While the suprachiasmatic nucleus (SCN) coordinates the majority of daily rhythms, some circadian patterns of expression are controlled from outside of the SCN. These include responses to daily methamphetamine (MAP) injection, or daily restricted feeding. The mechanisms underlying these SCN‐independent circadian rhythms are unknown. A circadian oscillation in the expression of mPer1 and/or mPer2, mouse period, in the SCN is considered necessary to generate an SCN‐dependent circadian rhythm. Therefore, in this experiment, we examined the association between mPer gene expression and the MAP‐induced, SCN‐independent circadian rhythm. Acute injection of MAP caused an elevation of mPer1, mBmal1, and mNpas2 gene expression in the striatum and mPer1 in the liver. Daily MAP injection at a fixed time for 6 days shifted the rhythmic mPer1 and mPer2 expression in the striatum from a nocturnal to a diurnal rhythm, but failed to affect that in the SCN. Although lesion of the SCN ‘flattened’mPer gene oscillation in the striatum and liver, daily MAP injection caused both behavioural and mPer gene expression rhythms. Daily MAP injection at variable injection intervals (12–36 h) for 6 days, however, failed to produce mPer gene rhythm in the striatum. Daily repeated MAP signals may strengthen the oscillatory force of SCN‐independent circadian behavioural and molecular rhythms. The present results suggest that daily oscillation of mPer genes outside the SCN is closely associated with the regulation of SCN‐independent rhythms. Thus, the present experiment highlights strongly the important role of clock gene expression, in the brain, that underlies the circadian behavioural rhythm.

Aging alters circadian components such as the free-running period, the day-to-night activity ratio and photic entrainment in behavioral rhythms, and 2-deoxyglucose uptakes and neuronal firing in the suprachiasmatic nucleus (SCN). A core clock mechanism in the mouse SCN appears to involve a transcriptional feedback loop in which Period (Per) and Cryptochrome (Cry) genes play a role in negative feedback. The circadian rhythm systems include photic entrainment, clock oscillation, and outputs of clock information such as melatonin production. In this experiment, we examined clock gene expression to determine whether circadian input, oscillation, and output are disrupted with aging. Circadian expression profiles of rPer1, rPer2, or rCry1 mRNA were very similar in the SCN, the paraventricular nucleus of the hypothalamus (PVN), and the pineal body of young and aged (22-26 months) rats. On the other hand, the photic stimulation-induced rapid expression of Per1 and Per2 in the SCN was reduced with aging. The present results suggest that the molecular mechanism of clock oscillation in the SCN, PVN, and pineal body is preserved against aging, whereas the impairment of Per1 induction in the SCN after light stimulation may result in impaired behavioral photic entrainment in aged rats.

Methamphetamine (MAP) causes the sensitization phenomena not only in MAP-induced locomotor activity, dopamine release, and Fos expression, but also in MAP-induced circadian rhythm. Cocaine-induced sensitization is reportedly impaired in Drosophila melanogaster mutant for the Period (Per) gene. Thus, sensitization may be related to induction of the Per gene. A rapid induction of mPer1 and/or mPer2 in the suprachiasmatic nucleus after light exposure is believed to be necessary for light-induced behavioral phase shifting. Although the caudate/putamen (CPu) expresses mPer1 and/or mPer2 mRNA, the function of these genes in this nucleus has not yet been elucidated. Therefore, we examined whether MAP affects the expression of mPer1 and/or mPer2 mRNA in the mouse CPu. Injection of MAP augmented the expression of mPer1 but not mPer2 or mPer3 in the CPu, and this MAP-induced increase in mPer1 expression lasted for 2 h. Also, the MAP-induced increase of mPer1 mRNA was strongly antagonized by pretreatment with a dopamine D1 receptor and N-methyl-D-aspartate (NMDA) receptor antagonist, but not by a D2 receptor antagonist. Interestingly, application of either the D1 or the D2 agonist alone did not cause mPer1 expression. The present results demonstrate that activation of both NMDA and D1 receptors is necessary to produce MAP-induced mPer1 expression in the CPu. Repeated injection of MAP caused a sensitization in not only the locomotor activity but also mPer1 expression in the CPu without affecting the level of mPer2, mPer3, or mTim mRNA. Thus, these results suggest that MAP-induced mPer1 gene expression may be related to the mechanism for MAP-induced sensitization in the mouse.

