Kazuhiko Shibata

Localization of the site of the anticonflict action of benzodiazepines in the amygdaloid nucleus of rats

Abstract The present study was designed to identify the definitive site in the amygdala of the anticonflict action of benzodiazepines (BZD). Diazepam 20 μg/μl, chlordiazepoxide 60 μg/μl and midazolam 30 μg/μl, bilaterally injected into the central amygdaloid nucleus (ACE), significantly increased the punished responses, but BZD injected into the medial and basolateral amygdaloid nucleus did not. These results suggest that the ACE could be a potential site of antianxiety actions of BZD.

Transient upregulation of the AT2 receptor mRNA level after global ischemia in the rat brain

The present study examined changes in angiotensin receptors (AT1 and AT2) and angiotensinogen mRNA level after global ischemia in the rat brain. The AT2 mRNA level increased by three-fold in both the cortex and hippocampus, which are known to be sensitive to ischemic injury, 3 h after ischemia. The increase thus appeared only during the early reperfusion period. In the striatum, amygdala and cerebellum, the level increased moderately 3 h and/or 24 h after ischemia; there was no change in the hypothalamus. On the other hand, the AT1A and AT1B receptor mRNA levels were not altered in the cortex or hippocampus during the early reperfusion period, even 3 h and 24 h after ischemia. There was no significant alteration in angiotensinogen mRNA level 3 h or 24 h after ischemia. These results suggest that the transient upregulation of AT2 receptor mRNA occurs in the cortex and hippocampus after injury and these changes may be in some way related to the molecular events which lead to delayed neuronal cell death.

Contribution of Anaphylatoxin C5a to Late Airway Responses After Repeated Exposure of Antigen to Allergic Rats

We attempted to elucidate the contribution of complement to allergic asthma. Rat sensitized to OVA received repeated intratracheal exposures to OVA for up to 3 consecutive days, and pulmonary resistance was then estimated for up to 6 h after the last exposure. Whereas the immediate airway response (IAR) in terms of RL tended to decrease in proportion to the number of OVA exposures, late airway response (LAR) became prominent only after three. Although premedication with two kinds of complement inhibitors, soluble complement receptor type 1 (sCR1) or nafamostat mesylate, resulted in inhibition of the IAR after either a single or a double exposure, the LAR was inhibited after the triple. Premedication with a C5a receptor antagonist (C5aRA) before every exposure to OVA also inhibited the LAR after three. Repeated OVA exposure resulted in eosinophil and neutrophil infiltration into the bronchial submucosa which was suppressed by premedication with sCR1 or C5aRA. Up-regulation of C5aR mRNA was shown in lungs after triple OVA exposure, but almost no up-regulation of C3aR. Pretreatment with sCR1 or C5aRA suppressed the up-regulation of C5aR expression as well as cytokine messages in the lungs. The suppression of LAR by pretreatment with sCR1 was reversed by intratracheal instillation of rat C5a desArg the action of which was inhibited by C5aRA. In contrast, rat C3a desArg or cytokine-induced neutrophil chemoattractant-1 induced cellular infiltration into the bronchial submucosa by costimulation with OVA, but these had no influence on the LAR. These differences might be explained by the fact that costimulation with OVA and C5a synergistically potentiated IAR, whereas that with OVA and either C3a or cytokine-induced neutrophil chemoattractant-1 did not. C5a generated by Ag-Ab complexes helps in the production of cytokines and contributes to the LAR after repeated exposure to Ag.

