Table 1.

Key features of mGluRs

Group	Receptor/splice variants	CNS expression	Synaptic localization	Signaling pathways of group
Group I	mGluR1 a,b,c,d,e,f Taste mGluR1	Widespread in neurons Taste buds	Predominantly  postsynaptic	Phospholipase C stimulation Stimulation of adenylyl cyclase (some systems) MAP kinase phosphorylation
	mGluR5 a,b	Widespread in neurons,  astrocytes
Group II	mGluR2	Widespread in neurons	Presynaptic and  postynaptic	Inhibition of adenylyl cylcase Activation of K+ channels Inhibition of Ca++ channels
	mGluR3 GRM3A2 GRM3A4 GRM3A2A3	Widespread in neurons,  astrocytes
Group III	mGluR4	Widespread in neurons,  High in cerebellum	Predominantly  presynaptic	Inhibition of adenylyl cylcase Activation of K+ channels Inhibition of Ca++ channels
	Taste mGluR4
		Taste buds
	mGluR6 a,b,c	Retina	Postsynaptic in  ON-bipolar retinal cells	Stimulation of cGMP  phosphodiesterase (mGluR6)
	mGluR7 a,b,c,d,e	Widespread in neurons	Active zone of presynaptic  terminals
	mGluR8 a,b,c	Lower and more restricted  expression than  mGluR4/7	Predominantly  presynaptic