Interactive effects of cholecystokinin-8S and various serotonin receptor agonists on the firing activity of neostriatal neuronesin rats

Interaction between the 5-HT system and the basal ganglia: functional implication and therapeutic perspective in Parkinson's disease

The neurotransmitter serotonin (5-HT) has a multifaceted function in the modulation of information processing through the activation of multiple receptor families, including G-protein-coupled receptor subtypes (5-HT1, 5-HT2, 5-HT4-7) and ligand-gated ion channels (5-HT3). The largest population of serotonergic neurons is located in the midbrain, specifically in the raphe nuclei. Although the medial and dorsal raphe nucleus (DRN) share common projecting areas, in the basal ganglia (BG) nuclei serotonergic innervations come mainly from the DRN. The BG are a highly organized network of subcortical nuclei composed of the striatum (caudate and putamen), subthalamic nucleus (STN), internal and external globus pallidus (or entopeduncular nucleus in rodents, GPi/EP and GPe) and substantia nigra (pars compacta, SNc, and pars reticulata, SNr). The BG are part of the cortico-BG-thalamic circuits, which play a role in many functions like motor control, emotion, and cognition and are critically involved in diseases such as Parkinson's disease (PD). This review provides an overview of serotonergic modulation of the BG at the functional level and a discussion of how this interaction may be relevant to treating PD and the motor complications induced by chronic treatment with L-DOPA.

Multiple controls exerted by 5-HT2C receptors upon basal ganglia function: from physiology to pathophysiology

Serotonin2C (5-HT2C) receptors are expressed in the basal ganglia, a group of subcortical structures involved in the control of motor behaviour, mood and cognition. These receptors are mediating the effects of 5-HT throughout different brain areas via projections originating from midbrain raphe nuclei. A growing interest has been focusing on the function of 5-HT2C receptors in the basal ganglia because they may be involved in various diseases of basal ganglia function notably those associated with chronic impairment of dopaminergic transmission. 5-HT2C receptors act on numerous types of neurons in the basal ganglia, including dopaminergic, GABAergic, glutamatergic or cholinergic cells. Perhaps inherent to their peculiar molecular properties, the modality of controls exerted by 5-HT2C receptors over these cell populations can be phasic, tonic (dependent on the 5-HT tone) or constitutive (a spontaneous activity without the presence of the ligand). These controls are functionally organized in the basal ganglia: they are mainly localized in the input structures and preferentially distributed in the limbic/associative territories of the basal ganglia. The nature of these controls is modified in neuropsychiatric conditions such as Parkinson's disease, tardive dyskinesia or addiction. Most of the available data indicate that the function of 5-HT2C receptor is enhanced in cases of chronic alterations of dopamine neurotransmission. The review illustrates that 5-HT2C receptors play a role in maintaining continuous controls over the basal ganglia via multiple diverse actions. We will discuss their interest for treatments aimed at ameliorating current pharmacotherapies in schizophrenia, Parkinson's disease or drugs abuse.

A critical interaction between dopamine D2 receptors and endocannabinoids mediates the effects of cocaine on striatal gabaergic Transmission

Compelling evidence indicates that endocannabinoids are implicated in drug addiction. In the present study, we have addressed the interaction between cocaine and endocannabinoid system by means of neurochemical and neurophysiological experiments in rat brain slices. Using gas chromatography-electron impact mass spectrometry, we have found that cocaine increased the levels of the endocannabinoid anandamide in the striatum, a brain area primarily involved in the compulsive drug-seeking and drug-taking behaviors typical of addiction. This effect was attenuated by pharmacological inhibition of D2-like receptors but not D1-like receptors, and it was mimicked by D2-like but not D1-like receptor stimulation. The cocaine-induced increase in anandamide concentrations was attributable to both stimulation of its synthesis and inhibition of its degradation, as suggested by the ability of cocaine and quinpirole, a D2-like receptor agonist, to enhance the activity of NAPE-phospholipase D and to inhibit fatty acid amide hydrolase. By means of electrophysiological recordings from single striatal neurons, we have then observed that the ability of cocaine to inhibit, via D2-like receptors, GABA transmission was partially prevented following blockade of cannabinoid receptors, suggesting that endocannabinoids may act as downstream effectors in the action of cocaine in the striatum. Understanding the molecular and physiological effects of drugs of abuse in the brain is essential for the development of effective strategies against addiction.