Characteristics of long-duration inhibitory postsynaptic potentials in rat neocortical neurons in vitro.
The characteristics of long-duration inhibitory postsynaptic potentials (1-IPSPs) which are evoked in rat frontal neocortical neurons by local electrical stimulation were investigated with intracellular recordings from an in vitro slice preparation. Stimulation with suprathreshold intensities evoked 1-IPSPs with typical durations of 600-900 msec at resting membrane potential. Conductance increases of 15-60% were measured at the peak amplitude of 1-IPSPs (150-250 msec poststimulus). The duration of the conductance increases during 1-IPSPs displayed a significant voltage dependence, decreasing as the membrane potential was depolarized and increasing with hyperpolarization. The reversal potential of 1-IPSPs is significantly altered by reductions in the extracellular potassium concentration. Therefore it is concluded that 1-IPSPs in rat neocortical neurons are generated by the activation of a potassium conductance. 1-IPSPs exhibit stimulation fatigue. Stimulation with a frequency of 1 Hz produces a complete fatigue of the conductance increases during 1-IPSPs after approximately 20 consecutive stimuli. Recovery from this fatigue requires minutes. 1-IPSPs are not blocked by bicuculline but are blocked by baclofen.
D000818:Animals; D002540:Cerebral Cortex / Q000502:physiology*; D004558:Electric Stimulation; D005071:Evoked Potentials; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009431:Neural Conduction; D009474:Neurons / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013569:Synapses / Q000502:physiology*