Release of neuropeptide Y and noradrenaline during afferent nerve stimulation

Interaction between somatic and vagal afferent inputs in control of ventilation in 2-week-old rabbits

Effects of saphenous nerve stimulation (SNS) on the Hering-Breuer expiratory-promoting reflex evoked by a positive tracheal pressure (PTR; 5 cmH2O) and on the diaphragmatic EMG (EMG(DI)), inspiratory (TI) and expiratory (TE) time, were studied in 16 urethane-anesthetized (1.2-1.6 g/kg, i.p.) spontaneously breathing 2-week-old rabbits. Positive P(TR) applied at the end of T(I) increased the subsequent TE to 255+/-29% (+/-S.E.; P < 0.0001) of control. SNS (1 sec train, 2 msec pulse, 6 Hz) applied at the onset of TE, shortened this TE by 42+/-3% (P < 0.0001). When SNS preceded positive PTR or positive PTR preceded SNS, the TE increased to 163+/-20 and 184+/-21% of control, respectively. These responses were not different, and smaller than that provoked by the PTR test alone (P < 0.003 and 0.05, respectively). The results show that in newborns somatic afferent stimulation attenuates the vagally mediated respiratory inhibition, whether immediately before or during the vagal stimulation.

Effect of losartan on afferent nerve stimulation

The present study was undertaken to investigate the effects of losartan, a non-peptide angiotensin II subtype 1 (AT1) receptor antagonist, on both the pressor responses elicited by stimulation of afferent vagal nociceptive fibres and the involvement of the sympathetic nervous system (evaluated by plasma levels of noradrenaline and its co-neurotransmitter neuropeptide Y) in dogs. Electrical stimulation of the afferent fibres of the vagus (1, 5, 10 and 20 Hz) elicited a frequency-dependent increase in blood pressure and heart rate. Plasma noradrenaline levels only increased after stimulation at frequencies of 10 and 20 Hz. Plasma neuropeptide Y levels did not change. Losartan (10 mg/kg i.v.) induced both a decrease in resting blood pressure and an increase in basal plasma levels of noradrenaline and neuropeptide Y. Losartan failed to modify the magnitude of the electrically-evoked pressor and positive chronotropic responses. The angiotensin AT1 receptor antagonist elicited a fall in plasma noradrenaline values after a 1 Hz stimulation and abolished the increase in plasma noradrenaline levels induced by the 10 (but not 20) Hz stimulation. The data suggest that angiotensin AT1 receptors are not directly involved in acute pressor responses induced by stimulation of afferent vagal fibres. Moreover, the results show that, besides its sympatho-inhibitory effect, losartan can exert a sympatho-excitatory action as shown by the increase in the plasma levels of both noradrenaline and its coneurotransmitter, neuropeptide Y.

Trypsin enhances sympathetic neuron-dependent plasma extravasation in the rat knee joint

Perfusion of 6-hydroxydopamine through the rat knee joint causes an increase in plasma extravasation by activation of sympathetic neuron terminals. Similarly, the increase in plasma extravasation in the rat knee joint produced by the inflammatory mediator bradykinin is dependent on the sympathetic post-ganglion neuron. There is evidence that both 6-hydroxydopamine and bradykinin release a number of mediators, some of which appear to enhance plasma extravasation and some which inhibit it. We attempted to determine the nature of inhibitory factor(s) by co-infusing trypsin (which rapidly cleaves peptides) with 6-hydroxydopamine. We observed a marked enhancement of 6-hydroxydopamine-induced plasma extravasation by trypsin. This effect appeared to be specific to neurogenic plasma extravasation since trypsin alone had little effect on plasma extravasation and trypsin did not affect non-neurogenic plasma extravasation (that produced by platelet activating factor). Taken together, the data suggests that 6-hydroxydopamine not only releases mediators from the sympathetic neuron that produce plasma extravasation, but also an inhibitor(s) of plasma extravasation that is peptide in nature.