Regulation of striatal nitric oxide synthesis by local dopamine and glutamate interactions

Abstract

Nitric oxide (NO) is a key neuromodulator of corticostriatal synaptic transmission. We have shown previously that dopamine (DA) D1/5 receptor stimulation facilitates neuronal NO synthase (nNOS) activity in the intact striatum. To study the impact of local manipulations of D1/5 and glutamatergic NMDA receptors on striatal nNOS activity, we combined the techniques of in vivo amperometry and reverse microdialysis. Striatal NO efflux was monitored proximal to the microdialysis probe in urethane-anesthetized rats during local infusion of vehicle or drug. NO efflux elicited by systemic administration of SKF-81297 was blocked following intrastriatal infusion of: (i) the D1/5 receptor antagonist SCH-23390, (ii) the nNOS inhibitor 7-nitroindazole, (iii) the non-specific ionotropic glutamate receptor antagonist kynurenic acid, and (iv) the selective NMDA receptor antagonist 3-phosphonopropyl-piperazine-2-carboxylic acid. Glycine co-perfusion did not affect SKF-81297-induced NO efflux. Furthermore, intrastriatal infusion of SKF-81297 potentiated NO efflux evoked during electrical stimulation of the motor cortex. The facilitatory effects of cortical stimulation and SKF-81297 were both blocked by intrastriatal infusion of SCH-23390, indicating that striatal D1/5 receptor activation is necessary for the activation of nNOS by corticostriatal afferents. These studies demonstrate for the first time that reciprocal DA-glutamate interactions play a critical role in stimulating striatal nNOS activity.

Figure 1. Position of implants in the frontal cortex and dorsal striatum

A) Stimulating electrodes were implanted into the frontal cortex. B) NO microsensors were implanted into the striatum in close proximity to a microdialysis probe. Abbreviations: ac, anterior commissure; CX, frontal cortex; LV, lateral ventrical; CC, corpus callosum.

Figure 2. Facilitation of nNOS activity elicited via DA D1/5 receptor stimulation is dependent on NMDA receptor co-activation

A) Representative recordings showing the effects of systemic administration of the D1/5 receptor agonist SKF (500 μg/kg, i.v.) delivered following intrastriatal infusion (120 min) of either aCSF, SCH (10 μM), or 7-NI (300 μM). Dotted line indicates time of SKF-81297 injection. B) Representative recordings showing the effects of systemic administration of the D1/5 receptor agonist SKF (500 μg/kg, i.v.) delivered following intrastriatal infusion of either KYN (100 nM), CPP (100 μM), or GLY (1 mM). Dotted line indicates time of SKF injection. C) The mean ± S.E.M. increase in NO efflux evoked by DA D1/5 receptor activation was significantly reduced following intrastriatal infusion of SCH, 7-NI, KYN, CPP (*p<0.05 as compared to SKF+aCSF group using ANOVA with Dunnett's post-hoc test, n=5–6 rats/group), but not GLY (p>0.05, n=4 rats).

Figure 3. Intrastriatal infusion of D1/5 agonist increases NO efflux evoked via train stimulation of the frontal cortex

A) Representative traces of cortically-evoked NO efflux recorded prior to, and 10–20 (#1) or 30–40 (#2) min following intrastriatal SKF (5 μM for 10 min) infusion. Electrical stimuli were delivered for 100 sec as trains (30 Hz, 750 μA, 800 ms train duration, 2 sec inter-train interval) and all stimulations were separated by >15 min. B) The mean ± S.E.M. increase in NO efflux evoked by cortical train stimulation was transiently potentiated by intrastriatal infusion of SKF (*p<0.05 as compared to pre-SKF group using one-way ANOVA with Bonferroni post-hoc test, n=6 rats).

Figure 4. Intrastriatal infusion of D1/5 antagonist attenuates NO efflux evoked via train stimulation of the frontal cortex and blocks the facilitatory effects of D1/5 agonism

A) Recordings of NO efflux evoked prior to, and following, intrastriatal SCH infusion. Electrical stimuli were delivered as described above. B) Representative traces of NO efflux evoked approximately 90 mins following intrastriatal SCH (100 μM) infusion and 10–20 and 30–40 min following intrastriatal SKF infusion (5 μM for 10 min). Electrical stimuli were delivered as described above. C) The mean ± S.E.M. increase in NO efflux evoked by cortical train stimulation was significantly attenuated following SCH infusion as compared to pre-drug conditions (**p<0.001 as compared to pre-SKF group using one-way ANOVA with Bonferroni post-hoc test, n=5 rats). The mean ± S.E.M. increase in NO efflux evoked by cortical train stimulation applied during intrastriatal SKF infusion was significantly attenuated at both time points as compared to pre-drug conditions (**p<0.001 as compared to pre-SKF group using one-way ANOVA with Bonferroni post-hoc test, n=5 rats). No significant differences in measures of NO efflux were observed during SCH and SCH+SKF infusion periods.