Different behavioral reactivity of 5-HT1 sites between killer and non-killer rats after midbrain raphe lesion

A behavioral reactivity study on 5-HT1 and 5-HT2 sites of isolated killer and non-killer rats and on raphe lesioned killer and non-killer animals was undertaken, 5-HT1 reactivity was measured by a rank intensity scale on the forepaw treading and hind-limb abduction induced by 5-MeODMT. 5-HT2 reactivity was determined by the "shaking" behavior following 5-HTP. No behavioral differences on 5-HT1 and 5-HT2 sites were observed between isolated killer or non-killer animals. Similarly, comparable values of "shakes" were obtained on killer and non-killer lesioned rats. On the contrary, 5-MeODMT, induced a lower behavioral response on lesioned killer as compared to lesioned non-killer. This different behavioral response can not be explained by a probable difference of 5-HT terminals denervation since a similar reduction of 5-HT brain uptake was observed between both groups of rats. Finally, the decreased reactivity of 5-HT1 sites may be an index of a lower 5-HT neurotransmission and could therefore provide an explanation of the appearance of muricidal activity in some but not in all the lesioned rats.