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

BACKGROUND: 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. METHODS: In the behavioural experiments, the accumulated response time of nociceptive behaviour consisting of scratching, biting and licking in conscious mice was determined during a 25-min period starting after i.t. injection. The distribution and localization of AT1 or Mas receptors were analysed using a MapAnalyzer and confocal microscope, respectively. Phosphorylation of p38 MAPK in the dorsal spinal cord was measured by Western blotting. RESULTS: The nociceptive behaviour induced by Ang II was dose-dependently inhibited by the co-administration of Ang (1-7). The inhibitory effect of Ang (1-7) was reversed by the co-administration of A779, a Mas receptor antagonist. Western blot analysis showed that the increase in spinal p38 MAPK phosphorylation following the i.t. administration of Ang II was also inhibited by Ang (1-7), and the Ang (1-7) induced-inhibition was prevented by A779. CONCLUSIONS: Our data show that the i.t. administration of Ang (1-7) attenuates an Ang II-induced nociceptive behaviour and is accompanied by the inhibition of p38 MAPK phosphorylation mediated through Mas receptors.

Decreased CaMKII and PKC activities in specific brain regions are associated with cognitive impairment in neonatal ventral hippocampus-lesioned rats.

Neonatal ventral hippocampus (NVH)-lesioned rats represent a neurodevelopmental impairment model of schizophrenia. Previous observations indicate that postpubertal NVH-lesioned rats exhibit impairments in prepulse inhibition (PPI), spontaneous locomotion and social interaction behavior. Here, we document the neurochemical basis of those defects. PPI impairment but not cognitive impairment was improved by acute risperidone treatment (0.30mg/kgi.p.). Immunohistochemical analyses using anti-autophosphorylated Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) antibody indicated significantly reduced CaMKII autophosphorylation, especially in the medial prefrontal cortex (mPFC), striatum and hippocampal CA1 region, of NVH-lesioned rats relative to control animals. We also confirmed that reduced CaMKII autophoshorylation in the mPFC, striatum and hippocampal CA1 region causes decreased phosphorylation of α-amino-3-hydroxy-5-methyl-4-isoxazolpropionic acid-type glutamate receptor subunit 1 (GluR1) (Ser 831), a CaMKII substrate. Like CaMKII, PKCα (Ser 657) autophosphorylation and NR1 (Ser 896) phosphorylation were decreased both in the mPFC and CA1 region. Interestingly, phosphorylation of DARPP-32 (Thr 34) was decreased in the mPFC but increased in the striatum and CA1 region of NVH-lesioned rats compared to controls. Risperidone treatment restored increased DARPP-32 phosphorylation in the striatum and CA1 regions of NVH-lesioned rats but did not rescue CaMKII and PKCα autophosphorylation. Taken together, we find that impaired cognition observed in NVH-lesioned rats is associated with decreased CaMKII and PKCα activities in memory-related brain regions, changes not rescued by risperidone treatment.

Enhanced head-twitch response to 5-HT-related agonists in thiamine-deficient mice.

While many studies suggest an involvement of brain serotonergic systems in neuro-psychiatric disorders such as schizophrenia and depression, their role in Wernicke-Korsakoff syndrome (WKS) remains unclear. Since dietary thiamine deficiency (TD) in mice is considered as a putative model of WKS, it was used in the present study to investigate the function of serotonergic neurons in this disorder. After 20 days of TD feeding, the intensity of tryptophan hydroxylase immunofluorescence was found to be significantly decreased in the dorsal and medial raphe nuclei. In addition, the head-twitch response (HTR) elicited by the intracerebroventricular administration of the 5-HT(2A) agonist 2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) was significantly increased in TD versus control mice, whereas the injection of ketanserin, a 5-HT(2A) receptor antagonist, prevented this enhancement. A single injection of thiamine HCl on the 19th day of TD feeding did not reduce the enhanced DOI-induced HTR. On the other hand, the administration of d-fenfluramine, a 5-HT releaser, did not enhance the HTR in TD mice. Together, our results indicate that TD causes a super-sensitivity of 5-HT(2A) receptors by reducing presynaptic 5-HT synthesis derived from degenerating neurons projecting from the raphe nucleus.

Effects of NMDA receptor-related agonists on learning and memory impairment in olfactory bulbectomized mice.

