No abstract

Activation of p38 mitogen-activated protein kinase (p38) in spinal microglia is implicated in spinal nociceptive processing. Minocycline, a tetracycline derivative, displays selective inhibition of microglial activation, a function that is distinct from its antibiotic activity. In the present study we examined antinociceptive effects of intrathecal (IT) administration of minocycline in experimental models of inflammation-evoked hyperalgesia in addition to the effect of minocycline on stimulation-induced activation of p38 in spinal microglia. Intrathecal minocycline produced a dose-dependent reduction of formalin-evoked second-phase flinching behaviour in rats, and prevented thermal hyperalgesia induced by carrageenan injection into the paw. In contrast, systemic delivery (intraperitoneally) of minocycline inhibited the first but not the second phase of formalin-induced flinching, and it had no effect on carrageenan-induced hyperalgesia. Centrally mediated hyperalgesia induced by IT delivery of N-methyl-d-aspartate was completely blocked by IT minocycline. An increase in phosphorylation (activation) of p38 (P-p38) was observed in the dorsal spinal cord after carrageenan paw injection, assessed by both Western blotting and immunohistochemistry. The increased P-p38 immunoreactivity was seen primarily in microglia but also in a small population of neurons. Minocycline, at the IT dose that blocked carrageenan-induced hyperalgesia, also attenuated the increased P-p38 in microglia. In addition, minocycline suppressed lipopolysaccharide-evoked P-p38 in cultured spinal microglial cells. Taken together, these findings show that minocycline given IT produces a potent and consistent antinociception in models of tissue injury and inflammation-evoked pain, and they provide strong support for the idea that this effect is mediated by direct inhibition of spinal microglia and subsequent activation of p38 in these cells.

Demyelination is a hallmark of several human diseases, including multiple sclerosis. To understand better the process of demyelination and remyelination, we explored the use of an in vitro organotypic cerebellar slice culture system. Parasagittal slices of postnatal Day 10 (P10) rat cerebella cultured in vitro demonstrated significant myelination after 1 week in culture. Treatment of the cultures at 7 days in vitro (DIV) with the bioactive lipid lysolecithin (lysophosphatidylcholine) for 15-17 hr in vitro produced marked demyelination. This demyelination was observed by immunostaining for the myelin components myelin basic protein (MBP), myelin oligodendrocyte glycoprotein (MOG), and 2', 3'-cyclic nucleotide 3'-phosphodiesterase (CNPase). After a transient demyelinating insult with lysolecithin in vitro, the cultures recovered with oligodendrocyte differentiation recapitulating a normal time course; there was initially re-expression of CNPase and MBP during this recovery, and this was followed by MOG. In addition, there seemed to be some limited remyelination during the recovery phase. Lysolecithin thus induces demyelination in an in vitro organotypic cerebellar slice culture system, providing a model system for studying myelination, demyelination, and remyelination in vitro.

No abstract

1 The reversible fatty acid amide hydrolase (FAAH) inhibitor OL135 reverses mechanical allodynia in the spinal nerve ligation (SNL) and mild thermal injury (MTI) models in the rat. The purpose of this study was to investigate the role of the cannabinoid and opioid systems in mediating this analgesic effect. À/À mice. 5 OL135 given i.p. resulted in a dose-responsive reversal of mechanical allodynia in both MTI and SNL models in the rat with an ED 50 between 6 and 9 mg kg À1 . The plasma concentration at the ED 50 in both models was 0.7 mM (240 ng ml À1 ). 6 In the rat SNL model, coadministration of the selective CB 2 receptor antagonist SR144528 (5 mg kg À1 i.p.), with 20 mg kg À1 OL135 blocked the OL135-induced reversal of mechanical allodynia, but the selective CB 1 antagonist SR141716A (5 mg kg À1 i.p.) was without effect. 7 In the rat MTI model neither SR141716A or SR144528 (both at 5 mg kg À1 i.p.), or a combination of both antagonists coadministered with OL135 (20 mg kg À1) blocked reversal of mechanical allodynia assessed 30 min after dosing. 8 In both the MTI model and SNL models in rats, naloxone (1 mg kg À1 , i.p. 30 min after OL135) reversed the analgesia (to 15% of control levels in the MTI model, to zero in the SNL) produced by OL135.