Long-term Potentiation of Polysynaptic Responses in Layer V of the Sensorimotor Cortex Induced by Theta-patterned Tetanization in the Awake Rat

Werk, Christine M.
Chapman, C. Andrew

Center for Studies in Behavioral Neurobiology, Department of Psychology, Concordia University, Montréal, Québec, Canada H3G 1M8

Address correspondence to C.A. Chapman, Center for Studies in Behavioral Neurobiology, Department of Psychology, Concordia University, Montréal, Québec, Canada H3G 1M8. Email: [email protected].

Cerebral Cortex 13(5):p 500-507, May 2003.

Although the neocortex in awake, adult animals is resistant to the induction of long-term potentiation (LTP), synaptic potentiation may be enhanced by rhythmic patterns of activation that evoke short- term synaptic facilitation effects. The effectiveness of stimulation patterned after the theta (4–12 Hz) EEG rhythm for the induction of LTP of sensorimotor cortex responses to corpus callosum stimu- lation was assessed in vivo by inducing LTP using either high- frequency (300 Hz) trains or paired trains delivered at a 100 ms (10 Hz) interval. High-frequency trains caused a reduction of the early field potential component, reflecting a potentiation of direct layer V activation, and a potentiation of the late component, reflecting enhanced polysynaptic activation in layer V. Paired trains resulted in a much larger potentiation of polysynaptic responses than was observed following 300 Hz trains. To determine if short-term facilitation effects contributed to the enhanced LTP induction by theta-patterned trains, facilitation effects induced by the trains were challenged with NMDA receptor antagonists. NMDA-receptor antagonism reduced responses to single pulses, and also reduced facilitated responses evoked by theta-patterned stimulation. The effectiveness of theta-patterned stimulation for the induction of LTP of layer V polysynaptic responses is therefore likely due to frequency-dependent synaptic facilitation effects that enhance NMDA receptor activation.