Takeshi Tadano

Angiotensin II produces nociceptive behavior through spinal AT1 receptor-mediated p38 mitogen-activated protein kinase activation in mice

BackgroundIt has been demonstrated that angiotensin II (Ang II) participates in either the inhibition or the facilitation of nociceptive transmission depending on the brain area. Neuronal Ang II is locally synthesized not only in the brain, but also in the spinal cord. Though the spinal cord is an important area for the modulation of nociception, the role of spinal Ang II in nociceptive transmission remains unclear. Therefore, in order to elucidate the role of Ang II in nociceptive transmission in the spinal cord, we examined the effect of intrathecal (i.t.) administration of Ang II into mice.ResultsI.t. administration of Ang II produced a behavioral response in mice mainly consisting of biting and/or licking of the hindpaw and the tail along with slight hindlimb scratching directed toward the flank. The behavior induced by Ang II (3 pmol) was dose-dependently inhibited by intraperitoneal injection of morphine (0.1-0.3xa0mg/kg), suggesting that the behavioral response is related to nociception. The nociceptive behavior was also inhibited dose-dependently by i.t. co-administration of losartan (0.3-3xa0nmol), an Ang II type 1 (AT1) receptor antagonist, and SB203580 (0.1-1xa0nmol), a p38 MAPK inhibitor. However, the Ang II type 2 (AT2) receptor antagonist PD123319, the upstream inhibitor of ERK1/2 phosphorylation U0126, and the JNK inhibitor SP600125 had no effect on Ang II-induced nociceptive behavior. Western blot analysis showed that the i.t. injection of Ang II induced phosphorylation of p38 MAPK in the lumbar dorsal spinal cord, which was inhibited by losartan, without affecting ERK1/2 and JNK. Furthermore, we found that AT1 receptor expression was relatively high in the lumbar superficial dorsal horn.ConclusionsOur data show that i.t. administration of Ang II induces nociceptive behavior accompanied by the activation of p38 MAPK signaling mediated through AT1 receptors. This observation indicates that Ang II may act as a neurotransmitter and/or neuromodulator in the spinal transmission of nociceptive information.

Angiotensin (1–7) prevents angiotensin II-induced nociceptive behaviour via inhibition of p38 MAPK phosphorylation mediated through spinal Mas receptors in mice

We have recently demonstrated that intrathecal (i.t.) administration of angiotensin II (Ang II) induces nociceptive behaviour in mice accompanied by a phosphorylation of p38 mitogen‐activated protein kinase (MAPK) mediated through Ang II type 1 (AT1) receptors. The N‐terminal fragment of Ang II, Ang (1–7), plays a pivotal role in counterbalancing many of the well‐established actions induced by Ang II. However, the role of Ang (1–7) in spinal nociceptive transmission remains unclear. Therefore, we examined whether i.t. administration of Ang (1–7) can inhibit the Ang II‐induced nociceptive behaviour in mice.

Alpha-methylated tryptamine derivatives induce a 5-HT receptor-mediated head-twitch response in mice

The two alpha-methylated tryptamine derivatives, 5- (5-FMT) and 6-fluoro-alpha-methyltryptamine (6-FMT), rapidly induced a head-twitch response (HTR) in mice. Two derivatives that lack the methyl group in their chemical structures, 5- (5-FT) and 6-fluorotryptamine (6-FT), did not induce the HTR. The induced HTR was depressed by pretreatment with cycloheptadine, p-chlorophenylalanine or fluoxetine, but was potentiated by 5,7-dihydroxytryptamine. Both 5- and 6-FMT increased brain 5-HT levels in hypothalamus, hippocampus, brainstem, striatum and cortex. 5-FMT decreased the levels of 5-hydroxyindoleacetic acid in those regions, but 6-FMT caused a significant decrease in only the hypothalamus and cortex. The two methylated derivatives inhibited mouse brain MAO-A activity more selectively than non-methylated derivatives. The results suggest that the HTR induced by 5- and 6-FMT may result from increased activity of central 5-HT neurons, probably due to increased 5-HT levels after MAO-A inhibition. This probably results in release of 5-HT with a concomitant increased interaction with postsynaptic 5-HT2 receptors. The present results also indicate the importance of the methyl group to selective MAO-A inhibition by the substrate-analogues tested, and the concomitantly induced animal behavior.

