strychnine and 4-trans-2-carboxy-5-7-dichloro-4-phenylaminocarbonylamino-1-2-3-4-tetrahydroquinoline

The nucleus of the tractus solitarius (NTS) plays an important role in the control of several autonomic reflex functions and has glutamate and GABA as main neurotransmitters. In this work, we used patch-clamp recordings in transverse slice preparations from rats to study whether the glycine binding site of the N-methyl-D-aspartate (NMDA) receptor is saturated or not in neurons of the subpostremal NTS. Except at hyperpolarized voltages and close to the reversal potential, glycine potentiated the NMDA responses in a concentration-dependent manner. The total charge transferred by glutamatergic currents was enhanced by glycine (500 microM; from 28 +/- 13 to 42 +/- 18 pC at +50 mV, n = 7, P < 0.05). Glycine increased the conductance of the postsynaptic membrane, without altering its reversal potential, both in the presence (from 2.4 +/- 0.06 to 3.4 +/- 0.09 nS; n = 7) and absence (from 3.1 +/- 0.06 to 4.4 +/- 0.10 nS; n = 8) of Mg2+ in the bathing solution. d-serine, in the presence of strychnine, also increased the amplitude of the NMDA component (by 68 +/- 19%, P < 0.05, n = 5). The membrane potential was hyperpolarized (16 +/- 6 mV, n = 8) by glycine, suggesting the presence of inhibitory glycinergic receptors. Our results indicate that the glycine site of the NMDA receptor in neurons of the subpostremal NTS is not saturated and that glycine may act as a modulator of the NMDA transmission in this nucleus.

Topics: Aminoquinolines; Animals; Animals, Newborn; Binding Sites; Dose-Response Relationship, Drug; Electric Stimulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Glycine; Glycine Agents; In Vitro Techniques; Membrane Potentials; N-Methylaspartate; Neurons; Patch-Clamp Techniques; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Serine; Solitary Nucleus; Strychnine; Synapses

Experimental lesions followed by binding of [3H]4-trans-2-carboxy-5,7-dichloro-4-phenylamino-carbonylamino-1,2 ,3,4- tetrahydroquinoline ([3H]L-689,560, a novel ligand that binds to the glycine modulatory site), [3H]glycine and [3H]glutamate (N-methyl-D-aspartate (NMDA) sensitive) to cryostat sections and quantitative autoradiography were used to investigate the cellular localization of the NMDA receptor complex in the neocortex of the rat. The lesions were produced by intrastriatal injections of either volkensin (2 and 6 ng) or ricin (10 ng): both are suicide transport agents but only the former is retrogradely transported in the CNS. The binding of [3H]L-689,560 was significantly reduced in rats receiving 2 or 6 ng volkensin in deep cortical layers of Fr1/Fr2 ipsilateral to the striatal lesion. Similar reductions were also seen in [3H]glycine and [3H]glutamate binding, but only in rats receiving 6 ng volkensin. Quantitative histological analysis had previously revealed a loss of large infragranular pyramidal neurones with sparing of both interneurones and supragranular pyramidal neurones. There were no significant reductions in binding of any ligand in the superficial layers. In cortical areas Par1/Par2, [3H]L-689,560 was also significantly reduced in deep layers but only in rats receiving 6 ng volkensin. Binding was also reduced in the superficial layers by contrast to Fr1/Fr2. [3H]Glycine and [3H]glutamate binding were unaffected in this area. Binding of [3H]L-689,560 was unaffected in any area following intrastriatal ricin injection. The present study indicates that the NMDA receptor complex is present on pyramidal cells forming the corticofugal pathways. This is discussed in terms of the 5-HT1A receptor which is enriched on these cells.

Topics: Aminoquinolines; Animals; Autoradiography; Cerebral Cortex; Glutamates; Glutamic Acid; Glycine; Male; N-Methylaspartate; Neural Pathways; Neurons, Efferent; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Strychnine; Tritium