Ionic mechanisms underlying spontaneous firing in isolated type B medial vestibular nucleus neurons

Medial vestibular nucleus (MVN) neurons are found to have spontaneous electrical activity in the absence of any detectable synaptic input. To investigate the contributions of intrinsic mechanisms to the spontaneous activity of type B MVN neurons, we examined the effects of various channel blockers on spontaneous firing by means of patch clamp recordings. Coronal slice (400 micrometer) of the vestibular nucleus region was sequentially treated with pronase 0.2 mg/ml and thermolysin 0.2 mg/ml, then single neurons were mechanically dissociated. MVN neurons recorded in neonatal rat were shown to have either a single deep afterhyperpolarization (AHP; type A cells), or an early fast and a delayed slow AHP (type B cells). In 300 nM TTX, spontaneous firing was blocked in type B cells tested. In 8 of 11 cells, underlying fluctuation or oscillations in membrane potential was not remained, and hyperpolarization did not produce rebound low-threshold calcium spikes. Although type B MVN neurons possessed hyperpolarization activated cation current (Ih), cesium had no effect on firing rates. The spike AHP is calcium dependent. When Ca2+ influx was blocked in external Ca2+ free solution, repetitive firing was abolished and the cell rested at depolarized membrane potentials. Application of apamin (300 nM) caused a profound reduction in the amplitude of the AHP and produced rhythmic burst firing. These findings suggest that the spontaneous activity of type B MVN neurons is regulated by interactions between the membrane depolarization mainly due to a persistent sodium conductances and hyperpolarization due to the calcium-activated potassium conductances.

Voltage-Dependent Sodium And Potassium Currents In Acutely Isolated Rat Trigeminal Caudal Neurons

The Relationship between Depression and Malnutrition in the Elderly Diabetics

BACKGROUND : There are various factors affecting the nutritional status of the elderly. Depression has been known as an important factor of malnutrition in them. We had already reported the poor nutritional status of elderly diabetics [J Kor Diabetes Association 22(1):71, 1998]. We investigated to document the prevalence of malnutrition and its relationship to depression in elderly diabetic patients. METHODS : We studied 52 patients aged 65 and over (65-00 y, mean 76.7 y; 22 men, 30 women) with diabetes mellitus admitted during from 1996 through 1997. Malnutrition was diagnosed on presence of 1 or more criteria; 10% weight loss in last 3 months, serum albumin <3.3 g/dL, serum transferrin <200 mg/dL, and blood total lymphocyte<1,800/mm3. There was no significant differences between depressed Group and non-depressed Group in duration of diabetes, body mass index, fasting plasma glucose, HbA1c, and number of complication including hypoglycemic episodes. Depression was assessed on Hamilton Depression Scale score of 16 or more. Data were analyzed by Chi square test. RESULTS : 28/52 (53.9%) were malnourished, 12/52 (23.1%) having depression. Of the 12 patients with depression, only 5 had malnutrition. No significant relation between depression and malnutrition was found (Chi squre=2.689, p=0.992). CONCLUSION : Depression might have no significant relationship to malnutrition in the elderly diabetic in-patients.