Reciprocal regulation of inhibitory synaptic transmission by nicotinic and muscarinic receptors in rat nucleus accumbens shell.

Medium spiny neurones (MSNs) in the nucleus accumbens (NAc) are the principal neurones whose activities are regulated by GABAergic inputs from MSNs and fast-spiking interneurones (FSNs). Cholinergic interneurones play important roles in the regulation of activity in MSNs; however, how acetylcholine modulates inhibitory synaptic transmission from MSNs/FSNs to MSNs remains unknown. We performed paired whole-cell patch-clamp recordings from MSNs and FSNs in rat NAc shell slice preparations and examined cholinergic effects on unitary inhibitory postsynaptic currents (uIPSCs). Carbachol (1 µM) suppressed uIPSC amplitude by 58.3 ± 8.0% in MSN→MSN connections, accompanied by increases in paired-pulse ratio and failure rate, suggesting that acetylcholine reduces the probability of GABA release from the synaptic terminals of MSNs. Carbachol-induced uIPSC suppression was antagonised by 100 µM atropine, and was mimicked by pilocarpine (1 µM) and acetylcholine (1 µM) but not nicotine (1 µM). Application of AM251 slightly reduced carbachol-induced uIPSC suppression (30.8 ± 8.9%), suggesting an involvement of endocannabinoid signalling in muscarinic suppression of uIPSCs. In contrast, FSN→MSN connections showed that pilocarpine had little effect on the uIPSC amplitude, whereas both nicotine and acetylcholine facilitated uIPSC amplitude, with decreases in failure rate and paired-pulse ratio, suggesting that nicotine-induced uIPSC facilitation is mediated by presynaptic mechanisms. Miniature IPSC recordings support these hypotheses of presynaptic cholinergic mechanisms. These results suggest a differential role for muscarinic and nicotinic receptors in GABA release, which depends on presynaptic neuronal subtypes in the NAc shell.

Factors associated with the maintenance in food texture for dependent older people with dysphagia living in nursing home - A retrospective cohort study.

OBJECTIVES: Maintaining the texture of the food that nursing home residents eat is critical for maintaining quality of life and preventing malnutrition. The aim of the present study was to identify the conditions necessary for maintaining food texture for this population. MATERIALS AND METHODS: The study included 143 people for whom reevaluation 1-year post-baseline was possible from among 256 dependent older people who consumed solid food on admission to a nursing home (baseline). The age, sex, primary disease, activities of daily living, nutritional status, oral status, swallowing ability, primitive reflexes, and food texture of the participants were determined. The participants who ate pureed or jelly after 1 year were identified and evaluated to determine factors related to maintenance of a solid diet. RESULTS: A total of 21 participants (14.7%) changed to a pureed or jelly diet after 1 year. Multivariate analysis showed good activities of daily living (p < .05), good swallowing ability (p < .05), and maintained nutritional status (p < .05) to be correlated with solid food maintenance. CONCLUSIONS: Maintaining activities of daily living, feeding and swallowing ability, and nutritional status appear to be important factors for the maintenance of a solid diet.

[Dysphagia rehabilitation in visiting home care].

Dysphagia can cause aspiration pneumonia. The condition of dysphagia is difficult to evaluate from outside. Therefore, a careful examination is necessary to grasp the state of swallowing of a patient accurately. However, it has been a difficult situation for a patient who cannot come to hospital for some reason to be examined by video fluoroscopy or video endoscopy. In recent years, a usefulness of video endoscopy in visiting home examination for dysphagia has been reported several times. And this video endoscopy examination is a valuable tool to detect a discrepancy between swallowing function and nutritional intake of the patient. Cooperative rehabilitation with such a careful examination is an important issue to be successful in dysphagia rehabilitation.

Suppressive regulation of lateral inhibition between medium spiny neurons via dopamine D1 receptors in the rat nucleus accumbens shell.

The nucleus accumbens (NAc) shell is closely associated with reward, psychiatric disorders (depression or schizophrenia), and drug abuse. Dopamine, released from the ventral tegmental area, is involved in these physiological functions and pathophysiological changes of NAc shell. Medium spiny neurons (MSNs), which are only GABAergic projection neurons in NAc, also innervate adjacent MSNs, forming the lateral inhibition network. Previous studies demonstrate that dopamine suppresses the lateral inhibition via D2-like (D2 and D3) receptors. However, the regulation to MSN-MSN synaptic transmission via D1 receptors remained unclear. In present study, aiming to reveal this issue, we examined the effects of the potent dopamine D1 receptor selective agonist SKF82958 on unitary IPSCs (uIPSCs) between two MSNs. SKF82958 (10µM) decreased the amplitude of uIPSCs in about half of MSNs. The actions of SKF82958 was eliminated by pre-application of SCH23390 (1µM), a dopamine D1 receptor selective antagonist. These results suggest that lateral inhibition between MSNs was suppressed via the activation of D1 receptors. Taken our previous findings, dopamine exclusively abolish the lateral inhibition in a stepwise pattern: (1) at low concentration of dopamine, only D3 receptors take part in the regulation of MSN-MSN synaptic transmissions, (2) dopamine concentration becomes higher, D2 receptors become involved in the suppression of lateral inhibition, and (3) at the maximal activity of the mesolimbic dopaminergic pathway, all dopamine receptor subtypes (i.e., D1, D2, and D3) are recruited for disinhibition of MSN activities.

Histaminergic effects on the frequency of repetitive spike firing in rat insular cortex.

The insular cortex (IC) processes multimodal sensory information including gustatory, visceral, nociceptive, and thermal sensation, and is considered to play a role in the regulation of homeostasis. The IC receives dense histaminergic projection from the tuberomamillary nucleus in the hypothalamus, and recent studies have demonstrated that the blockage of histaminergic receptors impairs physiological functions in the IC. However, little is known about the effects of histamine on the electrophysiological properties of the IC. To explore the effects of histamine on the subthreshold responses and action potential properties in the IC, intracellular recording with a sharp glass electrode was obtained from IC pyramidal cells in cortical slice preparations. Application of histamine (30 µM) increased the frequency of repetitive spike firing in response to a long depolarizing current pulse injection; accompanied by an increase in input resistance. The frequency of repetitive spike firing was estimated by the slope of the frequency-current (f/I) curve. Histamine caused an increase from 23.3±2.3 Hz/nA to 40.3±4.3 Hz/nA. The histamine-induced facilitation of repetitive spike firing was blocked by pre-application of 50 µM cimetidine, an H(2) receptor antagonist, but not 30 µM pyrilamine, an H(1) receptor antagonist. R-α-methylhistamine (10 µM), an H(3) autoreceptor agonist, had little effect on the slope of the f/I curve. These results suggest that the histamine-induced facilitation of firing frequency is mediated via H(2) and not H(1) receptors. In addition, H(3) receptors have a minor role in the intrinsic membrane and firing properties of IC pyramidal cells.