A significant impairment of learning and memory-related behavior was induced in mice on the 7th and 14th days after olfactory bulbectomy (OBX), as measured by a passive avoidance task. The involvement of the N-methyl-D-aspartate (NMDA) receptor ion-channel complex for learning and memory-related behavior impairment was examined by the intracerebroventricular administration of several NMDA receptor-related agonists and in combination with antagonists. The NMDA receptor agonist NMDA (1 ng/mouse) and the polyamine site agonist spermidine (1 micro g/mouse) improved learning and memory-related behavior impairment. In contrast, the glycine agonist D-cycloserine (0.2, 1 and 5 micro g/mouse) had no effect on learning and memory-related behavior impairment. The improved effects by NMDA and spermidine were reversed by the coadministration of D-APV, a competitive NMDA receptor antagonist, MK-801, an NMDA ion-channel blocker and ifenprodil, a polyamine site antagonist, respectively. These results suggest that the degeneration of NMDA receptors and polyamine sites in the NMDA receptor ion-channel complex may be involved in the OBX-induced impairment of learning and memory-related behavior.

Effect of kami-untan-to on the impairment of learning and memory induced by thiamine-deficient feeding in mice.

We have recently reported that thiamine deficient (TD) mice show an impairment of learning and memory on the 20th day after start of TD feeding. Interestingly, it has been reported that the kampo medicine, "kami-untan-to" (KUT) may be useful as a potential therapeutic agent in diseases associated with cholinergic deficit such as Alzheimer's disease. In the present study, we investigated the effects of KUT on the impairment of memory-related behavior concomitant with psychoneuronal symptoms after TD feeding in mice. Oral administration of KUT had no effect on the food intake, body weight or locomotor activity in TD mice, but the mortality rate in the KUT-treated TD group was significantly lower compared with that in the non-treated TD group. Daily administration of KUT from the 1st day of TD feeding protected against the impairment of memory-related behavior induced by TD. The intensity of the choline acetyltransferase fluorescence decreased in the field of CA1 and dentate gyrus in the hippocampus in TD mice compared with pair-fed mice as the control group, and KUT treatment inhibited this decrease. These results suggest that the effect of KUT on the impairment of memory-related behavior induced by TD feeding may be closely related to the activation of cholinergic neurons in the hippocampus.

Enhancement of 5-hydroxytryptamine-induced head-twitch response after olfactory bulbectomy.

5-Hydroxytryptamine(2A) receptor agonists evoke the head-twitch response in mice. The head-twitch response in olfactory bulbectomized mice elicited by the administration of 5-hydroxytryptamine (40 microgram/mouse, i.c.v.) was increased about threefold as compared with controls on the 14th day after the operation. The injection of ketanserin (1 mg/kg, i.p.), a 5-hydroxytryptamine(2A) receptor antagonist, inhibited this enhancement of 5-hydroxytryptamine-induced head-twitch response after olfactory bulbectomized. On the 14th day, the number of head-twitch response induced by 5-hydroxytryptophan (40, 80 and 160 mg/kg, i.p.), a precursor of 5-hydroxytryptamine, did not differ between olfactory bulbectomized and control mice. Monoamine oxidase-B activity in the forebrain of olfactory bulbectomized mice was higher than that in controls while monoamine oxidase-A activities were unchanged. The 5-hydroxytryptamine uptake into synaptosomes in the forebrain homogenates of olfactory bulbectomized mice was lower than that in controls. These findings indicate that olfactory bulbectomized causes the enhancement of head-twitch response by a supersensitivity of 5-hydroxytryptamine(2A) receptors in cerebral cortex derived from degeneration of neurons projecting from the olfactory bulb.

Antinociceptive effect following dietary-induced thiamine deficiency in mice: involvement of substance P and somatostatin.

