Aim: 

Stimulation of the dl-PAG in rats evokes a cardiorespiratory response characterised by tachypnoea, tachycardia and hypertension. In previous studies we have shown a functional interaction between the A5 region and the dl-PAG.

Methods: 

In order to characterize the role of glutamate in the cardiorespiratory response to dl-PAG stimulation, experiments were carried out in spontaneously breathing anaesthetized rats (sodium pentobarbitone 60 mg/kg i.p, suplemented with 20 mg/Kg ip.). The cardiorespiratory response evoked by electrical stimulation of the dl-PAG (1ms pulses, 20-50 mA, given at 100 Hz, during 5s) was analysed before and after the microinjection of Kinurenic acid (5-10nmol), DAP-5 (1pmol), MCPG (0,1nmol) and CNQX (1pmol) within the A5 region.

Results: 

Microinjection of Kinurenic acid decreased the intensity of the respiratory response (p<0.05) and tachycardia (p<0.05) to dl-PAG stimulation. No changes were observed in the pressor response. The inhibition of no-NMDA receptors with CNQX reduced the increase of respiratory frequency and heart rate to dl-PAG stimulation (p<0.05, p<0.001 respectively). No changes were observed in the pressor response. The inhibition of NMDA receptors with DAP-5 or metabotropic receptors with MCPG reduced the increase of heart rate to dl-PAG stimulation (p<0.05; p<0.01 respectively). No changes were observed in the pressor and respiratory responses.

Conclusion: 

These results confirm a role of glutamate in the A5 region for the modulation of the cardiorespiratory responses evoked from the dl-PAG and shows that the ventrolateral pons plays an important role in the neuronal circuits of respiratory and heart rate control.

Supported by DGESIC PM99-0163