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

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 D1 and D2 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 D1 receptor antagonist SCH23390 (1 μg/rat) and dopamine D2 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 D1 and D2 receptors is necessary for mediating anxiolytic-like effects of physostigmine.