Increase In Rate Of Spontaneous Discharges Research Articles

Phencyclidine affects firing activity of basolateral amygdala neurons related to social behavior in rats

Negative symptoms of schizophrenia, such as social withdrawal and blunted affect, usually persist for a long period, making rehabilitation difficult. Many studies have demonstrated a close relationship between function of the amygdala and social behavior. Normal social behavior is disturbed in animals administered phencyclidine (PCP), which is now considered a reliable pharmacological model of schizophrenia. Recent studies have reported that disruption of social behavior in PCP-treated rats involved dysfunction of the amygdala. Disturbance of function of the amygdala has also been reported in schizophrenic patients. However, no study has yet examined the effects of PCP on the firing activity of amygdala neurons. In the present study, we recorded the unit activity of basolateral amygdala neurons while rats engaged in socially interactive behavior. After identifying the response properties of recorded neurons, we then recorded the same neurons with systemic PCP administration. Approximately half of the neurons recorded from exhibited an increase in spontaneous discharge rate during social interaction. Only a few neurons exhibited suppression of discharge rate during social interaction. Systemic administration of PCP induced long-lasting activation in half of the neurons that exhibited an increase in firing rate during social interaction. PCP activated half of basolateral amygdala neurons related to socially interactive behavior, and might in this fashion produce dysfunction of social behavior.

Effects of streptomycin and amiloride on the function of the pigeon inner ear

In vitro, streptomycin and amiloride block the mechano-electrical transduction channels in isolated auditory hair cells of mammals and birds. The present in vivo experiments investigate their action in the intact pigeon inner ear. Streptomycin dissolved in artificial endolymph at concentrations between 1.0 and 6.2 mmol/l was applied into the scala media. After a bolus injection (0.09 to 0.36 μl) the endocochlear potential (EP) was elevated from 6.8 to 7.9 mV. Similarly applied boli of 0.09 to 0.55 μl of amiloride in concentrations of 1–2 mmol/l did not significantly elevate EP (8.7 versus 9.4 mV). Compound action potential (CAP) frequency threshold curves (FTCs) were elevated by both streptomycin and amiloride. The threshold elevation increased with frequency. With streptomycin injection, a complete loss of CAPs was found at frequencies above 1.2 kHz. With amiloride, the loss in sensitivity was 40 dB for the same frequency range. Single fibre recordings showed elevated thresholds and decreased sharpness of tuning with both drugs. With streptomycin, the evoked activity was affected regard-less of stimulation frequencies (above or below the fibre's characteristic frequency). Amiloride, however, preferentially elevated thresholds at frequencies above characteristic frequency. Thus amiloride seems to interfere with hair cell tuning mechanisms. Spontaneous activity decreased by about 30%, following the application of streptomycin. In contrast, injections of amiloride into the scala media were followed by an increase in spontaneous discharge rates.

Effects of calcitonin gene-related peptide and efferent nerve stimulation on afferent transmission in the lateral line organ

1. Calcitonin gene-related peptide (CGRP) is a 37-amino acid peptide immunolocalized in efferent fibers innervating hair-cell organs, including the lateral line organ of Xenopus laevis. CGRP, applied in nanomolar concentrations, increased the spontaneous discharge rate in afferent fibers innervating hair cells of the lateral line organ. 2. The increase in spontaneous discharge rate with application of CGRP was associated with an increase in the rate of occurrence of spontaneous excitatory postsynaptic potentials (EPSPs) and with little change in the amplitude of the EPSPs. 3. Prolonged (several hundred seconds) application of CGRP produced an increase in afferent fiber discharge rate that returned to control values in the continued presence of the peptide. 4. Efferent fibers were electrically stimulated to look for a non-cholinergic effect on spontaneous afferent discharge that might be attributed to CGRP. Electrical stimulation of the efferent fibers produced a rapid (100 ms) suppression of discharge rate followed by a rapid (100 ms) increase in discharge rate. However, both the rapid suppression and rapid excitation were likely to be mediated by the release of acetylcholine, because they were blocked by the application of the cholinergic blocking agents curare and atropine as well as by strychnine. 5. In almost one-half of the preparations examined, electrical stimulation of efferent fibers also produced a slowly developing increase in afferent discharge that could persist for several minutes after termination of the shocks. 6. This slow excitation by efferent stimulation was not blocked by concentrations of curare that blocked the rapid effects of efferent stimulation. Thus the slow effect is likely to be mediated by a receptor different from that for the rapid cholinergic effects. One possibility is that the excitation is mediated by the release of CGRP from the efferent nerve fibers.

Direct effects of ethanol on central nervous system cultures: An electrophysiological and morphological study

Ethanol was applied directly to cultures of mouse cerebellum and cerebral neocortex while spontaneous electrical activity was monitored in the former and stimulus-elicited responses were monitored in the latter. Ethanol characteristically demonstrated an initial excitatory effect on cerebellar cultures, manifested by an increase in spontaneous discharge rate, followed by a depression of spontaneous activity. Only depressant effects were noted in ethanol-treated cerebral neocortex cultures. In both instances, removal of ethanol by washing with normal medium resulted in a return to baseline electrical activity. The rapid reversibility of the depressant effects was thought to favor a membrane-altering mechanism which impairs ionic exchange. Light and electron microscopic studies of cerebellar cultures treated with 0.21 to 1.55 g ethanol/100 ml medium for 6 to 15 days demonstrated only nonspecific changes, i.e., an increase in lysosomes and autophagic vacuoles, particularly in astrocytes. Both electrophysiological and morphological studies revealed that the effects of ethanol in vitro were generally manifested at concentrations well above levels producing effects in vivo.