Involvement of the dorsal hippocampus in mediation of the antianxiety action of tandospirone, a 5-hydroxytryptamine1A agonistic anxiolytic

The effect of tandospirone, a 5-hydroxytryptamine (5-HT)1A agonist/anxiolytic, injected directly into dorsal hippocampus, on Vogel-type conflict behavior in rats was investigated and the findings were compared with the effects of diazepam and zopiclone. Tandospirone (30 micrograms/2 microliters and 60 micrograms/2 microliters) and diazepam (40 micrograms/2 microliters) but not zopiclone (20 micrograms/2 microliters), produced a potent anticonflict action in rats. The anticonflict action of tandospirone (30 micrograms/2 microliters), injected into the dorsal hippocampus, was significantly blocked by (-)-propranolol (5 mg/kg i.p.). The present findings provide evidence that suggests that tandospirone has an antianxiety action, presumably by stimulating 5-HT1A receptors in the dorsal hippocampus.

The mammillary body is a potential site of antianxiety action of benzodiazepines

The present study was designed to examine the anticonflict action of benzodiazepines injected into the mammillary body (MB) using the rat conflict-punishment procedure. Diazepam 20 micrograms/microliters, chlordiazepoxide 60 micrograms/microliters and midazolam 30 micrograms/microliters, bilaterally injected into the MB, produced a significant increase in the punished responses without changes in the unpunished responses. These findings have demonstrated for the first time that the MB could be a potential site of antianxiety action of benzodiazepines.

An important role of the central amygdaloid nucleus and mammillary body in the mediation of conflict behavior in rats

The present study was designed to elucidate the functional role of central amygdaloid nucleus (ACE) and mammillary body (MB) in the mediation of behavioral suppression using rat conflict punishment procedure. Lesion of ACE produced a significant and long-lasting increase in the punished responding during the experimental period. Rats with lesion of MB also showed a significant increase in the punished response 10-14 days after brain lesioning. These results demonstrated the important role of ACE and MB in the mediation of behavioral suppression such as conflict behavior.

Nicotine blocks apomorphine‐induced disruption of prepulse inhibition of the acoustic startle in rats: possible involvement of central nicotinic α7 receptors

Nicotine has been reported to normalize deficits in auditory sensory gating in the cases of schizophrenia, suggesting an involvement of nicotinic acetylcholine receptors in attentional abnormalities. However, the mechanism remains unclear. The present study investigated the effects of nicotine on the disruption of prepulse inhibition (PPI) of the acoustic startle response induced by apomorphine or phencyclidine in rats. Over the dose range tested, nicotine (0.05–1 mg kg−1, s.c.) did not disrupt PPI. Neither methyllycaconitine (0.5–5 mg kg−1, s.c.), an α7 nicotinic receptor antagonist, nor dihydro‐β‐erythroidine (0.5–2 mg kg−1, s.c.), an α4β2 nicotinic receptor antagonist, had any effect on PPI. Nicotine (0.01–0.2 mg kg−1, s.c.) dose‐dependently reversed the disruption of PPI induced by apomorphine (1 mg kg−1, s.c.), but had no effect on the disruption of PPI induced by phencyclidine (2 mg kg−1, s.c.). The reversal of apomorphine‐induced PPI disruption by nicotine (0.2 mg kg−1) was eliminated by mecamylamine (1 mg kg−1, i.p.), but not by hexamethonium (10 mg kg−1, i.p.), indicating the involvement of central nicotinic receptors. The antagonistic action of nicotine on apomorphine‐induced PPI disruption was dose‐dependently blocked by methyllycaconitine (1 and 2 mg kg−1, s.c.). However, dihydro‐β‐erythroidine (1 and 2 mg kg−1, s.c.) had no effect. These results suggest that nicotine reverses the disruption of apomorphine‐induced PPI through central α7 nicotinic receptors.

