Effects of scopolamine and its quaternary analogue in the murine elevated plus-maze test of anxiety.
Several lines of evidence suggest that muscarinic cholinergic receptors may play a role in fear/anxiety reactions in animals. In the present study, the behavioural effects of the muscarinic receptor antagonist scopolamine (0.125-1.0mg/kg) were examined in male mice exposed to the elevated plus-maze. In contrast to scopolamine methyl bromide, which was behaviourally inert under present test conditions, scopolamine hydrobromide produced behavioural changes indicative of enhanced anxiety. The effects included a reduction in percentage of open arm entries and a marked stimulation of risk assessment measures (i.e. stretched attend postures and closed arm returns), as well as more subjective signs of enhanced fear/anxiety such as vocalisation, struggling and escape-oriented behaviour. Although scopolamine also enhanced total arm entries, perhaps suggesting a general stimulant action, this effect was specific to the closed arms and was not accompanied by systematic increases in either rearing or head-dipping. Data are discussed in relation to the possible involvement of central muscarinic substrates in risk assessment behaviour in animals and hypervigilance states in humans.
Ethopharmacology Laboratory, Department of Psychology, University of Leeds, Leeds LS2 9JT, UK.
R.J.
RJ
Rodgers
J.C.
JC
Cole