Characterization of striatal activity in conscious rats: Contribution of NMDA and AMPA/kainate receptors to both spontaneous and glutamate‐driven firing

Abstract

Single-unit activity in the striatum of unrestrained, conscious rats was characterized by extracellular recording in combination with iontophoresis. To avoid the confounding effect of motor-related changes in firing rate, measurements were restricted to periods when animals were at quiet rest. Recording electrodes were lowered stepwise through 4.0 mm of anterior striatum in 36 equal ventral movements of 111 microm to assess the ratio of spontaneously active vs. silent neurons. Spontaneous activity was assessed at each step followed by iontophoretic glutamate (GLU) application to expose silent neurons. Eleven such experimental sessions resulted in a total of 100 spontaneously active and 264 silent neurons, indicating that without overt movement the large majority (72.7%) of striatal cells are silent. Spontaneously active neurons, moreover, discharged at low rates (4.85 +/- 0.85 spikes/s). In separate experiments, both the AMPA/kainate (CNQX: 6-cyano-2,3-dihydroxy-7-nitro-quinoxaline disodium salt) and NMDA (AP5: D-(-)-2-amino-5-phosphonovaleric acid) GLU-receptor antagonists blocked the activity of most spontaneously active (83% CNQX, 69% AP5), and GLU-stimulated silent (68% CNQX, 98% AP5) units. Collectively, our results are consistent with an overall low level of striatal activity in the absence of strong excitatory input. When neuronal activity is initiated, however, it appears that both NMDA and AMPA/kainate receptors are critical for maintaining continuous impulse activity.

Dopamine-modulated dynamic cell assemblies generated by the GABAergic striatal microcircuit

“…In this approximate tonic dopamine range, Figure 7 shows the firing statistics are consistent with known properties of striatal cells. That is, MSNs are relatively quiet, while some FSIs fire strongly (Sandstrom & Rebec, 2003;Mallet et al, 2005). Figure 7 also shows that our model predicts a linear change in the firing rates of both neuron types with increasing dopamine.…”

Competition between Feedback Loops Underlies Normal and Pathological Dynamics in the Basal Ganglia

“…The role of the striatum in the dynamics of the BG network According to recent estimates (Sandstrom and Rebec, 2003;Slaght et al, 2004), most of the striatal projection neurons are Figure 12. Response of the network to external inputs in the high DA depletion condition, D ϭ 20%.…”

“…For simplicity, we take T i␣ ϭ T ␣ independently of i for ␣ ϭ Ctx, GPi, Th, STN. In contrast, we take a broad Gaussian distribution for the thresholds of the striatal neurons (average, T Str ; SD, T Str /2) to reproduce the distribution of spontaneous activity of the striatal projection neurons observed in experiments (Sandstrom and Rebec, 2003;Slaght et al, 2004), as shown in Results.…”

A Physiologically Plausible Model of Action Selection and Oscillatory Activity in the Basal Ganglia

“…Cortical input stimulates both AMPA and NMDA receptors on the postsynaptic membrane of these neurons (Sandstrom and Rebec, 2003), and the efficacy of this input is modulated by tonic levels of dopamine. As noted in the description of the basal ganglia architecture, striatal projection neurons are divided into two populations on the basis of their dominant dopamine receptor type, either D 1 or D 2 [notwithstanding evidence for some colocalization of these receptors (Surmeier et al, 1996;Aizman et al, 2000)].…”