Considerations upon the anatomical model of reward-based learning in the basal ganglia

Therapeutic potential of targeting G protein-gated inwardly rectifying potassium (GIRK) channels in the central nervous system

G protein-gated inwardly rectifying potassium channels (Kir3/GirK) are important for maintaining resting membrane potential, cell excitability and inhibitory neurotransmission. Coupled to numerous G protein-coupled receptors (GPCRs), they mediate the effects of many neurotransmitters, neuromodulators and hormones contributing to the general homeostasis and particular synaptic plasticity processes, learning, memory and pain signaling. A growing number of behavioral and genetic studies suggest a critical role for the appropriate functioning of the central nervous system, as well as their involvement in many neurologic and psychiatric conditions, such as neurodegenerative diseases, mood disorders, attention deficit hyperactivity disorder, schizophrenia, epilepsy, alcoholism and drug addiction. Hence, GirK channels emerge as a very promising tool to be targeted in the current scenario where these conditions already are or will become a global public health problem. This review examines recent findings on the physiology, function, dysfunction, and pharmacology of GirK channels in the central nervous system and highlights the relevance of GirK channels as a worthful potential target to improve therapies for related diseases.

Temporal and site-specific brain alterations in CB1 receptor binding in high fat diet-induced obesity in C57Bl/6 mice

The cannabinoid CB1 receptor has been implicated in the regulation of appetite and the consumption of palatable foods. This experiment aimed to explore the involvement of the CB1 receptor in the early and late stages of high fat diet-induced obesity in C57BL/6 mice. The C57Bl/6 mice were placed on a high fat (HF) or low fat/high carbohydrate (LF) diet for 3 or 20 weeks. Quantitative autoradiography revealed that binding of [3H] CP-55,940 (CB1 receptor ligand) was elevated following 3 weeks of HF feeding in areas including the medial/ventral anterior olfactory nucleus (22.1%), agranular insular cortex (24.0%) and the hypothalamus (31.5%) compared to LF controls. This increased level of binding was correlated with an increase in plasma leptin in the hypothalamus, raising the possibility that this hormone may exert inhibitory control over endocannabinoid signalling at this stage of obesity. Mice fed a HF diet for 20 weeks were obese, hyperphagic and had decreased CB1 receptor binding levels in the substantia nigra (12.8%) and ventral tegmental area (17.1%) compared to LF controls. The low [3H] CP-55,940 binding density seen in these reward-related areas in the late stage of obesity may be indicative of increased endocannabinoid release due to the chronic HF diet consumption.

The basal ganglia and disorders of movement: pathophysiological mechanisms

The basal ganglia are part of a neuronal network organized in parallel circuits. The "motor circuit" is most relevant to the pathophysiology of movement. Abnormal increment or reduction in the inhibitory output activity of basal ganglia give rise, respectively, to poverty and slowness of movement (i.e., Parkinson's disease) or dyskinesias.

Neural modulation of visuomotor functions underlying prey-catching behaviour in anurans: perception, attention, motor performance, learning

The present review points out that visuomotor functions in anurans are modifiable and provides neurophysiological data which suggest modulatory forebrain functions. The retino-tecto/tegmento-bulbar/spinal serial processing streams are sufficient for stimulus-response mediation in prey-catching behaviour. Without its modulatory connections to forebrain structures, however, these processing streams cannot manage perceptual tasks, directed attention, learning performances, and motor skills. (1) Visual prey/non-prey discrimination is based on the interaction of this processing stream with the pretectal thalamus involving the neurotransmitter neuropeptide-Y. (2) Experiments applying the dopamine agonist apomorphine in combination with 2DG mapping and single neurone recording suggest that prey-catching strategies in terms of hunting prey and waiting for prey depend on dose dependent dopaminergic adjustments in the neural macronetwork in which retinal, pretecto-tectal, basal ganglionic, limbic, and mesolimbic structures participate. (3) Visual response properties of striatal efferent neurones support the concept that ventral striatum is involved in directed attention. (4) Various modulatory loops involving the ventral medial pallium modify prey-recognition in the course of visual or visual-olfactory learning (associative learning) or are responsible for stimulus-specific habituation (non-associative learning). (5) The circuits suggested to underlie modulatory forebrain functions are accentuated in standard schemes of the neural macronetwork. These provide concepts suitable for future decisive experiments.