Vasopressin-sensitive neurons in the lateral paraventricular nucleus area in a guinea pig slice preparation

The effects of vasopressin (VP) on hypothalamic neurons located in the region of the paraventricular nucleus (PVN) were analyzed using intracellular techniques in slices of guinea pig brains. Two different classes of neurons were electrophysiologically identified in the magnocellular lateral part of the PVN and in the adjacent area. In the former area, vasopressinergic neurons were identified according to their phasic activity and their endogenous properties. These neurons were not responsive to VP, applied through the perfusion medium or locally by pressure. On the other hand, nonmagnocellular neurons exhibiting low-threshold Ca2+ spikes (LTS) were recorded in the area adjacent to the lateral part of the PVN. LTS were deinactivated at hyperpolarized membrane levels and induced short bursts of action potentials. On these neurons, VP evoked depolarizations accompanied by increases in firing, without modification of membrane resistance. VP effects were not blocked by TTX, suggesting a postsynaptic action of the peptide. These data indicate that VP controls the firing pattern of LTS neurons and suggest that this action may involve collaterals of axons originating from neighbouring vasopressinergic neurons.