Actions of buspirone in a putative model of anxiety in the mouse

In a two-compartment box divided into a dark area and a brightly illuminated white area, mice taken from a dark environment showed aversion to the light and exhibited preference for exploratory rearings and line crossings in the black area. The peripheral administration of buspirone, and its injection into the dorsal raphe nucleus, lead to an increased time spent in the white area associated with enhanced exploratory behaviour with a decreased incidence of rearings and line crossings in the black section. In contrast, the injection of 5-hydroxytryptamine and 2-methyl-5-hydroxytryptamine into the dorsal raphe nucleus increased exploratory behaviour in the black section with decreased activity in the white area: the effects of 2-methyl-5-hydroxytryptamine were antagonized by buspirone administered peripherally. Ritanserin, methysergide, metergoline and cyproheptadine failed, in non-sedative doses, to influence exploratory behaviour in the two-compartment system and ritanserin and methysergide also failed to antagonize the effects caused by 2-methyl-5-hydroxytryptamine. It is concluded that in the mouse model the ability of buspirone to reduce the aversive response to a brightly illuminated area may reflect an anxiolytic action, that the dorsal raphe nucleus may be an important locus of action, and that the effects of buspirone may reflect an interaction at 5-hydroxytryptamine receptors.