Medial prefrontal cortex modulation of the baroreflex parasympathetic component in the rat

The ventral portion of the medial prefrontal cortex (vMPFC) that comprises the prelimbic and infralimbic cortex is involved in arterial blood pressure and heart rate control. In the present study, we attempted to verify the effect of an acute and reversible blockade of vMPFC activity by local bilateral microinjections of either lidocaine (a local anesthetic) or CoCl2 (a nonselective synapse blocker) on the baroreflex response of unanesthetized rats. Bilateral microinjection of lidocaine into the vMPFC did not affect the tachycardiac response to mean arterial pressure (MAP) decreases caused by i.v. infusion of sodium nitroprusside or the baroreflex gain in unanesthetized rats. However, lidocaine caused a reversible shift of the reflex threshold pressure toward higher (MAP) increases in response to i.v. infusion Of phenylephrine, thus indicating an action on the parasympathetic component of the baroreflex. The effects of the blockade of local synapses in the vMPFC by COCl2 were similar to those observed after the acute ablation of that area caused by lidocaine. Bilateral microinjection Of CoCl2 into the vMPFC also caused a shift of the reflex threshold pressure bradycardiac responses to MAP increases toward higher MAP values, without affecting the baroreflex gain. In conclusion, our data indicate that the vMPFC is involved in baroreflex control, and more specifically in the modulation of the parasympathetic baroreflex component. The temporary ablation of this area by local microinjections of lidocaine caused a shift of the reflex threshold pressure toward higher MAP values, which is compatible with the idea that the vMPFC has a modulatory action on the baroreflex. The observation that CoCl2 and lidocaine microinjections had similar effects on the baroreflex also suggests that this modulation involves local synaptic neurotransmission within the vMPFC. (C) 2004 Elsevier B.V. All rights reserved.