Brain research
-
Spinal cord injury (SCI) pain in humans is difficult to treat, and the lack of valid methods to measure behavior comparable to the complex human pain experience preclinically represents an important obstacle to finding better treatments for this type of central pain. The place escape/avoidance paradigm (PEAP) relies on the active choice of an animal between its natural preference for a dark environment or pain relief, and it has been suggested to measure the affective-motivational component of pain. We have modified the method to a T10 spinal cord contusion model (SCC) of at-level central neuropathic pain in Sprague-Dawley rats. ⋯ Third, we demonstrated a decrease in escape/avoidance behavior in response to treatment with the analgesic drug pregabalin. Thus, the PEAP may be applicable as a surrogate correlate of human pain. In conclusion, the primary finding in this study was a sensitivity to change in escape/avoidance behavior induced by pharmacological modulation with analgesics, supporting the use of the PEAP as a central outcome measure in preclinical SCI pain research.
-
There is increasing evidence that traumatic brain injury (TBI) induces hypofunction of the striatal dopaminergic system, the mechanisms of which are unknown. In this study, we analyzed the activity of striatal tyrosine hydroxylase (TH) in rats at 1 day, 1 week, and 4 weeks after TBI using the controlled cortical impact model. There were no changes in the level of TH phosphorylated at serine 40 site (pser40TH) at 1 day or 4 weeks. ⋯ There were no significant differences in dopamine release at 1 day and 4 weeks between sham and injured groups. At 1 week, there was a significant decrease (injured: 0.067±0.015 μM, sham: 0.127±0.027 μM, p≤0.05). These results suggest that TBI-induced dopamine neurotransmission deficits are, at least in part, attributable to deficits in TH activity.
-
Status epilepticus-induced hippocampal neuronal loss is mainly associated with excitotoxicity induced by increased levels of extracellular glutamate which is normally neutralized by high-affinity uptake mechanism. The energy source for the glutamate uptake is the electrochemical Na(+) gradient maintained by Na(+)/K(+) ATPase pump. In this study, we investigated the effect of early-life-induced status epilepticus on hippocampal Na(+)/K(+) ATPase activity and glutamate uptake. ⋯ However, 12 and 24 h after SE induction the pump activity and glutamate uptake returned to control levels. SE early in life increased hippocampal number of degenerating neurons in the CA1 subfield and dentate gyrus 24 h after SE induction. In conclusion, SE induced early in life causes short-term disruption in hippocampal Na(+)/K(+) ATPase activity and glutamate uptake, which may be related to neuronal death found in CA1 subfield.
-
The TRPV1 receptor functions as a molecular integrator, and blockade of this receptor modulates enhanced somatosensitivity across several animal models of pathological pain, including models of osteoarthritic (OA) pain. In order to further characterize the contributions of TRPV1 to OA-related pain, we investigated the systemic effects of a selective TRPV1 receptor antagonist, A-889425, on grip force behavior, and on the evoked and spontaneous firing of spinal wide dynamic range (WDR) and nociceptive specific (NS) neurons in the monoiodoacetate (MIA) model of OA. Administration of A-889425 (10-300 μmol/kg, p.o.) alleviated grip force impairment in OA rats 3 weeks after the MIA injection. ⋯ In addition to an effect on mechanotransmission, systemic administration of A-889425 reduced the elevated spontaneous firing of WDR neurons in OA rats but did not alter spontaneous firing in sham rats. The present data demonstrate that blockade of TRPV1 receptors modulates the firing of two important classes of spinal nociceptive neurons in a rat model of OA. The effect of A-889425 on neuronal responses to intense mechanical stimulation of the knee and on the spontaneous firing of WDR neurons adds to the growing appreciation for the role of TRPV1 receptors in pathological mechanotransmission and possibly non-evoked discomfort, respectively.
-
Local perfusion of morphine produces increased levels of extracellular ascorbic acid (AA) in the nucleus accumbens (NAc) of freely moving rats. However, the pathways that regulate morphine-induced AA release in the NAc are unclear. In the present study, we used high performance liquid chromatography with electrochemical detection (HPLC-ECD) to examine the effects of intra-ventral tegmental area (VTA) administration of a GABA(A) agonist and antagonist on morphine-induced increases in AA of the NAc. ⋯ Intra-VTA infusion of bicuculline (150 ng/rat), a GABA receptor antagonist, not only abolished the enhanced extracellular AA and GABA levels produced by local perfusion of morphine but also decreased the basal release of extracellular GABA and increased the basal release of extracellular DA in the NAc. Muscimol (100 ng/rat), a GABA receptor agonist, affected the basal release of GABA and DA, but not the basal AA levels, or the morphine-induced changes in AA and GABA levels. These findings suggest that the GABA(A) receptors in the VTA play an important role in the modulation of morphine-induced AA release in the NAc, and the effect of morphine on AA release in the NAc is partially regulated by the GABA(A) receptor-mediated action of DA afferents from the VTA.