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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.

Background: A physiological increase in extracellular ascorbate (AA), an antioxidant vitamin found throughout the striatum, elevates extracellular glutamate (GLU). To determine the role of behavioral arousal in this interaction, microdialysis was used to measure striatal GLU efflux in rats tested in either a lights-off or lights-on condition while reverse dialysis either maintained the concentration of AA at 250 µM or increased it to 1000 µM to approximate endogenous changes.

The effects of 6-hydroxydopamine (6-OHDA)-induced lesions of the dorsal noradrenergic bundle (DNB) were assessed in animals trained in a task designed to measure sustained attention, or vigilance. Infusions of 6-OHDA reduced frontal cortical noradrenaline contents but did not significantly affect striatal and hypothalamic noradrenaline contents. The performance of lesioned animals did not differ significantly from sham-lesioned controls. The performance of both the lesioned and sham-lesioned animals was impaired by the presentation of a visual distractor and by a decrease in the probability for a signal. The results from this study largely coincide with the results from previous studies on the effects of noradrenergic lesions on various aspects of attention. In contrast to the attentional functions assessed in this experiment, the ability to detect and select stimuli that are associated with activation of sympathetic functions is hypothesized to be sensitive to the effects of DNB lesions.