Electrical stimulation of locus coeruleus strengthens the surround inhibition in layer V barrel cortex in rat

It is believed that locus coeruleus (LC) influences the sensory information processing. However, its role in cortical surround inhibitory mechanism is not well established. In this experiment, using controlled mechanical displacement of whiskers; we investigated the effect of electrical stimulation of LC on response of layer V barrel cortical neurons in anesthetized rat. LC was stimulated 0, 50, 100, 200 and 400 ms before principal or adjacent whiskers deflection. For assessing the effect of LC stimulation on inhibitory receptive filed of barrel neurons, adjacent whisker was also deflected 20 ms before principal whisker deflection, and LC stimulation was applied 0-400 ms before principal whisker displacement. We found that LC stimulation increase the response magnitude of layer V neurons to principal whisker deflection (significant in 50-400 ms intervals). This increase was also observed in response to adjacent whisker deflection (significant in 100 ms interval). The response latency of neurons was decreased when LC was stimulated 400 ms before principal whisker deflection but LC stimulation did not affect the neuronal response latency to adjacent whisker displacement. Inhibitory effect of adjacent whisker deflection on neuronal response magnitude was increased by LC stimulation, tested in combined whisker displacement. These findings suggest that LC, by modulating the neuronal responses, enhances the neuronal responsiveness to sensory stimuli and increases their surround inhibition in cortex.