Pressor and tachycardic responses evoked by microinjections of l-glutamate into the medial prefrontal cortex of unanaesthetized rats

Authors

  • L. B. M. Resstel,

    1. Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, 14049–900, Brazil
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  • F. M. A. Corrêa

    1. Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, 14049–900, Brazil
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Dr F. M. A. Corrêa, as above.
E-mail: fmdacorr@fmrp.usp.br

Abstract

The ventral medial prefrontal cortex (vMPFC) is involved in central cardiovascular control. In the present study, we studied the cardiovascular effects of injections of l-glutamate into the vMPFC of unanaesthetized rats and the mechanisms of these effects. Male Wistar rats were used and l-glutamate was microinjected in the vMPFC in a final volume of 200 nL. Microinjections of l-glutamate (9, 27, 81, 150 or 300 nmol) caused long-lasting, dose-related pressor and tachycardic responses in unanaesthetized rats. No differences were observed among cardiovascular responses when l-glutamate was injected into the three sub-areas that comprise the vMPFC, namely the prelimbic, the infralimbic and the dorsal peduncular cortices. No responses were observed when the dose of 81 nmol of l-glutamate was microinjected into surrounding structures such as the cingulate cortex area 1, the corpus callosum and the tenia tecta, indicating a predominant action on the vMPFC. The cardiovascular response to l-glutamate into the vMPFC was blocked by intravenous pretreatment with the ganglion blocker pentolinium (10 mg/kg, i.v.) or the beta1-adrenoceptor antagonist atenolol (1.5 mg/kg, i.v.), supporting the involvement of the cardiac sympathetic nervous system in the response to l-glutamate. Pretreatment with the muscarinic antagonist homatropine methyl bromide (1 mg/kg, i.v.) reduced the latency to the onset of the pressor and tachycardic responses to l-glutamate injected into the vMPFC without significant effects on response duration or maximum effect. We conclude that stimulation of the vMPFC with l-glutamate caused pressor and tachycardic responses in unanaesthetized rats, responses which were dependent on cardiac sympathetic nerve activation and were potentiated by blockade of peripheral muscarinic receptors.

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