Responses of single unit in the caudate nucleus to thalamic stimulation

Influence of parafascicular thalamic input on neuronal activity within the nucleus accumbens is mediated by nitric oxide - an in vivo study

AIMS

Thalamostriatal fibers are involved in cognitive tasks such as acquisition, learning, processing of sensory events, and behavioral flexibility and might play a role in Parkinson's disease. The aim of the present study was the in vivo electrochemical characterization of the projection from the lateral aspect of the parafascicular thalamus (Pfl) to the dorsolateral aspect of the nucleus accumbens (dNAc). Since nitric oxide (NO) plays a crucial role in striatal synaptic transmission, its implication in Pfl-evoked signaling within the dNAc was investigated.

MAIN METHODS

The Pfl was electrically stimulated utilizing paired pulses and extracellular potentials were recorded within the dNAc. Simultaneously, the dNAc was superfused using the push-pull superfusion technique for local application of compounds and for assessing the influence of NO on release of glutamate, aspartate and GABA.

KEY FINDINGS

Stimulation of the Pfl evoked a negative-going component at 9-14 ms followed by a positive-going component at 39-48 ms. The early response was current-dependent and diminished by superfusion of the dNAc with tetrodotoxin, kynurenic acid or N(G)-nitro-l-arginine methyl ester (L-NAME), while 3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine (PAPA/NO) increased this evoked potential. Transmitter release was inhibited by L-NAME and facilitated by PAPA/NO.

SIGNIFICANCE

This study describes for the first time in vivo extracellular electrical responses of the dNAc on stimulation of the Pfl. Synaptic transmission within the dNAc on stimulation of the Pfl seems to be facilitated by NO.

Origins of post synaptic potentials evoked in spiny neostriatal projection neurons by thalamic stimulation in the rat

Stimulation of thalamic intralaminar nuclei or structures along the intrathalamic trajectory of thalamostriatal axons evoked complex EPSPs and subsequent hyperpolarizations in rat neostriatal spiny neurons identified by intracellular injection of horseradish peroxidase and/or antidromic activation from substantia nigra. In intact urethane-anesthetized rats, the initial EPSP portion of the response consisted of several components and lasted up to 75 ms. Short (1-10 ms) latency components exhibiting latency variations suggestive of a polysynaptic origin were often observed, and sometimes were the earliest components of the response. However, individual components of the excitatory response could not be clearly distinguished in most neurons and the earliest excitatory component usually appeared to be monosynaptic. After large acute aspiration lesions of ipsilateral cerebral cortex, the early polysynaptic EPSP components of thalamic-evoked EPSPs were absent or greatly attenuated. This suggested that most or all of the short latency polysynaptic EPSP components arose via a thalamo-cortico-striatal route. A short latency (1.6-4.0 ms) monosynaptic EPSP and a second excitatory component with a longer and more variable latency (8-28 ms) remained intact after acute decortication. These were not dependent upon intact corticothalamic or corticostriatal axons, since they were both still present in experiments performed as long as 4 days following ipsilateral hemidecortication. The longer latency excitatory response was shown to be polysynaptic by its latency variation with changes in stimulus intensity and frequency. This component of the response was abolished after acute thalamic hemitransections separating thalamostriatal neurons from their axons. In these experiments, stimulation of thalamostriatal axons rostral to the transection continued to evoke monosynaptic EPSPs in neostriatal spiny neurons. These EPSPs ranged from 1.8 to 3.0 ms in latency, had peak amplitudes up to 11 mV and were 20-37 ms in duration.

Electrophysiological correlates among the radial nerve, the caudate and the entopeduncular nuclei in cats

The entopeduncular nucleus (EPN), as the medial part of the globus pallidum, has been considered the efferent structure of the striatum. Based on this, we decided to study its possible somatosensory projections and the electrophysiological relationship with the caudate nucleus (CN). Radial nerve stimulation produced evoked responses (ER) in CN and EPN. The ERs recorded in EPN are of shorter latencies (11 msec) than those in CN (23 msec). Electrical stimulation of CN elicited ERs in EPN. These ERs are bigger when the stimulation sites coincide with the regions of CN where somatic stimulation also elicited ERs. The same regions of CN yielding ERs by somatic stimulation respond to EPN stimulation. The ERs recorded in EPN by radial nerve stimulation diminished when the CN was stimulated 7 msec after the radial nerve, while other intervals were less effective. The results show that the radial nerve probably has direct ipsi and contralateral projections to the EPN and a bidirectional connection between EPN and CN. We suggest a feedback response of EPN to CN stimulation, an arrangement which would be the functional basis for the central motor regulation.