Afterpotentials following penicillin-induced paroxysmal depolarizations in rat hippocampal CA1 pyramidal cells in vitro

Epileptic discharges were induced by superfusion of rat hippocampal slices with penicillin. Under these conditions the neurons generated paroxysmal depolarization shifts (PDS) after electrical stimulation of Schaffer collaterals. The PDS were followed by large afterhyperpolarizations lasting about 2 s. The mechanisms causing these afterhyperpolarizations were studied in CA1 pyramidal cells. A late component of the after hyperpolarizations, which determined their overall duration, was blocked by intracellular application of EGTA and reduced by superfusion with 8-Br-cAMP. In the same neurons these drugs had a comparable effect on after hyperpolarizations following depolarizing current injections; it was therefore concluded that the late component of the PDS afterhyperpolarizations was caused by a slow Ca²⁺-activated K⁺ current. An initial fast component of PDS afterhyperpolarizations, which peaked about 60 ms after PDS onset, was reduced by EGTA but not affected by 8-Br-cAMP suggesting that the fast Ca²⁺-activated K⁺ current also contributed to the PDS afterhyperpolarizations. Superfusion of the slice with the -aminobutyric acid B receptor (GABA_B) antagonists phaclofen or 5-aminovalerate reduced the amplitude of the afterhyperpolarizations during the first 1000 ms but did not affect the late Ca²⁺-dependent component, indicating that a GABA_B-mediated K⁺ inhibitory postsynaptic potential (IPSP) contributed to the PDS afterhyperpolarization. Intracellular injection of Cl^– revealed that an early part of the afterhyperpolarizations lasting about 500 ms was Cl^–-dependent. This component was blocked by superfusion of the slices with bicuculline, suggesting that a GABA_A-mediated Cl^– IPSP contributed to the PDS afterhyperpolarization. The experiments show that different synaptic and intrinsic components with different time courses participate in the generation of PDS afterpotentials.     

Sleep-wake rhythm in an irregular shift system

Sleep in shift work has been studied extensively in regular shift systems but to a lesser degree in irregular shifts. Our main aim was to examine the sleep-wake rhythm in shift combinations ending with the night or the morning shift in two irregular shift systems. Three weeks' sleep/work shift diary data, collected from 126 randomly selected train drivers and 104 traffic controllers, were used in statistical analyses including a linear mixed model and a generalized linear model for repeated measurements. The results showed that the sleep-wake rhythm was significantly affected by the shift combinations. The main sleep period before the first night shift shortened by about 2 h when the morning shift immediately preceded the night shift as compared with the combination containing at least 36 h of free time before the night shift (reference combination). The main sleep period before the night shift was most curtailed between two night shifts, on average by 2.9 and 3.5 h among the drivers and the controllers, respectively, as compared with the reference combination. Afternoon napping increased when the morning or the day shift immediately preceded the night shift, the odds being 4.35-4.84 in comparison with the reference combination. The main sleep period before the morning shift became 0.5 h shorter when the evening shift preceded the morning shift in comparison with the sleep period after a free day. The risk for dozing off during the shift was associated only with the shift length, increasing by 17 and 35% for each working hour in the morning and the night shift, respectively. The results demonstrate advantageous and disadvantageous shift combinations in relation to sleep and make it possible to improve the ergonomy of irregular shift systems.     

Acceleration of the Menstrual Cycle by Intercourse

Hazard statistics were applied to an extensive set of prospective data to test for an acceleration of the menstrual cycle by intercourse. Intercourse appeared to accelerate both the basal body temperature (BBT) shift and the onset of menses. Menses was accelerated more by a combination of follicular and luteal intercourse than by luteal intercourse alone (using the BBT shift as an ovulation indicator). The accelerator effects of intercourse therefore appear to cumulate across the menstrual cycle.     

A prospective study of fatal occupational accidents -- relationship to sleeping difficulties and occupational factors

Very little is known about the association between sleep and (fatal) occupational accidents. This study investigated this relationship using register data of self-rated sleep difficulties, together with occupational and demographic characteristics. The variables were related to subsequent occupational fatal accidents. A national sample of 47,860 individuals was selected at regular intervals over a period of 20 years, and interviewed over the phone on issues related to work and health. The responses were linked to the cause of death register (suicides excluded) and the data set was subjected to a (multivariate) Cox regression survival analysis. One hundred and sixty six fatal occupational accidents occurred, and the significant predictors were: male vs. female: relative risk (RR)=2.30 with a 95% confidence interval (CI) of 1.56-3.38; difficulties in sleeping (past 2 weeks): RR=1.89 with CI=1.22-2.94; and non-day work: RR=1.63 with CI=1.09-2.45. No significant effect was seen for age, socio-economic group, hectic work, overtime (>50 h per week), or physically strenuous work. It was concluded that self-reported disturbed sleep is a predictor of accidental death at work, in addition to non-day work and male gender.     

