Proceedings of The Physiological Society

University College Cork (2004) J Physiol 560P, PC8

Communications

SINO-AORTIC AFFERENTS (SAAS) AND POSITIVE PRESSURE VENTILATION (PPV) RELATED SYMPATHETIC MUSCLE AND THERMOREGULATORY VASOCONSTRICTOR RHYTHMS IN ANAESTHETISED RATS

Huang,Chunhua ; Marina,N. ; Gilbey,Michael Phillip;

1. Department of Physiology, UCL, London, United Kingdom.


Häbler et al. (1993; 1996) frequently observed PPV-related (PPVR) modulation of preganglionic cervical sympathetic activity that was abolished by sino-aortic denervation (SAD), whereas few postganglionic vasoconstrictor neurones supplying hairy skin or muscle (MVC) had similar characteristics under comparable conditions. In contrast, rhythmic discharges at PPV frequency (fPPV) were observed in sympathetic vasoconstrictor fibres regulating thermoregulatory circulations (CVCs: Chang et al. 2000 & Häbler et al. 1999). Here we analyse the simultaneously recorded activity of MVCs and CVCs for such rhythmic discharges and the involvement of SAAs. Sprague-Dawley rats (male, 260-340g; n=6) were anaesthetised (sodium pentobarbitone 60 mg kg-1 I.P.; supplemented with α-chloralose (5-10 mg I.V.) as required until humane killing with anaesthetic I.V.) and vagotomised. Three rats were additionally SAD. Simultaneous population recordings (glass suction electrodes) were made from a gastrocnemius nerve (GN, MVC activity) and an ipsilateral tibial nerve at a point distal to the main muscle branches 'plantar' branch (TNp activity typical of CVCs) (Huang & Gilbey, 2003). GN and TNp activities were abolished following ganglionic blockade (trimetaphan, 12mg.kg-1). Rats were in central apnoea (hypocapnic) and fPPV was manipulated (0.8-2.0 Hz; stroke volume, 2 ml). Autospectra and coherence spectra were computed from rectified and smoothed nerve activities (τ=20ms), arterial blood pressure (BP) and tracheal pressure (TP) (see Chang et al. 2000). In SAA intact group TP-GN and TP-TNp coherences increased as fPPV decreased: a linear relationship was indicated (regression analysis, TNp data: 16 pts, slope -0.55±0.08 (S.E., p<0.001) r2 = 0.76; GN data: 16 pts, slope -0.39±0.10 (p=0.02), r2 = 0.52. Following SAD this relationship ceased (32 pts,GN & TNp data pooled, slope -0.008±0.10 (p>0.09), r2 = 0.11). In SAA intact group, as fPPV was decreased the power in BP autospectrum at fPPV increased (non-linear regression analysis, 16 pts, Y=A*XB+C*XD; Runs test, P=0.90; best fit, A, B, C and D values = 0.64, -2.63, -0.15 and -0.40). Linear correlation analysis (Spearson r) indicated that BP wave and nerve activity power at fPPV were correlated (BP_TNp, 14 pts, r=0.89, p<0.0001; BP_GN, 14 pts, r=0.67, p<0.01). In SAA intact group there was a peak at heart rate frequency (fHR) in GN, but not TNp autospectra. The data support the hypothesis that PPVR variations in SAA inputs, secondary to BP oscillations, contribute to MVC and CVC PPVR rhythms. Such modulation of CVC activity occurs in the absence of a peak in autospectra at fHR.

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