Peripheral chemoreceptor inputs to the parabrachial nucleus of the rat.

In the urethan-anesthetized rat, extracellular recordings were made from 60 neurons within the region of the parabrachial nucleus (PBN). The activity of 37 of 44 neurons was altered by selective stimulation of peripheral chemoreceptors via intracarotid injection of NaH2PO4 or CO2-saturated NaHCO3. Most of these neurons (28 of 37) were excited during chemoreceptor stimulation. Twenty-four of 48 neurons responded to changes in baroreceptor input via changes in blood pressure. Most of these neurons (18 of 24) were inhibited during baroreceptor stimulation. Eleven of 32 neurons were affected by both chemoreceptor and baroreceptor inputs. Seven of these neurons had opposite responses during selective afferent stimulation; that is, they were excited during chemoreceptor activation and inhibited during baroreceptor activation. Our observations reveal that neurons within the medial and lateral PBN are responsive to peripheral chemoreceptor input. A subgroup of PBN neurons was shown to integrate information from chemoreceptors and baroreceptors. These results suggest that both the medial and lateral PBN may play a role in the central integration of cardiovascular inputs.