FUNCTIONAL-PROPERTIES OF AMPA AND NMDA RECEPTORS EXPRESSED IN IDENTIFIED TYPES OF BASAL GANGLIA NEURONS

AMPA- and NMDA-type glutamate receptors (AMPARs and NMDARs) mediate ex citatory synaptic transmission in the basal ganglia and may contribute to excitotoxic injury. We investigated the functional properties of A MPAR's and NMDARs expressed by six main types of basal ganglia neurons in acute rat brain slices (principal neurons and cholinergic interneu rons of striatum, GABAergic and dopaminergic neurons of substantia nig ra, globus pallidus neurons, and subthalamic nucleus neurons) using fa st application of glutamate to nucleated and outside-out membrane patc hes. AMPARs in different types of basal ganglia neurons were functiona lly distinct. Those expressed in striatal principal neurons exhibited the slowest gating (desensitization time constant tau = 11.5 msec, 1 m M glutamate, 22 degrees C), whereas those in striatal cholinergic inte rneurons showed the fastest gating (desensitization time constant tau = 3.6 msec). The lowest Ca2+ permeability of AMPARs was observed in ni gral dopaminergic neurons (P-Ca/P-Na = 0.10), whereas the highest Ca2 permeability was found in subthalamic nucleus neurons (P-Ca/P-Na = 1. 17). NMDARs of different types of basal ganglia neurons were less vari able in their functional properties; those expressed in nigral dopamin ergic neurons exhibited the slowest gating (deactivation time constant of predominant fast component tau(1) = 150 msec, 100 mu M glutamate), and those of globus pallidus neurons showed the fastest gating (tau(1 ) = 67 msec). The Mg2+ block of NMDARs was similar; the average chord conductance ratio g(-60mV)/g(+40mV) was 0.18-0.22 in 100 mu M external Mg2+. Hence, AMPARs expressed in different types of basal ganglia neu rons are markedly diverse, whereas NMDARs are less variable in functio nal properties that are relevant for excitatory synaptic transmission and neuronal vulnerability.