Neuromodulating effect of Pregabalin on neurotransmitter release at the mouse Calyx of Held

DI GUILMI, MN, URBANO FJ, GONZALEZ INCHAUSPE C AND UCHITEL OD.

Chicago, EE.UU,

Conferencia; 39th Annual Meeting of Society for Neuroscience (SFN); 2009

Pregabalin [S-[+]-3-isobutylGABA, Lyrica] is an anticonvulsant and analgesic medication which was originally synthesized with the intention of modulating brain GABA receptors, resulting ineffective. The mechanism of action of pregabalin (PGB) has been only partially characterized; it is generally accepted that PBG subtly reduce calcium-dependent overflow of neurotransmitters in several tissues. However, the cellular and molecular basis of its inhibitory action on neurotransmitter release is unknown. The α2-δ type 1 auxiliary subunit of voltage-gated calcium channels is the primary high-affinity binding site for PGB (Gee et al., 1996). The exact action of PGB on presynaptic calcium channels function is still a matter of controversy.   Here, we studied the effect of PGB on the Calyx of Held-Medial Nucleus of the Trapezoid Body (MNTB) synapse in brainstem slices using whole cell patch clamp recordings. Excitatory postsynaptic currents (EPSCs) and presynaptic calcium currents were recorded at Calyx of Held-MNTB complex at both low and high frequency stimulation.   The amplitude of EPSCs at the Calyx – MNTB was reduced by a 30%. No differences were observed in the depression rate from high frequency trains but a faster rate of recovery from synaptic depression at 100 Hz was observed in the presence of PGB (500 μM)(p=0.043). We found no differences in the mean amplitude of miniature EPSCs (39± 2pA in -PGB (n =11) and 38± 2pA in +PGB (n =10), while observing greater minis frequencies –PGB versus +PGB conditions (1.71±0.35 Hz and 0.49±0.06 Hz, respectively (p=0.0044)). The release probability (Pr) was 0.45 ± 0.024 (n =6) for -PGB and 0.35 ± 0.015 (n =6) for +PGB (p = 0.00014) indicating a decrement of the Pr after PGB application. On the other hand, P/Q-type calcium channels mediated currents decreased in presence of PGB (500 μM) after high frequency trains (100-300Hz). The calcium current was partially recovered by isoleucine (1.5 mM), suggesting specific PGB-mediated effects. Calcium currents activation curves, obtained from plotting tail currents versus command voltage showed no differences. However, two pulses inactivation protocol shows a larger rescue of the inactivation.    These results suggest that PGB effects on Calyx of Held-MNTB synapse is two fold: 1) blocking presynaptic P/Q-type mediated calcium currents that would reduce synaptic transmission, and 2) accelerating the recovery of P/Q channels from inactivated states that would allow for lower recovery times after high frequency synaptic stimulation.