Functional and anatomical connection between the paraventricular nucleus of the thalamus and dopamine fibers of the nucleus accumbens.

The shell of the nucleus accumbens (NacSh) receives a dense innervation from dopamine (DA) neurons in the ventral tegmental area (VTA) and from glutamate neurons in the paraventricular nucleus of the thalamus (PVT). The present study examined in urethane-anesthetized rats the effects of electrical stimulation of the PVT on DA levels in the NacSh as measured with amperometry and chronoamperometry. Stimulation of the PVT (40 Hz, 1.0 ms, 400 microA, 5 seconds) resulted in a brief increase in electrochemical currents detected in the NacSh. Inhibition of DA neurons in the VTA using lidocaine (4%, 500 nL) or intravenous apomorphine (0.15 mg/kg) decreased the resting voltammetric signal but had no effect on PVT-evoked responses. Blocking of ionotropic glutamate receptors in the NacSh with local administration of kynurenic acid attenuated the PVT-evoked responses. Anterograde tracing with biotinylated dextran amine demonstrated that PVT targets regions of very dense tyrosine hydroxylase fiber staining in the NacSh. Consistent with the projection pattern of the PVT to the NacSh, stimulation of the PVT evoked the largest oxidation current changes in the NacSh, whereas small or no changes were elicited in other areas of the striatum. This study suggests that glutamate release from PVT terminals can act on ionotropic glutamate receptors in the NacSh to induce DA efflux. Modulation of DA levels in the NacSh by the PVT may be linked to arousal-induced increases in DA tone and could be involved in the facilitation of specific behavioral patterns associated with arousal or stressful situations.