Effects of basal forebrain stimulation on the distribution of cholinergic receptors in the sensorimotor cortex of rat brain

Abstract

In this thesis, the effects of basal forebrain stimulation on the distirbution of α4 and α7 type nicotinic acetylcholine receptors were studied in three different brain areas: primary motor cortex, hindlimb somatosensory cortex and barrel field somatosensory cortex. Basal forebrain, the main source of cholinergic inputs, was electrically stimulated (for each trial: 0.5-ms bipolar pulses with 50 µA, at 100 Hz for 0.5 s). In total, the experiment was carried out with 12000 pulses and it took 4 hours. After stimulation, transcardially perfusion was applied, and their brains were used for immunofluorescence staining. According to hemisphere in which the stimulation was applied and histological sections were obtained, the animals were separated into three experimental groups: control (no stimulation, n=7), ipsilateral (same hemisphere as stimulation, n=7) and contralateral (opposite hemisphere of stimulation, n=7). The results show that basal forebrain stimulation has a significant effect on the distribution of only α7 type nicotinic acetylcholine receptor. Ipsilateral and contralateral groups are statistically different from control group but there is no difference between ipsilateral and contralateral experimental groups. Specifically the number of receptor α7 complexes and their density of receptor complexes (normalized with layer thicknesses) were increased significantly with respect to control. Additionally, the number of α7 type receptor complexes and the density in primary motor cortex were mostly lower than those in the hindlimb area and barrel field of primary somatosensory cortex. A similar finding was found for only α4 type receptor count but not for the density. Overall, this thesis shows anatomical evience for cholinergic modulation of somatosensory system. The results may be important for understanding attentional processes, and neuropsychiatric diseases which affect them.|Keywords : Somatosensory, Cholinergic system, Attention, Nicotinic acetylcholine receptor.