Catechol-O-methyltransferase (COMT) protein expression and activity after dopaminergic and noradrenergic lesions of the rat brain.

The occurrence of catechol-O-methyltransferase (COMT) in presynaptic neurons remains controversial. This study utilized dopaminergic and noradrenergic toxins to assess the presence of COMT in the presynaptic neurons originating from the substantia nigra, ventral tegmental area or locus coeruleus. Destruction of dopaminergic and noradrenergic neurons was assessed by measuring the dopamine and noradrenaline content in the projection areas of these neurons. Additionally, COMT protein expression and activity were examined in several projection areas to determine whether there are any changes in COMT values. Colocalization studies were done to identify COMT-containing postsynaptic neurons. Despite successful lesioning of dopaminergic and noradrenergic neurons, no changes in COMT protein expression or activity could be noted. These results strongly suggest that COMT is not present in presynaptic dopaminergic and noradrenergic neurons. There was a high colocalization of COMT with the GABAergic marker of short neurons both in the striatum and cortex but only a weak, if any, with the cholinergic marker in the cortex.

A transient inhibition and permanent lack of catechol-O-methyltransferase have minor effects on feeding pattern of female rodents.

Abnormal feeding behaviours have long been linked to disruptions in brain dopaminergic activity. Dopamine is metabolized, amongst others, by catechol-O-methyltransferase (COMT). Normally, COMT only plays a subordinate role in dopamine metabolism. However, changes in COMT activity, especially in the prefrontal cortex, become more important during events that evoke dopamine release. The current study investigated the effect of acute COMT inhibition on feeding in Wistar rats and C57BL/6 mice using a selective, brain penetrating COMT inhibitor (OR-1139). Furthermore, the effect of a long-term lack of COMT on feeding behaviour was studied in COMT-deficient (COMT -/-) mice. Apart from following the gross feeding behaviour of fasted rats and mice, the first 4 hr of re-feeding were recorded with a video camera to allow a more detailed analysis of feeding microstructure. In the acute study, rats and mice received a single injection of OR-1139 (3, 10 or 30 mg/kg), just before the experiment. We found that rats and mice receiving OR-1139 had fewer very short meals but more long meals than the controls. Treated mice even ate more frequently than the controls, but other feeding parameters remained unchanged. Conversely, COMT -/- mice displayed an increased latency to initiate the first meal and spent less total time eating than wild-type mice. In conclusion, although decreased/lack of COMT activity did not robustly alter feeding behaviour of female rodents, we observed some alterations in the microstructure of feeding. However, these minor changes were highly dependent on the extent and fashion in which COMT was manipulated.

Amantadine protects dopamine neurons by a dual action: reducing activation of microglia and inducing expression of GDNF in astroglia [corrected].

Amantadine is commonly given to alleviate L-DOPA-induced dyskinesia of Parkinson's disease (PD) patients. Animal and human evidence showed that amantadine may also exert neuroprotection in several neurological disorders. Additionally, it is generally believed that this neuroprotection results from the ability of amantadine to inhibit glutamatergic NMDA receptor. However, several lines of evidence questioned the neuroprotective capacity of NMDA receptor antagonists in animal models of PD. Thus the cellular and molecular mechanism of neuroprotection of amantadine remains unclear. Using primary cultures with different composition of neurons, microglia, and astroglia we investigated the direct role of these glial cell types in the neuroprotective effect of amantadine. First, amantadine protected rat midbrain cultures from either MPP(+) or lipopolysaccharide (LPS), two toxins commonly used as PD models. Second, our studies revealed that amantadine reduced both LPS- and MPP(+)-induced toxicity of dopamine neurons through 1) the inhibition of the release of microglial pro-inflammatory factors, 2) an increase in expression of neurotrophic factors such as GDNF from astroglia. Lastly, differently from the general view on amantadine's action, we provided evidence suggesting that NMDA receptor inhibition was not crucial for the neuroprotective effect of amantadine. In conclusion, we report that amantadine protected dopamine neurons in two PD models through a novel dual mechanism, namely reducing the release of pro-inflammatory factors from activated microglia and increasing the expression of GNDF in astroglia.

Distribution of catechol-O-methyltransferase (COMT) proteins and enzymatic activities in wild-type and soluble COMT deficient mice.

Catechol-O-methyltransferase (COMT) has both soluble (S-COMT) and membrane-bound (MB-COMT) isoforms. A specific COMT antibody was used in immunohistochemical and confocal co-localization studies to explore the distribution of COMT in general in normal mice and MB-COMT in particular, in an S-COMT deficient mouse line. In the peripheral tissues, high COMT protein and activity levels were observed in liver and kidney, whereas in the brain, COMT expression and activity were much lower. MB-COMT was widely distributed throughout all tissues, and overall, the MB-COMT distribution mimicked the distribution of S-COMT. MB-COMT displayed some preference for brain tissue, notably in the hippocampus. MB-COMT related enzymatic activity was also pronounced in the cerebral cortical areas and hypothalamus. MB-COMT, like S-COMT, was found to be an intracellular enzyme but it was not associated with plasma membranes in the brain. Both COMT forms were abundantly found in microglial cells and intestinal macrophages, but also in astroglial cells. COMT was also present in some neuronal cells, like pyramidal neurons, cerebellar Purkinje and granular cells and striatal spiny neurons, but not in major long projection neurons. Finally, it seemed that nuclear COMT is not visible in S-COMT deficient mice.