Validation of a novel technique allowing assessment of the functional role of cardiac prejunctional receptors in the rat.
1. The electrical stimulation of the thoracic portion of the spinal cord (preganglionic nerve fibres) in the pithed rat is a widely used technique to investigate drug effects on the sympathetic nervous system. However, it does not allow discrimination between ganglionic and neuronal ending sites of action of drugs. This report describes and validates an experimental approach in which postganglionic nerve fibres are stimulated in pithed rats, thereby overcoming the above mentioned difficulty. 2. Electrical stimulation of a nerve below the thymus gland produced frequency-related increases in heart rate which were not modified by the ganglion blockers, hexamethonium or mecamylamine, but were reduced by the beta 1-adrenoceptor antagonist, betaxolol. Thus, the studied nerve fibres can be classified as sympathetic postganglionic neurons. 3. The parameters for electrical stimulation of postganglionic cardioaccelerator nerve fibres giving optimal responses were of similar pulse widths as required for the stimulation of the thoracic spinal cord, but of lower strength of current, higher frequencies and shorter stimulation times to achieve steady-state responses. 4. Clonidine reduced the tachycardia evoked by sustained electrical stimulation of postganglionic cardioaccelerator nerve fibres. This effect was antagonized entirely by the selective alpha 2-adrenoceptor antagonist, idazoxan. Therefore, sympathetic cardiac postganglionic nerve fibres are endowed with alpha 2-adrenoceptors.
Cavero
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I
Laboratoire d'Etudes et de Recherches Synthélabo, Paris, France.
Thiry
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C
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology; D004558:Electric Stimulation; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D009469:Neuromuscular Junction / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology; D013950:Thymus Gland / Q000187:drug effects / Q000502:physiology
D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D001285:Atropine; D003000:Clonidine