Neuroscience
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Comparative Study
Regions of alpha-amino-5-methyl-3-hydroxy-4-isoxazole propionic acid receptor subunits that are permissive for the insertion of green fluorescent protein.
The green fluorescent protein can be fused to the ends of a mature glutamate receptor subunit to produce functional, fluorescent receptors. However, there are good reasons to search for internal regions of receptor subunits that can tolerate green fluorescent protein insertion. First, internal insertions of green fluorescent protein may produce functional, fluorescent subunits that traffic more correctly. ⋯ Finally, internal green fluorescent protein insertions could potentially produce subunits capable of signaling conformational changes through intrinsic changes in fluorescence intensity. To identify regions of receptor subunits that are permissive for green fluorescent protein insertion, we used a series of recombinant transposons to create fluorescent protein insertions in three alpha-amino-5-methyl-3-hydroxy-4-isoxazole propionic acid receptor subunits. A combined analysis of the relative fluorescence intensity and glutamate-gated ion channel function of 69 different green fluorescent protein fusion proteins identified permissive zones for the creation of bright and fully functional receptor subunits in the C-terminal portion of the amino terminal domain, the intracellular tail of the carboxy terminal domain, and within the pore-forming regions of the channel.
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Comparative Study
Habituation to the test cage influences amphetamine-induced locomotion and Fos expression and increases FosB/DeltaFosB-like immunoreactivity in mice.
Pre-exposure to the testing cage (habituation or familiarization) is a common procedure aimed at reducing the interference of novelty-induced arousal and drug-independent individual differences on neural and behavioral measures. However, recent results suggest that this procedure might exert a major influence on the effects of addictive drugs. The present experiments tested the effects of repeated exposure to a test cage (1 h daily for four consecutive days) on amphetamine-induced locomotion and Fos expression as well as on FosB/DeltaFosB-like immunoreactivity in mice of the C57BL/6J and DBA/2J inbred strains that differ for the response to amphetamine, stress and novelty. ⋯ These results demonstrate indexes of stress-like plasticity in the brains of mice exposed to a procedure of familiarization to the testing environment. Moreover, they suggest that the procedure of daily familiarization influences the pattern of brain Fos expression induced by amphetamine. Finally, they indicate complex interactions between experience with the testing environment, genotype and drug.
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Comparative Study
Chronic morphine administration results in tolerance to delta opioid receptor-mediated antinociception.
Delta opioid receptor agonists produce only a moderate degree of antinociception, possibly reflecting the predominantly intracellular location of delta opioid receptor. However, recent studies suggest that short term morphine pretreatment can increase delta opioid receptor-mediated antinociception by promoting the translocation of delta opioid receptor to the cell surface. Even more striking sensitization has been reported after long term morphine pretreatment and withdrawal in locomotor tests. ⋯ However, consistent with previous reports, short term (2 day) pretreatment with morphine did result in sensitization to [D-Ala2,Glu4]-deltorphin. Subsequent in vitro analysis, using [125I][D-Ala2,Glu4]-deltorphin or guanosine 5'(gamma-35S-thio) triphosphate autoradiography, did not reveal any changes in delta opioid receptor binding or function resulting from chronic morphine pretreatment. In conclusion, chronic morphine pretreatment caused tolerance to delta opioid receptor-mediated behavioral effects with no clear change at the receptor level.
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Comparative Study
Maturation of firing pattern in chick vestibular nucleus neurons.
The principal cells of the chick tangential nucleus are vestibular nucleus neurons participating in the vestibuloocular and vestibulocollic reflexes. In birds and mammals, spontaneous and stimulus-evoked firing of action potentials is essential for vestibular nucleus neurons to generate mature vestibular reflex activity. The emergence of spike-firing pattern and the underlying ion channels were studied in morphologically-identified principal cells using whole-cell patch-clamp recordings from brain slices of late-term embryos (embryonic day 16) and hatchling chickens (hatching day 1 and hatching day 5). ⋯ From embryonic day 16 to hatching day 5, the gain for evoked spike firing increased almost 10-fold. At hatching day 5, a persistent sodium channel was essential for the generation of spontaneous spike activity, while a small conductance, calcium-dependent potassium current modulated both the spontaneous and evoked spike firing activity. Altogether, these in vitro studies showed that during the perinatal period, the principal cells switched from displaying no spontaneous spike activity at resting membrane potential and generating one spike on depolarization to the tonic firing of spontaneous and evoked action potentials.
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Comparative Study
Sensitivity of rat temporalis muscle afferent fibers to peripheral N-methyl-D-aspartate receptor activation.
The temporalis muscle is a common source of pain in headache and chronic craniofacial pain conditions such as temporomandibular disorders, which have an increased prevalence in women. The characteristics of slowly conducting temporalis afferent fibers have not been investigated. Therefore, the aim of the present study was to examine the characteristics of slowly conducting temporalis muscle afferent fibers and to determine whether these fibers are excited by activation of peripheral N-methyl-D-aspartate receptors. ⋯ Co-injection of ketamine (20 mM) with the second injection of N-methyl-D-aspartate significantly decreased N-methyl-D-aspartate-evoked afferent discharge in both sexes. This concentration of ketamine is greater than that needed to attenuate afferent discharge evoked by injection of glutamate into the masseter muscle. These results suggest that unlike masseter afferent fibers, temporalis afferent fibers are relatively insensitive to peripheral N-methyl-D-aspartate receptor activation.