Responses of rubrospinal neurons (RSNs) to iontophoretic applications of L-glutamate (L-Glu), L-aspartate (L-Asp), quisqualate (Quis) and N-methyl-D-aspartate (NMDA) have been studied in the rat red nucleus (RN) in vivo. All agonists produced a dose-dependent increase of the firing rate and Quis was found to be the most efficient. The responses to NMDA and to a lesser extent to L-Asp were abolished by steady application of 2-amino-5-phosphonovalerate (2APV) whereas responses to Quis were unaffected and those to L-Glu poorly antagonized. On the other hand, NMDA-mediated excitations were insensitive to steady application of 6,7-dinitroquinoxaline-2,3-dione (DNQX) which abolished responses to Quis and to a lesser extent to L-Glu while those to L-Asp were less affected. These results show the presence of both NMDA and non-NMDA receptors on RSNs in the rat. A specific localization of the NMDA receptors on distal dendrites of these neurons is suggested.
"The different effects produced on classical eyeblink conditioning by the transient inactivation of the cerebral cortex and the cerebellar IP nucleus could be explained by their different innervation of RN neurons. Cerebral cortical axonal projections seem to synapse on distal dendrites activating NMDA and non-NMDA glutamate receptors (Davies et al., 1994), while IP axons seem to terminate on non-NMDA receptors located preferentially on the soma and proximal dendrites of rubral neurons (Billard et al., 1991). Thus, and as originally proposed by Tsukahara et al. (1981), the presence of NMDA receptors could explain the delayed changes in synaptic strength taking place in rubral circuits after the inactivation of the sensorimotor cortex. "
[Show abstract][Hide abstract] ABSTRACT: The red nucleus (RN) is a midbrain premotor center that has been suggested as being involved in the acquisition and/or performance of classically conditioned nictitating membrane/eyelid responses. We recorded in rabbits the activity of RN and pararubral neurons during classical eyeblink conditioning using a delay paradigm. Neurons were identified by their antidromic activation from contralateral facial and accessory abducens nuclei and by their synaptic activation from the ipsilateral motor cortex (MC) and the contralateral cerebellar interpositus (IP) nucleus. For conditioning, we used a tone as a conditioned stimulus (CS) followed 250 ms later by a 100 ms air puff as an unconditioned stimulus (US) coterminating with it. Conditioned responses (CRs) were determined from the evoked changes in the electromyographic activity of the orbicularis oculi (OO) muscle. Recorded neurons were classified by their antidromic activation and by their changes in firing rate during the CS-US interval. Identified neurons increased their firing rates in relation to the successive conditioning sessions, but their discharge rates were related more to the EMG activity of the OO muscle than to the learning curves. Reversible inactivation of the IP nucleus with lidocaine during conditioning evoked a complete disappearance of both conditioned and unconditioned eyelid responses, and a progressive decrease in CR-related activity of RN neurons. In contrast, MC inactivation evoked a decrease in the acquisition process and an initial disfacilitation of neuronal firing (which was later recovered), together with the late appearance of CRs. Thus, RN neurons presented learning-dependent changes in activity following MC inactivation.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 08/2012; 32(35):12129-43. DOI:10.1523/JNEUROSCI.1782-12.2012 · 6.34 Impact Factor
"There is ample evidence suggesting that L-glutamate and L-aspartate are the endogenous transmitters of these pathways (Altmann et al., 1976; Rouget et al., 1993). Electrophysiological (Billard et al., 1991; Sanner et al., 1994), immunocytochemical (Martin et al., 1993; Petrelia and Wenthold, 1992), and in situ hybridization data (Sato et al., 1993; Watanabe et al., 1994) suggested that RN neurons express ionotropic glutamate receptors (GluRs) of the N-methyl-Daspartate (NMDA) and a-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA) subtypes. In addition, different types of voltage-gated currents were described in RN neurons (Kubota et al., 1985). "
[Show abstract][Hide abstract] ABSTRACT: The red nucleus (RN) has been widely used to study the formation and remodeling of synaptic connections during development and in post-lesion plasticity. Since glial cells are thought to contribute to synaptic plasticity, and information on functional properties of brain stem glia is missing, we analyzed voltage-gated ion channels as well as glutamate receptors expressed by glial cells of the RN. The patch-clamp technique was applied to identified cells in acute brain stem slices of 5- to 12-days-old rats. Based on their pattern of membrane currents, two types of glial cells could be distinguished. A first type was characterized by passive, symmetrical currents. The second population of cells, which was the focus of the present study, expressed a complex pattern of voltage-gated channels. These cells could be labeled with antibodies against glutamine synthetase and S100 beta, suggesting an astroglial origin. Depolarizing voltage steps activated transient and delayed rectifier K+ currents as well as Na+ currents. In addition, a subset of cells expressed Ba2+ sensitive inward rectifier K+ currents activated by hyperpolarization. All "complex" glial cells analyzed possessed ionotropic glutamate receptors of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype, while functional kainate and N-methyl-D-aspartate (NMDA) receptors could not be detected. Receptor activation blocked outward rectifying K+ currents, similar to previous observations in glial cells of the hippocampus and the corpus callosum.
[Show abstract][Hide abstract] ABSTRACT: NMDA receptors play key roles in synaptic plasticity and neuronal development, and may be involved in learning, memory, and compensation following injury. A polyclonal antibody that recognizes four of seven splice variants of NMDAR1 was made using a C-terminus peptide (30 amino acid residues). NMDAR1 is the major NMDA receptor subunit, found in most or all NMDA receptor complexes. On immunoblots, this antibody labeled a single major band migrating at M(r) = 120,000. The antibody did not cross-react with extracts from transfected cells expressing other glutamate receptor subunits, nor did it label non-neuronal tissues. Immunostained vibratome sections of rat tissue showed labeling in many neurons in most structures in the brain, as well as in the cervical spinal cord, dorsal root and vestibular ganglia, and in pineal and pituitary glands. Staining was moderate to dense in the olfactory bulb, neocortex, striatum, some thalamic and hypothalamic nuclei, the colliculi, and many reticular, sensory, and motor neurons of the brainstem and spinal cord. The densest stained cells included the pyramidal and hilar neurons of the CA3 region of the hippocampus, Purkinje cells of the cerebellum, supraoptic and magnocellular paraventricular neurons of the hypothalamus, inferior olive, red nucleus, lateral reticular nucleus, peripheral dorsal cochlear nucleus, and motor nuclei of the lower brainstem and spinal cord. Ultrastructural localization of immunostaining was examined in the hippocampus, cerebral cortex, and cerebellar cortex. The major staining was in postsynaptic densities apposed by unstained presynaptic terminals with round or mainly round vesicles, and in associated dendrites. The pattern of staining matched that of previous in situ hybridization but differed somewhat from that of binding studies, implying that multiple types of NMDA receptors exist. Comparison with previous studies of localization of other glutamate receptor types revealed that NMDAR1 may colocalize with these other types in many neurons throughout the nervous system.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 03/1994; 14(2):667-96. · 6.34 Impact Factor
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