We produced thiamine deficiency by treating mice with a thiamine deficient (TD) diet, but not with pyrithiamine, a thiamine antagonist. Twenty days after TD feeding, a significant antinociceptive effect was observed in the formalin test. A single injection of thiamine HCl (50 mg/kg, s.c.) on the 19th day after TD feeding (on the late TD stage) failed to reverse the antinociceptive effect, the muricide effect, and impairment of avoidance learning induced by TD feeding, as compared to pair-fed controls. These results indicate the possibility that the TD-induced antinociceptive effect may result from irreversible changes in the spinal and/or brain neurons. To clarify the involvement of substance P (SP) and somatostatin (SST) systems in the spinal cord, we examined the effect of intrathecal (i.t.) injections of these agonists on TD feeding-inducd elevation of pain threshold. I.t. injection of SP and SST elicited a behavioral response consisting of reciprocal hindlimb scratching, biting and/or licking of hindpaws. There was no significant difference in the behavioral response to SP between TD mice and PF mice on the 5th day after feeding. However, on the 10th and 20th day after TD feeding the response to SP was significantly increased compared with PF mice. This phenomenon was also observed with SST on the 20th day after TD feeding. These results indicate the possibility that TD feeding may produce an increased behavioral response to SP and SST through an enhanced sensitivity of neurokinin-1 and SST receptors in the spinal cord. Taken together, the antinociceptive effect following TD feeding may result from a decrease in spinal SP and SST contents.

Characteristics of depressive behavior induced by feeding thiamine-deficient diet in mice.

We produced thiamine-deficient (TD) mice by TD diet treatment. The growth curve of mice on TD feeding was sharply increased until on the 10th day and subsequently the body weight gradually decreased. The mortality rate in mice was about 67% on the 30th day after the start of TD feeding. We performed the forced swimming test on the 10th and 20th day after the start of TD feeding. The duration of immobility in the forced swimming test was increased on the 20th day of TD feeding. Locomotor activity and motor co-ordination between the pair-fed control group and TD group on the 20th day of TD feeding were not significantly changed. Only a single injection of thiamine HCI (50 mg/kg, s.c.) on the 10th day after the start of a TD diet shortened the increased duration of immobility in the forced swimming test on the 20th day after the start of TD feeding. Whereas these reversal effects of thiamine treatment on the 20th day were not found when the treatment was given on the 19th day after the start of a TD diet. On the 20th day after the start of TD feeding, the increased duration of immobility time induced by TD was shortened by chronic administration of the tricyclic antidepressant imipramine (10 mg/kg, i.p.). These results suggested that behavioral changes in the forced swimming test might be involved in the degeneration of serotonergic and noradrenergic neurons.

Pharmacological studies of geissoschizine methyl ether, isolated from Uncaria sinensis Oliv., in the central nervous system.

The pharmacological properties of geissoschizine methyl ether, isolated from Uncaria sinensis Oliv., were analyzed in vitro and in vivo using mice central serotonin neurons. In the in vitro experiment, geissoschizine methyl ether inhibited [3H]8-hydroxy-2-(di-n-propylamino)tetralin) ([3H]8-OH-DPAT) (K(i)=0.8 microM), [3H]mesulergine (K(i)=0.9 microM) and [3H]ketanserin (K(i)=1.4 microM), but had less affinity toward [3H]prazosin (K(i) > 10 microM) and [3H]spiperone (K(i) >15 microM) binding to mouse brain membranes. The in vivo studies showed that geissoschizine methyl ether dose-dependently reduced 5-hydroxy-L-tryptophan (I-5-HTP) plus clorgyline-induced head twitch response without inhibiting the I-5-HTP plus clorgyline and 8-OH-DPAT-induced head weaving. On the other hand, geissoschizine methyl ether also decreased the rectal temperature of mice (hypothermic response) in a dose-dependent manner. These results suggest that geissoschizine methyl ether possesses mixed 5-HT(1A) receptor agonist/5-HT(2A/2C) receptor antagonist activities and inhibits the head twitch response by blocking the 5-HT(2A) receptors, and possibly, at least in part, by stimulating the 5-HT(1A) receptors in the central nervous system.

Antinociceptive action of amlodipine blocking N-type Ca2+ channels at the primary afferent neurons in mice.

We investigated the antinociceptive action of amlodipine, a dihydropyridine derivative, which acts on both L- and N-type voltage-dependent Ca2+ channels (VDCCs), in mice. Intrathecal injection of amlodipine (300 nmol/kg) significantly shortened the licking time in the late phase of a formalin test, while no effect was found with another dihydropyridine derivative, nicardipine (300 nmol/kg). Cilnidipine and omega-conotoxin GVIA also showed marked analgesic effects under the same experimental conditions. Transcripts of alpha1A, alpha1B, alpha1E, alpha1F, alpha1H, beta3, and beta4 subunits were detected by polymerase-chain reaction (PCR) in the dorsal root ganglion, suggesting the existence of a variety of voltage-dependent Ca2+ channels. Electrophysiological experiments showed that amlodipine and cilnidipine inhibit N-type currents in the dorsal root ganglion cells. These results suggest that amlodipine, cilnidipine, and omega-conotoxin GVIA exert their antinociceptive actions by blocking N-type Ca2+ channels in the primary nociceptive afferent fibers. Blocking of the Ca2+ channels results in attenuation of synaptic transmission of nociceptive neurons. Furthermore, it is suggested that some N-type Ca2+ channel blockers might have therapeutic potential as analgesics when applied directly into the subarachnoidal space.

