HIPPOCAMPAL 5-HT1A RECEPTOR-BINDING SITE DENSITIES, 5-HT1A RECEPTOR MESSENGER-RIBONUCLEIC-ACID ABUNDANCE AND SEROTONIN LEVELS PARALLEL THE ACTIVITY OF THE HYPOTHALAMO-PITUITARY-ADRENAL AXIS IN RATS

We have previously demonstrated that susceptibility of the Lewis rat t o inflammatory disease, compared to the relatively resistant Fischer F 344 rat, is related to a hyporesponsive hypothalamopituitary adrenal a xis to inflammatory and other stress mediators. Since 5-HT and the 5HT (1A) receptor are important stimulators of this axis, we have investig ated the levels of 5-HT1A receptor binding sites and encoding mRNA, 5- HT and 5-hydroxyindole acetic acid in various brain regions of Lewis, Harlan Sprague Dawley and Fischer F344 rats. Lewis rats expressed sign ificantly less hippocampal and frontal cortical 5-HT1A receptor bindin g sites and mRNA than Harlan Sprague-Dawley and Fischer F344 rats. Adr enalectomy increased the number of 5HT(1A) receptor binding sites and mRNA expression in the hippocampus of all three strains. The levels of hippocampal 5-HT in Fischer F344 rats were significantly greater than levels detected in the same regions for the other two strains. Hypoth alamic 5-HT and 5-hydroxyindole acetic acid levels in Harlan Sprague-D awley rats were higher than the same area from the other two strains. Adrenalectomy increased the levels of 5-hydroxyindole acetic acid in t he hypothalamus of all three strains. We conclude that hippocampal 5-H T1A receptor densities and 5-HT levels in the rat parallel the activit y and responsiveness of the hypthalamopituitary-adrenal axis. We have published these data in an earlier report.