Neuroscience
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Cocaine- and amphetamine-regulated transcript peptide mRNA was discovered in the rat striatum following cocaine and amphetamine administration. Since both psychostimulants elicit memory-related effects, localization of cocaine- and amphetamine-regulated transcript peptide in the hippocampal formation may have functional importance. Previous studies demonstrated different cellular localizations of cocaine- and amphetamine-regulated transcript peptide in humans and in rodents. ⋯ Our results show that cocaine- and amphetamine-regulated transcript positive neurons in the dentate gyrus of non-human primates are similar to that of the human. Furthermore, in the hippocampal formation of the tree shrew similar cocaine- and amphetamine-regulated transcript-immunoreactive cell-types were observed as in monkeys, supporting their evolutionary relationship with primates. Mossy cells and granule cells are members of a mutual excitatory intrahippocampal circuitry, therefore cocaine- and amphetamine-regulated transcript-immunoreactivity of these neurons in primates and rodents suggests that psychostimulants cocaine and amphetamine may induce memory-related effects at different points of the same excitatory circuitry in the hippocampal formation.
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Neuronal responses to complex prey-like stimuli and rectangles were investigated in the tectum of the salamander Plethodon shermani using extracellular single-cell recording. Cricket dummies differing in size, contrast or movement pattern or a rectangle were moved singly through the excitatory receptive field of a neuron. Paired presentations were performed, in which a reference stimulus was moved inside and the different cricket dummies or the rectangle outside the excitatory receptive field. ⋯ The response properties of tectal neurons at single or paired presentation of stimuli indicate that tectal neurons integrate information across a much larger part of visual space than covered by the excitatory receptive field. The spike number of a tectal neuron and the spatio-temporal extent of its excitatory receptive field are not fixed but depend on the context, i.e. the stimulus type and combination. This dynamic processing corresponds with the selection of the stimuli in the visual orienting behavior of Plethodon investigated in a previous study, and we assume that tectal processing is modulated by top down processes as well as feedback circuitries.
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It has been well documented that the activation of c-Jun N-terminal protein kinase (JNK) pathway and caspase-3 signal are involved in the delayed neuronal cell death in cerebral ischemia. In this study, we first detected the activation pattern of JNK signaling including mixed lineage kinase (MLK)3, mitogen-activated protein kinase kinase (MKK)7 and JNK3 in hippocampal CA1 and CA3/DG regions at various time points after 15 min of ischemia. These results indicated that cerebral ischemia induced the continuous activation of MLK3/MKK7/JNK3 cascade, which all had two active waves only in the CA1 region. ⋯ Additionally, pretreatment of K252a significantly increased the number of the surviving CA1 pyramidal cells at 5 days of reperfusion. Our results suggest that K252a play a neuroprotective role in ischemic injury via inhibition of the JNK pathway, involving the death effector of caspase-3. Thus, JNK signaling may eventually emerge as a prime target for novel therapeutic approaches to treatment of ischemic stroke, and K252a may serve as a potential and important neuroprotectant in therapeutic aspect in ischemic stroke.
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We have localized cannabinoid receptor 2 protein in rat and mouse somatic sensory nervous system, using an antibody that recognizes mouse cannabinoid receptor 2. Little or no cannabinoid receptor 2 immunoreactivity was found in sections of naive rat or mouse dorsal root ganglia or spinal cord. This was in accord with the lack of detectable cannabinoid receptor 2 mRNA in (dorsal root ganglion) neurons by in situ hybridization experiments described in the literature. ⋯ In the peripheral nerve, accumulation of cannabinoid receptor 2 immunoreactivity was seen in nerve sections proximal, but not distal, to the ligation site, suggesting transport down the nerve from the cell bodies. Although convincing cannabinoid receptor 2 immunoreactivity was seen in neither uninjured nor injured dorsal root ganglion neuron cell bodies in tissue sections, expression was detectable in isolated, cultured neurons that had received a prior axotomy in vivo. This clear demonstration of CB(2) receptors on sensory neurons suggests an additional cellular target for CB(2) agonist induced analgesia, at least in neuropathic models.
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Comparative Study
Opposite behaviours in the forced swimming test are linked to differences in spatial working memory performances in the rat.
Despite consistent evidence of an association between depression and impaired memory performance, only a few studies have investigated memory processes in animal models of depression. The aim of the present study was to determine if rats selected for marked differences in their immobility response in the forced swimming test (FST, i.e. high-immobility, [HI] and low-immobility [LI] rats) exhibit differences in spatial and non-spatial memory performances. In a classic radial maze elimination task, we observed that HI rats made significantly more errors than LI rats, and their first error appeared significantly earlier. ⋯ On the other hand, performances in the two groups of animals were similar in a non-spatial task, the object recognition task. Complementary behavioral data indicate that the differences observed between the two groups are not attributable to opposite locomotor activities or to different levels of anxiety. Overall we can conclude that opposite swimming behavior in the FST could parallel some differences in cognitive performances, more specifically linked to spatial working memory.