Calcitonin gene-related peptide (CGRP) is a neuropeptide that has potent vasodilator properties and is involved in various behavioral disorders. The relationship between CGRP and depression-like behavior is unclear. In this study, we used chronically stressed mice to investigate whether CGRP is involved in depression-like behavior. Each mouse was exposed to restraint and water immersion stress for 15 days. After stress exposure, mice were assessed using behavioral tests: open field test, forced swim test and sucrose preference test. Serum corticosterone levels, hippocampal proliferation and mRNA expression of neurotrophins were measured. After stress exposure, mice exhibited depression-like behavior and decreased CGRP mRNA levels in the hippocampus. Although intracerebroventricular CGRP administration (0.5 nmol) did not alter depression-like behavior after 15-day stress exposure, a single CGRP administration into the brain, before the beginning of the 15-day stress exposure, normalized the behavioral dysfunctions and increased nerve growth factor (Ngf) mRNA levels in stressed mice. Furthermore, in the mouse E14 hippocampal cell line, CGRP treatment induced increased expression of Ngf mRNA. The NGF receptor inhibitor K252a inhibited CGRP's antidepressant-like effects in stressed mice. These results suggest that CGRP expression in the mouse hippocampus is associated with depression-like behavior and changes in Ngf mRNA levels.Depression is a major psychiatric disorder that is associated with high rates of suicide, and is considered one of the most important causes of human disability. Excessive exposure to stressful life events induces the onset of behavioral disorders, including depression and post-traumatic stress disorder. The mechanisms underlying the psychopathology of depression are multifaceted, however, it is known to be accompanied by a decrease or impairment of neurogenesis in the hippocampus 1,2 . Therefore, mechanistic investigations of depression that target neurogenesis in the hippocampus are crucial. Calcitonin gene-related peptide (CGRP), a potent vasodilator 3 and neurotransmitter in the central nervous system 4 , is a 37-residue amino acid. CGRP receptors are distributed in the hypothalamus, central gray matter, ventromedial nucleus of the thalamus, amygdala, hippocampus and dentate gyrus 5 . CGRP-containing neurons are found in the hypothalamus, preoptic area, amygdala, thalamus, hippocampus (CA3 pyramidal cells), and dentate gyrus granule cells 3,6 . CGRP is reported to be involved in various behaviors suggestive of anxiety. Intracerebroventricular (i.c.v.) CGRP infusions evoke fear-like freezing 7 and anxiety behavior 8 , and improve learning and memory processing 9 . However, it is less well understood whether CGRP is involved in depression-like behavior. Clinical research shows that CGRP levels may be altered in depressed patients 10 . With this in mind, the aim of the present study was to examine whether CGRP is involved in behavioral development using a 15-day stress exposure model in mice...

We have shown previously that stimulation of the angiotensin II type 2 receptor (AT2R) results in nerve facilitation. In this study, we determined the capacity of candesartan to correct expression patterns characteristic of neuropathy and AT2R-mediated neurite outgrowth in the fructose-induced insulin-resistant rat, which is one of the human hyperinsulinemia models. Wistar rats received a 15% (w/v) fructose solution in their drinking water for 4 weeks (fructose-drinking rats [FDRs]), with or without candesartan (5 mg/kg/day). We evaluated physiological and behavioral parameters and performed immunohistochemical studies. We found that the FDR developed insulin resistance and downregulated both AT2R neuronal function and phosphorylated Akt expression in dorsal root ganglia (DRG) neurons. Candesartan improved neurite outgrowth in the FDR, which was associated with the restoration of AT2R and phosphorylated Akt expression. Furthermore, downregulation of phosphoinositide 3-kinase (PI3K) inhibited AT2R-mediated neurite outgrowth in control DRG cells. PI3K activation increased AT2R-mediated neurite outgrowth and phosphorylated Akt expression in FDR DRG cells. These results suggest that the decrease of AT2R-mediated neurite outgrowth in FDRs is likely to be the result of decreased PI3K-dependent Akt activation. Candesartan improved AT2R neuronal function and Akt phosphorylation, which were associated with sensory nerve defects and insulin sensitivity in the FDR.

The gastric ulcer drug teprenone has central nervous system effects, specifically reducing depression-like behavior in mice.

