Cirone J.; Salt T.E.; (2000)
Physiological role of group III metabotropic glutamate receptors in visually responsive
neurons of the rat superficial superior colliculus.
European Journal of Neuroscience, 12: 847-855.
There is evidence from immunohistochemical and in situ hybridization studies
for the presence of Group I, II and III metabotropic glutamate receptors (mGluRs)
in the rat superficial superior colliculus (SSC). The purpose of this study was
to investigate if manipulation of Group III mGluRs affects visual responses in
the SSC. Drugs were applied by iontophoresis and single neuron activity was
recorded extracellularly. L-AP4 (Group III agonist) resulted in a reduction
of visual responses in most neurons, but also a potentiation in others.
The effect of L-AP4 is drug- and stereospecific in that application of
D-AP4 did not significantly affect visual responses. L-AP4 application also
resulted in a potentiation of the response to iontophoretically applied NMDA.
The effects of MPPG and CPPG (Group III antagonists) were compared with the
effect of L-AP4 in the same neuron and were found to produce the opposite
effect to L-AP4. Furthermore, the effect of L-AP4 could be blocked by
coapplication of MPPG or CPPG. Presynaptic depression of glutamate release
is a possible mechanism by which L-AP4 could reduce visual responses in the
SSC whereas the potentiation of visual responses by L-AP4 could be due to a
reduction of GABAergic inhibition. The finding that MPPG and CPPG, as well as
antagonizing the L-AP4 effect, have a direct effect on visual responses suggests
that Group III mGluRs are activated by endogenous transmitter released during
visual stimulation.
Full text is available at European Journal of Neuroscience.