Preganglionic sympathetic activity in normal and in reserpine‐treated cats

Abstract

Reserpine causes a loss of noradrenaline and of 5-hydroxytryptamine from the brain, and many attempts have been made to correlate the clinical effects of reserpine with this loss. One of the difficulties in attempting such a correlation lies in the lack of knowledge about the part played by noradrenaline and 5-hydroxytryptamine in normal brain function. Regions containing the central representation of the sympathetic system (hypothalamus, reticular formation of mid-brain and of medulla) are rich in both these amines. If the stores of the amines have an essential role in central sympathetic activity, one might expect such activity to be impaired after the administration of reserpine. The following observations would appear to support such a possibility: peripheral adrenergic neurones fail to excite the tissues they innervate when reserpine has reduced their stores of amines to 10 % or less (Muscholl & Vogt, 1958); continued sympathetic activity, elicited by drugs which stimulate the sympathetic centres, is accompanied by a reduction in the noradrenaline content of these centres, a fact which demonstrates some connexion between nervous activity and noradrenaline turnover (Vogt, 1954).The object of this work, on which a preliminary note has been published (Iggo & Vogt, 1959), was to test central sympathetic activity in cats in which reserpine administration had reduced the cerebral noradrenaline and 5-hydroxytryptamine to very low figures. Efferent discharge of the preganglionic fibres of the cervical sympathetic was used as a measure of central sympathetic activity. In order to assess possible changes produced by reserpine, it was necessary first to observe the preganglionic sympathetic activity of normal cats in the same experimental conditions, and to devise some simple means of eliciting reproducible changes in activity.

The Effect of Pithing and of Nerve Stimulation on the Depletion of Noradrenaline by Reserpine in the Rat Anococcygeus Muscle and Vas Deferens

“…For example, the main difference between the heart and the other two tissues is in the rate of depletion rather than the extent of depletion eventually achieved. It is known that there is a continuous discharge in the sympathetic nerves to the heart (Bronk, Ferguson, Margaria & Solandt, 1936) and that this is reflexly increased as reserpine lowers systemic blood pressure (Iggo & Vogt, 1960 (Holzbauer & Vogt, 1956;Karki et al, 1959;Hertting et al, 1959;Mirkin, 1961;Benmiloud & Euler, 1963). One conflicting report is that of Sj6strand & Swedin (1968) who found that pre-ganglionic hypogastric section had no effect on the NA depletion of the vas deferens by reserpine.…”

Effect of Clonidine on Blood Pressure, Heart Rate and Body Temperature in Conscious Rats

“…Reduction of the bradycardia to clonidine is, however, partly due to an antagonism of the presynaptic inhibition of the drug on the cardiac sympathetic nerve terminals by an a-adrenoceptor blocking agent (20,21). Reserpine shows a significant potentiation of the bradycardia to clonidine in conscious rats and this potentiation is con sidered to be caused by summation of the activities of the baroceptor-vagal reflex with a combination of clonidine and reserpinc, since it is well known that reserpine itself causes a vagal stimulation as a result of the increase in the central parasympathetic activity (22)(23)(24)(25).…”

The reflex effects of alterations in lung volume on systemic vascular resistance in the dog

“…A respiratory rhythm has also been observed in the cervical and abdominal sympathetic nerves, but was found to persist after cutting the vagus nerves (Adrian, Bronk & Phillips, 1932;Tang, Maire & Amassian, 1957). It was ascribed to an irradiation of impulses from the respiratory centre to the vasomotor centre by Adrian et al (1932) and to the reflex effects of the changes in arterial baroreceptor activity engendered by respiratory variations in blood pressure by others (Tang et al 1957;Iggo & Vogt, 1960). There is clearly a need here for further studies of this problem under controlled conditions.…”