Chemical ablation of the hypothalamic arcuate nucleus and its effect on electroencephalographic tracings and pain threshold in the tail flick test

  The present study was carried out to explore the possible involvement of the arcuate nucleus of the hypothalamus in the inhibitory descending pain control system associated with the tail flick test and EEG recordings. Adult male (NMRI) albino rats weighing 200 ± 20 g were used. Rats were divided into three groups: experimental, sham and control. The arcuate nucleus was destroyed unilaterally by kianic acid under general anesthesia in the experimental group. In the sham-operated group, a vehicle of kianic acid was administered unilaterally to the arcuate nucleus while the control group was left intact. EEG rhythms were recorded by implanting electrodes placed on the frontal and occipital areas of the skull. Following the recovery period, pain threshold was measured by the tail flick test along with and without EEG recording. The results following unilateral chemical lesions of the arcuate nucleus showed a decreased pain threshold when compared to the sham and control groups. EEG recording and mean frequency showed no significant changes before and after noxious stimulation. Comparison of the EEG recordings before and after pain induction in the experimental, sham and control groups showed a significant reduction in alpha rhythm and also a significant increase in delta rhythm and mean frequency following noxious stimulation. Beta and theta rhythms showed no significant changes.