GABAB modulation of neuronal activity related to visually guided movement in the monkey premotor cortex

Activity of different classes of neurons of the motor cortex during locomotion

This study examines the activity of different classes of neurons of the motor cortex in the rabbit during two locomotion tasks: a simple (on a flat surface) and a complex (overstepping a series of barriers) locomotion. Four classes of efferent neurons were studied: corticocortical (CC) neurons with ipsilateral projection (CCIs), those with contralateral projection (CCCs), descending corticofugal neurons of layer V (CF5s), and those of layer VI (CF6s). In addition, one class of inhibitory interneurons (SINs) was investigated. CF5 neurons and SINs were the only groups that were strongly active during locomotion. In most of these neurons a clear-cut modulation of discharge in the locomotion rhythm was observed. During simple locomotion, CF5s and SINs were preferentially active in opposite phases of the step cycle, suggesting that SINs contribute to formation of the step-related pattern of CF5s. Transition from simple to complex locomotion was associated with changes of the discharge pattern of the majority of CF5 neurons and SINs. In contrast to CF5 neurons, other classes of efferent neurons (CCI, CCC, CF6) were much less active during both simple and complex locomotion. That suggests that CC interactions, both within a hemisphere (mediated by CCIs) and between hemispheres (mediated by CCCs), as well as corticothalamic interactions via CF6 neurons are not essential for motor coordination during either simple or complex locomotion tasks.

Alpha-2 adrenergic modulation of prefrontal cortical neuronal activity related to a visual discrimination task with GO and NO-GO performances in monkeys

The effects of clonidine (a selective agonist for alpha-2 receptor) and B-HT920 (an agonist for both alpha-2 and D2 receptors) were examined iontophoretically on neurons in the prefrontal cortex of three monkeys performing a visual discrimination task with GO and NO-GO responses. A total of 212 task-related neurons were sampled, of which 120 neurons were related to the visual signals (visually-related neurons; 32 neurons were related to the warning signal, 45 to the GO signal and 43 to the NO-GO signal), 34 neurons were related to both the GO signal and GO response ('intermediate'-related neurons), and 58 neurons were related to GO response (movement-related neurons). Clonidine and B-HT920 were tested in 137 and 115 neurons, respectively, and showed mainly a facilitatory effect on the neurons. Clonidine enhanced the visually-related activity in 83.0% of modulated neurons, the intermediate-related activity in 81.0% neurons and the movement-related activity in 85.0% neurons. Similarly, B-HT920 enhanced the visually-related activity in 80.0% of modulated neurons, the intermediate-related activity in 77.8% neurons and the movement-related activity in 81.0% neurons. The facilitatory effect of clonidine or B-HT920 on the visually-related activity was stronger than that on the movement-related activity. In 22 visually-related neurons enhanced by clonidine and-or B-HT920 (6 WS-, 7 GS- and 9 NS-related neurons), the alpha-2 antagonist yohimbine suppressed the visually-related activities. In 13 neurons enhanced by B-HT920, the facilitatory effect of B-HT920 was blocked by yohimbine, but not by the D2 antagonist sulpiride. The present results suggest that alpha-2 adrenoceptors in the monkey prefrontal cortex are involved in neural processing related to visual discrimination and selection of GO and NO-GO responses, and that the facilitatory effect of B-HT920 may be mediated vis alpha-2 adrenoceptors instead of D2-receptors.