Masaki Sakaue

Altered psychomotor behaviors in mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP)

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been conserved remarkably during evolution and is widely expressed in the mammalian brain. In Drosophila, mutation of the PACAP homologue results in behavioral defects, including impaired olfaction-associated learning and changes in ethanol sensitivity. Here, we report the generation of mice lacking the PACAP gene (PACAP−/−). PACAP−/− mice were born in the expected Mendelian ratios but had a high early-mortality rate. The surviving adult PACAP−/− mice displayed remarkable behavioral changes; they exhibited hyperactive and explosive jumping behaviors in an open field, increased exploratory behavior, and less anxiety in the elevated plus maze, emergence, and novel-object tests. Analysis of PACAP−/− mice brains revealed that the serotonin metabolite 5-hydroxyindoleacetic acid was slightly decreased in the cortex and striatum compared with wild-type mice. The present study provides evidence that PACAP plays a previously uncharacterized role in the regulation of psychomotor behaviors.

Postsynaptic 5-hydroxytryptamine1A receptor activation increases in vivo dopamine release in rat prefrontal cortex

5‐Hydroxytryptamine (5‐HT) plays a role in the regulation of 3,4‐dihydroxyphenylethylamine (dopamine) neurons in the brain, but the precise mechanism of regulation by 5‐HT1A receptors of dopamine release has not been defined. The present study describes the effect of 5‐{3‐[[(2S)‐1,4‐benzodioxan‐2ylmethyl]amino]propoxy}‐1,3‐benzodioxole HCl (MKC‐242), a highly potent and selective 5‐HT1A receptor agonist, on dopamine release in the prefrontal cortex using microdialysis in the freely moving rat. Subcutaneous injection of MKC‐242 (0.3–1.0 mg kg−1) increased extracellular levels of dopamine in the prefrontal cortex. The effect of MKC‐242 in the prefrontal cortex was antagonized by pretreatment with the selective 5‐HT1A receptor antagonist, N‐[2‐[4‐(2‐methoxyphenyl)‐1‐piperazinyl]ethyl]‐N‐(2‐pyridinyl)cyclohexanecarboxamide (WAY100635; 1 mg kg−1, i.p.). Local application of WAY100635 (10 μM) via a microdialysis probe antagonized the effect of systemic MKC‐242 in an increasing dopamine release, and locally infused 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (10 μM) increased dopamine release in the prefrontal cortex. MKC‐242 increased cortical dopamine release in the rats pretreated with 5,7‐dihydroxytryptamine (150 μg, i.c.v.) that caused an almost complete reduction in cortical 5‐HT content. The effect of MKC‐242 to increase dopamine release was also observed in the hippocampus, but not in the striatum or nucleus accumbens. Fluoxetine, a selective serotonin reuptake inhibitor, increased dopamine release in the prefrontal cortex, but not in the nucleus accumbens, while buspirone, a 5‐HT1A receptor agonist, increased dopamine release in both brain regions. The present results indicate that activation of postsynaptic 5‐HT1A receptors increases dopamine release in a brain region‐specific manner.

Selective reduction by isolation rearing of 5-HT1A receptor-mediated dopamine release in vivo in the frontal cortex of mice.

Serotonin (5‐HT)1A receptors modulate in vivo release of brain monoaminergic neurotransmitters which may be involved in isolation‐induced aggressive behavior. The present study examined the effect of isolation rearing on the 5‐HT1A receptor‐mediated modulation of dopamine (DA), 5‐HT and noradrenaline (NA) release in the frontal cortex of mice. The selective 5‐HT1A receptor agonist (S)‐5‐{3‐[(1,4‐benzodioxan‐2‐ylmethyl)amino]propoxy}‐1,3‐benzodioxole HCl (MKC‐242) increased the release of DA and NA and decreased the release of 5‐HT in the frontal cortex of mice. The effect of MKC‐242 on DA release was significantly less in isolation‐reared mice than in group‐reared mice, while effects of the drug on NA and 5‐HT release did not differ between both groups. The effect of the other 5‐HT1A receptor agonist 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin on cortical DA release was also less in isolation‐reared mice than in group‐reared mice, and that of the drug on cortical 5‐HT release did not differ between both groups. In contrast to MKC‐242‐induced DA release, amphetamine‐induced increase in cortical DA release in vivo was greater in isolation‐reared mice. The present findings suggest that isolation rearing enhances the activity of cortical dopaminergic neurons and reduces selectively the 5‐HT1A receptor‐mediated release of DA in the cortex.

