Activity Of Postganglionic Neurons Research Articles

Chronotropic and dromotropic responses to localized glutamate microinjections in the rat nucleus ambiguus

The cardioinhibitory effects of cardiac vagal motoneurons (CVMs) are mediated by activation of postganglionic neurons in the epicardial ganglia which have been shown to exert functionally selective effects on heart rate and atrioventricular conduction in the rat. Here we investigate whether CVMs producing these responses may occupy different rostrocaudal positions within the nucleus ambiguus. Excitation of CVMs was attempted by microinjections of glutamate into the nucleus ambiguus of an arterially perfused preparation in a grid extending over 2mm in the rostrocaudal plane using the obex as a reference point. Microinjections were paired, one made during pacing to measure changes in atrioventricular conduction (P-R interval) independent of changes in heart rate and the other looking for changes in heart period (P-P interval) un-paced. Although evidence of a differential distribution was found in 7 cases, in the majority (13/20), sites producing maximal effects on both variables coincided. Maximal changes in atrioventricular conduction resulted from more rostral sites in 6 cases and from a more caudal site in only one. Overall, the ratio of the change in atrioventricular conduction to the change in heart rate for a given site was significantly greater 1mm rostral to the obex than at either end of the test grid. We conclude that while CVMs controlling atrioventricular conduction are distributed with a peak somewhat rostral to those controlling heart rate in a number of animals, there is a significant overlap and much greater variability in this distribution in the rat than in cats and dogs.

Stability of enzymatic indicators of metabolic and neuronal activity in post-ganglionic neurons supplying the urinary tract of aged rats

Aged post-ganglionic neurons supplying the urinary tract exhibit stability in their metabolic and functional status, as demonstrated by quantification of enzyme histochemical reaction products. The major pelvic and thirteenth thoracic (T13) ganglia from 4- and 24-month-old male Wistar rats were incubated under standardized conditions to demonstrate succinate dehydrogenase, NADH-tetrazolium reductase and cytochrome oxidase activities. The amount of reaction product for each enzyme, localized in neuronal perikarya throughout the ganglia, was quantified by microdensitometry. Comparison of mean totals demonstrated stability of all three enzymes with age in both the major pelvic and T13 ganglia and in target organs. Also, the distribution and range of reaction product densities were similar. In both ganglia, the number of NADH-tetrazolium reductase-stained neurons per unit area was reduced in the aged animals. Additionally, nicotinic (DMPP) and muscarinic (McN-A-343) agonists were used to mimic the effects of preganglionic stimulation in the major pelvic ganglia before performing enzyme histochemical reaction. Quantification of these activities demonstrated that the response of aged neurons to preganglionic stimulation was unchanged. These results indicate an overall metabolic stability in post-ganglionic autonomic neurons innervating the urinary tract and in their targets in aged rats. © 1998 Chapman & Hall

Respiratory modulation of the activity in postganglionic neurons supplying skeletal muscle and skin of the rat hindlimb.

1. The respiratory modulation of activity in postganglionic neurons of the lumbar sympathetic outflow to skeletal muscle and hairy skin of the hindlimb was studied in anesthetized rats, either breathing spontaneously or paralyzed and artificially ventilated, using single- and multifiber recordings. The activity of the neurons was analyzed with respect to the phrenic nerve discharges or with respect to the cycle of artificial ventilation under various experimental conditions. 2. In total, 19 single and 62 multiunit preparations supplying skeletal muscle and 42 single and 95 multiunit preparations supplying skin were analyzed. Qualitatively, both populations and single- and multiunit preparations exhibited similar patterns. The majority (187/218 preparations) exhibited a depression of activity during inspiration and a peak of activity during expiration that was mostly accentuated during early expiration. The remainder exhibited a peak of activity at the transition between expiration and inspiration (n = 15) or showed no respiratory modulation (n = 16). 3. Respiratory modulation in the postganglionic neurons was similar in animals breathing spontaneously and in those that were paralyzed and artificially ventilated. 4. Systemic hypercapnia and asphyxia in most cases enhanced both the peak of activity during early expiration and the depression of activity during inspiration. 5. No peripheral (reflex) component mediated by arterial baroreceptors was found in vagotomized animals that was related to the cycle of artificial ventilation using a tidal volume of 1-2 ml and a ventilation frequency of 70 +/- 7 (SD) strokes, min-1. However, a small ventilation-related rhythm of arterial baroreceptor activity recorded from the aortic nerve was found under these conditions. 6. Respiratory modulation of postganglionic activity was similar before and after bilateral vagotomy. 7. It is concluded that respiratory modulation of sympathetic activity in rats is less differentiated than in cats. The observed differences between neurons supplying different targets are only quantitative. Possible mechanisms involved in the generation of respiratory modulation are discussed.

Discharge patterns of sympathetic neurons supplying skeletal muscle and skin in man and cat

Skeletal muscle and skin of humans and cats are supplied by various sympathetic systems: vasoconstrictor neurons, sudomotor neurons, vasodilator neurons and pilomotor neurons. Only vasoconstrictor and sudomotor neurons have resting activity in both species. Discharge patterns of spontaneous activity in postganglionic neurons with resting activity as well as their reflex responses to various stimuli have been compared for both species: (1) muscle vasoconstrictor neurons react similarly in both species; they are under dominant control of arterial baroreceptors; (2) in both species cutaneous vasoconstrictor neurons are under no or weak control of arterial baroreceptors and they are influenced in similar ways by thermal stimuli. In contrast, other (somatic and visceral) stimuli elicit largely inhibition in these neurons in cats but excitation in humans. This may be due to the different experimental situations (anesthesia, etc.); (3) sudomotor neurons in humans are involved in thermoregulation, in cats they are not. The differences in the reflexes may also be due to the different experimental situations and to species differences; (4) the implications of studies on sympathetic neurons in humans and animals for the progress of research in this field have been discussed.