Brain research
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Comparative Study
Release of GABA from sensory neurons transduced with a GAD67-expressing vector occurs by non-vesicular mechanisms.
We have demonstrated that dorsal root ganglion neurons transduced with a recombinant replication-defective herpes simplex virus vector coding for glutamic acid decarboxylase (QHGAD67) release GABA to produce an analgesic effect in rodent models of pain. In this study, we examined the mechanism of transgene-mediated GABA release from dorsal root ganglion neurons in vitro and in vivo. ⋯ The amount of GABA released from a spinal cord slice preparation, prepared from animals transduced by subcutaneous inoculation of QHGAD67 in the hind paws, was substantially increased compared to animals transduced with control vector Q0ZHG or normal animals, but the amount of GABA released was not changed by stimulation of the dorsal roots at either low (0.1 mA, 0.5-ms duration) or high (10 mA, 0.5-ms duration) intensity. We conclude that QHGAD67-mediated GABA release from dorsal root ganglion neurons is non-vesicular, independent of electrical depolarization, and that this efflux is mediated through reversal of the GABA transporter.
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Comparative Study
Transhemispheric depolarizations persist in the intracerebral hemorrhage swine brain following corpus callosal transection.
Spontaneous episodes of spreading depression (SD) originating in multiple sources adjacent to a focal intracerebral hemorrhage (ICH) propagate into brain regions away from the lesion site soon after injury onset. Although these transient depolarizations have not been established in the opposite hemisphere of the swine ICH model, we have reported a diminishing of sensory responsiveness in this homotopic brain region following induction of a unilateral hemorrhage lesion. This study examined whether transient depolarizations exist in this distant brain region contralateral to the ICH site. ⋯ These transient depolarizations also persisted throughout 11-h recording period indicating that the corpus callosal transection did not hinder these remote propagating waves of depolarization. The presence of SD in the SI cortices of both hemispheres in all experimental groups of this study suggests that a focal mechanical or hemorrhagic injury increases the susceptibility of distant ipsilateral and contralateral brain regions to depolarizing perturbations. The mechanism for these transient depolarizations in the contralateral hemisphere apparently does not involve transhemispheric propagation along corpus callosal fibers.
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The suprachiasmatic nucleus (SCN) of the hypothalamus contains the primary circadian pacemaker in both diurnal and nocturnal mammals. The lower subparaventricular zone (LSPV) immediately dorsal to the SCN may also play an important role in the regulation of circadian rhythms. The SCN contains a multitude of oscillator cells that generate circadian rhythms through transcriptional/translational feedback loops involving a set of clock genes including per1 and per2. ⋯ Rhythmic expression of PER1 and PER2 was also seen in the LSPV providing support for the hypothesis that this region might participate in circadian time keeping in the diurnal grass rat. In addition, rhythms were seen lateral to the LSPV and the SCN. Results of this study are discussed in light of similarities and differences in the circadian time-keeping systems of day- and night-active animals.
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Comparative Study
Comparison of the in vitro efficacy of mu, delta, kappa and ORL1 receptor agonists and non-selective opioid agonists in dog brain membranes.
Morphine and related opioid agonists are frequently used in dogs for their analgesic properties, their sedative effects and as adjuncts to anesthesia. Such compounds may be effective through a combined action at mu-, delta- and kappa-opioid receptors. In this work, the in vitro relative agonist efficacy of ligands selective for mu (DAMGO)-, delta (SNC80)- and kappa (U69593)-opioid receptors as well as the opioid receptor-like receptor ORL(1) (orphaninFQ/nociceptin) which may mediate nociceptive or antinociceptive actions was determined using the [35S]GTPgammaS binding assay in membrane homogenates from the frontal cortex, thalamus and spinal cord of beagle dogs. ⋯ There was no significant difference in the potency of compounds to stimulate [35S]GTPgammaS binding between cortex and thalamus, with the exception of etorphine. Buprenorphine, the partial mu-opioid receptor agonist and kappa-, delta-opioid receptor antagonist, which does have analgesic efficacy in the dog, showed no agonism in any tissue but was an effective mu-opioid receptor > ORL1 receptor antagonist. The results show that the ability of agonists to stimulate [35S]GTPgammaS binding relates to the receptor distribution of opioid and ORL1 receptors in the dog.
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The phosphorylated Extracellular Signal-regulated Kinase (pERK) and Fos expression and masticatory muscle activity were analyzed in rats with capsaicin-induced acute inflammation of the tooth pulp in order to clarify the role of the spinal trigeminal nucleus and upper cervical spinal cord in tooth pulp pain. Digastric and masseteric muscle activities were significantly increased following capsaicin injection into the molar tooth pulp but not after vehicle treatment. The pERK-like immunoreactive (LI) neurons were observed in the subnuclei interpolaris-caudalis transition (Vi/Vc) zone, the paratrigeminal nucleus (Pa5) and the superficial laminae of the caudal Vc/C2 zone. ⋯ After capsaicin application into the upper molar tooth pulp, no pERK-LI cells were observed in the ventral part of the Vi/Vc zone, whereas many Fos protein-LI cells were expressed in this region. The difference in the distribution pattern of pERK- and Fos protein-LI cells in the Vi/Vc zone suggests their differential temporal expression profiles after capsaicin. The present findings suggest that tooth-pulp-driven neurons in the spinal trigeminal nucleus are involved in tooth pulp pain through activation of the intracellular signal transduction pathway that involves earlier ERK phosphorylation and subsequent Fos expression.