Evidence in favor of a neurotransmitter role of glycine in the rat cerebral cortex

Abstract In the present study we analyze whether glycine satisfies some electrophysiological and biochemical criteria to consider it as a putative transmitter in the rat cerebral cortex. Intracellular recordings from rat sensory-motor cortex showed that in 15–20% of the tested neurons glycine hyperpolarized the cell membrane, decreased the firing rate and flattened the evoked EPSP-IPSP sequence by increasing the membrane conductance. The iontophoretic application of strychnine antagonized the block of ‘spontaneous’ firing and the membrane hyperpolarization induced by glycine. Moreover, in a group of neurons, strychnine decreased the amplitude and duration of the IPSP and brought back the membrane potential to resting values. Previously accumulated [ 3 H]glycine and endogenous glycine were released from cortical synaptosomal preparations by depolarizing stimuli in a Ca 2+ -dependent way. The release pattern of glycine was qualitatively similar in cortical and in spinal synaptosomes. [ 14 C]Glycine was rapidly synthetized from [ 14 C]serine in cortical synaptosomal preparations, and the newly formed [ 14 C]glycine was released by depolarizing stimuli in a Ca 2+ -dependent way. It is concluded that glycine, which is generally considered as an inhibitory neurotransmitter in the spinal cord, medulla and pons, may also have a transmitter role in a discrete number of cortical neurons of some mammalian species.