Yuichiro Arai

Characteristics of changes in cholinergic function and impairment of learning and memory-related behavior induced by olfactory bulbectomy.

Memory function after olfactory bulbectomy (OBX) was examined in two tasks, namely, step-through passive avoidance task and elevated plus-maze task. OBX mice showed a significant impairment of learning and memory-related behavior on the 7th and 14th day, as measured by passive avoidance task but not elevated plus maze task. The impairment of learning and memory-related behavior on the 14th day was improved by administration of the cholinesterase inhibitor physostigmine (0.1 mg/kg, i.p.), the non-selective muscarinic agonist oxotremorine (0.1 mg/kg, i.p.) or the selective muscarinic M(1) agonist McN-A-343 (10 microg/mouse, i.c.v.). In contrast, administration of the nicotinic agonist lobeline (5-9.8 mg/kg, i.p.) or the selective muscarinic M(2) antagonist methoctramine (2.25-18 microg/mouse, i.c.v.) has no effect on the impairment of learning and memory-related behavior induced by OBX. In addition, we have demonstrated that the intensity of choline acetyltransferase (ChAT) fluorescence is significantly decreased in the cortex, hippocampus and amygdala on the 14th day after OBX. These results suggest that the impairment of learning and memory-related behavior induced by OBX may be caused by degeneration of cholinergic neurons and muscarinic M(1) receptors play an important role in the improvement process.

Immunohistochemical fluorescence intensity reduction of brain somatostatin in the impairment of learning and memory-related behaviour induced by olfactory bulbectomy

The role of brain somatostatin (SST) on memory function after olfactory bulbectomy (OBX) was investigated by using the passive-avoidance task and immunohistochemical analyses in mice. The present study indicated that the learning and memory-related behaviour was impaired on the 7th and 14th day, but not on the 1st day after OBX. The impairment of learning and memory-related behaviour on the 14th day after OBX was dose-dependently reversed by intracerebroventricularly administered SST (1 microg per mouse). To ascertain the correlation between SST in mouse brain and the impairment of learning and memory-related behaviour induced by OBX, the immunohistochemical distribution of brain SST was determined by fluorescence intensity using two-dimensional microphotometry. The intensity of SST fluorescence was low in the hippocampus on the 14th day after OBX in comparison with Sham controls. These results suggest that SST in the hippocampus is related to the impairment of learning and memory-related behaviour induced by OBX.

A possible mechanism of antidepressant activity of beta-amyrin palmitate isolated from Lobelia inflata leaves in the forced swimming test

A mechanism of antidepressant activity of beta-amyrin palmitate was studied using the forced swimming method in mice. Beta-amyrin palmitate (10 mg/kg) reduced the increase in the duration of immobility induced by tetrabenazine (100 and 200 mg/kg), but showed no effect on that in mice treated with alpha-methyl-para-tyrosine (500 mg/kg). Beta-amyrin palmitate (5 and 10 mg/kg) decreased the duration of immobility in mice treated with desipramine plus 6-hydroxy-dopamine (50 micrograms/mouse), but did not affect that induced by nomifensine plus 6-hydroxydopamine. The decreased immobility produced by desipramine (15 mg/kg) was not affected by beta-amyrin palmitate. A study of norepinephrine release in mouse brain synaptosomes indicated that beta-amyrin palmitate caused a release of [3H]norepinephrine. The results of the present study suggest that beta-amyrin palmitate might release norepinephrine from newly synthesized pools, and thus, it might activate noradrenergic activity.

Enhancement by tetraphenylboron of inhibition of mitochondrial respiration induced by 1-methyl-4-phenylpyridinium ion (MPP+)

The effect of tetraphenylboron (TPB(?)), an activator of a membrane transport of lipophilic cations, on the inhibition of mouse liver mitochondrial respiration induced by a neurotoxin, 1-methyl-4-phenylpyridinium ion (MPP(+)), and by some structurally related compounds was studied. Of the compounds tested, MPP(+) and 4-phenylpyridine (4-PP) significantly inhibited the respiration in an ADP-activated oxidation of substrates (state 3). TPB(?), dose-dependently, shortened the lag time of MPP(+)-induced inhibition and thus lowered the concentrations of MPP(+) for the inhibition. However, TPB(?), even at the high concentration (10 ?M), did not significantly affect 4-PP-induced inhibition. Carbonyl-cyanide-m-chlorophenylhydrazone (CCCP) blocked the respiratory inhibition by MPP(+), independent of K(+) concentration in the medium, and valinomycin blocked the inhibition only in the medium containing high K(+) concentration. Determination of the intramitochondrial MPP(+) concentration revealed about 1000-fold concentrated MPP(+) from that in the medium during the incubation with TPB(?), indicative of potentiation of MPP(+) transport into mitochondria by TPB(?). This might account for the enhancement of respiratory inhibition by MPP(+). In the case of 4-PP, it will penetrate the mitochondrial membrane and intrinsically inhibit the respiration, but cannot accumulate in mitochondria. The present results indicate that, although the inhibitory potency of MPP(+)per se is similar to 4-PP, MPP(+) will be highly concentrated within mitochondria by the membrane potential, as the drive force for its transport.

