GABA(A) receptor-mediated presynaptic inhibition on glutamatergic transmission.

We investigated the functional roles of presynaptic GABA(A) receptors on excitatory nerve terminals in contributing to spontaneous and action potential-evoked glutamatergic transmission to rat hippocampal CA3 pyramidal neurons. Single CA3 neurons were mechanically isolated with adherent nerve terminals, namely the 'synaptic bouton preparation', and spontaneous glutamatergic excitatory synaptic potentials (sEPSCs) and EPSCs evoked by focal electrical stimuli of a single presynaptic glutamatergic boutons (eEPSCs) were recorded using conventional whole-cell patch recordings. Selective activation of presynaptic GABA(A) receptors on these excitatory nerve terminals by muscimol, markedly facilitated sEPSCs frequency but inhibited eEPSC amplitude. The facilitation of sEPSC frequency was completely occluded by GABA(A) receptor-Cl⁻ channel blockers bicuculline or penicillin (PN). PN itself concentration-dependently inhibited the GABA(A) receptor response induced by bath application of muscimol, but had no effect on the glutamate receptor response. In addition, pretreatment with a blocker of the Na(+), K(+), 2Cl⁻ co-transporter type 1 (NKCC-1), bumetanide, prevented the muscimol-induced inhibition of eEPSCs. The results indicate that activation of presynaptic GABA(A) receptors directly depolarizes glutamatergic excitatory nerve terminals and thereby differentially modulates sEPSCs and eEPSCs.

Comparative study on the actions of toxin extracts from two different puffer fishes on I(Na) and respiratory N-M transmission in the rat.

We performed a comparative study on the effects of toxin extracts prepared from muscle and liver of two different puffer fishes on voltage dependent sodium current (I(Na)), and compared the results with that of tetrodotoxin (TTX). The amount of toxin contained in the muscle or liver expressed as an amount of equipotent TTX differed in the two species (0.11-57.98 microg TTX/g tissue). In addition, we observed the effects of TTX or toxin extracts on the twitch contraction evoked by direct muscle stimulation of the rat hemidiaphragm or indirect phrenic nerve stimulations, in an attempt to understand the mechanisms involved in the transmission failure in the respiratory muscles, due to the ingestion of TTX bearing puffers, and found that TTX or toxin extracts preferentially affect motor nerve rather than muscle.

Inhibition of Na currents by the toxin extracts from puffer fishes captured in the sea coast of Japan.

The inhibitory effects of toxin extracted from muscle or liver of five different puffer fishes (hereafter referred as puffer(s)) captured on the Japanese sea coast were examined on voltage-dependent sodium current (I(Na)) recorded from dissociated single rat hippocampal CA1 neurons. The inhibitory effects estimated from IC(50) values of toxin extracts on I(Na) were in the order of Takifugu vermicularis > Lagocephalus wheeleri > Canthigaster rivulata > Takifugu rubripes > Arothron reticularis from muscle and T. vermicularis > T. rubripes > L. wheeleri > A. reticularis > C. rivulata from liver, thereby indicating that the amount of toxin in the liver or muscle differs between puffers. In addition, the present results indicate that the muscle of T. vermicularis, which is eaten in Japan, contains relatively higher amounts of toxin compared to those of T. rubripes, also eaten. This observation suggests that caution should be taken concerning the maximal edible amount of muscle prepared from T. rubripes.

Alcohol consumption by older adults in central and southern Japan.

This study ascertained the level of alcohol intake and alcoholic beverages consumed by Japanese older adults. Persons aged 55 to 75 years residing in central and southern Japan were recruited and interviewed face-to-face on their habitual alcohol consumption. Among the 577 (359 men and 218 women) participants from 10 districts/prefectures, 60.5% (75.5% for men and 35.7% for women) regularly drank alcoholic beverages on at least a monthly basis. Beer was the most preferred beverage (45.2%), followed by shochu (19.8%) and sake (16.1%). The mean alcohol consumption was 22.2 g/day (95% confidence interval 19.3-25.2) overall, but drinkers had a much higher mean intake of 36.6 g/day (95% CI 32.4-40.8). Moreover, it is alarming that 25.5% of male drinkers were heavy drinkers consuming more than 60 g of alcohol on average per day. Alcohol control measures should be developed to curtail the excessive drinking by older adults.

Smoking by older adults in central and southern Japan.

The study ascertained the smoking status among Japanese older adults. Persons aged 55-75 years residing in middle and southern Japan were recruited and interviewed face-to-face on their habitual tobacco consumption. Among the 576 (358 male and 218 female) participants from 10 prefectures, 18.4% were current smokers the great majority of whom (89%) smoked daily. Although the average cigarette consumption was similar between ex-smokers and current smokers, men had significantly higher consumption level than women in both categories (p < 0.05). The prevalence of current smoking was also significantly higher (p < 0.01) for older men (26.3%) than older women (5.5%). About 75% of male smokers and 25% of female smokers smoked on average at least one pack of cigarettes daily. It is alarming to find the higher prevalence of smoking among Japanese elderly men than other countries. The implementation of a coordinated tobacco control program targeting older adults is needed.