Neuroscience
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Comparative Study
The rodent amygdala contributes to the production of cannabinoid-induced antinociception.
The amygdala is a temporal lobe region that is implicated in emotional information processing. The amygdala also is associated with the processing and modulation of pain sensation. Recently, we demonstrated that in nonhuman primates, the amygdala is necessary for the full expression of cannabinoid-induced antinociception [J Neurosci 21 (2001) 8238]. ⋯ In rats treated with intra-CeA muscimol, however, these effects of WIN55,212-2 were significantly reduced. The results constitute the first causal data demonstrating the necessity of descending pain-modulatory circuitry (of which the CeA is a component) for the full expression of cannabinoid-induced antinociception in the rat. Furthermore, the results complement previous findings suggesting an overlap in neural circuitry activated by opioids and cannabinoids.
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Comparative Study
Association of gephyrin and glycine receptors in the human brainstem and spinal cord: an immunohistochemical analysis.
Gephyrin is a postsynaptic clustering molecule that forms a protein scaffold to anchor inhibitory neurotransmitter receptors at the postsynaptic membrane of neurons. Gephyrin was first identified as a protein component of the glycine receptor complex and is also colocalized with several GABAA receptor subunits in rodent brain. We have studied the distribution of gephyrin and glycine receptor subunits in the human brainstem and spinal cord using immunohistochemistry at light and confocal laser scanning microscopy levels. ⋯ Colocalization of immunoreactivities for gephyrin and glycine receptor subunits was detected in the dorsal and ventral horns of the spinal cord, the hypoglossal nucleus and the medial vestibular nucleus of the medulla. The results clearly establish that gephyrin is ubiquitously distributed and is colocalized, with a large proportion of glycine receptor subunits in the human brainstem and spinal cord. We therefore suggest that gephyrin functions as a clustering molecule for major subtypes of glycine receptors in the human CNS.
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Comparative Study
Ampakines reduce methamphetamine-driven rotation and activate neocortex in a regionally selective fashion.
It has been proposed that glutamatergic and dopaminergic systems are functionally opposed in their regulation of striatal output. The present study tested the effects of drugs that enhance AMPA-receptor-mediated glutamatergic transmission (ampakines) for their effects on dopamine-related alterations in cortical activity and locomotor behavior. Rats with unilateral 6-hydroxydopamine lesions of the ascending nigro-striatal dopamine system were sensitized to methamphetamine and then tested for methamphetamine-induced circling behavior in the presence and absence of ampakines CX546 and CX614. ⋯ Still larger ampakine-elicited effects were obtained in parietal cortex of the dopamine-depleted hemisphere where labeling densities were increased by approximately 60% above values found in methamphetamine-alone rats. With these effects, the hemispheric asymmetry of cortical activation was less pronounced in the ampakine-cotreatment group as compared with the methamphetamine-alone group. These results indicate that positive modulation of AMPA-type glutamate receptors 1) can offset behavioral disturbances arising from sensitized dopamine receptors and 2) increases aggregate neuronal activity in a regionally selective manner that is probably dependent upon behavioral demands.
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Comparative Study
In vivo and in vitro effects of peripheral galanin on nociceptive transmission in naive and neuropathic states.
Galanin is widely distributed in the nervous system and is consistently upregulated in both dorsal root ganglion and spinal neurones by peripheral nerve injury. This study investigates the peripheral effects of galanin on nociceptive neurones using in vitro and in vivo electrophysiological techniques in naive and neuropathic rats. Using an in vitro skin-nerve preparation recording from single nociceptive fibres, galanin (1 microM) significantly inhibited firing induced by noxious heat in 65% of fibres examined. ⋯ Injection of galanin (0.1-10 microg) into hindpaw receptive fields inhibited responses to innocuous mechanical, noxious mechanical and noxious heat stimuli in a proportion of neurones in each animal group and facilitated the remaining neurones. However, a higher proportion of neurones (80-90%) was inhibited by peripheral galanin administration in SNL rats compared with naive (45-55%) and sham (70-80%) rats. These results show that galanin can have both excitatory and inhibitory effects on peripheral sensory neurones, perhaps reflecting differential receptor activation, and that the proportion of these receptors may change following peripheral neuropathy.
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Comparative Study
Low-threshold heat receptor in chick sensory neurons is upregulated independently of nerve growth factor after nerve injury.
In mammals, the cloned low-threshold heat receptor, vanilloid receptor subtype 1 (VR1), is involved in the genesis of thermal hyperalgesia after inflammation. However, there is evidence that VR1 is not involved in the thermal hyperalgesia that occurs after nerve injury. In search for other heat receptors which might be involved in this phenomenon, we previously demonstrated that chick dorsal root ganglion neurons, which are insensitive to capsaicin, respond to low-threshold heat. ⋯ On the molecular level, there was an increase of chick VR1 mRNA level in dorsal root ganglion cells cultured for 3 days in medium lacking NGF. In rat dorsal root ganglion neurons cultured for 1-4 days without NGF, patch-clamp experiments revealed that after 1 day almost all neurons responding to heat also responded to capsaicin, whereas after 3-4 days, more than one-half of the heat-responsive neurons did not respond to capsaicin. These data suggest the existence of low-threshold heat receptors in chick dorsal root ganglion neurons, the expression of which is regulated independently of NGF.