Metabotropic glutamate receptors are involved in the control of breathing at the medulla oblongata level of anaesthetized rats

The goal of the present study was to identify sites in the medulla oblongata where metabotropic glutamate receptors are involved in regulating respiration. Unilateral microinjections (50 nl) of l -glutamate ( l -glu) (10–25–50 mM) into the nucleus tractus solitarii (NTS) of anaesthetized rats elicited apnea (8.6 ± 0.3 sec; 21.3 ± 3.6 sec; 66.3 ± 16.5 sec respectively; N = 6) and arterial hypotension (7.3 ± 2.4 mmHg; 10.1 ± 2.3 mmHg; 35.3 ± 7.5 mmHg respectively; N = 6). Similarly, in other rats 1-aminocyclopentane-1, 3-dicarboxylic acid (ACPD) (1–5–10 mM), a selective agonist of metabotrophic glutamate receptors, also induced apnea (22.4 ± 2.5 sec; 32.5 ± sec; 92.5 ± 1.4 sec respectively; N = 6) and arterial hypotension (12.7 ± 2.2 mmHg; 19.6 ± 4.3 mmHg; 26.5 ± 1.5 mmHg respectively; N = 6). Paired experiments showed that unilateral microinjections of l -glu (50 mM) and ACPD (1 mM) into the nucleus retroambigualis (NRA) of anaesthetized rats elicited apnea (20.2 ± 2.6 sec and 33.8 ± 3.2 sec respectively; N = 6) and arterial hypotension (15.7 ± 3.7 mmHg and 22.5 ± 4.5 mmHg respectively; N = 6). The ACPD effects on apnea and hypotension in NTS and NRA were not prevented by a 3 min pretreatment with L-AP3 (30 mM), a putative antagonist of metabotropic glutamate receptors (19.5 ± 1.4 sec; 12.3 ± 3.2 mmHg and 30.6 ± 2.9 sec; 23.4 ± 3.8 mmHg respectively; N = 6). These data suggest that metabotropic glutamate receptors are involved in NTS and NRA regulation of cardiorespiratory functions. Moreover, these findings may also indicate that at particular doses L-AP3 could be considered a partial agonist of the metabotropic glutamate receptors in the medulla oblongata in anaesthetized rats.