Effect and possible mechanism of melatonin on the firing rate of pain neurons in lateral habenular nucleus / 中国应用生理学杂志

<p><b>AIM</b>The effect and possible mechanism of Melatonin (MEL) on firing rate of pain neurons in lateral habenular nucleus of rats were investigated in the experiment.</p><p><b>METHODS</b>Single extracellular firing were recorded to study the firing rate changes of pain neurons and sensitivity changes to pain stimulation induced by MEL in LHb of rats. Reverse effect of naloxone on the analgesia induced by melatonin was also observed.</p><p><b>RESULTS</b>Melatonin showed the effects on the firing of pain neurons in the LHb and decreased the sensitivity of pain neurons to pain stimulation, which could be reversed by naloxone.</p><p><b>CONCLUSION</b>Melatonin can change the responses of pain neurons to pain stimulation via opioid receptor in the LHb, which might be one of analgesic mechanisms by MEL.</p>

Pregnanolone effects on the blood pressure of stress-induced hypertension in rats / 生理学报

This study was conducted to determine the effect of pregnanolone (PGN) on blood pressure of a rat model of stress-induced hypertension (SIH). This model was established by applying electric shock to animal feet together with noise. PGN was administered intraperitoneally at 0.24 mg/kg.d(-1) and blood pressure, angiotensin II (Ang II) levels, and the expression of Fos-like protein immunoreactive (FLI) neurons in brain areas were determined. Rats were randomly divided into five groups: (1) control, (2) stressed for 1 h, (3) stressed for 1 h after PGN pretreatment, (4) stressed for a 2 h session, twice a day, for 15 d, and (5) stressed for a 2 h session after PGN pretreatment, twice a day, for 15 d. The results showed that increased systolic pressure of tail artery caused by a 15-d stress treatment was significantly reduced by PGN pretreatment (P<0.001). Ang II levels, measured by radioactive immunoreactivity, were significantly elevated (P<0.001) after the rats were stressed for 1 h or 15 d, the Ang II level was significantly reduced by PGN treatment in both 1 h and 15 d stress groups (P<0.05). Only a small number of FLI neurons were found in the brain areas of the control group, 15 d stress group, and 15 d stress with PGN group. In the 1 h stress group, more FLI neurons were found in the lateral habenular nucleus, the medial habenular nucleus, the paraventricular nucleus, the central nucleus of amgydaloid and the lateral hypothalamus compared with the control group. PGN pretreatment significantly prevented the increase in the number of FLI neurons. These results indicate that PGN pretreatment prevents elevation of tail artery systolic pressure in SIH rats and that this effect of PGN may be mediated through reducing Ang II level and inhibiting the activity of cardiovascular center involved in stress.