Neuroscience
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Orexins (OXs) regulate sleep with possible interactions with brain noradrenergic neurons. In addition, noradrenergic activity affects barbiturate anesthesia. As we have also recently reported that OXs selectively evoke norepinephrine release from rat cerebrocortical slices we hypothesized that barbiturate anesthesia may result from of an interaction with central orexinergic systems. ⋯ A GABAA antagonist, bicuculline, did not modify the inhibitory effects of thiopental and the GABAA agonist, muscimol, did not inhibit norepinephrine release. In addition there was no interaction of barbiturates with either OX1 or OX2 receptors. Collectively our data suggest that orexinergic neurons may be an important target for barbiturates, and GABAA, OX1 and OX2 receptors may not be involved in this interaction.
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We investigated the role of in vivo synaptic activity upon trafficking of the N-methyl-D-aspartate (NMDA) receptor subunit, NR2B, at mature synapses by electron microscopic immunocytochemistry. In vivo blockade of NMDA receptors was achieved by applying the NMDA receptor antagonist, D-2-amino-5-phosphonovalerate (D-APV), onto the cortical surface of one hemisphere of anesthetized adult rats. Inactive L-2-amino-5-phosphonovalerate (L-APV) was applied to the contralateral hemisphere for within-animal control and to assess basal level of NR2B subunits at synapses. ⋯ The data demonstrate that blockade of NMDA receptors induces trafficking of NR2B subunits out of synaptic membranes, spines, and terminals. This is in sharp contrast to a previous observation that NR2A subunits move into spines and axon terminals following in vivo blockade with D-APV. These findings point to yet unknown, NMDA receptor activity-dependent mechanisms that separately regulate the localization of NR2A and NR2B subunits at synapses.
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Comparative Study
Exacerbated status epilepticus and acute cell loss, but no changes in epileptogenesis, in mice with increased brain-derived neurotrophic factor signaling.
Several studies suggest that brain-derived neurotrophic factor (BDNF) can exacerbate seizure development during status epilepticus (S. E.) and subsequent epileptogenesis in the adult brain. On the other hand, evidence exists for the protective effect of BDNF. ⋯ Our data support the role of BDNF and trkB signaling in seizure generation and acute cellular damage after S. E. Long-term outcome was not, however, exacerbated by trkB overexpression.
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Comparative Study
Combined intrastriatal dopamine D1 and serotonin 5-HT2 receptor stimulation reveals a mechanism for hyperlocomotion in 6-hydroxydopamine-lesioned rats.
Loss of dopaminergic innervation to the striatum increases the sensitivity of dopamine (DA) D1 and serotonin (5-HT) 5-HT2 receptor signaling. Previous work from our laboratory has shown that systemic co-administration of D1 and 5-HT2 receptor agonists leads to the synergistic overexpression of striatal preprotachykinin mRNA levels in the DA-depleted, but not intact animals. In the present study, we examined this mechanism as related to locomotor behavior. ⋯ Combined administration of subthreshold SKF82958 and DOI doses (0.1 microg+0.1 microg) synergistically increased locomotor behavior only in 6-OHDA-lesioned rats. These effects were blocked by either the D1 antagonist SCH23390 3-methyl-1-phenyl-2,3,4,5-tetrahydro-7-chloro-8-hydroxy-(1H)-3-benzazepine or the 5-HT2 antagonist ritanserin (each 1.0 microg in 0.8 microl/side). The results of this study suggest that the behavioral synergy induced by local co-stimulation of D1 and 5-HT2 receptors within the 6-OHDA-lesioned striatum may lead to hyperkinesias that can occur with continued pharmacological treatment of Parkinson's disease.
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Intracellular recordings were made from neurones in the thalamic reticular nucleus (TRN) and ventro-basal (VB) thalamus in slices of rat midbrain in vitro. Electrical stimulation of the medial lemniscus or TRN resulted in the generation of complex synaptic potentials containing disynaptic inhibitory post-synaptic potentials (IPSPs) in VB thalamocortical neurones. Analysis of the excitatory synaptic responses in TRN neurones indicates they can produce burst output response irrespective of the level of sub-threshold membrane potential. ⋯ This is consistent with the location of these receptor types on the presynaptic terminals of TRN axons in the VB thalamus. This raises the possibility that, during periods of intense excitatory activity, glutamate release could influence the release of GABA from TRN axon terminals in the thalamus. In addition, as NAAG is located in the axons and terminals arising from the TRN, there is the possibility that this dipeptide is also released by these terminals to control the release of GABA during periods of high activity in the TRN.