Neuroscience
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Fear-conditioned analgesia is an important survival response which is expressed upon re-exposure to a context previously paired with a noxious stimulus. The aim of the present study was to characterize further the behavioral, monoaminergic and hypothalamo-pituitary-adrenal axis alterations associated with expression of fear-conditioned analgesia. Rats which had received footshock conditioning 24 h earlier, exhibited reduced formalin-evoked nociceptive behavior upon re-exposure to the footshock chamber, compared with non-footshocked formalin-treated rats. ⋯ These data extend behavioral characterization of the phenomenon of fear-conditioned analgesia and suggest that measurement of ultrasound emission may be used as an ethologically relevant index of the defense response during fear-conditioned analgesia. Ultrasonic vocalization may also be a useful behavioral output to aid separation of nociception and aversion. The data provide evidence for discrete alterations in dopaminergic activity in the periaqueductal gray and thalamus and for altered hypothalamo-pituitary-adrenal axis activity following expression of defensive behavior.
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Neurons in the region of dorsomedial hypothalamus are involved in the organization of the physiological responses to emotional stress. We have recently shown that the cardiovascular response evoked by activation of dorsomedial hypothalamus neurons is largely dependent on a synaptic relay with the lateral/dorsolateral periaqueductal gray region. In this study, we aimed to investigate whether excitatory amino acid receptors at the lateral/dorsolateral periaqueductal gray region are involved in mediating the response evoked by activation of dorsomedial hypothalamus neurons. ⋯ In an additional series of experiments, microinjection of the N-methyl-D-aspartate receptor agonist, N-methyl-D-aspartate, into the lateral/dorsolateral periaqueductal gray region, evoked an increase in heart rate and a pressor response that was accompanied by an increase in locomotor activity. These effects were not altered by pretreatment of lateral/dorsolateral periaqueductal gray region neurons with 6-cyano-7-nitroquinoxaline-2,3-dione but were completely abolished by MK-801. Altogether, these findings indicate that the cardiovascular response evoked by dorsomedial hypothalamus activation involves a synaptic relay at the lateral/dorsolateral periaqueductal gray region that is mediated at least in large part by excitatory amino acid receptors, possibly N-methyl-D-aspartate receptors.
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Neurofibromatosis type I is a common autosomal dominant disease characterized by formation of multiple benign and malignant tumors. People with this disorder also experience chronic pain, which can be disabling. Neurofibrinomin, the protein product of the NF1 gene (neurofibromin gene (human)), is a guanosine triphosphate activating protein for p21(ras). ⋯ When nerve growth factor was removed 48 h before conducting release experiments, nerve growth factor-induced augmentation of immunoreactive calcitonin gene-related peptide release from Nf1+/- neurons was more pronounced than in Nf1+/- sensory neurons that were treated with nerve growth factor continuously for 5-7 days. Thus, sensory neurons from mice with a heterozygous mutation of the Nf1 gene that is analogous to the human disease neurofibromatosis type I, exhibit increased sensitivity to chemical stimulation. This augmented responsiveness may explain the abnormal pain sensations experienced by people with neurofibromatosis type I and suggests an important role for guanosine triphosphate activating proteins, in the regulation of nociceptive sensory neuron sensitization.
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Comparative Study
Fatty acids differentially affect serotonin receptor and transporter binding in the rat brain.
The aim of this study was to examine the influence of different fat diets on serotonin receptor and transporter binding. Male Sprague-Dawley rats were fed a diet of either high saturated fat, omega-6 polyunsaturated fatty acid, omega-3 polyunsaturated fatty acid or low fat (control) for eight weeks. ⋯ Overall, the omega-6 polyunsaturated fatty acid diet exerted the most influence on serotonin receptor and transporter binding. These results may be of importance in relation to neuropsychiatric diseases such as schizophrenia, where associations between altered fatty acid levels and the serotonergic system have been made.
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It has been reported recently that mice lacking both alleles of the LIM-homeobox gene Lhx7, display dramatically reduced number of forebrain cholinergic neurons. In the present study, we investigated whether the Lhx7 mutation affects male and female mice differently, given the fact that gender differences are consistently observed in forebrain cholinergic function. Our results show that in adult male as well as female Lhx7 homozygous mutants there is a dramatic loss of choline acetyltransferase immunoreactive forebrain neurons, both projection and interneurons. ⋯ Furthermore, there was an increase of M1-, but not M2-, muscarinic acetylcholine receptor binding site density in the somatosensory cortex and basal ganglia of only the female homozygous mutant mice. Such an increase can be regarded as a mechanism acting to compensate for the dramatically reduced cholinergic input, raising the possibility that the forebrain cholinergic system in female mice may be more plastic and responsive to situations of limited neurotransmitter availability. Finally, our study provides additional data for the sexual dimorphism of the forebrain cholinergic system, as female mice appear to have a lower density of M1-muscarinic acetylcholine receptors in the striatal areas of the basal ganglia and a higher density of M2-muscarinic acetylcholine receptors, in a number of cortical areas, as well as the striatal areas of the basal ganglia.