Behavioral and biochemical changes following acute administration of MPTP and MPP

The acute effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenylpyridinium ion (MPP+) on mouse locomotor activity and striatal dopamine (DA) and 5-hydroxytryptamine (5-HT) levels were investigated. A single dose of either MPTP (10-30 mg/kg, i.p.) or MPP+ (5-20 ug/mouse, i.c.v.) decreased locomotor activity 10-40 min after injection: this locomotor effect was significantly suppressed by either pretreatment with nomifensine or 1-deprenyl alone, or by the combination of desmethylimipramine and 6-hydroxydopamine. Pretreatment with clorgyline did not suppress this behavior and a single dose of haloperidol enhanced the effect. The striatal levels of DA, 3-methoxytyramine and 5-HT increased in parallel with the decrease in locomotor activity caused by MPTP or MPP+. In contrast, levels of 3,4-dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindoleacetic acid were decreased by injection of either MPTP or MPP+. Possible mechanism(s) of the behavioral and biochemical changes caused by the acute actions of MPTP and MPP+ with respect to their neurotoxic effects on the nigrostriatal DA system are discussed.

Inhibition of Brain Type A Monoamine Oxidase and 5‐Hydroxytryptamine Uptake by Two Amphetamine Metabolites, p‐Hydroxyamphetamine and p‐Hydroxynorephedrine

Two amphetamine metabolites, p‐hydroxyam‐phetamine (p‐OHA) and p‐hydroxynorephedrine (p‐OHN), selectively inhibited the A form of monoamine oxidase (MAO) in rat and mouse forebrain homogenates. Of these two metabolites, p‐OHA inhibited MAO‐A more strongly than p‐OHN. This MAO‐A‐selective inhibition by p‐OHA or p‐OHN was found to be competitive with respect to deamination of its substrate, 5‐hydroxytryptamine (5‐HT). The degree of MAO‐A inhibition was not changed by 90 min of preincubation of the enzyme preparations with either metabolite, and the activity inhibited by p‐OHA after the preincubation recovered completely to the control level after repeated washing. Uptake of 5‐HT or dopamine into mouse forebrain synaptosomes was highly reduced by both p‐OHA and p‐OHN. Both metabolites were more potent in reducing dopamine uptake than in reducing 5‐HT uptake. In reduction of 5‐HT and of dopamine uptake, p‐OHA was more potent than p‐OHN. These results indicate that p‐OHA is a more selective inhibitor of brain MAO‐A activity and 5‐HT uptake than its subsequent metabolite, p‐OHN. These two actions of p‐OHA might, together with possible 5‐HT efflux into the synaptic cleft, greatly contribute to head twitch, a brain 5‐HT‐mediated animal behavior induced by p‐OHA.

Alterations in cognitive function in prepubertal mice with protein malnutrition : Relationship to changes in choline acetyltransferase

We have found that protein malnutrition (PM) causes a significant impairment of memory-related behavior on the 15th and 20th day after the start of PM (5% casein) feeding in prepubertal mice but not in postpubertal mice, as measured by a passive-avoidance task. This impairment was almost completely reversed by merely switching to a standard protein (20% casein) diet on the 10th day after the start of PM. However, the reversal was not observed when the switching to a standard protein regimen was done on the 15th day of the PM diet. Interestingly, the impairment of memory-related behavior on the 20th day was improved by the chronic administration of physostigmine (0.1 mg/kg/day x last 10 days, i.p.), a cholinesterase inhibitor. To correlate brain cholinergic neuron function with the memory-related behavior impairment induced by PM, microphotometry was used to determine the histological distribution of the imunofluorescence intensity for choline acetyltransferase (ChAT), a functional marker of presynapse in cholinergic neurons. The change in the intensity of fluorescence indicated that ChAT protein was decreased in the hippocampus (CA1, CA3 and dentate gyrus) on the 20th day after PM feeding in comparison with controls. These results suggest the possibility that the memory-related behavior deficits observed in prepubertal mice with PM are caused by a dysfunction of the 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.

Monoamine oxidase and head-twitch response in mice mechanisms of α-methylated substrate derivatives

It is well known that head-twitch response (HTR) in mice represents hallucinations, since administration of lysergic acid diethylamide (LSD) produces hallucinations in humans, and the HTR in mice is induced by administration of LSD as a hallucinogen. The HTR is produced by excitation of 5-hydroxytryptamine (5-HT)2A receptors. In this paper, we review the mechanisms of HTR induced by various drugs such as 5-HT precursor, 5-HT receptor agonist, 5-HT releaser, hallucinogenic compounds, benzodiazepins and cannabinoid. The response induced by HTR-inducers is significantly enhanced by combined treatment with a non-selective form of monoamine oxidase (MAO) inhibitor. Thus, the relationship between MAO activity and HTR caused by these drugs (especially, alpha-methylated analogous compounds which 5-fluoro-alpha-methyltryptamine, 6-fluoro-alpha-methyltryptamine and p-hydroxyamphetamine) is presented in detail.

Immunohistochemical determination of rat spinal cord substance P, and antinociceptive effect during development of thiamine deficiency

During 30 days of thiamine deficiency (TD) feeding, the rat antinociceptive effect (pain threshold) to noxious heat stimulation was significantly increased in proportion to the decrease substance P (SP) fluorescent intensity in the spinal cord. Only a single injection of thiamine HCl (0.5 mg/kg, s.c.) on the early treatment day during TD feeding effectively reversed the analgesic effect to the pair-fed control level. Whereas this reversal effect by thiamine treatment was not found if this treatment was done on the relatively late day. However, either treatment day, except muricide, complete disappearance of various animal behaviours induced by TD was found. These results indicate that, after certain degree of TD development, TD-induced behavioral effects might be reversible, but the afferent nerve fibers might be irreversibly damaged, probably by the similar mechanism as found for an excitotoxin(s) mediated injury in the certain brain region(s). The results also suggest a possibility that SP and an excitotoxin, glutamate, in the dorsal part of the spinal cord greatly contribute to the pain transmission induced by noxious heat stimulation.