Involvement of the dopaminergic receptors of the rat basolateral amygdala in anxiolytic-like effects of the cholinergic system

Abstract

Cholinergic system stimulation in some parts of the brain may affect anxiety-related behaviors. This system has many interactions with dopaminergic neurotransmission in the brain. We have studied the effect of cholinergic system activation in the basolateral amygdala on anxiety-related behaviors in adult male wistar rats using the acetylcholinesterase inhibitor physostigmine. Furthermore, the possible involvement of dopamine D 1 and D 2 receptors of basolateral amygdala in physostigmine induced effects has been evaluated. The elevated plus-maze task was used to assess anxiety parameters and all drugs were delivered into basolateral amygdala via bilaterally implanted chronic cannulas. Physostigmine (20 μg/rat) increased the percentage of open arm time (%OAT) and open arm entries (%OAE), revealing an anxiolytic-like effect. However, muscarinic receptor antagonist scopolamine (8 μg/rat) decreased %OAT indicating anxiogenic-like effect. A sub-effective dose of scopolamine (2 μg/rat) plus physostigmine decreased %OAT and %OAE in comparison to saline plus physostigmine (20 μg/rat). Muscarinic receptor agonist pilocarpine (5 μg/rat), dopamine D 1 receptor antagonist SCH23390 (1 μg/rat) and dopamine D 2 receptor antagonist sulpiride (5 μg/rat) significantly increased %OAT which may show anxiolytic-like effects of drugs. Sulpiride (5 μg/rat) also increased %OAE parameter. Pre-treatment with SCH23390 (0.5 and 1 μg/rat) or sulpiride (5 μg/rat) blocked anxiolytic-like effect of physostigmine (20 μg/rat). All drugs were devoid of any significant effect on locomotor activity. It is concluded that intra-basolateral amygdala administration of physostigmine has anxiolytic-like effects which may be via muscarinic mechanisms. Furthermore, dopaminergic system activation probably via dopamine D 1 and D 2 receptors is necessary for mediating anxiolytic-like effects of physostigmine.