title: Release of [3H]L-glutamine acid (L-Glu) and [3H]D-aspartic acid (D-Asp) in the area of nucleus tractus solitarius in vivo produced by stimulation of the vagus nerve.
abstract: We have investigated the effects of bilateral electrical stimulation of the vagus nerves in anesthetized, paralyzed rats on the release of exogenously administered [3H]L-glutamic acid ([3H]L-Glu) or [3H]D-aspartic acid ([3H]D-Asp) from the intermediate portion of the nucleus tractus solitarius (NTS). Electrical stimulation of afferent fibers with the frequency, pulse, duration, and intensity required to activate C-fibers, elicited hypotension and bradycardia. Such stimuli induced the release of [3H]L-Glu, or its stable analogue [3H]D-Asp, from the NTS into perfusate collected through push-pull cannulae. The release of radioactive materials, calculated as a percent of increase in radioactivity above the prestimulation level, was for [3H]L-Glu 114.4 +/- 25.1% (n = 20) during bilateral vagal stimulation, and 45.6 +/- 11.3% (n = 9) (P less than 0.001) during unilateral stimulation. The release of [3H]D-Asp induced by bilateral vagal stimulation was 100.4 +/- 31.9%. The release, which was anatomically specific and restricted to the NTS, was directly related to stimulus (and hence reflex) intensity. Overflow of the inert substances [14C]urea OR [14C]sucrose, co-administered with the [3H] amino acids, did not increase at the same time. Local depolarization of the cells in the NTS by K+ (53mM) increased the overflow of [3H]L-Glu, as well as [14C]urea, and was able to induce the release of [3H]L-Glu when electrical stimulation failed to have an effect. The results are consistent with the hypothesis that L-Glu is a neurotransmitter of neurons in the NTS mediating vasodepressor response from vagal afferents, including those from systemic baroreceptors.
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000502:physiology*; D001794:Blood Pressure; D004558:Electric Stimulation; D005971:Glutamates / Q000502:physiology*; D018698:Glutamic Acid; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D018377:Neurotransmitter Agents; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000502:physiology; D009435:Synaptic Transmission; D014630:Vagus Nerve / Q000502:physiology*
chemical_list: D005971:Glutamates; D018377:Neurotransmitter Agents; D001224:Aspartic Acid; D018698:Glutamic Acid; D011188:Potassium