Abstract. Calcitonin gene-related peptide (CGRP) is a major neurotransmitter and CGRPcontaining primary sensory neurons play an important role in nociception and potent vasodilation. CGRP-containing nerves in mesenteric arteries are decreased in pathological animal models (hypertension, diabetes, and atherosclerosis). In apolipoprotein E-knockout mice, which have atherosclerosis and peripheral sensory nerve defects, nerve growth factor (NGF)-mediated CGRP nerve facilitation was down-regulated, which may have been caused by the impairment of the Akt-NOcGMP pathway. In addition, NGF-mediated CGRP neurite outgrowth was decreased in fructoseinduced insulin-resistant rats. We recently discovered that renin-angiotensin inhibitors improved CGRP innervation in spontaneously hypertensive rats, indicating that rescuing CGRP nerve innervation might improve pathophysiological conditions. To find a novel reagent that facilitates CGRP nerves, a new model, phenol-injured perivascular nerve model rats, was established. Adrenomedullin, hepatocyte growth factor, and angiotensin II type 2 receptor activation induced CGRP nerve distribution in phenol-injured rats. Furthermore, in insulin-resistant model rats, the down-regulation of CGRP nerves was likely due to the depression of phosphoinositide 3-kinase (PI3K)-dependent Akt activation. Administration of candesartan improves CGRPergic function via the PI3K-Akt pathway in insulin-resistant rats. Thus, clarification of the mechanisms of CGRP nerve defects may constitute future therapeutic targets.

Abstract. The endothelium in rat mesenteric vascular beds has been demonstrated to regulate vascular tone by releasing mainly endothelium-derived hyperpolarizing factor (EDHF), which is involved in the activation of K + channels and gap-junctions. However, it is unclear whether the endothelial system in mouse resistance arteries contributes to regulation of the vascular tone. The present study was designed to investigate the role of the endothelium using acetylcholine and A23187 (Ca 2+ ionophore) in mesenteric vascular beds isolated from male C57BL/6 mice and perfused with Krebs solution to measure perfusion pressure. In preparations with active tone produced by methoxamine in the presence of guanethidine, injections of acetylcholine, A23187, and sodium nitroprusside (SNP) caused a concentration-dependent decrease in perfusion pressure due to vasodilation. The vasodilator responses to acetylcholine and A23187, but not SNP, were abolished by endothelium dysfunction and significantly inhibited by N ω -nitro-L-arginine methyl ester (nitric oxide synthase inhibitor) and tetraethylammonium (K + -channel inhibitor) but not glibenclamide (ATP-sensitive K + -channel inhibitor). Indomethacin (cyclooxygenase inhibitor) significantly blunted only A23187-induced vasodilation, while 18α-glycyrrhetinic acid (gap-junction inhibitor) attenuated only acetylcholine-induced vasodilation. These results suggest that the endothelium in mouse mesenteric arteries regulates vascular tone by prostanoids, EDHF, and partially by nitric oxide, different from the endothelium of rat mesenteric arteries.

Apolipoprotein E (apo)-deficient [apoE(Ϫ/Ϫ)] mice have peripheral sensory nerve defects and a reduced and delayed response to noxious thermal stimuli. However, to date, no report has focused on the influence of apoE deficiency on calcitonin gene-related peptide (CGRP)-containing nerve fiber extensions. We have shown that the density of CGRP-containing nerve fibers decreases in mesenteric arteries of apoE(Ϫ/Ϫ) mice compared with wild-type mice. Here, we investigated whether apoE deficiency is involved in nerve growth factor (NGF)-induced CGRP-containing nerve regeneration using apoE(Ϫ/Ϫ) mice. NGF-mediated CGRP-like immunoreactivity (LI)-neurite outgrowth in apoE(Ϫ/Ϫ) cultured dorsal root ganglia (DRG) cells was significantly lower than that in wild-type cultures. However, the level of NGF receptor mRNA in apoE(Ϫ/Ϫ) DRG cells was similar to that in wild-type mice. To clarify the mechanism of the impaired ability of NGF-mediated neurite outgrowth, we focused on the Akt-nitric oxide (NO)-cGMP pathway. Expression of phosphorylated Akt was significantly reduced in apoE(Ϫ/Ϫ) DRG. The NO donor, sodium nitroprusside or S-nitroso-N-acetylpenicillamine, did not affect NGFmediated neurite outgrowth in apoE(Ϫ/Ϫ) cultured DRG cells. However, 8-bromoguanosine 3Ј,5Ј-cyclic monophosphate sodium salt n-hydrate, a cGMP analog, induced NGF-mediated nerve facilitation similar to wild-type NGF-mediated neurite outgrowth levels. Furthermore, in apoE(Ϫ/Ϫ) DRG, soluble guanylate cyclase expression was significantly lower than that in wild-type DRG. These results suggest that in apoE(Ϫ/Ϫ) mice the Akt-NO-cGMP pathway is impaired, which may be caused by NGF-mediated CGRP-LI-neurite outgrowth defects.

