Cardiovascular responses to microinjections of excitatory amino acids intothe area postrema of the rat

Although, area postrema (AP) as been implicated in the regulation of cardio vascular function, there is no consensus regarding the type of responses el icited by stimulation of this brain structure. Microinjections (50 nl) of s maller concentrations of excitatory amino acid receptor agonists (e.g., NMD A, KA and trans-ACPD, 10 mu M each) into the AP elicited presser and tachyc ardic responses in unanesthetized decerebrate as well as urethane-anestheti zed rats. Microinjections of higher concentrations (e.g., 50 mu M NMDA) of excitatory amino acids (EAAs) into the AP elicited an initial pressor and t achycardic response which was followed by a depressor and bradycardic respo nse; when high concentrations of NMDA were microinjected into the AP, enoug h concentration may have reached the nucleus tractus solitarius (nTS) to el icit depressor and bradycardic responses. Alternatively, high concentration s of NMDA may excite known projections from AP to the nTS. (C) 1999 Elsevie r Science B.V. Ail rights reserved.