The mapped pattern of kainate on blood pressure responses is similar to that of l-proline in the ventrolateral medulla of the rat

Kainate is an excitatory amino acid receptor agonist with a structure similar to the amino acid l-proline. Our previous studies demonstrated that microinjections of l-proline into the ventrolateral medulla (VLM) of the rat induce a mapped pattern of blood pressure responses distinct from l-glutamate, and the depressor response to l-proline in the caudal VLM (CVLM) is abolished by the kainate/AMPA receptor antagonist CNQX. The present study investigated whether kainate produces the l-proline-mapped pattern of responses in the VLM, compared with the pattern by AMPA. Kainate is known to activate AMPA receptors at higher concentrations. Therefore, responses to kainate were investigated at a low concentration. Microinjections of AMPA or NMDA showed the pattern of the l-glutamate-type; a pressor response in the rostral VLM and caudal pressor area (CPA) and a depressor response in the CVLM. Microinjections of kainate showed depressor responses in the CVLM but minor pressor responses in the rostral VLM, suggesting the same responses to l-proline. However, the response sites in the CPA did not enable us to clearly determine the l-proline-type. Further trials at sites defined by a pressor response to l-glutamate in the CPA, successive injections of l-proline and kainate produced no response, indicating that l-glutamate responding neurons in the CPA are not sensitive to l-proline and kainate. These results suggest that kainate stimulation in the VLM produces a mapped pattern of ABP responses similar to the mapped pattern with l-proline. Kainate receptors could therefore be involved in the depressor response to l-proline in the medulla.