Effects of pineal factors on the action potentials of sympathetic neurons

alpha7 receptor-selective agonists and modes of alpha7 receptor activation

The alpha7-selective agonists 3-(2, 4-dimethoxybenzylidene)-anabaseine (GTS-21), also known as DMXB, and 3-(4-hydroxy,2-methoxybenzylidene)anabaseine (4OH-GTS-21) produce a variety of behavioral and cytoprotective effects that may be related to the activation of either large transient currents at high concentrations or small sustained currents at lower agonist concentrations. We are using acutely dissociated hypothalamic neurons, which express a central nervous system (CNS) alpha7-type receptor, to test a model for the concentration-dependent desensitization of alpha7-mediated responses. Our results confirm that 4OH-GTS-21 is a potent activator of neuronal alpha7 nicotinic-acetylcholine receptor. The rapid application of agonist leads to a brief period of maximal receptor-activation followed by desensitization. Rise rates, decay rates, and the degree to which current was desensitized were all concentration-dependent. Following the initial peak response to a 300-microM 4OH-GTS-21 application, current is reduced to baseline values within about 100 ms. Application of 30 microM 4OH-GTS-21 produced both a transient peak current and a sustained current that decayed only slowly after the removal of agonist. In the case of a 300-microM 4OH-GTS-21 application, after agonist was removed, we saw a rebound response up to the level of the 30-microM sustained current. The data, therefore, suggest that a sufficient level of agonist occupation can be retained on the receptor to promote activation for up to several hundred milliseconds.

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.