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

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Literature Review
GABAB-mediated responses could be measured in either mice (Prosser et al.,
2001; Schuler et al., 2001).
GABAB receptors play an important role in maintaining excitatory–
inhibitory balance in brain and alterations can lead to seizures (Hossein et al.,
2008). GABAB receptors, the metabotropic receptors for GABA, are G protein-
coupled receptors (GPCR) which regulate neuronal excitability both pre and
postsynaptically. The action of GABA at presynaptic GABAB receptors is to
reduce Ca 2+ influx and thus inhibit neurotransmitter release (Takahashi et al.,
1998). These receptors exist on GABAergic terminals (autoreceptors), or on
terminals arising from cells containing other neurotransmitters, such as glutamate
(heteroreceptors). Postsynaptically, GABAB receptors are responsible for the
generation of the late inhibitory postsynaptic potential (IPSP), via the opening of
K + channels and inhibit adenylate cyclase (Bettler et al., 1998). Abnormality in
either of these functions could have consequences for the generation and/or
prevention of epileptic seizures. Multiple laboratories have demonstrated altered
expression of GABABR1 and GABABR2 in animal models for seizure disorders
(Princivalle et al., 2003; Straessle et al., 2003). Han et al. (2006) found that as a
result of multiple seizures, there was a long-term decrease in GABABR1 (15 days)
and GABABR2 (30 days) expression in rat hippocampus. Taken together, these
animal studies suggest that the changes in the number GABAB receptors lead to
epilepsy, due to changes in transmitter release (presynaptic) and inhibition
(postsynaptic). Accordingly, GABA neurons have been alternately proposed to be
highly vulnerable or relatively invulnerable after insults known to cause epilepsy
(Ribak et al., 1979; Sloviter et al., 1987) and GABA-mediated inhibition is
reportedly decreased, in animal models of epilepsy (Dalby et al., 2001).
GABAC Receptors
GABAC receptors, which are a subfamily of GABAA receptors, are
members of the Cys-loop superfamily of ligand-gated ion channels (LGICs), an