The NMDA receptors, CB1 receptors and nitric oxide within the dorsal hippocampus modulate the cardiac baroreflex in rats

NC Ferreira-Junior, DC Lagatta, LBM Resstel. School of Medicine of Ribeirao Preto-USP, Sao Paulo, Brazil

The dorsal hippocampus (DH) influences the cardiovascular system . NMDA receptors and the nitric oxide synthase (NOS) are present within DH . Moreover, CB1 receptors can modulate the glutamatergic neurotransmission in the DH . Therefore, our goal was studying the involvement of NMDA receptors, CB1 receptors and NO into DH modulating the cardiac baroreflex. Male Wistar rats (190-240g) had bilaterally implanted cannulae into DH and catheters were implanted into both femoral artery and vein. The artery was used for recording of mean arterial pressure (MAP) and heart rate (HR). The vein was used for baroreflex activation using phenylephrine or sodium nitroprusside. The drugs microinjected into DH did not affect baseline of either MAP or HR. AP7 (10nmol), NMDA receptor antagonist, decreased the baroreflex activity. Both bradycardic (before= -2.10± 0.12 and after= -1.49± 0.09 bpm, F(2,23)= 10.73, P<0.01) and tachycardic (before= -2.74± 0.18 and after= -1.85± 0.18 bpm; F(2,23)= 8.36, P<0.01) linear regression slope was reduced. The non-linear regression slope was decreased (before= -1.84 ± 0.07 and after= -1.53± 0.07 bpm, F(2,23)= 5.71, P<0.01). AM251 (10pmol), CB1 receptor antagonist, increased the baroreflex activity. Both bradycardic (before= -1.45± 0.14 and after= -1.94± 0.13 bpm, F(2,32)= 3.84, P<0.05) and tachycardic (before= -1.92± 0.12 and after= -2.59± 0.15 bpm; F(2,32)= 3.71, P<0.05) linear regression slope was increased. The non-linear regression slope increased too (before= -0.94 ± 0.05 and after= -1.87± 0.06 bpm, F(2,32)= 98.26, P<0.01). N-Propyl (0.1nmol), inhibitor of the neuronal NO synthase, decreased the baroreflex activity. Both bradycardic (before= -2.67± 0.31 and after= -1.59± 0.21 bpm, F(2,20)= 5.93, P<0.01) and tachycardic (before= -2.56± 0.12 and after= -2.59± 0.15 bpm; F(2,20)= 3.78, P<0.05) linear regression slope was reduced. The non-linear regression slope decreased too (before= -1.59± 0.09 and after= -1.24± 0.07 bpm, F(2,20)= 4.47, P<0.05). Thus, the results show that NMDA receptors, CB1 receptors and NO into DH modulate the cardiac baroreflex activity.

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