The capacity of central and peripheral catecholaminergic neurons to innervate the pineal organ and cerebral cortex of the rat: in vitro immunohistochemical observations

Corticotropin-releasing factor promotes growth of brain norepinephrine neuronal processes through Rho GTPase regulators of the actin cytoskeleton in rat

Cognitive aspects of the acute stress response are partly mediated through activation of the locus coeruleus (LC)-norepinephrine (NE) system via corticotropin-releasing factor (CRF). Apart from mediating the acute responses to stress, CRF can mediate the long-term impact of stress on the brain through its potent modulation of neuronal morphology. Importantly, the cellular pathways engaged by stress in general, and CRF in particular, in remodeling neuronal structure are poorly understood. Here, we demonstrate that apart from its well-established acute effects on LC neuronal activity, CRF also stimulates growth and arborization of LC neuronal processes. By contrast, urocortin 2 (UCN 2), a related peptide, inhibits outgrowth of such processes. These opposing effects are transduced by a common receptor (CRF(1)) but distinct intracellular signaling pathways. The structural effects of CRF required protein kinase A and mitogen-activated protein kinase, as well as Rac1, a member of the Rho family of GTPases that regulates the actin and microtubule cytoskeleton. By contrast, the effects of UCN II were mediated by the protein kinase C and RhoA pathways. This is the first study to link stress-related substrates to molecular mediators of actin cytoskeletal remodeling in the LC. We propose a model of dynamic LC neuronal plasticity that is reciprocally controlled by CRF and UCN II, eventually determining actin rearrangement by Rho-specific pathways. By regulating the extension of processes into pericoerulear regions where limbic afferents terminate, these peptides may determine the degree to which the LC-NE system is influenced by limbic structures that mediate emotional expression.

Neurotrophic effects of the pineal gland: role of non-neuronal cells in co-cultures of the pineal gland and superior cervical ganglia

The pineal gland (PG) is a source of several trophic factors. In this study, PG and superior cervical ganglia (SCG) from Sprague-Dawley neonates (1-day-old) were co-cultured to test the hypothesis that endogenous release of PG NGF (or an NGF-like cytokine) is sufficient to promote survival of SCG neurons. Neuronal density of SCG neurons was significantly enhanced when co-cultured with PG for 7 days compared to SCG cultured alone. SCG survival and neurite formation in PG co-cultures was less than in SCG treated with exogenous NGF (100 ng/ml). The neurotrophic effect of PG co-cultures was abolished when 1% anti-NGF was added to the medium. Co-cultures of SCG neurons with established 7-day PG cultures induced extensive SCG neurite formation within 24 hr compared to SCG co-cultured with 1-day PG cultures. This suggests that PG neurotrophic effects are due to PG non-neuronal cells (nnc) that proliferate to confluency by 7 days in culture. S-antigen-positive pinealocytes did not proliferate in culture. There was decreased SCG survival when neurons were seeded onto PG cultures that had been previously killed by drying, which suggests that the neurotrophic effects of nnc are not substrate-dependent. Immunocytochemical characterization of PG nnc revealed a heterogenous mixture of astrocytes, macrophage/microglia, and fibroblasts. These findings support the hypothesis that NGF is actively secreted by PG and that nnc are the principal source of this neurotophin.