Combined Low Calcium and Lack Magnesium Is a Risk Factor for Motor Deficit in Mice

The populations of the Kii Peninsula in Japan and of Guam present high incidences of amyotrophic lateral sclerosis and Parkinsonism-dementia complex. It is thought that low levels of calcium (Ca) and magnesium (Mg) in the drinking water are involved in the pathogenesis of these diseases. The present study aimed to test the hypothesis that catalepsy, behavioral immobility and a Parkinsonian symptom results from functionally impaired dopaminergic neurons in mice fed low amounts of Ca and Mg (LCa/Mg). A group of mice fed a LCa/Mg diet for 6 weeks was compared to a control group on a standard diet. Cataleptic symptoms such as akinesia and rigidity were measured by the bar test. The anti-parkinsonian drugs dopamine (DA) precursor L-3,4-dihydroxy phenylamine (L-DOPA), the selective DA receptor D(2) agonist bromocriptine, and the DA releaser amantadine were tested for their effects on induced catalepsy. The mice developed catalepsy after 3 weeks on the LCa/Mg diet. LCa/Mg diet-induced catalepsy was improved by the administration of L-DOPA (50-200 mg/kg i.p.) in combination with benserazide (25 mg/kg i.p.), or of bromocriptine (0.25-4 mg/kg i.p.) or of amantadine (5-20 mg/kg i.p.). Immunohistochemical staining revealed that the intensity of tyrosine hydroxylase fluorescence was significantly decreased in the substantia nigra at the 6th week of LCa/Mg feeding in comparison with pair-fed controls. These results suggest that catalepsy in LCa/Mg mice results from hypofunction of the dopaminergic neurons. Moreover, our results support the hypothesis that LCa/Mg intake is one etiological factor in neurodegenerative disorders, including Parkinsons disease.

Involvement of p38 MAPK activation mediated through AT1 receptors on spinal astrocytes and neurons in angiotensin II- and III-induced nociceptive behavior in mice

We have previously demonstrated the possibility that angiotensin (Ang) II and its N-terminal metabolite Ang (1-7) act as neurotransmitters and/or neuromodulators in the spinal transmission of nociceptive information. Ang III, which is a C-terminal metabolite of Ang II, can also act on AT1 receptors, but its role in spinal nociceptive transmission remains unclear. Therefore, we examined the role of Ang III on the spinal nociceptive system in comparison with that of Ang II. Intrathecal (i.t.) administration of Ang III into mice produced a nociceptive behavior, which was dose-dependently inhibited by the co-administration of the AT1 receptor antagonist losartan and the p38 MAPK inhibitor SB203580, but not by the AT2 receptor antagonist PD123319, MEK1/2 inhibitor U0126 and JNK inhibitor SP600125. In addition, Ang III increased the phosphorylation of p38 MAPK in the dorsal lumbar spinal cord, which was inhibited by losartan. These effects were similar to those of observed with Ang II. The nociceptive behavior produced by Ang II or III was also attenuated by the administration of the astrocytic inhibitor L-α-aminoadipic acid, but not by the microglial inhibitor minocycline. Double immunohistochemical staining showed that spinal AT1 receptors were expressed on neurons and astrocytes, and that i.t. administration of either Ang II or III phosphorylated p38 MAPK in both spinal astrocytes and neurons. These results indicate that Ang III produces nociceptive behavior similar to Ang II, and suggest that the phosphorylation of p38 MAPK mediated through AT1 receptors on spinal astrocytes and neurons contributes to Ang II- and III-induced nociceptive behavior.

Roles played by histamine in strenuous or prolonged masseter muscle activity in mice

Bruxism and/or clenching, resulting in fatigue or dysfunction of masseter muscles (MM), may cause temporomandibular disorders. Functional support of the microcirculation is critical for prolonged muscle activity. Histamine is a regulator of the microcirculation and is supplied by release from its stores and/or by de novo production via the induction of histidine decarboxylase (HDC). Interleukin (IL)‐1, a cytokine involved in temporomandibular disorders, is an inducer of HDC. In the present study, we examined the roles of histamine, HDC and IL‐1 in MM activity. Experiments were conducted using our R+G+ model. A mouse restrained (R+) inside a narrow cylinder (front end blocked with a thin plastic strip) gnaws away (G+) the strip to escape, with the weight reduction in the strip serving as an index of MM activity. Fexofenadine (a peripherally acting histamine H1 receptor antagonist) reduced MM activity in normal mice. Both H1 receptor‐deficient and HDC‐deficient mice exhibited low MM activity. Prolonged R+G+ induced HDC activity in MM. Mast cell‐deficient mice exhibited strikingly low HDC induction in MM (and also in the quadriceps femoris muscle) in response to muscle activity or IL‐1β. Mast cells were present around blood vessels and nerves in the epimysium and perimysium of MM. These results, together with others reported previously, suggest that: (i) peripheral histamine supports strenuous MM activity; (ii) strenuous MM activity stimulates mast cells to release histamine and to induce HDC (which replenishes the histamine pool in mast cells, possibly mediated by IL‐1); and (iii) peripheral histamine H1 receptor antagonists may be effective in treating temporomandibular disorders or preventing prolonged clenching and/or bruxism.

