Effect of phasic electrical locus coeruleus stimulation on inhibitory and excitatory receptive fields of layer V barrel cortex neurons in male rat

Introduction: It is believed that Locus Coeruleus (LC) influences the sensory information processing. However, its role in cortical surround inhibitory mechanism is not understood. In this experiment, using controlled mechanical displacement of whiskers; we investigated the effect of phasic electrical stimulation of LC on response of layer V barrel cortical neurons in anesthetized rat. Methods: LC was stimulated 0, 50, 100, 200 and 400ms before principal or adjacent whiskers deflection. For assessing the effect of LC stimulation on inhibitory receptive field of the barrel neurons, adjacent whisker was also deflected 20ms before principal whisker deflection, and LC stimulation was applied 0-400ms before principal whisker displacement. Results: We found that LC stimulation increased the response magnitude of layer V neurons to principal whisker deflection (significance level (p<0.05) at 50-400ms intervals). This increase in response magnitude was observed to adjacent whisker deflection too (significant (p<0.01) at 100ms interval). The response latency of neurons was decreased when LC was stimulated 400ms before principal whisker deflection (p<0.01). LC stimulation did not affect the neuronal response latency to adjacent whisker displacement or spontaneous activity of neurons. Inhibitory effect of adjacent whisker deflection on neuronal response magnitude was increased by LC stimulation when tested when combined whisker displacement. Conclusion: These findings suggest that LC by modulating the neuronal responses enhances the neuronal responsiveness to sensory stimuli and increases their surround inhibition in cortex.