Fig. 1. Amphetamine and scopolamine alter dopamine neurotransmission. (A) Amphetamine regulates dopamine transmission. The amphetamine first binds to the dopamine DAT and vesicular monoamine transporter (VMAT) competitively with dopamine or norepineprine. Then, it faciliates DAT mediated reverse transport of DA. These functions of amphetamine result in the increase of the concentration of dopmaine in the synpatic cleft. (B) Scopolamine is invloved in acetylcholine and dopamine transmission. The scopolamine binds non-specifically to muscarinic acetylcholine receptors (M-M5) in all brain regions. Specifically, M2/M4 subtypes of mAChR that are linked to an inhibitory G-protein in the neuronal terminal of mesopotine cholinergic neurons are autoreceptors that exert negative feedback. This negative feedback is blocked by scopolamine, resulting in disinhibition of cholinergic transmission. Increased acetylcholine release into postsynaptic neurons of mesopotine, which are mainly dopaminergic neurons in VTA or substantia nigra, elevate DA release. The orange neuron located in the top-right indicates the dopaminergic presynaptic neuron whereas lower orange neuron indicates a postsynptic neron. The yellow neuron denotes the mesopotine cholinergic neuron. DAT, dopamine active receptor; D1/2R, dopamine receptor D1 and dopamine receptor D2; mAchR, muscarinic acetylcholine receptor.
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