Proceedings of The Physiological Society

University of York (2002) J Physiol 539P, S002

Communications

Recordings of ongoing activity made from sympathetic fibres innervating blood vessels of the spinotrapezius muscle in the anaesthetized rat

Steven Hudson, Christopher D. Johnson*, Andrew M. Coney and Janice M. Marshall

Department of Physiology, The Medical School, University of Birmingham, Birmingham B15 2TT, UK and *Medical Biology Centre, Queen's University, 97 Lisburn Road, Belfast BT9 7BL, Northern Ireland


Activity in the sympathetic supply to skeletal muscle has generally been recorded from fibres in the mixed nerve some distance from the muscle. We have recorded from nerve fibres on the surface of arterial vessels in the spinotrapezius muscle of the rat whose sympathetic innervation has been described in detail (Marshall, 1982).

Experiments were performed on spontaneously breathing male Wistar rats (250-350 g) anaesthetised with Saffan (7-12 mg kg-1 h-1, I.V.). All studies were carried out in accordance with the UK Animals (Scientific Procedures) Act 1986. Recordings of tracheal pressure were made via a tracheal cannula to monitor respiration. A femoral artery and vein were cannulated to allow arterial blood pressure (ABP) recordings to be made and the administration of drugs, respectively. The right spinotrapezius muscle was exteriorised and mounted ventral surface uppermost on a Perspex column set into a bath (Marshall, 1982). A border of dental impression material was constructed around the lateral border of the muscle so that a shallow pool filled with Krebs solution could be created over the muscle. By applying the focal recording technique (see Johnson & Gilbey, 1994) a glass microelectrode (tip diameter of < 40 µm) was used to record nerve activity from the surface of arterial vessels (vessel diameters 80-120 µm) of the spinotrapezius muscle. The animal was killed with an anaesthetic overdose at the end of the experiment.

Arterial vessels of the spinotrapezius have 2-3 paravascular sympathetic fibres running along side and over them and a perivascular nerve network (Marshall, 1982). Under resting conditions ongoing multiunit activity was recorded from the surface of these vessels. The different sizes of the action potentials indicated that 2-3 fibres were present. Cross-correlation histogram analysis showed the recorded nerve activity (n = 9) had strong respiratory and cardiac rhythms, showing corresponding rhythmicities with frequencies of ~1.6 and ~7 Hz, respectively, as expected of sympathetic fibres supplying skeletal muscle (Häbler et al. 1994). A bolus injection of sodium nitroprusside (60 µg kg-1 I.V.) reduced mean ABP from 117 ± 3 to 58 ± 2 mmHg and evoked a concomitant 330 ± 65 % increase in nerve activity over a 10 s period (n = 8), as expected as part of the baroreceptor reflex. Nerve activity was abolished by the short-acting autonomic ganglion blocker trimetaphan (9-10 mg kg-1 I.V.) which also induced a fall in ABP; nerve activity reappeared as ABP returned to baseline.

We propose we have developed a new method for recording the activity of sympathetic fibres supplying identified sections of the arterial tree in skeletal muscle.

We acknowledge the support of the British Heart Foundation.


Where applicable, experiments conform with Society ethical requirements