Buffer Nerve Reflexes in Barbiturate Anaesthesia

Douglas, William Wilton (1949) Buffer Nerve Reflexes in Barbiturate Anaesthesia. MD thesis, University of Glasgow.

Abstract

Following upon the observation that electrical stimulation of the central end of the vagus nerve caused a rise of blood pressure in a cat overdosed with nembutal, experiments have been carried out to analyse the phenomenon, which is referred to as the 'reversed' response. Part 1. The anatomical and functional considerations are first presented in some detail and their complexity indicated. The author's work is then set out in two sections. In the first are described the experiments forming the main theme of the investigation which culminate in a broad interpretation of the 'reversed' response. In the second are discussed various other aspects of the buffer nerve reflexes which have been studied, including a more detailed consideration of the mechanism of the 'reversed' response. Part 11. The original observation is confirmed by experiment, and 'reversed' responses to vagal stimulation Chap. 1. achieved by administration of excess nembutal. It is found that the drug has a similar effect on the normal depressor response to stimulation of the more purely 'moderator' sinus nerve. The effect of nembutal on these Chap. II. two buffer nerve reflexes is then discussed in greater detail, and the transition from the normal to the abnormal response is shown to involve Chap. III. intermediate stages which are dependent on the method method of dosage. Single massive doses cause periods of complete absence of any response whatsoever, despite the fact that during this areflexic stage the afferent sympathetic mechanism is active. This mode of administration most readily effects a 'reversal', and the total nembutal required (including the anaesthetizing dose) is then about 60 mg/Kg. body weight, although less may be required in the case of the sinus nerve. When similar, or even greater amounts are given slowly - either intravenously or by repeated small intraperitoneal injections - biphasic effects appear and 'reversed' responses are less readily gained. The abnormal buffer nerve responses revert spontaneously to normal after some time, but can be readily regained by additional nembutal. Having firmly established the effect of nembutal, the Chap. IV. barbiturate antidote picrotoxin is then studied. It is found rapidly to restore the depressor response in the overdosed animal, the transition responses being similar to those encountered in spontaneous reversion. The antagonism is reciprocal. , for the 'reversed' response can be regained by subsequent administration of nembutal, and again abolished by picrotoxin. The antidotal effect of picrotoxin on the buffer nerve reflexes may occur without any other evidence of its analeptic actions. The mechanism of action of the two drugs, Chap. V. is further pursued by studies involving serial section of the brain stem in the decerebrate preparation, and they are shown to be effective even when all brain matter above/ above the eighth nerve is removed. It is concluded that the locus of action of both nembutal and picrotoxin responsible for the vasomotor phenomena under discussion, lies at or below the known medullary vasomotor centres. With this established, attention is focussed on the afferent sinus nerve mechanisms, Chap. VI. for it is found that in addition to the classical depressor response, stimulation of that nerve readily elicits a pressor effect in the cat normally (lightly) anaesthetized with nembutal. No such effect lias been previously described, and this fact, coupled with the knowledge that nembutal in excess reverses the normal response, suggests that it might be due to the anaesthetic. Nevertheless, since this pressor response is obtained regularly with stimulus intensities less than those effective in lowering the blood pressure, it is considered as possibly a function of the stimulus. Experiments on the unanaesthetized decerebrate preparation confirm the Chap. VII. latter view, pressor effects being very prominent with less powerful stimuli. It is essential, therefore, that an analysis of the sinus nerve responses be made before the results observed in nembutal overdosage can be Chap. VIII. interpreted. (Abstract shortened by ProQuest.).

• Item Type: Thesis (MD)
• Qualification Level: Doctoral
• Keywords: Medicine, Surgery
• Date of Award: 1949
• Depositing User: Enlighten Team
• Unique ID: glathesis:1949-79717
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 03 Mar 2020 10:44
• Last Modified: 03 Mar 2020 10:44
• URI: https://theses.gla.ac.uk/id/eprint/79717