The ventral septal area: Electrophysiological evidence for putative arginine vasopressin projections onto thermoresponsive neurons

Abstract

The present experiments were conducted to identify thermoresponsive neurons in the ventral septal area and to characterize such units with respect to their connectivity to potential sources of arginine vasopressin in this area (the paraventricular nucleus and the bed nucleus of the stria terminalis) and to other brain regions (fornix and amygdala). Single unit in vivo microelectrode techniques were used to classify warm responsive, cold responsive, dynamic, biphasic and phasically active thermoresponsive neurons in the ventral septal area which altered their spontaneous activity in response to thermal stimulation of the scrotal skin. The fornix provided a large number of primarily inhibitory afferents to ventral septal thermoresponsive neurons while the amygdala projection consisted of approximately equal excitatory and inhibitory inputs. Electrical stimulation of the paraventricular nucleus resulted in orthodromic inhibition in 9 of 12 thermoresponsive units while projections from the bed nucleus of the stria terminalis appeared to preferentially inhibit warm responsive neurons in this area. These findings implicate the ventral septal area in thermoregulatory pathways by identifying neurons in this area responsive to peripheral thermal stimulation. Further, evidence in support of arginine vasopressin acting in this area to influence thermoregulation is provided by (1) the identification of the paraventricular nucleus and bed nucleus of the stria terminalis as possible sources of afferents to the ventral septal area, and (2) the characterization of the influence of this afferent input on thermoresponsive neurons in this region.