Probable neurophysiological and neurochemical mechanisms of the pyrogenic reaction evoked by introduction of a bacterial toxin into rats

Abstract

Intraperitoneal injection of 5 µg/kg lipopolysaccharide (LPS) of Escherichia coli in acute experiments on anesthetized rats under thermostabilized conditions (26°C) led to an increase in the frequency of multineuronal afferent impulsation in the n. vagus (recording at the cervical level); this increase began 10 min after injection and was preserved until the end of the observation period (160 min). Injection of apyrogenic physiological saline (APS) did not influence the above parameter. Rectal temperature (RT) increased 130 min after injection of LPS, as compared with the control (injection of APS), by 2.5°C, on average, and remained increased until the end of the recording period. Under these conditions, the activities of NADPh diaphorase, lactate dehydrogenase, succinate dehydrogenase, and acetylcholinesterase (cytochemical measurements) in neurons of the nucl. tractus solitarius (NTS) increased. A blocker of synthesis of nitric oxide, L-NAME (25 mg/kg), when injected i.p. 30 min before injection of 5 µg/kg LPS, prevented intensification of afferent impulsation in the n. vagus and a rise in RT. In this case, the activity of enzymes of energetic metabolism and intensity of synthesis of NO in neurons of the NTS decreased. The data obtained allow us to hypothesize that NO functions as a modulator in the central and peripheral thermoregulatory mechanisms.