Dorsal raphe nucleus stimulation modulates the response of layers IV and V barrel cortical neurons in rat

The effect of dorsal raphe nucleus (DRN) electrical stimulation on response properties of layers IV and V barrel cortical neurons was studied. To assess the receptive field characteristics of cortical neurons, responses of neurons were recorded following the displacement of principal and adjacent whiskers individually or in a condition test paradigm. Then neuronal responses to the displacement of whiskers were analyzed following DRN stimulation at 0, 50, 100, 200 and 400 ms inter-stimulation intervals. Considering On responses, DRN stimulation suppressed the response magnitude of layer V neurons to principal whisker deflection, while it slightly increased that of layer IV neurons (not statistically significant). The response latency of layer IV neurons increased when DRN was stimulated 200 or 400 ms before principal whisker deflection, while the response latency of layer V was not changed. DRN stimulation had no effect on either magnitude or latency of neuronal response to the adjacent whisker deflections. We observed a decrease in the inhibitory effect of the adjacent whisker deflection on the magnitude of neuronal response to the principal whisker deflection in layer IV when DRN was stimulated 200 ms before the principal whisker deflection. Off responses did not show any significant effect of DRN stimulation. Our results suggest a modulating role for DRN in processing of the incoming information into barrel cortex. This effect might be location dependent.