Differential responsivity of corticosterone and prolactin to stress following lesions of the septum or amygdala: implications for psychoneuroendocrinology

Abstract

Attempts to use neuroendocrine challenge tests to reflect suspected CNS dysfunction are popular, but frought with problems of interpretation. The dexamethasone suppression test of cortisol is thought to reflect limbic system function. Hormone responses to the triple bolus challenge test have also been reported to reflect limbic system dysfunction, but interpretation is dependent upon the hormone chosen for study. Challenge tests using prolactin have fallen out of favour because the final common pathway for its regulation lies outside the blood brain barrier. Thus, the ability of prolactin to reflect CNS and, specifically limbic system activity has been questioned. The present study undertook to determine corticosterone and prolactin responses in response to a variety of stimuli in rats that had selected limbic system damage following stereotoxically placed electrolic lesions. Surgical groups included: normal, sham-operated, septal lesion, cortico-medial amygdala lesion or baso-lateral amygdala lesion. All CNS damage was verified histologically. The stimuli chosen for neuroendocrine challenge were 3 minutes of exposure to, a novel environment, noise, ether vapour or cold water. These stimuli were chosen for their presumed level of neural input to the hypothalamic-pituitary axis. In the normal group, prolactin, but not corticosterone evidenced a differential response to the four stimuli. Following surgery, corticosterone responses to all stimuli were significantly influenced only in the septal lesion group. There was no interaction between the location of lesion with the type of stimuli used to elicit the corticosterone response. Prolactin, in contrast, evidenced significantly different responses depending on the location of the lesion, the type of stimulus and an interaction of these two variables. This level of differential responsiveness suggests that prolactin may have potential for diagnosis of limbic system dysfunction if appropriate test stimuli are employed to elicit its response.