Muscarinic M1, M3, Nicotinic,GABAA and GABAB Receptor ...

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Literature Review
nucleus, although the boundaries of the pedunculopontine nucleus are unclear
resulting in some cholinergic neurons invading surrounding regions. These
cholinergic neurons innervate the spinal cord, brainstem, thalamus, hypothalamus,
basal forebrain and medial frontal cortex (Woolf & Butcher, 1986; Rye et al.,
1987). Mesopontine cholinergic neurons are intermingled with separate
populations of glutamatergic and GABAergic cells (Wang & Morales, 2009).
Mesopontine cholinergic neurons to the thalamus and basal forebrain play roles in
higher cognitive functions, such as gating sensory input, attention and mediating
level of consciousness. Cholinergic and GABAergic circuits in the mesopontine
region have been shown to inhibit the startle response, a response that is necessary
for gating sensory inputs (Bosch & Schmid, 2008). Some studies link mesopontine
cholinergic cells with attention, but not all studies are in agreement (Rostron et al.,
2009). In one such study, lesions of the pedunculopontine tegmental nucleus
produced an increase in errors and latency times on a serial reaction time task
testing attention (Inglis et al., 2001).
Brain sites capable of producing coma and neurotransmitter correlates of
coma point to a role for cholinergic mesopontine neurons in consciousness.
Damage to mesopontine areas containing cholinergic neurons produces coma
(Parvizi & Damasio, 2003). Many anesthetics block central cholinergic receptors
and overdose can lead to central anticholinergic syndrome and coma (Moos,
2007). The role of cholinergic systems in consciousness is additionally illustrated
by the pharmacology of anesthetic drugs that markedly diminish conscious
awareness. Many known anesthetic compounds target nicotinic acetylcholine
receptors and GABAA receptors (among other receptors). Muscarinic
acetylcholine receptors and GABAB receptors represent potential targets for future
anesthetics (Sanders et al., 2008; Van Dort et al., 2008). The cholinergic basal
forebrain plays a role in selective attention, learning, memory, perception and
consciousness (Sarter et al., 2003). Specific regions of the basal forebrain play
particular roles, even though each region takes a part in multiple functions and