Brain research
-
Depression is associated with deficiencies in monoaminergic transmitters and possibly neurotrophins. A common cellular response to these molecules is the activation of extracellular signal-regulated kinase (ERK). ⋯ As expected, the CLI rats exhibited significantly lower sexual activities and also exhibited (1). significant decreases of pERK1/2 in the frontal cortex and pERK1 in the hippocampus, (2). slight but significant reduction of ERK2 in the frontal cortex and hippocampus, (3). no change of pERK1/2 levels in the temporal cortex, occipital cortex, parietal cortex, midbrain, and medulla, (4). significantly higher levels of PP1 in both the frontal cortex and hippocampus, (5). no change in MKP-2 in any examined region, and (6). all five measures of sexual function were significantly correlated with ERK2 and pERK2 in the frontal cortex. These findings suggest that a deficiency in the ERK signaling pathway is involved in the display of depressive behaviors.
-
We evaluated the ability of spinally administered nitric oxide (NO) synthase inhibitor to modulate antinociceptive action of intrathecal (i.t.) morphine in rats by measuring the early and late phases of flinching and licking/biting in the formalin test. To determine the contribution of spinal NO and glutamate, we measured the release of NO metabolites (nitrite/nitrate) and glutamate from the spinal cord in rats, using a microdialysis probe placed in the lumbar space. The i.t. administration of NG-nitro L-arginine methyl ester (L-NAME) produced a dose-dependent reduction in the number of flinches during the late phase, whereas there were no significant alterations in the late phase licking/biting, and early phase flinching and licking/biting. ⋯ In the present study, we have confirmed our prior results that injection of formalin (5.0%) into the plantar surface of the paw evoked a biphasic spinal release of nitrite/nitrate and a transient release of glutamate. Formalin-evoked release of nitrite/nitrate and glutamate was also reduced markedly by i.t. combined administration of L-NAME and morphine. These behavioural and biochemical results suggest that i.t. administered L-NAME may enhance morphine-induced antinociception through an increased inhibition of nitrite/nitrate and glutamate releases evoked by formalin injection at the spinal cord level.
-
Comparative Study
P2X3-immunoreactive primary sensory neurons innervating lumbar intervertebral disc in rats.
The P2X(3) receptor is normally localized in a sub-population of small-diameter dorsal root ganglion (DRG) neurons, and is thought to be related to pain perception. The aim of this study in rats was to examine P2X(3)-immunoreactivity in DRG neurons innervating the lumbar disc and in DRG neurons innervating cutaneous tissues. Fluoro-Gold was applied to the L5-L6 disc, the plantar skin of the hind paw (L4-L5 dermatomes), and the back skin (L1-L2 dermatomes). ⋯ The proportion of P2X(3)-immunoreactive neurons was significantly larger in the DRG neurons innervating the plantar or the back skin, than in the DRG neurons innervating the lumbar disc. These results suggest that the P2X(3) receptors are abundant in DRG neurons innervating cutaneous tissues, but not in neurons innervating the lumbar disc. It is likely therefore that the P2X(3) receptor is less related to the mechanism of discogenic pain, than to cutaneous tissue pain.
-
It is well documented that VMAT2 protects nigrostriatal DA neurons against MPP(+) by sequestering it inside vesicles away from its mitochondrial site of neurotoxic action. However, the implication of the VMAT2 in the mechanism of action exerted by 6-OHDA has received little attention. Therefore, the aim of the present study was to determine whether the vesicular sequestration of 6-OHDA would protect dopaminergic neurons from its toxicity similarly to what is observed with MPP(+). ⋯ A hypothermia similar to that induced by TBZ was obtained by a forced swimming test of putting mice into cool water (23 degrees C). The hypothermia prevented both 6-OHDA and MPP(+)-induced neurotoxicity. We finally reported that VMAT2 inhibition potentiates both MPP(+) and 6-OHDA neurotoxicity.
-
The transcription factor cAMP responsive element binding protein (CREB) is important in regulating immediate-early genes and some late-effector genes involved in neuroplasticity in response to peripheral injury and stressful insults. Partial nerve injury elicited neuropathic pain is accompanied by increased phosphorylation of CREB in the ipsilateral spinal cord dorsal horn (Ma and Quirion, Pain 93 (2001) 295; Miletic et al., Pain 99 (2002) 493). The aim of this study is to determine whether increased phosphorylation of CREB in the dorsal horn contributes to the pathogenesis of neuropathic pain. ⋯ Total CREB and phosphorylated CREB in both ipsilateral and contralateral dorsal horn neurons were dramatically reduced in antisense ODN injected PSNL rats 1 week after injection. The extent of reduction of total CREB and phosphorylated CREB containing cells in the dorsal horn ipsilateral to injury was greater than in the contralateral dorsal horn. These data suggest that phosphorylation of CREB is an important contributing event in the central plasticity of nerve injury and in the pathogenesis of neuropathic pain.