Distribution of various calcium channel alpha(1) subunits in murine DRG neurons and antinociceptive effect of omega-conotoxin SVIB in mice.

Immunohistological study revealed the differential localization of subtypes of voltage-dependent calcium channels in the dorsal root ganglion neurons. Intrathecal injection of omega-conotoxin SVIB, an analogue of omega-conotoxin GVIA, which acts on N-type voltage-dependent calcium channels, significantly shortened the licking time in the late phase of a formalin test.

Central serotonergic mechanisms on head twitch response induced by benzodiazepine receptor agonists.

Intraperitoneal injection of benzodiazepine receptor agonists (estazolam, zopiclone, triazolam: 0.03-0.24 mmol/kg) induces the head twitch response (HTR). The present study was undertaken to examine the possible participation of the serotonergic system in the mechanism of head twitches induced by benzodiazepine receptor agonists (BZ-RAs). The HTR induced by BZ-RAs was suppressed by pretreatment with ketanserine (1 mg/kg, i.p.), a selective 5-HT(2) receptor antagonist. Pretreatment with fluoxetine (10 mg/kg, i.p.), a 5-HT reuptake inhibitor, and 8-hydroxy-2-(di-n-propylamino)tetralin, a 5-HT(1A) receptor agonist, also suppressed the HTR induced by BZ-RAs. These results suggest that the HTR induced by BZ-RAs may be the result of an activation of postsynaptic 5-HT(2) receptors, probably due to direct action.

Antinociceptive effect produced by intracerebroventricularly administered dynorphin A is potentiated by p-hydroxymercuribenzoate or phosphoramidon in the mouse formalin test.

The antinociceptive effects of intracerebroventricularly (i.c.v.) administered dynorphin A, an endogenous agonist for kappa-opioid receptors, in combination with various protease inhibitors were examined using the mouse formalin test in order to clarify the nature of the proteases involved in the degradation of dynorphin A in the mouse brain. When administered i.c.v. 15 min before the injection of 2% formalin solution into the dorsal surface of a hindpaw, 1-4 nmol dynorphin A produced a dose-dependent reduction of the nociceptive behavioral response consisting of licking and biting of the injected paw during both the first (0-5 min) and second (10-30 min) phases. When co-administered with p-hydroxymercuribenzoate (PHMB), a cysteine protease inhibitor, dynorphin A at the subthreshold dose of 0.5 nmol significantly produced an antinociceptive effect during the second phase. This effect was significantly antagonized by nor-binaltorphimine, a selective kappa-opioid receptor antagonist, but not by naltrindole, a selective delta-opioid receptor antagonist. At the same dose of 0.5 nmol, dynorphin A in combination with phosphoramidon, an endopeptidase 24.11 inhibitor, produced a significant antinociceptive effect during both phases. The antinociceptive effect was significantly antagonized by naltrindole, but not by nor-binaltorphimine. Phenylmethanesulfonyl fluoride (PMSF), a serine protease inhibitor, bestatin, a general aminopeptidase inhibitor, and captopril, an angiotensin-converting enzyme inhibitor, were all inactive. The degradation of dynorphin A by mouse brain extracts in vitro was significantly inhibited only by the cysteine protease inhibitors PHMB and N-ethylmaleimide, but not by PMSF, phosphoramidon, bestatin or captopril. The present results indicate that cysteine proteases as well as endopeptidase 24.11 are involved in two steps in the degradation of dynorphin A in the mouse brain, and that phosphoramidon inhibits the degradation of intermediary delta-opioid receptor active fragments enkephalins which are formed from dynorphin A.

Pain threshold, learning and formation of brain edema in mice lacking the angiotensin II type 2 receptor.

