MODULATION OF MINIATURE INHIBITORY POTENTIALS IN MOTONEURONS OF THE TURTLE SPINAL CORD
BU GROUP II METABOTROPIC GLUTAMATE RECEPTORS
V. M. Kozhanov, 1 0. A. Karamian, 1 N. M. Chmykhova, 1
N. P. Vesselkin, 1
H. P. Clamann 2
1 Institute of Evolutionary Physiology and Biochemistry RAS, St. Petersburg, Russia and
2 Department of Physiology, University of Bern, Switzerland;
e-mail: vk@VK5501.spb.edu
The role of group II metabotropic glutamate receptors (mGluRs) in modulation of inhibitory synaptic activity was studied
by intracellular recording of motoneuron miniature inhibitory spontaneous postsynaptic potentials (mlPSPs) in isolated lumbar segments
of the turtle spinal cord in the medium containing TTX, CNQX, AP-5. The ratio of mlPSPs with fast and slow kinetics (83% vs) is in
accordance with the ratio shown for glycine- and GA-BA-mediated IPSP or IPSCs (Jones et al., 1988; Gao et al., 2001). In the majority of
investigated motoneurons, the selective group II mGluRs antagonist EGLU (100-250 μM) increased the frequency of mlPSPs by
106.6 ± 74.4 % (n = 9) without affecting average amplitude, suggesting a presynaptic site of mGluRs action providing for the
transmitter release reduction. The analysis of EGLU action on mlPSPs with different time courses (selection by half-width) showed that
the frequency of inhancement of miniature inhibitory activity is caused by predominantly short-duration mlPSPs (ba 84.0 ± 18.2 %;
n = 9), which are probably glycineergic. However, EGLU did not influence the mlPSPs frequency under condition of GABA-receptor
blockade by bicuculline (20 μM). This fact suggest that group II mGluRs could modulate glycinergic transmission to the turtle spinal
motoneurons on the necessary condition that GABergic system is active.
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