Involvement of benzodiazepine binding sites in an antiaggressive effect by 5-HT1A receptor activation in isolated mice

The effect of the benzodiazepine receptor antagonist flumazenil was examined on an antiaggressive effect of (S)-5-[3-[(1,4-benzodioxan-2-ylmethyl)amino]propoxy]-1,3- benzodioxole HCl (MKC-242), a 5-HT(1A) receptor agonist. MKC-242 (0.1-1.0 mg/kg, p.o.) selectively reduced isolation-induced aggressive behavior in a dose-dependent manner. Flumazenil (10 mg/kg, i.p.) antagonized the antiaggressive effects of MKC-242 and diazepam, although it alone did not affect the behaviors of isolated mice. These findings suggest that a gamma-aminobutyric acid(A) (GABA(A)) receptor system is involved in the antiaggressive effect by 5-HT(1A) receptor activation.

Na+–Ca2+ exchanger isoforms in rat neuronal preparations: different changes in their expression during postnatal development

We examined the relative amounts of Na(+)-Ca(2+) exchanger (NCX) isoform mRNAs in cultured neurons, astrocytes and developmental rat brain. NCX1 transcript was predominant in neurons and astrocytes, but NCX2 transcript was about four-fold higher than NCX1 or NCX3 transcript in adult rat cortex. NCX2 transcript in the cortex increased markedly during postnatal development, whereas NCX1 and NCX3 transcripts decreased. Na(+)-dependent 45Ca(2+) uptake in the cortical homogenate increased significantly during postnatal development.

MKC-242, a novel 5-HT1A receptor agonist, facilitates cortical acetylcholine release by a mechanism different from that of 8-OH-DPAT in awake rats

We have previously reported that 5-¿3-[((2S)-1,4-benzodioxan-2-ylmethyl)amino]propoxy¿-1,3-be nzodioxole (MKC-242), a potent and selective serotonin (5-HT)1A receptor agonist, exerts anxiolytic- and antidepressant-like effects in animal models and that the antidepressant-like effect may be mediated by postsynaptic 5-HT1A receptors. The present study, using a microdialysis technique, was undertaken to characterize in vivo the effect of MKC-242 on cholinergic neurons. Subcutaneous injection of MKC-242 (0.5-1.0 mg/kg), like the typical 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), increased extracellular acetylcholine (ACh) levels in the rat cerebral cortex. The increase in ACh release by MKC-242 was also observed in the hippocampus. The effect of MKC-242 on cortical ACh release was attenuated by pretreatment with the 5-HT1A receptor antagonists (10 mg/kg, s.c.) propranolol and N-tert-butyl-3-(4-(2-methoxyphenyl)piperazin-1-yl)-2-phenylpropana mide. The increase in cortical ACh release by MKC-242 was blocked by lesion of serotonergic neurons with 5,7-dihydroxytryptamine, whereas that by 8-OH-DPAT was not. Lesion of noradrenergic neurons with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine did not affect the MKC-242-induced increase in ACh release. These results suggest that systemic injection of MKC-242 facilitates in vivo ACh release via an activation of somadendritic 5-HT1A autoreceptors, and that MKC-242 and 8-OH-DPAT affect cholinergic neurons in the rat cerebral cortex via different mechanisms.

The 5-HT1A receptor agonist MKC-242 increases the exploratory activity of mice in the elevated plus-maze.

The effect of (S)-5-[3-[(1,4-benzodioxan-2-ylmethyl)amino]propoxy]-1,3-benzodioxole HCl (MKC-242), a 5-HT(1A) receptor agonist, on mouse behavior was examined in the elevated plus-maze. MKC-242 significantly increased the percentage of open-arm entries and the percentage of open-arm time, indices of anxiety reduction, while it did not increase the enclosed-arm entries and time spent in enclosed arms. The effect of MKC-242 was antagonized by a low dose of the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide which alone did not affect the behavior. These findings suggest that MKC-242 increases the exploratory activity of mice in the elevated plus-maze via activation of 5-HT(1A) receptors, probably the presynaptic autoreceptors.