Cardiovascular regulation of supraoptic neurons in the rat: Synaptic inputs and cellular signals

The supraoptic nucleus of the hypothalamus contains a population of neurons that project to the posterior pituitary where they release peptides into systemic circulation. The system has two main secretory products - vasopressin and oxytocin. The main systemic affects of vasopressin are related to body fluid homeostasis while circulating oxytocin is involved in parturition and lactation. The circulating levels of both hormones are, to a large part, determined by the electrical activity of the supraoptic neurons and other neurosecretory cells, which is in turn determined by synaptic inputs. More recent work suggests that there may be other dimensions to the cellular response of supraoptic neurons to these synaptic inputs. For example, it has been demonstrated that supraoptic neurons alter their synthesis of vasopressin and oxytocin in response to prolonged stimulation and that the morphology of cells in the supraoptic nucleus and its number of synaptic inputs change with the physiological conditions of the animal. These responses would appear to require some type of activity-dependent set of cellular signals. Candidates for such signals include members of the AP-1 transcription factor family whose expression in neurons has been linked to synaptic stimulation. This review will describe the effects of cardiovascular-related stimuli on the expression of different members of the AP-1 family in the supraoptic nucleus.