Ta. Lovick et al., MODULATION OF THE CARDIOVASCULAR DEFENSE RESPONSE BY LOW-FREQUENCY STIMULATION OF A DEEP SOMATIC NERVE IN RATS, Journal of the autonomic nervous system, 50(3), 1995, pp. 347-354
In rats anaesthetised with alphaxalone/alphadolone, electrical stimula
tion in the dorsal part of the periaqueductal grey matter (FAG) produc
ed a presser response with tachycardia and vasodilatation in the hind
limb, a pattern known as the 'cardiovascular defence reaction' owing t
o its resemblance to fear-induced hemodynamic changes. Following a 20-
min period of stimulation of the peroneal nerve at 10 Hz with current
intensities sufficient to recruit group II and III fibres the presser
component of the response was significantly reduced compared to contro
l rats. The maximum decrease of the PAG-evoked pressor response was ab
out 50% (from 32.0 +/- 0.7 to 16.6 +/- 15.9 mmHg). The effect lasted f
or between 60 and 290 min and was not correlated to baseline blood pre
ssure changes observed after the stimulation of the nerve. In contrast
, the tachycardia and hind limb vasodilator components of the defence
response as well as their baseline values remained unchanged. Resting
blood pressure did not change significantly in control rats but showed
a small progressive increase in stimulated rats which reached signifi
cance 90-100 min after the stimulation. These results suggest that the
afferent input from high threshold fibres in a muscle nerve can produ
ce a selective and long-lasting depression of the vasoconstrictor comp
onents of the midbrain-evoked cardiovascular defence response. This ef
fect is discussed in relation to the long-lasting sympathoinhibitory e
ffects of acupuncture-like stimulation or sustained physical exercise.