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

Abstract

Although, area postrema (AP) as been implicated in the regulation of cardiovascular function, there is no consensus regarding the type of responses elicited by stimulation of this brain structure. Microinjections (50 nl) of smaller concentrations of excitatory amino acid receptor agonists (e.g., NMDA, KA and trans-ACPD, 10 μM each) into the AP elicited pressor and tachycardic responses in unanesthetized decerebrate as well as urethane-anesthetized rats. Microinjections of higher concentrations (e.g., 50 μM NMDA) of excitatory amino acids (EAAs) into the AP elicited an initial pressor and tachycardic response which was followed by a depressor and bradycardic response; when high concentrations of NMDA were microinjected into the AP, enough concentration may have reached the nucleus tractus solitarius (nTS) to elicit depressor and bradycardic responses. Alternatively, high concentrations of NMDA may excite known projections from AP to the nTS.