Noradrenergic Effects on Activity of Prefrontal Cortical Neurons in Behaving Monkeys

Abstract

This chapter summarizes that iontophoretic application of the α 2 -receptor antagonist yohimbine to prefrontal neurons in the monkey attenuated delay-period activity, indicating that activation of α 2 receptors plays a critical role in maintaining the directional or mnemonic coding of prefrontal neurons. Of 57 neurons recorded during oculomotor delayed-response (ODR) performance, the researchers concentrate on 31 neurons that showed delay-period activity of which magnitude differed significantly with the direction of cue-response, because such directional delay-period activity has been suggested to play a central role in the working memory process for visuospatial information. These neurons are located in the principal sulcus or immediately adjacent cortex. It has been demonstrated that iontophoretic application of the selective α 2 -adrenergic receptor antagonist, yohimbine, attenuate the directional delay-period activity of prefrontal neurons during ODR performance. At the same time, yohimbine attenuated the sharpness of directional tuning, examined by fitting to a cosine function, of directional delay-period activity. These findings suggest that the activation of α 2 receptors plays a modulatory role in maintaining the directional tuning of delay-period activity of prefrontal cortical neurons during ODR performance. As the directional delay-period activity with tuning is considered to represent mnemonic coding for visuospatial working memory, it can be concluded that the activation of α 2 receptor plays a modulatory role in maintaining mnemonic coding of neuronal activity for the working-memory process in primate prefrontal cortex.