CENTRAL SEROTONERGIC SYSTEMS IN THE SPONTANEOUSLY HYPERTENSIVE AND LEWIS RAT STRAINS THAT DIFFER IN THE ELEVATED PLUS-MAZE TEST OF ANXIETY

The spontaneously hypertensive (SHR) and Lewis (LEW) strains differ in numerous behavioral tests, including the elevated plus-maze. In keepi ng with the crucial role of central serotonin (5-HT) in anxiety, we ch ecked for strain differences regarding several determinants of 5-HT ac tivity, in addition to confirming that LEW rats displayed anxious beha viors in the plus-maze compared with SHR, we found that in vitro, cent ral tryptophan hydroxylase activity was higher in LEW rats than in SHR , However, ex vivo studies in midbrains and hippocampi revealed that n either 5-HT synthesis nor 5-HT and 5-hydroxyindoleacetic acid levels d iffered between strains. [H-3]8-Hydroxy-2-(di-n-propylamino)tetralin b inding at midbrain 5-HT1A autoreceptors and hippocampal 5-HT1A postsyn aptic receptors, [H-3]ketanserin binding at cortical and striatal 5-HT 2A receptors and [H-3]citalopram binding at midbrain and hippocampal 5 -HT transporters did not vary between strains. The inhibition of 5-HT synthesis by 5-HT1A autoreceptor stimulation was similar in both strai ns. Forepaw treading and flat body posture after 5-HT1A postsynaptic r eceptor stimulation were higher and lower, respectively, in SHR than i n LEW rats. Last, 1-(4-iodo-2,5-dimethoxy-phenyl)-2-aminopropane- and quipazine-elicited head shakes, a 5-HT2A receptor-mediated response, w ere increased in the SHR strain compared with the LEW strain; on the o ther hand, 1-(3-chlorophenyl)piperazine triggered similar 5-HT2B/2C re ceptor-mediated decreases in motor activity in the two strains. This s tudy shows that although the low-anxiety (SHR) and high-anxiety (LEW) strains vary in some aspects of 5-HT function, key components such as the 5-HT1A autoreceptors are not different.