Akira Yuyama

Effects of arsenic on cholinergic parameters in brain in vitro

The effects of sodium arsenite (arsenite) on the cholinergic system in the brain of the mouse were investigated in vitro and compared with those of N-ethylmaleimide (NEM) and iodoacetate, both of which are alkylating sulfhydryl reagents. Arsenite, at concentrations greater than 10(-4) M, inhibited depolarized and nondepolarized release of acetylcholine (ACh) from cerebral slices, the synthesis of ACh in the slices, high-affinity uptake of choline into synaptosomes and activity of acetylcholinesterase (AChE). On the other hand, arsenite potentiated dose-dependently the activity of choline acetyltransferase (ChAT). N-Ethylmaleimide and iodoacetate showed inhibitory effects similar to those of arsenite. However, some exceptions were that N-ethylmaleimide did not have any effect on the nondepolarized release of ACh while iodoacetate had no effect on high affinity uptake of choline and activity of AChE. In contrast to arsenite, N-ethylmaleimide and iodoacetate inhibited the activity of ChAT. Neither of arsenite, N-ethylmaleimide nor iodoacetate showed any effect on the binding of [3H]quinuclidinyl benzilate to muscarinic ACh receptors. Although arsenite is thought to inhibit the cholinergic system in brain in vivo, its potentiating effect on ChAT and inhibition of AChE may reduce this harmful effect.

Cholinergic system of brain tissue in rats poisoned with the organophosphate, 0,0-dimethyl 0-(2,2-dichlorovinyl) phosphate

The cholinergic system of the brain was investigated in rats acutely poisoned with the organophosphate, 0,0-dimethyl 0-(2,2-dichlorovinyl) phosphate (DDVP), (6 mg/kg, sc, with saline as a control). The amounts of three fractions of acetylcholine (ACh)--free (extraterminal), labile-bound (intraterminal/cytoplasmic), and stable-bound (intraterminal/vesicular)--increased in the rats over a period of 5 to 60 min after injection of DDVP, showing peaks which were 2.45, 1.82, and 1.4 times as high as the respective control amounts. No difference was seen in the amount of any fraction of ACh between treated and control rats killed 3 and 24 hr after injection. Acetylcholinesterase (AChE) activity decreased to between 12 and 43% of the control over a period of 5 to 180 min and recovered almost completely within 24 hr after injection. No appreciable changes were seen in either spontaneous or potassium-induced ACh release in brain tissue slices obtained from rats treated with DDVP. ACh synthesis in slices was suppressed significantly 20 min, but not 24 hr, after injection of DDVP. In the brain crude synaptosomal preparation, high-affinity choline uptake, which is generally thought to be a rate-limiting step for ACh synthesis, was suppressed 20 min after DDVP. No appreciable changes were seen in high-affinity choline uptake at 24 hr low-affinity choline uptake, and choline acetyltransferase activity after injection of DDVP. These results suggest that ACh synthesis and high-affinity choline uptake may be in a suppressed state when ACh concentration, especially intraterminal ACh, is increased and AChE activity is decreased in the brain cholinergic system of rats poisoned with DDVP. The increase in the intraterminal ACh may be due to an inhibition of AChE activity at this site and/or a re-uptake of ACh in the synaptic cleft, not to an inhibition of ACh release or an increase in ACh synthesis.

Effect of methylmercury on brain acetylcholine concentration and turnover in mice

Effects of methylmercury chloride (MMC) on regional acetylcholine (ACh) concentrations and turnover in the mouse brain were studied and compared with those of 3′-chloro-4-stilbazole (CS) and of hemicholinium-3 (HC-3). A long-term treatment with MMC (5 mg Hg/kg/day) induced nervous signs and decreased ACh in striatum and cerebral cortex, and conversion ratios of [14C]ACh in cerebellum, striatum, and cerebral cortex of mice. A single administration of CS (200 mg/kg) decreased ACh in the cortex and the conversion ratios in the three brain regions. An intracerebral injection of HC-3 (100 μg/kg) also decreased ACh and the conversion ratios in striatum and cortex. It is postulated that ACh concentration and ACh turnover rate in brain of methylmercury-poisoned animals may be reduced.

Effects of organophosphorus compounds, O,O-dimethyl O-(2,2-dichlorovinyl)phosphate (DDVP) and O,O-dimethyl O-(3-methyl 4-nitrophenyl)phosphorothioate (fenitrothion), on brain acetylcholine content and acetylcholinesterase activity in Japanese quail

Effects of 2 organophosphorus compounds, O,O-dimethyl O-(2,2-dichlorovinyl)phosphate (DDVP) and O,O-dimethyl O-(3-methyl 4-nitrophenyl)phosphorothioate (fenitrothion), on the brain cholinergic system were investigated in Japanese quail. Cholinergic signs, such as salivation and convulsions in legs and wings, were seen 7-15 min after administration with DDVP (3-4 mg/kg) or 6-120 min after administration with fenitrothion (250-350 mg/kg). In the DDVP-treated quail (10 min after dosage of 3 mg/kg), free acetylcholine (ACh), labile-bound ACh, increased significantly and acetylcholinesterase (AChE) decreased to 28% of the value determined in untreated quail. In the fenitrothion-treated group (60 min after dosage of 300 mg/kg), only free ACh increased and AChE activity decreased to 20% of the control value. In vitro, DDVP and fenitrothion inhibited AChE activity in brain homogenate with an I50 of 10(-8) M and 10(-5) M, respectively. It appeared that both organophosphorus compounds might have essentially the same effect on the brain cholinergic system. There were only small differences in the effect on various fractions of ACh between the 2 compounds, although there was a hundred-fold range in dose.

マウスの中枢コリン作動性神経機構および行動に及ばすカーバメイト薬, BPMC, の影響

O-sec-butylphenyl methylcarbamate (BPMC), an anticholinesterase carbamate, was injected once (100 mg/kg, s.c.) or repeatedly (50 mg/kg/day for 10 days) into mice. Animals were examined for their behavior and for parameters of cholinergic activity in the forebrain. Mice that received only a single injection exhibited reduced ambulation, hypothermia, and impairment of rotarod performance for up to 3 hr after a single injection. BPMC increased levels of acetylcholine (ACh) in the forebrain for up to 6 hr, and decreased acetylcholinesterase (AChE) activity for up to 24 hr. Both high-affinity choline uptake (HACU) and binding of [3H]quinuclidinyl benzilate (QNB) were reduced 20 min after a single injection without any effect on choline acetyltransferase (ChAT) activity. In behavioral tests conducted 10 min prior to the daily injections, rotarod performance and ambulation were slightly impaired for a few days before and after cessation of injection. Repeated treatment decreased HACU and binding of [3H]QNB for 24 hr after the final injection without any changes in levels of ACh content, AChE activity and ChAT activity. BPMC may reversibly impair cholinergic functions through effects not only on AChE activity but also on HACU and binding of [3H]QNB.