The Journal of Neurophysiology Vol. 85 No. 1 January 2001, pp. 332-340
Copyright ©2001 by the American Physiological Society

cAMP-Dependent Presynaptic Regulation of Spontaneous Glycinergic IPSCs in Mechanically Dissociated Rat Spinal Cord Neurons

Cellular and System Physiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan

Katsurabayashi, Shutaro, Hisahiko Kubota, Zhi Ming Wang, Jeong Seop Rhee, and Norio Akaike. cAMP-Dependent Presynaptic Regulation of Spontaneous Glycinergic IPSCs in Mechanically Dissociated Rat Spinal Cord Neurons. J. Neurophysiol. 85: 332-340, 2001. Spontaneous miniature glycinergic inhibitory postsynaptic currents (mIPSCs) in mechanically dissociated rat sacral dorsal commissural nucleus (SDCN) neurons attached with intact glycinergic presynaptic nerve terminals and evoked IPSCs (eIPSCs) in the slice preparation were investigated using nystatin-perforated patch and conventional whole cell recording modes under the voltage-clamp conditions. Trans-ACPD (tACPD) reversibly reduced the mIPSC frequency without affecting the mean amplitude. The effect was mimicked by a specific metabotropic glutamate receptor (mGluR) II subtype agonist, (2S, 1'S, 2'S)-2-(carboxycyclo propyl) glycine (L-CCG-I), and a specific mGluRIII subtype agonist, 2-amino-4-phosphonobutyrate (L-AP4). These inhibitory effects on mIPSC frequency were blocked by the specific antagonists for mGluRII, -methyl-1-(2S, 1'S, 2'S)-2-(carboxycyclo propyl) glycine and (RS)--cyclopropyl-4-phosphonophenylglycine. In the slice preparation, eIPSC amplitude and mIPSC frequency were decreased reversibly by L-CCG-I (10⁶ M) and L-AP4 (10⁶ M). In K⁺-free or K⁺-free external solution with Ba²⁺ and Cs⁺, Ca²⁺-free or Cd²⁺ external solution, the inhibitory effect of tACPD on mIPSC frequency was unaltered. Forskolin and 8-Br-cAMP significantly increased presynaptic glycine release, and prevented the inhibitory action of tACPD on mIPSC frequency. Sp-cAMP, however, did not prevent the inhibitory action of tACPD on mIPSC frequency. It was concluded that the activation of mGluRs inhibits glycine release by reducing the action of cAMP/PKA pathway.