PubMed · 12627191
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J Pedlar. 2003-02-22. Prolonged paraesthesia.. https://doi.org/10.1038/sj.bdj.4809905
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The effect of tityustoxin (TsTX) on the release of [3H] dopamine in rat brain prefrontal cortical slices was investigated. The stimulatory effect of TsTX was dependent on incubation time and TsTX concentration with an EC50 of 0.05 microM. The release of [3H] dopamine stimulated by TsTX is dependent of Na+ channels and thus, was completely, inhibited by tetrodotoxin. Tityustoxin-induced release of [3H] dopamine was not blocked by ethylene glycol-bis(beta-aminoethyl) ether (EGTA) and thus was independent of extracellular calcium. However, [3H] dopamine release induced by TsTX was inhibited by 52% by BAPTA, a calcium chelator. Moreover, dantrolene (100 microM) and tetracaine (500 microM) partially inhibited by 38 and 29%, respectively, the tityustoxin-induced release of [3H] dopamine from prefrontal cortical slices suggesting a role from intracellular calcium increase. In conclusion, part of the TsTX-induced release [3H] dopamine may be due to an effect of the toxin on the reversal of the dopamine transporter (DAT), but the majority of the toxin stimulated release of [3H] dopamine involves the mobilization of intracellular calcium stores.
To understand the functional significance of orofacial injury-induced neuronal activation, this study examined the rostral projection of caudal brainstem neurons that were activated by masseteric inflammation. Rats were injected with a retrograde tracer, Fluorogold, into the nucleus submedius of the thalamus (Sm), parabrachial nucleus (PB), lateral hypothalamus (LH), or medial ventroposterior thalamic nucleus (VPM) 7 days before injection of an inflammatory agent, complete Freund's adjuvant (CFA), into the masseter muscle. Rats were perfused at 2 hours after inflammation, and brainstem tissues were processed for Fos-Fluorogold double immunocytochemistry. Although there was no difference in Fos expression among the four groups (n=4 per site), the rostral projection of Fos-positive neurons showed dramatic differences. In the ventral portion of the trigeminal subnuclei interpolaris/caudalis (Vi/Vc) transition zone, the percentage of Fos-positive neurons projecting to the Sm (39.7%) was significantly higher than that projecting to the LH (5.4%) or VPM (5.6%; P<.001). The anesthesia alone also induced Fos expression in ventral Vi/Vc neurons, but these neurons did not project to Sm. In the caudal laminated Vc and dorsal Vi/Vc, the PB was the major site of rostral projection of Fos-positive neurons. In the caudal ventrolateral medulla and nucleus tractus solitarius, Fos-positive neurons projected to the Sm, PB, and LH. Most VPM-projecting neurons examined did not show Fos-like immunoreactivity after masseter inflammation. These findings emphasize the importance of the trigeminal Vi/Vc transition zone in response to orofacial deep tissue injury. Furthermore, the results differentiate the ventral and dorsal portions of the Vi/Vc transition zone, in that the Sm received projection mainly from activated neurons in the ventral Vi/Vc. The activation of Vi/Vc neurons and associated ascending pathways may facilitate somatoautonomic and somatovisceral integration and descending pain modulation after orofacial deep tissue injury.
While hippocampal lesions impair learning and memory in many tasks, such lesions also enhance learning and memory in other tasks. The present experiment examines the effects of inactivation of the hippocampus with lidocaine prior to learning, to find food in a place or response version of a four-arm plus-shaped maze. Rats received lidocaine injections 6 min prior to training. Rats were trained in a single session to a criterion of 9/10 correct responses. Compared to artificial cerebrospinal fluid (aCSF)-injected controls, rats with intra-hippocampal injections of lidocaine exhibited significantly retarded acquisition of place learning. In marked contrast, rats with intra-hippocampal injections of lidocaine exhibited significantly enhanced acquisition of response learning compared to their controls. In addition to showing that the hippocampus is important for learning the place task, these findings suggest that processing of information by the hippocampus interferes with learning a task dependent on a different neural system.