Role of N-methyl-D-aspartate and non-N-methyl-D-aspartate receptors in the cardiovascular effects of L-glutamate microinjection into the hypothalamic paraventricular nucleus of unanesthetized rats

✍ Scribed by Cristiane Busnardo; Rodrigo F. Tavares; Fernando M.A. Corrêa

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 408 KB
• Volume: 87
• Category: Article
• ISSN: 0360-4012
• DOI: 10.1002/jnr.22028

✦ Synopsis

Abstract

We report on the cardiovascular effects of L‐glutamate (L‐glu) microinjection into the hypothalamic paraventricular nucleus (PVN) as well as the mechanisms involved in their mediation. L‐glu microinjection into the PVN caused dose‐related pressor and tachycardiac responses in unanesthetized rats. These responses were blocked by intravenous (i.v.) pretreatment with the ganglion blocker pentolinium (PE; 5 mg/kg), suggesting sympathetic mediation. Responses to L‐glu were not affected by local microinjection of the selective non‐NMDA receptor antagonist NBQX (2 nmol) or by local microinjection of the selective NMDA receptor antagonist LY235959 (LY; 2 nmol). However, the tachycardiac response was changed to a bradycardiac response after treatment with LY235959, suggesting that NMDA receptors are involved in the L‐glu heart rate response. Local pretreatment with LY235959 associated with systemic PE or dTyr(CH~2~)~5~(Me)AVP (50 μg/kg) respectively potentiated or blocked the response to L‐glu, suggesting that L‐glu responses observed after LY235959 are vasopressin mediated. The increased pressor and bradycardiac responses observed after LY + PE was blocked by subsequent i.v. treatment with the V~1~‐vasopressin receptor antagonist dTyr(CH~2~)~5~(Me)AVP, suggesting vasopressin mediation. The pressor and bradycardiac response to L‐glu microinjection into the PVN observed in animals pretreated with LY + PE was progressively inhibited and even blocked by additional pretreatment with increasing doses of NBQX (2, 10, and 20 nmol) microinjected into the PVN, suggesting its mediation by local non‐NMDA receptors. In conclusion, results suggest the existence of two glutamatergic pressor pathways in the PVN: one sympathetic pathway that is mediated by NMDA receptors and a vasopressinergic pathway that is mediated by non‐NMDA receptors. © 2009 Wiley‐Liss, Inc.