Peripheral Blood Perfusion Induced By Electrical Stimulation Of The Anterior Cingulate Cortex

In the last decade, much research has implicated the anterior cingulate cortex (ACC) in the modulation of both emotion and visceral functions in primates and rats. Rat studies have shown that electrical stimulation of the ACC suppresses animal’s behaviors associated with noxious stimuli, and inhibits spinal cord dorsal horn neuron activity induced by nociception in the periphery. Electrical stimulation of the periaqueductal grey (PAG) is reported to inhibit spinal cord dorsal horn neuron activity induced by nociception, while it generates dorsal root reflex (DRR). This is an important contributor to peripheral vasodilatation, i.e. leading to increased blood flow. The purpose of the present study is to investigate whether electrical stimulation of the ACC will evoke DRR, which would provide some evidence of communication between the ACC and the PAG involved in inhibition of nociception. Preliminary experiments indicated no change of DRR after electrical stimulation of the ACC. However, a biphase change of cutaneous blood perfusion was associated with the stimulation. During the 60 second stimulation and right after the stimulation (around 100 seconds), there was a decrease in blood perfusion, followed by a long-term increase which could last up to 2 hours. The current experiment seeks to validate the possible contribution of lateral hypothalamus (LH) to the bi-phase change of blood perfusion induced by electrical stimulation of the ACC. The influence of peripheral sympathetic fibers might be involved, because 1) in skin, sympathetic fibers are the major factor on vasoconstriction, i.e. leading to decreased blood flow; 2) in intact animals, sympathetic fibers help maintain the volume of blood vessels by means of conducting spontaneous action potentials. In the rat brain, much of the literature suggests that the LH is a core region involved in regulating the autonomic nervous system, including the sympathetic branch. Therefore, the hypothesis is that the change of cutaneous blood perfusion induced by electrical stimulation of the ACC is attenuated or diminished in unilateral- LH-lesion rats. Result of the experiment fails to detect significant difference in the biphase peripheral blood perfusion between intact and lesion groups. This suggests that 1) unilateral LH lesion might not have sufficient influence on the change of blood perfusion induced by the ACC stimulation; 2) electrical stimulation of the ACC might evoke distinct neural pathway from the PAG stimulation; 3) direct projection from the ACC to the rostral ventrolateral medulla (rVLM), and peripheral interaction between primary afferent fibers and sympathetic fibers might account for the bi-phase change of blood perfusion induced by electrical stimulation of the ACC.