The main biological role of angiotensin II type 2 receptor (AT2) has not been established. We made use of targeted disruption of the mouse AT2 gene to examine the functional role of the AT2 receptor in the central nervous system (CNS). We have previously shown that AT2-deficient mice displayed anxiety-like behavior in comparisons with wild-type mice. In the present study, we analyzed the pain threshold, learning behavior and brain edema formation using the tail-flick test, the tail-pinch test, the passive avoidance task and cold injury, respectively. In the passive avoidance task and cold injury, no differences were found between wild-type mice and AT2-deficient mice. In contrast, the pain threshold was significantly lower in AT2-deficient mice, compared with findings in wild-type mice. The immunohistochemical distribution of beta-endorphin in the brain was analyzed quantitatively in AT2-deficient mice and wild-type mice, using microphotometry. The fluorescence intensity of beta-endorphin in the arcuate nucleus of the medial basal hypothalamus (ARC) was significantly lower in AT2-deficient mice, compared with findings in wild-type mice. We found that the AT2 receptor does not influence learning behavior and brain edema formation. As AT2-deficient mice have increased sensitivity to pain and decreased levels of brain beta-endorphin, AT2 receptors may perhaps mediate regulation of the pain threshold.

Antinociceptive effect of cilnidipine, a novel N-type calcium channel antagonist.

We investigated the antinociceptic effects of cilnidipine, a dihydropyridine derivative which acts on both L- and N-type voltage-dependent calcium channels, in mice. Intrathecally injected cilnidipine showed significant analgesic effect in formalin test. Cilnidipine significantly suppressed N-type currents in dorsal root ganglion (DRG) cells. Our findings apparently support the idea that cilnidipine attenuates synaptic neurotransmission by inhibiting N-type calcium channels in DRG neurons.

The effects of traditional tonics on fatigue in mice differ from those of the antidepressant imipramine: a pharmacological and behavioral study.

The present studies were undertaken to investigate the differences between the antidepressant drug, imipramine, and liquid nutritive and tonic drugs (NTDs) that consist of Ginseng radix, Epimedii herba, Holen and an additional eight to twelve crude drugs. After preloading forced swimming, the NTD (applied orally, 0.1 ml/10 g) significantly increased the duration time of swimming and decreased the duration time of immobility, while the administration of imipramine (5, 10 and 20 mg/kg, i.p.) under the same conditions and after the same treatment did not produce these positive effects. After pretreatment with 100 mg/kg tetrabenazine, the NTDs also elicited both the increased locomotor activity and the decreased duration time of immobility. The behavioral effect was similar to treatment with imipramine. The NTDs showed a long lasting effect on swimming behavior in the forced swimming test for 15 min, indicating a prolonged efficacy, not like the short effect of imipramine. The present results indicate that the effect of NTDs on fatigued subjects is different from that of imipramine, probably due to involvement of another factor in addition to the antidepressant effect.

Immunohistochemical estimation of brain choline acetyltransferase and somatostatin related to the impairment of avoidance learning induced by thiamine deficiency.

We have found that thiamine-deficient (TD) rats show significant impairment of avoidance learning on the 25th day after the start of TD diet, as measured by passive-avoidance task. Administration of physostigmine (0.1 mg/kg, i.p.) from the 14th day after the start of TD diet improved the impairment of avoidance learning to the pair-fed (PF) control level by the 25th day. However, the recovery effect of physostigmine did not occur on the 25th day when the treatment was begun on the 21st day. To ascertain the correlation between the cholinergic neuronal function in rat brain and the avoidance learning impairment induced by TD, the immunohistochemical distribution of brain choline acetyltransferase (ChAT) was determined by fluorescence intensity using two-dimensional microphotometry. The intensity of the ChAT fluorescence started to decrease in the cortex and hippocampus on the 14th day and showed a marked decrease in the cortex, hippocampus and thalamus on the 25th day of TD feeding in comparison with PF controls. The intensity of the somatostatin (SST) fluorescence was unchanged on the 14th day of TD feeding, but on the 25th day, SST was significantly decreased in comparison with PF controls. Furthermore, physostigmine treatment from 14th day after the start of TD diet reversed SST fluorescence intensity to the control level by the 25th day. These results suggest that the impairment of avoidance learning induced by TD may involve not only cholinergic but also somatostatinergic systems.

Intrathecally administered spermine produces the scratching, biting and licking behaviour in mice.

