Differential Effects of the Lateral Hypothalamus Lesion as an Origin of Orexin and Blockade of Orexin-1 Receptor in the Orbitoftontal Cortex and Anterior Cingulate Cortex on Their Neuronal Activity

Several studies revealed that orexins may take part in the regulation of the different forms of affective and cognitive processes during wakefulness. The orbitofrontal cortex (OFC) and anterior cingulate cortex (ACC) as an important part of the prefrontal cortex (PFC) have a crucial role in cognitive processes such as reward and decision-making and has a high density of orexin receptor type 1 (OX1Rs). In the present study, to find out the role of OX1Rs in the OFC neurons firing rate, the OX1Rs were inhibited in this area after a10-min baseline recording. In the second part, the lateral hypothalamus (LH) as the main source of orexinergic neurons was inhibited and its effect on the firing rate and activity pattern of the ACC or OFC neurons were detected by using single-unit recording technique in the rats. Results showed that blockade of OX1Rs in the OFC could excite 8 and inhibit 1 neuron out of 11. Besides, the blockade of OX1Rs in the ACC could excite 6 and inhibit 3 neurons out of 10. Also, LH inactivation excited 5 out of 12 neurons and inhibited 6 neurons in the ACC. It excited 8 and inhibited 6 neurons out of 14 in the OFC. These data suggested that blockade of the OX1Rs excited 72% of the neurons, but LH inactivation had an exciting effect on just 50% of neurons in two main subregions of PFC. It seems that the PFC neurons receive the orexinergic inputs from the LH and indirectly from other sources.