NMDA and Group I Metabotropic Glutamate Receptors Activation Modulates Substance P Release from the Arcuate Nucleus and Median Eminence

CARUSO CARLA; DURAND DANIELA; WATANOBE HAJIME; LASAGA MERCEDES

San Diego, California

Congreso; The Endocrine Society´s 87th annual meeting; 2005

The Endocrine Society

Glutamate participates in the regulation of secretion of several neuropeptides, including substance P (SP). Glutamate acts through ionotropic (iGluRS) and metabotropic (mGluRS) receptors. The iGluRS are subdivided in NMDA, kainate and AMPA receptors while mGluRs are classified into three groups. NMDA receptors have been proved to increase SP release from striatal neurons and from rat spinal cord. In order to determine if iGluRs and mGluRs receptor activation plays a role in the modulation of hypothalamic SP release in male rats, we investigated whether glutamate receptors agonists and antagonists could affect SP release from hypothalamic fragments containing the arcuate nucleus and the median eminence (ARC/ME). SP-like immunoreactivity (SP-LI) was determined by RIA. An increase in SP-LI release from ARC/ME was induced by glutamate (Control: 5.61 ±0.43 ng/mg protein; Glu 0.1 mM: 9.22 ±0.33, p0.05; Glu 1 mM: 11.33 ±1.23 p0.01) and NMDA (Control: 2.04 ±0.09, NMDA 0.1 mM: 3.93 ±0.23 p0.01, NMDA 1 mM: 5.13 ±0.61 p0.001). Hypothalamic SP-LI release induced by glutamate was prevented by DAPV (0.1 mM), a specific NMDA antagonist and by AIDA (0.1 mM), a selective antagonist of group I mGluR. The selective non-NMDA receptor antagonist, DNQX (0.1 mM) and a Group II and III mGluRs antagonis, MTPG (0.1 mM), did not affect the stimulatory effect of glutamate. A Group I selective agonist, DHPG, induced a significant increase in SP-LI release (Control: 3.11 ±0.29, DHPG 0.1 mM: 10.54 ±0.65, p0.01, DHPG 1 mM: 12.63 ±0.70 p0.01). Group II and III mGluRs agonists did not produce any changes in SP-LI release. Supporting the participation of nitric oxide (NO) in the effect of glutamate on SP-LI release, L-NAME (0.5 mM), a NO synthase inhibitor, reduced the glutamate-induced increase in SP-LI release from ARC/ME (Control: 2.72 ±0.301, Glu: 5.06 ±0.54, Glu+NAME: 3.54 ±0.19). Similarly, the stimulatory effect of glutamate was not observed in the presence of meloxicam (0.1 mM) (a cyclooxygenase-2 specific inhibitor) (Control: 4.96 ±0.39, Glu: 7.46 ±0.38, Glu+Melox: 5.52 ± 0.20) indicating that prostaglandins production may also be involved in glutamate effect. These data indicate that glutamate increases SP-LI release from the ARC/ME acting through NMDA and Group I mGluRs in the male rat. Our results also indicate that the stimulatory effect of glutamate could be mediated by nitric oxide and prostaglandins production. Supported by CONICET, UBA