Inhibition of monoamine oxidase by two substrate-analogues, with different preferences for 5-hydroxytryptamine neurons

Various intraperitoneal doses of 5-fluoro-alpha-methyltryptamine (5-FMT), given to mice, dose-dependently inhibited only MAOA activity, with similar degrees of inhibition in the striatum, hypothalamus and the rest of the forebrain. The activity inhibited in these regions, completely recovered to control levels within 24 hr after the injection. In contrast, p-chloro-beta-methylphenethylamine (p-CMP), selectively inhibited MAOB activity, with complete recovery within 45 min after the injection. Regardless of the differences in time interval and degree of inhibition of MAOA by 5-FMT or MAOB by p-CMP, both kinds of inhibition were competitive, with respect to oxidation of the respective substrate. 5-Fluoro-alpha-methyltryptamine markedly protected only MAOA against inhibition by phenelzine, without protecting MAOB. Also, 5-FMT greatly increased one kind of animal behaviour, the head-twitch and this behaviour was greatly reduced by treatment with fluoxetine, but increased by reserpine. The results indicate that p-CMP is a short-acting, probably reversible, MAOB-selective inhibitor and 5-FMT has the same characteristics of selectivity for MAOA in central serotonergic neurons.

Involvement of alpha-adrenoceptors in para-hydroxyamphetamine-induced head-twitch response

The effect of some drugs with a higher selectivity for either the alpha 1- or alpha 2-adrenoceptors on the head-twitches induced by intracerebroventricular administration of p-hydroxyamphetamine (p-OHA) in mice, have been studied. Pretreatment with yohimbine increased the number of head-twitches induced by p-OHA, whereas pretreatment with clonidine or prazosin reduced the number of responses. The decrease in head-twitches produced by clonidine was completely antagonized by pretreatment with yohimbine. Pretreatment with 6-hydroxydopamine prior to the combined treatment with clonidine and p-OHA, resulted in recovery of the reduced level head-twitches to the level induced by p-OHA alone. Pretreatment with 6-hydroxydopamine alone resulted in a marked increase in the number of p-OHA-induced head-twitches. These results clearly indicate that a noradrenaline system in the brain may, at least in part, be involved in the p-OHA-induced head-twitches in mouse, most probably by modulating a serotonergic system which is responsible for the head-twitch response.

Influence of a long-term powdered diet on the social interaction test and dopaminergic systems in mice.

It is well known that the characteristics of mastication are important for the maintenance of our physical well-being. In this study, to assess the importance of the effects of food hardness during mastication, we investigated whether a long-term powdered diet might cause changes in emotional behavior tests, including spontaneous locomotor activity and social interaction (SI) tests, and the dopaminergic system of the frontal cortex and hippocampus in mice. Mice fed a powdered diet for 17 weeks from weaning were compared with mice fed a standard diet (control). The dopamine turnover and expression of dopamine receptors mRNA in the frontal cortex were also evaluated. Spontaneous locomotor activity, SI time and dopamine turnover of the frontal cortex were increased in powdered diet-fed mice. On the other hand, the expression of dopamine-4 (D4) receptors mRNA in the frontal cortex was decreased in powdered diet-fed mice. Moreover, we examined the effect of PD168077, a selective D4 agonist, on the increased SI time in powdered diet-fed mice. Treatment with PD168077 decreased the SI time. These results suggest that the masticatory dysfunction induced by long-term powdered diet feeding may cause the increased SI time and the changes in the dopaminergic system, especially dopamine D4 receptor subtype in the frontal cortex.

Relations between MPTP (1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine), the Neurotoxin MPP+ (1-Methyl-4-Phenylpyridinium Ion), and MAO in Rat Brain

A fundamental biological characteristic of Parkinson’s disease is a damaged dopamine (DA) system between the substantia nigra and the corpus striata. This disease is a slowly progressive-neurodegenerative disorder pathologically characterized by the loss of neurons in the zona compacta of the substantia nigra. The etiology of this disease has been extensively investigated, but the precise reason for the loss of DA producing cells in this region remains obscure. Previous animal models of this disease were made by nigrostriatal lesion, depletion of DA with reserpine or α-methyl-p-tyrosine, blockage of the DA receptor with neuroleptics such as haloperidol, destruction of the substantia nigra with 6-hydroxy-DA (see review, Zigmond and Striker, 1984) or manganese intoxication (Donaldson et al., 1982).