Involvement of septal and striatal dopamine D-2 receptors in yawning behavior in rats

A behavioral study was performed in an attempt to understand the neuronal mechanisms involved in yawning behavior in rats. Subcutaneous injections of low doses of apomorphine (0.05–0.25 mg/kg) or piribedil (0.2–1.0 mg/kg), which preferentially activate presynaptic dopamine autoreceptors at those doses, evoked yawning. Marked yawning responses were also elicited by both 3-PPP (5–20 mg/kg, SC) and TL-99 (1–2 mg/kg, SC). SK & F 38393, a dopamine D-1 receptor agonist, at doses ranging from 0.1 to 8.0 mg/kg (SC) induced neither yawning nor stereotypy. However, bromocriptine (0.5–32.0 mg/kg, SC), a dopamine D-2 receptor agonist, induced yawning for which the dose-response curves showed a bell-shaped form. After a higher dose of 32 mg/kg (SC) bromocriptine, some rats occasionally showed sniffing and sawdust chewing. Yawning responses induced by systemic injection of apomorphine, piribedil, 3-PPP or bromocriptine were wholly suppressed after treatment with sulpiride (10 mg/kg SC), a dopamine D-2 receptor antagonist. Bilateral injections of apomorphine (20 μg/side×2), piribedil (100 μg/side×2) or 3-PPP (50, 100 μg/side×2) into the striatum or septum also elicited marked yawning. The results indicate that low doses of apomorphine, piribedil, 3-PPP, TL-99 or bromocriptine elicit yawning by stimulating dopamine D-2 receptors and striatal and septal dopaminergic systems may be related to the occurrence of yawning behavior.

Differential mechanisms involved in the anticonflict action of benzodiazepines injected into the central amygdala and mammillary body

The present study was designed to clarify the mechanism of action of benzodiazepines (BDZ) injected into the central amygdala (ACE) and mammillary body (MB). When gamma-aminobutyric acid (GABA) at doses of 30 and 70 micrograms, muscimol (0.01 and 0.03 microgram), valproate (200 micrograms), atropine (20 micrograms) and cyproheptadine (3 micrograms) were bilaterally injected into ACE, a significant and marked increase in the punished responses of conflict schedule was observed. These drugs injected into MB failed to increase the punished responses. In MB, only noradrenaline (NA, 20 micrograms) showed the anticonflict action. NA 20 micrograms also produced the anticonflict action in ACE. These results suggest that the mechanism of anticonflict action of BDZ is different in brain areas. The GABA-ergic, cholinergic, serotonergic and NA-ergic systems seem to be involved in the mechanism of anticonflict action of BDZ in ACE. While the NA-ergic system appears to be operative in MB.

Regulation of ghrelin secretion during pregnancy and lactation in the rat: possible involvement of hypothalamus

We investigated the plasma concentration of ghrelin peptide during pregnancy and lactation in rats. Plasma ghrelin levels on days 10 and 15 of pregnancy were significantly lower than those of the non-pregnant rats. Thereafter, the plasma ghrelin levels on day 20 of pregnancy sharply increased to levels comparable with those in non-pregnant rats. Ghrelin peptide concentrations in the stomach did not change significantly during pregnancy. In the hypothalamus, ghrelin mRNA levels were significantly lower on day 15 of pregnancy than in the non-pregnant rats. Also, plasma ghrelin levels were significantly lower in lactating dams than non-lactating controls on days 3 and 8 of lactation. We examined the possible involvement of prolactin and oxytocin in the regulation of plasma ghrelin concentrations during lactation. Although plasma prolactin levels were decreased by the administration of bromocriptine, plasma ghrelin levels did not differ significantly between vehicle- and drug-treated lactating rats. Administration of haloperidol produced a marked increase in plasma prolactin levels as compared with the non-lactating controls. However, plasma ghrelin levels were not significantly different between vehicle- and drug-treated rats. Administration of an oxytocin antagonist into the lateral ventricle significantly inhibited the increase in the plasma oxytocin level induced by acute suckling. However, plasma ghrelin levels did not significantly between the groups. These observations indicated that the decrease in serum ghrelin is caused by a loss of the contribution of hypothalamic ghrelin. Furthermore, the present results suggested that the suckling stimulus itself, but the release of prolactin or oxytocin, is the factor most likely to be responsible for the suppression of ghrelin secretion during lactation.