Globus pallidus lesions inhibit the induction of c-Fos by haloperidol in the basal ganglia output nuclei in rats

Pallidal origin of GABA release within the substantia nigra pars reticulata during high-frequency stimulation of the subthalamic nucleus

High-frequency stimulation of the subthalamic nucleus (HFS-STN) is an effective treatment for alleviating the motor symptoms of parkinsonian patients. However, the neurochemical basis of its effects remains unknown. We showed previously that 1 h of HFS-STN in normal rats increases extracellular glutamate (Glu) level in the output nuclei of the STN, the globus pallidus (GP), and the substantia nigra pars reticulata (SNr), consistent with an increase in the activity of STN neurons. HFS-STN also increases GABA levels in the SNr, but the origin of this increase is unclear. We investigated the effectiveness of HFS-STN for improving Parkinson's disease symptoms, using intracerebral microdialysis to determine the extracellular Glu and GABA levels of the GP and SNr in response to HFS-STN in anesthetized hemiparkinsonian rats [6-hydroxydopamine lesion of the substantia nigra pars compacta (SNc)]. Basal levels of Glu and GABA in the GP and SNr were significantly higher in hemiparkinsonian than in intact rats. HFS-STN did not affect extracellular Glu level in the SNr of hemiparkinsonian rats but doubled the level of GABA. Ibotenic acid lesion of the GP abolished the increase in GABA levels in the SNr induced by HFS-STN in SNc-lesioned rats. These results provide neurochemical confirmation of the hyperactivity of the STN after dopaminergic denervation and suggest that the therapeutic effects of HFS-STN may result partly from the stimulation of pallidonigral fibers, thereby revealing a potential role for pallidal GABA in the inhibition of basal ganglial output structures during HFS-STN.

Induction patterns of transcription factors of the nur family (nurr1, nur77, and nor-1) by typical and atypical antipsychotics in the mouse brain: implication for their mechanism of action

Monitoring gene expression has been intensively used to identify neurobiological and neuroanatomical substrates associated with administration of antipsychotic drugs. Transcription factors of the Nur family (Nurr1, Nur77, and Nor-1) are orphan nuclear receptors that have been recently associated with dopamine neurotransmission. Nurr1 is involved in midbrain dopamine neuron development. Nur77 and Nor-1 are expressed in dopaminoceptive areas such as the striatum, nucleus accumbens, and prefrontal cortex. To better understand the relationship between Nur and antipsychotic drug effects, we conducted a comprehensive evaluation of the effect of various typical and atypical antipsychotic drugs on the modulation of Nur mRNA levels. We show that differential patterns of Nur expression can be obtained with typical and atypical antipsychotic drugs. Modulation of Nur77 and Nor-1 mRNA expression by antipsychotics can be used to calculate an index that is predictive of the typical or atypical profile of antipsychotic drugs. Inductions of Nur by anti-psychotic drugs are correlated with dopamine D2 receptor in the striatum and D2 and D3 receptor subtypes in the nucleus accumbens. The 5-hydroxytryptamine 2A/D2 affinity ratio of antipsychotics can also predict these patterns of inductions. In addition to classical gene patterns induced in the striatal complex (striatum, accumbens) and cortex, most antipsychotic drugs tested strongly induced Nur77, Nor-1, and increased Nurr1 mRNA levels in the substantia nigra and ventral tegmental area. These data suggest that typical and atypical antipsychotic drugs might induce in multiple brain regions distinct Nur-dependent transcriptional activities, which may contribute to their pharmacological effects.

Distinct roles for nigral GABA and glutamate receptors in the regulation of dendritic dopamine release under normal conditions and in response to systemic haloperidol

The regulation of dendritic dopamine release in the substantia nigra (SN) likely involves multiple mechanisms. GABA and glutamate inputs to nigrostriatal dopamine neurons exert powerful influences on dopamine neuron physiology; therefore, it is probable that GABA and glutamate likewise influence dendritic dopamine release, at least under some conditions. The present studies used in vivo microdialysis to determine the potential roles of nigral GABA and glutamate receptors in the regulation of dendritic dopamine release under normal conditions and when dopamine signaling in the basal ganglia is compromised after systemic haloperidol administration. Nigral application of the GABA(A) receptor antagonist bicuculline by reverse dialysis significantly increased spontaneous dopamine efflux in the SN. However, spontaneous dopamine efflux in the SN was not significantly affected by local application of the glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione or (+/-)-3-[2-carboxypiperazine-4-yl]-propyl-1-phosphonic acid. Systemic haloperidol administration significantly increased the extracellular dopamine measured in the SN. Blockade of nigral GABA(A) receptors by local bicuculline application did not alter this effect of systemic haloperidol, despite the bicuculline-induced increase in spontaneous dendritic dopamine efflux. In contrast, nigral application of either glutamate receptor antagonist significantly attenuated the increases in dendritic dopamine efflux elicited by systemic haloperidol. These data suggest that under normal conditions, activity of GABA afferents to SN dopamine neurons is an important determinant of the spontaneous level of dendritic dopamine release. Circuit-level changes in the basal ganglia involving an increased glutamatergic drive to the SN appear to underlie the increase in dendritic dopamine release that occurs in response to systemic haloperidol administration.

Subthalamo-pallido-striatal axis: a feedback system in the basal ganglia

Systemic administration of a dopamine D2 receptor blocker, haloperidol, but not vehicle, significantly increased the number of c-Fos-immunoreactive neurons in the globus pallidus (GP) in rats. Dual immunohistochemistry, a combination of c-Fos immunohistochemistry and retrograde tracing experiments with cholera toxin B (ChB), revealed that a subset of the c-Fos-immunoreactive GP neurons was pallidostriatal feedback neurons. Lesioning of the subthalamic nucleus (STN) by local injection of ibotenic acid inhibited the haloperidol-induced c-Fos expression in the GP neurons, suggesting that the activation of GP neurons is a result of increased excitatory drives from the STN. Therefore, the present findings are evidence of the existence of the subthalamo-pallido-striatal axis as a feedback system in the internal circuits of the basal ganglia.