Increases in intracavernous penile pressure following injections of excitatory amino acid receptor agonists in the hypothalamic paraventricular nucleus of anesthetized rats

Purpose: We examined whether N-methyl-D-aspartate (NMDA), amino-3-hydroxy-5 -methyl-isoxazole-4-propionic acid (AMPA) or trans-1-amino-1,3-cyclo-pentad icarboxylic acid (ACPD) increase intracavernous pressures when injected in the paraventricular nucleus of the hypothalamus. Materials and Methods: Sprague-Dawley rats weighing 250 to 300 gm. were ane sthetized with pentobarbital and placed in a stereotaxic apparatus after ca theterization of the carotid artery and insertion of a 25 gauge needle in t he corpus cavernosum. Both catheters were coupled to pressure transducer sy stems. Electrical stimulations with glass tungsten microelectrodes and chem ical injections with a 0.5 mu l. syringe were done in the paraventricular n ucleus. At the end of each experiment rats were perfused with saline and 10 % formalin solutions. Brains slices 16 mu m. thick were mounted and stained with cresyl violet to identify chemical and electrical stimulation sites. Results: Electrical stimulations of the paraventricular nucleus increased i ntracavernous pressure from 15.5 +/- 5.7 to 50.02 +/- 20.4 cm. H2O in 10 ra ts (p <0.001) and decreased central pressure in 10 (p <0.001). Intracaverno us pressure increased from 17.2 +/- 5.26 to 60.6 +/- 14.36 cm. H2O with NMD A, 26.0 +/- 8.9 to 49.6 +/- 12.2 cm. H2O with AMPA and 18.0 +/- 2.3 to 41.0 +/- 22.68 cm. H2O with ACPD when injected in the paraventricular nucleus o f 5 rats (analysis of variance 12.18, df 3, p <0.007). Mean delays and dura tions varied between 3.6 to 4.0 and 5.6 to 7.0, respectively, and were simi lar for all agonists (analysis of variance not significant). Conclusions: Glutamate receptor subtypes NMDA, ACPD and AMPA cause an incre ase in intracavernous pressure when injected in the paraventricular nucleus . Therefore, increases in intracavernous pressure following injection of gl utamate must be initiated by the synergistic or additive effects of all of these receptor subtypes.