Desensitization and deactivation kinetics of AMPA receptors in motoneurons and dorsal horn neurons. A,B, Examples of responses evoked by 100 msec (A) and 1 msec (B) applications of 3 mm glutamate to nucleated macropatches from a motoneuron and a dorsal horn neuron, in 145 mmNa⁺ at −60 mV. The time of agonist application is indicated above each current trace by thejunction potential trace recorded after disrupting the patch after recording (see Materials and Methods). C, The bar graph shows the mean time constants determined from exponential fits to data as illustrated in A andB. Desensitization kinetics were measured by fitting the decay of responses to 100 msec glutamate applications with the sum of two exponentials (n = 14 motoneurons and 14 dorsal horn neurons); τ_des(fast) and τ_des (slow) are the time constants of the fast and slow components of desensitization, respectively. Deactivation kinetics were determined from the decay of the response to a 1 msec application of glutamate fitted with a single exponential with time constant τ_deact (n = 11 motoneurons and 9 dorsal horn neurons). There were no significant differences in the time constants of desensitization and deactivation between the two cell groups.