LESIONS OF THE MEDIAL GENICULATE NUCLEI SPECIFICALLY BLOCK CORTICOSTERONE RELEASE AND INDUCTION OF C-FOS MESSENGER-RNA IN THE FOREBRAIN ASSOCIATED WITH AUDIOGENIC STRESS IN RATS
S. Campeau et al., LESIONS OF THE MEDIAL GENICULATE NUCLEI SPECIFICALLY BLOCK CORTICOSTERONE RELEASE AND INDUCTION OF C-FOS MESSENGER-RNA IN THE FOREBRAIN ASSOCIATED WITH AUDIOGENIC STRESS IN RATS, The Journal of neuroscience, 17(15), 1997, pp. 5979-5992
Audiogenic stress is known to activate the hypothalamo-pituitary-adren
ocortical (HPA) axis in rats. The goal of the present study was to det
ermine whether the medial geniculate nuclei (including all auditory nu
clei of the thalamus), which are obligatory relays in the transmission
of auditory information to the forebrain, are critically involved in
HPA activation by audiogenic stress. To this end, corticosterone level
s and regional brain activity indexed by c-fos mRNA induction, elicite
d by 30 min of 105 dB white noise, were measured. Compared with unoper
ated and sham-operated rats, complete medial geniculate nuclei lesions
blocked corticosterone release normally induced by loud noise. The ef
fects of the lesions were specific to loud noise insofar as corticoste
rone release in response to restraint or ether stress was not reduced
in lesioned rats. We have determined previously that audiogenic stress
is associated with a specific regional pattern of c-fos mRNA inductio
n. Rats sustaining complete medial geniculate lesions demonstrated a b
lockade of c-fos mRNA induction in several audiogenic stress responsiv
e regions, also known to directly innervate medial parvocellular neuro
ns of the paraventricular hypothalamic nucleus. Thus, in addition to b
lockade in the paraventricular hypothalamic nucleus, c-fos mRNA induct
ion in the lesioned animals was abolished in the bed nucleus of the st
ria terminalis, especially its anterior medial and ventral aspects, th
e septohypothalamic nucleus, and the anteroventral preoptic area, comp
ared with unoperated and sham-operated rats. Several additional region
s in the lesioned rats failed to show reliable c-fos mRNA induction co
mpared with naive rat controls. Nearly all other regions that showed r
eliable c-fos mRNA induction in the unoperated and sham-operated rats
displayed either similar or slightly reduced levels in complete medial
geniculate-lesioned rats, suggesting that these regions are not part
of a critical HPA activational circuit in response to audiogenic stres
s. On the basis of these results, putative circuits from the medial ge
niculate nuclei to the paraventricular nucleus of the hypothalamus inv
olved in activation of the HPA axis by audiogenic stress are discussed
.