Effects of chronic hypothalamic lesions on diurnal and stress corticosteroid levels

Abstract

The effect of chronic lesions on plasma corticosteroid levels has been assessed in an attempt to differentiate neuronal areas affecting diurnal corticosteroid rise from those involved in acute response to stress. In unanesthetized, unrestrained rats blood samples were collected through a chronic indwelling catheter on each of four experimental days at 9 and 10 am and 5 pm with or without addition of a stress applied at 9:45 am. Anterior hypothalamic lesions bilaterally destroying the periventricular zone and arcuate nuclei were associated with inhibition of the normal 5 pm rise but with normal rise in plasma corticosteroid levels in response to sound or to a 1-min electrical stimulation of the posterior diencephalon. Posterior tuber cinereum lesions were associated with normal 5 pm rise but with inhibition of response to sound. Response to ether stress was unaffected by any lesion. Thus the integrity of anterior hypothalamic areas appears essential for normal diurnal rise in plasma corticosteroid levels while more posterior areas are involved in mediation of pituitary-adrenal response to acute stress of sound.