Burst Firing Induced by N-Methyl-D-Aspartate Requires Activation of an Electrogenic Sodium Pump in Rat Dopamine Neurons
In vitro, dopamine neurons in the ventral tegmental area (VTA) and substantia nigra zona compacta (SNC) fire action potentials in a regular pacemaker pattern (Sanghera et al., 1984; Johnson and North, 1992; Grace and Onn, 1989; Lacey et al., 1989). However, in vivo, dopamine neurons fire in bursts (Freeman et al., 1985; Sanghera et al., 1984). The fact that burst firing occurs in vivo but not in vitro implies that afferent connections essential for burst firing are severed in the process of cutting the brain slice (Sanghera et al., 1984). Svensson and Tung (1989) showed that cooling the pre-frontal cortex in the anesthetized rat reversibly blocked burst firing in VTA dopamine neurons. Because prefrontal cortex sends axons which contain excitatory amino acids (EAA’s) to the VTA (Christie et al., 1985), it was thought that cooling the cortex diminished the synaptic release of EAA’s onto dopamine neurons. This conclusion is supported by the findings that glutamate receptor antagonist drugs such kynurenate, 4-(3-phosphonopropyl)-2-piperazine carboxylic acid (CPP), and DL-aminophosphonovaleric acid (APV) reversibly blocked burst firing in dopamine VTA neurons recorded extracellularly in the rat (Charlety et al., 1991; Overton and Clark, 1992; Chergui et al., 1991). In this communication, we report on the mechanism of action underlying burst firing induced by N-methyl-D-aspartate (NMDA) in dopamine neurons in vitro.
KeywordsVentral Tegmental Area Excitatory Amino Acid Dopamine Neuron Tail Current Sodium Pump
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