Molecular mechanisms of neuroendocrine integration in the central nervous system: an approach through the study of the pineal gland and its innervating sympathetic pathway.

In the brain specialized cells known as 'neuroendocrine transducers' translate an input of neural activity into a hormonal output, e.g. oxytocin released into the blood stream. Other, more typical neurons make the reverse conversion constituting chemoreceptors which transform the hormonal 'language' into changes in their firing rate ('endocrine-neural' transduction). 'Endocrine-endocrine' transducing events occur at the level of the neurosecretory cells that translate a hormonal signal into another, different, hormone output. This article reviews the molecular aspects of several neuroendocrine integrative processes in the hypothalamus, the pineal gland and the cervical sympathetic pathway. The discussed results indicate that the pineal gland and its innervating sympathetic neurons located in the superior cervical ganglia constitute an easy-to-manipulate model system for the study of basic neuroendocrine mechanisms because: (i) receptors for various hormones exist in the mammalian pineal and sympathetic ganglia; (ii) the pattern of pineal steroid metabolism resembles that of the neuroendocrine hypothalamus; (iii) pineal estrophilic and androphilic receptors as well as the pattern of steroid metabolism are modulated by the sympathetic nerves; (iv) neuronal activity in the cervical sympathetic pathway is modified by hormone treatment at preganglionic, ganglionic and postganglionic sites.