Aging alters circadian components such as the free-running period, the day-to-night activity ratio and photic entrainment in behavioral rhythms, and 2-deoxyglucose uptakes and neuronal firing in the suprachiasmatic nucleus (SCN). A core clock mechanism in the mouse SCN appears to involve a transcriptional feedback loop in which Period (Per) and Cryptochrome (Cry) genes play a role in negative feedback. The circadian rhythm systems include photic entrainment, clock oscillation, and outputs of clock information such as melatonin production. In this experiment, we examined clock gene expression to determine whether circadian input, oscillation, and output are disrupted with aging. Circadian expression profiles of rPer1, rPer2, or rCry1 mRNA were very similar in the SCN, the paraventricular nucleus of the hypothalamus (PVN), and the pineal body of young and aged (22-26 months) rats. On the other hand, the photic stimulation-induced rapid expression of Per1 and Per2 in the SCN was reduced with aging. The present results suggest that the molecular mechanism of clock oscillation in the SCN, PVN, and pineal body is preserved against aging, whereas the impairment of Per1 induction in the SCN after light stimulation may result in impaired behavioral photic entrainment in aged rats.

No abstract

Ethenzamide (ETZ), an antipyretic analgesic categorized as a non-steroidal anti-inflammatory drug (NSAID), is widely used as an over-the-counter (OTC) drug in combination with other NSAIDs. However, its site of action and mechanism underlying its analgesic action have not yet been fully elucidated. In this study, we performed in vitro pharmacological assays to identify the mechanism underlying the analgesic action of ETZ, and also conducted the rat formalin test to investigate its analgesic effect and site of action.Of the 85 receptors, ion channels, transporters and enzymes tested, we found that ETZ binds to the 5-hydroxytryptamine (5HT) 2B receptor in concentration-dependent manner with modest inhibitory effects on monoamine oxidase-A and transient potential vanilloid 1 channel. The 5HT 2B receptor antagonist activity of ETZ was also confirmed in a cellular functional assay. Furthermore, the drug exerted no inhibitory effects on cycrooxygenase-1 and -2. In the rat formalin test, oral administration of ETZ significantly reduced the nociceptive responses of the second phase and also the number of c-Fos-expressing cells in the spinal dorsal horn, in a dose-dependent manner. Moreover, intrathecal administration of ETZ significantly reduced the nociceptive responses. These results suggest that the analgesic effect of ETZ is exerted at least in the spinal cord, and the effect would be attributed to multiple mechanisms of action including 5HT 2B receptor blockade.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are known to cause gastric mucosal damage, in which gastric hypermotility has been reported to play a primary role. The antipyretic analgesic drug ethenzamide (ETZ) is widely used in combination with other NSAIDs and, in a recent study, was found to possess 5hydroxytriptamine (5HT) 2B receptor antagonistic activity. Therefore, the inhibition of gastric contraction via 5HT 2B receptor blockade by ETZ might contribute to ETZ's protective effect against NSAIDs-induced gastric mucosal damage. In the present study, we examined the effects of ETZ on gastric contraction and ibuprofen (IBP)-induced gastric mucosal damage in rats. We found that ETZ suppressed both 5HT-and α-methyl-5HT (5HT 2 receptor agonist)-induced contractions of rat-isolated gastric fundus in a concentration-dependent manner. This suppressive effect of ETZ was not seen for either high-KCl-or acetylcholine-induced contractions. Furthermore, ETZ was confirmed to decrease ibuprofen-induced gastric mucosal damage in a dosedependent manner in rats. Similarly, clonidine is known to reduce gastric motility, and methysergide (a 5HT 2 receptor antagonist) is known to inhibit 5HT-induced contractions of the gastric fundus, which also decreases IBP-induced gastric mucosal damage, respectively. Although further research on other possible sites or mechanisms of action would be needed, these results suggest that ETZ exerts a protective effect against IBPinduced gastric mucosal damage and that suppressing the gastric contraction may play an important role in the gastroprotective effect of ETZ.

No abstract