Neuroscience
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The effects of 5-hydroxytryptamine on peripheral nociceptive fibres were studied in an in vitro preparation of the neonatal rat spinal cord with attached tail. The activation of peripheral fibres in the tail by noxious stimuli (bradykinin, capsaicin, heat) was recorded as a depolarization of a ventral root in the lumbar region of the spinal cord (L3-L5). Responses evoked by brief applications of submaximal or threshold concentrations of bradykinin or capsaicin to the tail were enhanced by 5-hydroxytryptamine and the 5-hydroxytryptamine1C/5-hydroxytryptamine2-receptor agonist alpha-methyl-5-hydroxtryptamine but not by the 5-hydroxytryptamine3-receptor agonist 2-methyl-5-hydroxytryptamine or the 5-hydroxytryptamine1-receptor agonist 5-carboxamidotryptamine. ⋯ The excitatory effect of 5-hydroxytryptamine was blocked by methiothepin but not by ICS 205-930 or ketanserin. Neither 5-hydroxytryptamine-induced sensitization nor 5-hydroxytryptamine-evoked activation of peripheral fibres was blocked by indomethacin. These data indicate that two types of receptor are involved in the peripheral actions of 5-hydroxytryptamine in nociception. 5-Hydroxytryptamine-induced sensitization involves a 5-hydroxytryptamine2-receptor, whereas 5-hydroxytryptamine-evoked excitation involves a 5-hydroxytryptamine1-like-receptor.
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Although many workers have appreciated the striking cytologic and neurochemical similarities of neostriatum, accumbens and olfactory tubercle, a compelling case for regarding these areas as territories in a striatal complex awaited the arguments made by Heimer and his colleagues based on their investigations of connections. A number of recent papers support this viewpoint and extend it with the characterization of three accumbal subterritories: core, shell and rostral pole. The case for separate classifications of systems traversing the accumbens has become more compelling with each study that demonstrates connectional, cytoarchitectural and neurochemical specificity conforming to the boundaries separating the core and its downstream targets from the shell and its projection fields. ⋯ Interestingly, histochemically distinct cell clusters tend to be numerous in boundary regions between adjacent territories and subterritories. The predominant organizational pattern appears to be one in which the core, shell and rostral pole engage different forebrain systems that possibly subserve entirely different functions mediated by distantly related mechanisms. In this regard, it is of paramount interest that the processing of information conveyed to the accumbens by diverse cortical and subcortical inputs occurs within distinct and perhaps very different dopaminergic environments in the core, shell and rostral pole (e.g., see Refs 24, 34, 90, 110).