The Effects of Intrahippocampal Scopolamine Infusions on Anxiety in Rats as Measured by the Black–White Box Test

Abstract

Hippocampal cholinergic projections mediate attention to arousing stimuli as demonstrated by behavioral, electrophysiological, and endocrine studies. We recently reported that peripheral injections of the cholinergic antagonist scopolamine (SCOP) increased anxiety-like behaviour (ALB) in rats and we sought to investigate if this response might be hippocampally mediated. Adult male, Lister Hooded rats were implanted bilaterally with hippocampal cannulae 3 weeks prior to testing. On the test day, rats were injected with vehicle (VEH; artificial CSF at 3 μl), 15 or 30 μg SCOP, 20 min prior to being placed into the white chamber of the black–white box ( n = 10/group). Rats were scored for latencies to exit and reenter the white chamber, total time spent in the white chamber, intercompartmental crossings, and activity. SCOP at 30 μg significantly reduced time to exit the white arena, while both doses of SCOP elevated latencies to reenter the white chamber. There were no effects of SCOP on intercompartmental crossing, time spent in the white chamber, or on activity levels. Loss of hippocampal cholinergic function impairs processing of threatening stimuli that manifests itself as increased ALB.