Intrathecal (i.t.) administration of spermine (0.1-10000 fmol), an endogenous polyamine, produced the behavioural response mainly consisting of biting and/or licking of the hindpaw along with a slight hindlimb scratching directed toward the flank in mice, which peaked at 5-15 min and almost disappeared at 30 min after an injection. The behaviour induced by spermine (10 pmol) was dose-dependently inhibited by intraperitoneal injection of morphine (0.125-0.5 mg/kg). The characteristic behaviour was also inhibited dose-dependently by i.t. co-administration of ifenprodil (62.5-4000 pmol), a competitive antagonist of the polyamine recognition site on N-methyl-D-aspartate (NMDA) receptor ion-channel complex, and D(-)-2-amino-5-phosphonovaleric acid (D-APV) (0.5-2 nmol) and 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) (7. 8-500 pmol), the competitive NMDA receptor antagonists, and (5R, 10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,b]cycloheptene-5, 10-imine hydrogen maleate (MK-801) (0.5-4 nmol), an NMDA ion-channel blocker, but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist. Both (2S, 3S)-[cis-2-(diphenylmethyl)-N-[(2-methoxyphenyl)-methyl]-1-azabicy clo [2.2.2]octane-3-amine] (CP-96,345), a non-peptidic neurokinin-1 (NK-1) receptor antagonist, and CP-96,344, its inactive 2R,3R enantiomer, inhibited spermine-induced behavioural response in a dose-dependent manner. However, [Tyr(6), D-Phe(7), D-His(9)]-substance P(6-11) (sendide) and [D-Phe(7), D-His(9)]-substance P(6-11), the selective antagonists for NK-1 receptors, were without affecting spermine-induced behaviour. These results indicate that spermine-induced behaviour is mediated through the polyamine recognition site on NMDA receptor ion-channel complex without the involvement of substance P system in the mouse spinal cord.

Inhibitory effect of intracerebroventricularly-administered [D-Arg(2), beta-Ala(4)]-dermorphin (1-4) on gastrointestinal transit.

The inhibitory effect of intracerebroventricularly-administered [D-Arg(2), beta-Ala(4)]-dermorphin (1-4) (TAPA), a highly selective mu(1)-opioid receptor agonist, on mouse gastrointestinal transit was compared with that of morphine and [D-Ala(2), N-methyl-Phe(4), Gly(5)-ol]-enkephalin (DAMGO). When administered intracerebroventricularly 5 min before the oral injection of charcoal meal, TAPA (10-100 pmol), morphine (0.25-4 nmol), and DAMGO (20-80 pmol) dose-dependently inhibited gastrointestinal transit of charcoal. The inhibitory effect of each mu-opioid receptor agonist was completely antagonized by naloxone, a nonselective opioid receptor antagonist. The inhibitory effects of morphine and DAMGO were significantly antagonized by both beta-funaltrexamine, a selective mu-opioid receptor antagonist, and naloxonazine, a selective mu(1)-opioid receptor antagonist. In contrast, the inhibitory effect of TAPA was not affected at all by beta-funaltrexamine, naloxonazine, nor-binaltorphimine (a selective kappa-opioid receptor antagonist), or naltrindole (a selective delta-opioid receptor antagonist). These results suggest that the inhibitory effect of TAPA on gastrointestinal transit may be mediated through an opioid receptor mechanism different from that of morphine and DAMGO.

Immunohistochemical estimation of rat brain somatostatin on avoidance learning impairment induced by thiamine deficiency.

In rats, on the 25th day after the start of a thiamine-deficient (TD) diet, impairment of avoidance learning was significantly induced in proportion to the decrease somatostatin (SST) fluorescence intensity in the cortex, amygdala, thalamus, hypothalamus, and hippocampus, including the CA1, CA2, and dentate gyrus (DG). Only a single injection of thiamine HCl (0.5 mg/rat, subcutaneous) on the 14th day after the start of a TD diet improved the amnesia to the level of the pair-fed control and prevented the decrease in the SST level. Whereas these reversal effects of thiamine treatment were not found when the treatment was given on the 21st day after the start of a TD diet. These results indicate that, after a certain degree of thiamine deficiency, TD-induced behavioral effects might be reversible, but some neuronal fibers might be irreversibly damaged, probably due to the reduction of thiamine-dependent enzymes in brain mitochondria. The results also suggest the possibility that SST in the brain may be closely related to the avoidance learning impairment induced by TD.