Saccades and multisaccadic gaze shifts are gated by different pontine omnipause neurons in head-fixed cats

 Pontine omnipause neurons (OPNs) have so far been considered as forming a homogeneous group of neurons whose tonic firing stops during the duration of saccades, when the head is immobilized. In cats, they pause for the total duration of gaze shifts, when the head is free to move. In the present study, carried out on alert cats with fixed heads, we present observations made during self-initiated saccades and during tracking of a moving target which show that the OPN population is not homogeneous. Of the 76 OPNs we identified, 39 were found to have characteristics similar to those of previously described neurons, ”saccade” (S-) OPNs: (1) the durations of their pauses were significantly correlated with the durations of saccades; (2) the discharge ceased shortly before saccade onset and resumed before saccade end; (3) visual responses to target motion were excitatory; and (4) during tracking, S-OPNs interrupted the discharge for the duration of saccades and resumed firing during perisaccadic ”drifts”. However, the characteristics of 37 neurons (”complex” (C-) OPNs) were different: (1) the pause duration was not correlated with the duration of self-initiated saccades; (2) time lead of pause onsets relative to saccades was, on average, longer than in the group of S-OPNs, and firing resumed after the saccade end; (3) visual target motion suppressed tonic discharges; and (4) during tracking, firing was interrupted for the total duration of gaze shifts, including not only saccades but also perisaccadic ”drifts”. We conclude that cat OPNs can be subdivided into two main groups. The first comprises neurons whose firing patterns are compatible with gating individual saccades (”saccade” OPNs). The second group consists of ”complex” OPNs whose firing characteristics are appropriate to gate total gaze displacements rather than individual saccades. The function of these neurons may be to disinhibit pontobulbar circuits participating in the generation of saccade sequences and associated perisaccadic drifts. Received: 20 January 1998 / Accepted: 22 October 1998     

Evaluation of the effect of shift working and sleep quality on semen parameters in men attending infertility clinic

We aimed to evaluate the effect of shift work on semen parameters together with the effect of sleep quality in men attending infertility clinic. The participants were divided into two groups as follows: 104 shift worker men (Group 1) and 116 nonshift worker men (Group 2). Groups were compared in terms of semen parameters, Depression Anxiety Stress Scale-21 (DASS-21), and Pittsburg Sleep Quality Index (PSQI) scores. A higher rate of oligozoospermia and poor sleep quality and a lower mean normal morphology percentage was observed in shift workers than nonshift workers (p = .006, .039 and .036 respectively). In addition, a positive correlation was seen between sleep duration and sperm concentration, while a negative correlation was found between sleep latency and total sperm count. Shift working together with high PSQI score was also a significant association with oligozoospermia when controlling for the other variables of age, total testosterone, DASS-21 stress score, smoking and varicocele (OR = 2.11, 95% CI 1.03–4.34 and OR = 1.18, 95% CI 1.01–1.39 respectively). In this study, infertile shift workers had a lower percentage of normal morphology and higher rates of oligozoospermia and poor sleep quality. Considering that shift workers have lower sleep quality, it seems that shift working negatively affects the circadian rhythm.     

The effects of bright light treatment on subjective and objective sleepiness during three consecutive night shifts among hospital nurses – a counter-balanced placebo-controlled crossover study

Objectives:The objective was to investigate effects of timed bright light treatment on subjective and objective measures of sleepiness during three consecutive night shifts among hospital nurses.Methods:Thirty-five nurses were exposed to bright light (10,000 lux) and red dim light (100 lux) during three consecutive night shifts in a counter-balanced crossover trial lasting nine days, which included three days before and three days after the three night shifts. Light exposure for 30 minutes was scheduled between 02:00–03:00 hours on night 1, and thereafter delayed by one hour per night in order to delay the circadian rhythm. Subjective sleepiness was measured daily (heavy eyelids, reduced performance) and every second hour while awake (Karolinska Sleepiness Scale, KSS). Objective sleepiness (Psychomotor Vigilance Task, PVT) was measured at 05:00 hours during each night shift. Beyond nocturnal light exposure on the night shifts, no behavioral restrictions or recommendations were given at or off work.Results:Bright light treatment significantly reduced heavy eyelids during night shifts. However, results on KSS and PVT were unaffected by bright light. There were no differences in subjective sleepiness during the three days following the night shifts.Conclusions:This bright light treatment protocol did not convincingly reduce sleepiness among nurses during three consecutive night shifts. Nor did bright light impede the readaptation back to a day-oriented rhythm following the night shift period. Too few consecutive night shifts, inappropriate timing of light, and possible use of other countermeasures are among the explanations for the limited effects of bright light in the present study.