Acute heating in young rats increases visceral sympathetic nerve discharge (SND), however, renal and splanchnic SND responses to hyperthermia are attenuated in senescent compared with young Fischer 344 (F344) rats (Kenney and Fels, Am J Physiol Regulatory Integrative Comp Physiol, 2002). Central mechanisms by which aging alters visceral SND responses to heating are not known. We tested the hypothesis that forebrain neural circuits are involved in suppressing sympathoexcitatory responses to heating in chloralose-anesthetized, senescent F344 rats. Renal and splanchnic SND responses to increased (38°C-41°C) internal temperature (Tc) were determined in midbrain-transected (MT) and sham-MT young (3-month-old), mature (12-month-old) and senescent (24-month-old) F344 rats and in cervical-transected (CT) and sham-CT senescent rats. Renal SND remained unchanged during heating in MT and sham-MT senescent rats but was increased in CT senescent rats. Splanchnic SND responses to heating were higher in MT compared with sham-MT senescent rats and in CT compared with MT senescent rats. SND responses to heating were similar in MT and sham-MT young and mature rats. Mean arterial pressure (MAP) was increased during heating in MT but not in sham-MT senescent rats whereas heating-induced increases in MAP were higher in sham-MT compared with MT young rats. These data suggest that in senescent rats the suppression of splanchnic SND to heating involves forebrain and brainstem neural circuits whereas the renal suppression is mediated solely by brainstem neural circuits. These results support the concept that aging alters the functional organization of pathways regulating SND and arterial blood pressure responses to acute heating.