A novel influence of adenosine on ongoing activity in rat rostral ventrolateral medulla
Section snippets
General methods
Experiments were performed on 32 male Sprague–Dawley rats (260–320 g; Royal Free Hospital, Comparative Biology Unit). Anaesthesia was induced with pentobarbitone sodium (Sagatal, May & Baker; 60 mg/kg, i.p.) and supplemented as necessary with α-chloralose (5 mg/kg, i.v.). During the surgery, anaesthesia was maintained such that a strong pinch of the paw did not evoke withdrawal of the paw and there were no spontaneous movements. All of the following procedures and protocols were carried out in
General details
This study reports on a total of 55 neurons recorded within the region of the RVLM as described anatomically by Paxinos and Watson.[15] Ten of the recorded neurons were identified as bulbospinal in that the evoked action potential on stimulation within the thoracic spinal cord had a constant latency (mean 6±1.6 ms, range 2–19 ms) and could be cancelled by collision with an ongoing occurring action potential (see Fig. 1A). The mean axonal conduction velocity of these neurons was 5±0.9 m/s.
Discussion
In the present study, neurons with a variety of electrophysiological characteristics, and inputs, have been investigated from the region of the RVLM. We have shown that ionophoretic application of adenosine and/or an adenosine receptor agonist can alter ongoing activity of these neurons and our observations suggest that several adenosine receptor subtypes are active in this region.
Some of these neurons were shown also to be spinally projecting and had some characteristics consistent with them
Conclusions
We have shown that the activity of neurons in the RVLM is modulated by adenosine acting at P1 receptors. These effects may involve more than one receptor subtype, and are likely to be mediated by an effect on neurotransmitter release in this region of the brainstem. Our data indicate that adenosine appears to have little tonic effect on RVLM neurons, since ionophoresis of adenosine receptor antagonists did not alter ongoing activity. Adenosine has long been termed a “retaliatory metabolite” and
Unlinked References
[27] is not cited in the text.[29] is not cited in the text.
Acknowledgements
We thank Miss Linda Hutchinson for technical assistance. This work was supported by the British Heart Foundation. CGS 21680 sodium salt was donated by Ciba Geigy.
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