serotonin reuptake inhibitors (SSRIs) during late pregnancy display clear signs of antidepressant withdrawal indicating that these drugs can penetrate fetal brain in utero at biologically significant levels. Previous studies in rodents have demonstrated that early exposure to some antidepressants can result in persistent abnormalities in adult behavior and indices of monoaminergic activity. Here, we show that chronic neonatal (postnatal days 8-21) exposure to citalopram (5 mg/kg, twice daily, s.c.), a potent and highly selective SSRI, results in profound reductions in both the rate-limiting serotonin synthetic enzyme (tryptophan hydroxylase) in dorsal raphe and in serotonin transporter expression in cortex that persist into adulthood. Furthermore, neonatal exposure to citalopram produces selective changes in behavior in adult rats including increased locomotor activity and decreased sexual behavior similar to that previously reported for antidepressants that are nonselective monoamine transport inhibitors. These data indicate that the previously reported neurobehavioral effects of antidepressants are a consequence of their effects on the serotonin transporter. Moreover, these data argue that exposure to SSRIs at an early age can disrupt the normal maturation of the serotonin system and alter serotonin-dependent neuronal processes. It is not known whether this effect of SSRIs is paralleled in humans; however, these data suggest that in utero, exposure to SSRIs may have unforeseen long-term neurobehavioral consequences.