Neuroanatomical characterization of imidazoline I2 receptor agonist-induced antinociception

Isoquinolone derivatives as lysophosphatidic acid receptor 5 (LPA5) antagonists: Investigation of structure-activity relationships, ADME properties and analgesic effects

Blockade of lysophosphatidic acid receptor 5 (LPA5) by a recently reported antagonist AS2717638 (2) attenuated inflammatory and neuropathic pains, although it showed moderate in vivo efficacy and its structure-activity relationships and the ADME properties are little studied. We therefore designed and synthesized a series of isoquinolone derivatives and evaluated their potency in LPA5 calcium mobilization and cAMP assays. Our results show that substituted phenyl groups or bicyclic aromatic rings such as benzothiophenes or benzofurans are tolerated at the 2-position, 4-substituted piperidines are favored at the 4-position, and methoxy groups at the 6- and 7-positions are essential for activity. Compounds 65 and 66 showed comparable in vitro potency, excellent selectivity against LPA1-LPA4 and >50 other GPCRs, moderate metabolic stability, and high aqueous solubility and brain permeability. Both 65 and 66 significantly attenuated nociceptive hypersensitivity at lower doses than 2 and had longer-lasting effects in an inflammatory pain model, and 66 also dose-dependently reduced mechanical allodynia in the chronic constriction injury model and opioid-induced hyperalgesia at doses that had no effect on the locomotion in rats. These results suggest that these isoquinolone derivatives as LPA5 antagonists are of promise as potential analgesics.

Activation of trace amine-associated receptor 1 selectively attenuates the reinforcing effects of morphine

BACKGROUND AND PURPOSE

Trace amine-associated TA₁ receptors play critical roles in regulating dopamine transmission. Previous studies showed that pharmacologically or genetically manipulating the activity of TA₁ receptors modulates addiction-like behaviours associated with psychostimulants. However, little is known about whether TA₁ receptor modulation would regulate the behavioural effects of opioids.

EXPERIMENTAL APPROACH

Effects of the selective TA₁ receptor partial agonist RO5263397 on the addiction-related and antinociceptive effects of morphine were systematically assessed in male rats and mice.

KEY RESULTS

RO5263397 attenuated the expression of morphine-induced behavioural sensitization in wildtype but not TA₁ receptor knockout mice. RO5263397 shifted the dose-effect curve of morphine self-administration downward and reduced the breakpoint in a progressive ratio schedule of reinforcement but did not affect food self-administration in rats. RO5263397 decreased the cue- and drug-induced reinstatement of morphine-seeking behaviour in rats. RO5263397 alone did not trigger reinstatement of morphine-seeking behaviour or change locomotor activity in rats with a history of morphine self-administration. However, RO5263397 did not affect the expression of morphine-induced conditioned place preference in mice or rats. RO5263397 did not affect naltrexone-precipitated jumping behaviour or naltrexone-induced conditioned place aversion in morphine-dependent mice. Furthermore, RO5263397 did not affect the analgesic effects of morphine in an acute nociception model in mice and a chronic pain model in rats.

CONCLUSION AND IMPLICATIONS

These results indicated that TA₁ receptor activation selectively attenuated the reinforcing, but not withdrawal or antinociceptive effects of morphine, suggesting that selective TA₁ receptor agonists might be useful to combat opioid addiction, while sparing the analgesic effects.

Agmatine modulates spontaneous activity in neurons of the rat medial habenular complex-a relevant mechanism in the pathophysiology and treatment of depression?

The dorsal diencephalic conduction system connects limbic forebrain structures to monaminergic mesencephalic nuclei via a distinct relay station, the habenular complexes. Both habenular nuclei, the lateral as well as the medial nucleus, are considered to play a prominent role in mental disorders like major depression. Herein, we investigate the effect of the polyamine agmatine on the electrical activity of neurons within the medial habenula in rat. We present evidence that agmatine strongly decreases spontaneous action potential firing of medial habenular neurons by activating I1-type imidazoline receptors. Additionally, we compare the expression patterns of agmatinase, an enzyme capable of inactivating agmatine, in rat and human habenula. In the medial habenula of both species, agmatinase is similarly distributed and observed in neurons and, in particular, in distinct neuropil areas. The putative relevance of these findings in the context of depression is discussed. It is concluded that increased activity of the agmatinergic system in the medial habenula may strengthen midbrain dopaminergic activity. Consequently, the habenular-interpeduncular axis may be dysregulated in patients with major depression.