Sm. Tanimura et Ag. Watts, Adrenalectomy dramatically modifies the dynamics of neuropeptide and c-fosgene responses to stress in the hypothalamic paraventricular nucleus, J NEUROENDO, 12(8), 2000, pp. 715-722
We have used in situ hybridization and radio-immunoassay to compare tempora
l dynamics of components in the hypothalamo-pituitary limb of the hypothala
mo-pituitary-adrenal axis during sustained hypovolemic stress in adrenalect
omized (ADX) rats to those previously reported in intact animals. We asked
three questions: first, does corticotropin-releasing hormone (CRH) gene tra
nscription occur in neuroendocrine neurones of the hypothalamic paraventric
ular nucleus (PVH) of ADX rats, and if so, how is it temporally organized;
second, what is the expression pattern of the vasopressin and other genes k
nown to be colocalized in these neuroendocrine neurones; third, if adrenoco
rticotropin hormone (ACTH) secretion occurs, what is its temporal profile?
We found that sustained hypovolemia evoked a brief episode of CRH gene tran
scription in ADX rats that occurred earlier than in intact rats. However, i
n contrast to saline-injected controls, this activation was not maintained
because declines in CRH hnRNA and mRNA were seen as the stress continued. A
lthough increased vasopressin gene transcription was not seen in intact hyp
ovolemic rats, robust increases were measured throughout in ADX rats, sugge
sting that in the absence of corticosterone the vasopressin gene is transcr
ibed preferentially to the CRH gene during sustained hypovolemia. c-fos and
preproenkephalin mRNA profiles also exhibited earlier onsets compared to i
ntact rats. Finally, the onset and duration of ACTH secretion was the same
in ADX rats as previously reported in intact rats. Collectively, these data
support two hypotheses regarding the actions of corticosterone. First, tha
t it provides some form of facilitatory signal allowing neuroendocrine CRH
transcriptional mechanisms to remain active during sustained hypovolemia. S
econd, that it strongly inhibits the response of the vasopressin gene to hy
povolemic stress.