Gates and filters: unveiling the physiological roles of nicotinic acetylcholine receptors in dopaminergic transmission.

Neuronal nicotinic acetylcholine receptors (nAChRs) in the brain have been enigmatic players on the cerebral stage. As ligand-gated ion channels they were expected to mediate fast cholinergic transmission, yet their influence appears to be modulatory. Two reviews in this issue of the BJP consider the relationship between nAChRs and endogenous ACh, with respect to the modulation of dopaminergic signalling. In his review, Maskos posits that in midbrain dopamine neurons, somatodendritic nAChRs activated by cholinergic inputs from the pedunculopontine tegmental nucleus (PPTg) and laterodorsal tegmental nucleus (LDTg) serve as a 'gate' that facilitates the switch to burst firing. In the terminal field, Exley and Cragg argue that nAChRs function as a 'presynaptic filter' to enhance the contrast between single and repetitive spike firing. Thus somatodendritic and presynaptic nAChRs exert subtle and complementary influences in responding to cholinergic inputs.