PRESSOR AND DEPRESSOR SITES ARE INTERMINGLED IN THE CINGULATE CORTEX OF THE RAT

Electrical stimulation of area infraradiata in the rat evokes transien t changes in arterial pressure, but the locations that evoke these res ponses have not been mapped by neurochemical methods. To localize more specifically the regions of area infraradiata that modify cardiovascu lar activity, the present study measured cardiovascular responses to l ocalized chemical stimulation of neurons in area infraradiata of ureth ane-anesthetized rats (n = 21). Microinjections (50-200 nl) of the glu tamate agonist D,L-homocysteic acid into area infraradiata evoked both increases and decreases in arterial pressure and heart rate. Injectio ns in the ventral subdivisions of rostral area infraradiata (IRa alpha and IRb alpha) produced cardiovascular responses with the highest pro bability and greatest magnitude. Of 53 injections in this area, 18 dec reased arterial pressure and heart rate, whereas 4 increased arterial pressure and heart rate. In contrast to the results from the ventral s ubdivision of rostral infraradiata cortex, injections of D,L-homocyste ic acid in the dorsal subdivision of rostral infraradiata cortex (IRc alpha) or any of the caudal subdivisions of area infraradiata (IR beta ) produced less consistent changes in arterial pressure. To demonstrat e that the general anesthesia did not significantly alter the evoked r esponses in this study, similar injections of D,L-homocysteic acid wer e made into area infraradiata of unrestrained, conscious rats (n = 10) and the responses were similar to the responses evoked in urethane-an esthetized rats. These results indicate that the ventral subdivisions of rostral area infraradiata (IRa alpha and IRb alpha) are more involv ed in cardiovascular regulation than other areas of infraradiata corte x (IRc alpha and IR beta), and that both presser and depressor sites a re present in both areas. (C) 1997 Elsevier Science B.V.