In severe myocardial ischemia, histamine 3 (H 3 ) receptor activation affords cardioprotection by preventing excessive norepinephrine release and arrhythmias; pivotal to this action is the inhibition of neuronal Na ϩ /H ϩ exchanger (NHE). Conversely, angiotensin II, formed locally by mast cell-derived renin, stimulates NHE via angiotensin II type 1 (AT 1 ) receptors, facilitating norepinephrine release and arrhythmias. Thus, ischemic dysfunction may depend on a balance between the NHE-modulating effects of H 3 receptors and AT 1 receptors. The purpose of this investigation was therefore to elucidate the H 3 /AT 1 receptor interaction in myocardial ischemia/reperfusion. We found that H 3 receptor blockade with clobenpropit increased norepinephrine overflow and arrhythmias in Langendorff-perfused guinea pig hearts subjected to ischemia/reperfusion. This coincided with increased neuronal AT 1 receptor expression. NHE inhibition with cariporide prevented both increases in norepinephrine release and AT 1 receptor expression. Moreover, norepinephrine release and AT 1 receptor expression were increased by the nitric oxide (NO) synthase inhibitor N G -methyl-L-arginine and the protein kinase C activator phorbol myristate acetate. H 3 receptor activation in differentiated sympathetic neuron-like PC12 cells permanently transfected with H 3 receptor cDNA caused a decrease in protein kinase C activity and AT 1 receptor protein abundance. Collectively, our findings suggest that neuronal H 3 receptor activation inhibits NHE by diminishing protein kinase C activity. Reduced NHE activity sequentially causes intracellular acidification, increased NO synthesis, and diminished AT 1 receptor expression. Thus, H 3 receptor-mediated NHE inhibition in ischemia/reperfusion not only opposes the angiotensin II-induced stimulation of NHE in cardiac sympathetic neurons, but also down-regulates AT 1 receptor expression. Cardioprotection ultimately results from the combined attenuation of angiotensin II and norepinephrine effects and alleviation of arrhythmias.

Abstract. Endothelium regulates vascular tone via release of endothelium-derived relaxing factors (EDRF) including nitric oxide (NO), prostaglandin I 2 (PGI 2 ), and endothelium-derived hyperpolarizing factor (EDHF). The mesenteric vascular bed produces vascular resistance to develop blood pressure and regulate tissue blood flow that plays an important role in maintenance of systemic blood pressure. There is now strong evidence that in these small resistance arteries, EDHF plays a major role in the response to vasoactive substances and regulation of vascular tone. Pharmacological analysis to investigate the role of the vascular endothelium in the regulation of α 1 -adrenoceptor agonist (methoxamine)-induced vasoconstriction in rat mesenteric vascular beds showed that vasoconstriction induced by continuous perfusion of methoxamine (7 μM), but not high KCl (60 mM), time-dependently decreased to 20% of the initial constriction. The time-dependent reduction of methoxamine-induced vasoconstriction was inhibited by endothelium removal, inhibitor of EDHF (30 mM KCl, K + -channel blockers), and gap-junction inhibitor, but not NO synthase inhibitor and cyclooxygenase inhibitor and ageing. These results suggest that vascular endothelium counteracts to normalize excess vasoconstriction of the mesenteric resistance arteries by releasing EDHF, which is associated with activation of multiple K + -channels and gap junction involvement and markedly decreases with ageing.