BACKGROUND: Although the inhibitory role of the 5-hydroxytrypatmine receptor 7(5-HT7R) on nociceptive processing is generally recognized, an excitatory effect associated with a reduced 5-HT7R expression has also been observed in the nerve injury model. In the carrageenan model, no significant effect is produced by the 5-HT7R activation, but the change in 5-HT7R expression has not been examined. Lesioning of the spinal serotonergic pathway enhances allodynia in the carrageenan model, but it also relieves several other pain states, including in the formalin model. While lesioning suppresses the activation of the extracellular signal-regulated kinase (ERK) of the spinal cord in the formalin model, its role in the carrageenan model has not been reported. METHODS: Following intraplantar injections of carrageenan, the spinal 5-HT7R expression was examined using Western blotting in male Sprague-Dawley rats. The effect of serotonergic pathway lesioning with intrathecal 5,7-dihydroxytryptamine (5,7-DHT) on the expression of the phospho-ERK was measured. RESULTS: The expression of the 5-HT7R in the carrageenan model was not significantly different from that of naive animals. The expression of the spinal p-ERK in the carrageenan model was significantly increased, but returned to the level of a naive rat 1 hour after the carrageenan injection. However, it remained significantly higher 1 hour after the injection in the animals treated with 5,7-DHT than in the naive and control rats. CONCLUSIONS: The expression of the spinal 5-HT7R is not altered by peripheral inflammation with carrageenan, suggesting that the lack of antinociceptive effect of the 5-HT7R activation is partly attributable to the absence of changes in the expression of the 5-HT7R in the spinal cord. The extended increase of the spinal p-ERK might be related to the enhanced pain behavior in the animals with lesions of the spinal serotonergic pathway in the carrageenan model.
5,7-Dihydroxytryptamine ; Animals ; Blotting, Western ; Carrageenan* ; Formaldehyde ; Humans ; Hyperalgesia ; Inflammation ; Male ; Phosphotransferases ; Rats* ; Rats, Sprague-Dawley ; Spinal Cord

OBJECTIVETo investigate the relationship between serotonin (5-HT) and epilepsy and the mechanism of learning-memory in pilocarpine (PILO)-induced epileptic rats after 5,7-dihydroxytryptamine (5,7-DHT) microinjection in median raphe nucleus.

METHODSAdult S D rats were randomly divided into 3 groups: PILO group, PILO+ 5,7-DHT group, vehicle control group; PILO group was divided into two groups by status epilepticus (SE): PILO + SE group and PILO - SE group. The rats' seizures and cortex electroencephalography (EEG) were observed by video EEG. The rats' spatial learning-memory was evaluated by Morris water maze. Finally, serotonergic neuron in raphe nuclei was observed by immunohistochemistry.

RESULTSAfter treatment of 5,7-DHT (PILO + 5,7-DHT group), the success rate, the mortality and the frequency of chronic spontaneous seizures in pilocarpine-induced epilepsy model were all improved. Compared with the control group, the number of serotonergic neuron in raphe nuclei was decrease in PILO + SE group (P < 0.05). Moreover, it's extremely decrease in PILO + 5,7-DHT group (P < 0.01). Compared with control group, the mean escape latency was prolonged, the times of crossing target was decreased and the retention time in target zone was shortened in PILO + SE group (P < 0.05), but there was no significant difference between PILO + SE group and PILO + 5,7-DHT group.

CONCLUSIONDepletion of serotonin may facility the rats' epileptic seizures, but we could not interpret which may cause epileptic rats' cognitive deficit.

5,7-Dihydroxytryptamine ; toxicity ; Animals ; Epilepsy ; chemically induced ; metabolism ; psychology ; Male ; Maze Learning ; Memory ; Pilocarpine ; adverse effects ; Raphe Nuclei ; Rats ; Rats, Sprague-Dawley ; Serotonin ; metabolism

In vivo extracellular recordings were made in the subthalamic nucleus (STN) of intact control rats and rats with 5,7-dihydroxytryptamine (5,7-DHT) -produced lesion of dorsal raphe nucleus (DRN). The results showed that the firing rate of STN neurons in control rats and DRN-lesioned rats were (6.93+/-6.55) Hz and (11.27+/-9.31) Hz, respectively, and the firing rate of DRN-lesioned rats significantly increased when compared to the control rats (P<0.01). In control rats, 13% of STN neurons discharged regularly, 46% irregularly and 41% in bursts. In DRN-lesioned rats, 9% of STN neurons discharged regularly, 14% irregularly and 77% in bursts, the percentage of STN neurons firing in bursts was obviously higher than that of the control rats (P<0.01). In addition, the mean interspike interval coefficient of variation of STN neurons in control rats and DRN-lesioned rats were (0.05+/-0.04) and (0.11+/-0.09), respectively. The mean interspike interval coefficient of variation of DRN-lesioned rats was significantly higher than that of the control rats (P<0.001). These results show that the firing rate and the bursting pattern rate of neurons in STN of DRN-lesioned rats increase significantly, suggesting that DRN inhibits the neuronal activity of the subthalamic neurons in the intact rat.
5,7-Dihydroxytryptamine ; pharmacology ; Adrenergic Agents ; pharmacology ; Animals ; Electrophysiological Phenomena ; Male ; Neurons ; physiology ; Random Allocation ; Raphe Nuclei ; drug effects ; pathology ; Rats ; Rats, Sprague-Dawley ; Subthalamic Nucleus ; physiopathology

The present study is aimed to investigated the firing activity of pyramidal neurons and interneurons in the medial prefrontal cortex (mPFC) in rats with bilateral intraventricular injection of 5,7-dihydroxytryptamine (5,7-DHT) by using in vivo extracellular recording. The results showed that the injection of 5,7-DHT reduced the 5-hydroxytryptamine (5-HT) levels in the mPFC and dorsal raphe nucleus in the rats. The firing rate of mPFC pyramidal neurons in rats with 5,7-DHT injection was significantly higher than that of normal rats, and the firing pattern of these neurons also changed significantly towards a more burst-firing, while the injection decreased the firing rate of mPFC interneurons and changed the firing pattern of the interneurons towards a more irregular. These results indicate that the lesions of the serotonergic neurons lead to the changes in the firing activity of mPFC pyramidal neurons and interneurons, suggesting that serotonergic system plays an important role in the regulation of the neuronal activity in the mPFC.
5,7-Dihydroxytryptamine ; pharmacology ; Action Potentials ; Animals ; Dorsal Raphe Nucleus ; cytology ; Injections, Intraventricular ; Interneurons ; drug effects ; Prefrontal Cortex ; cytology ; Pyramidal Cells ; drug effects ; Rats ; Serotonin ; metabolism