Central control of upper airway resistance regulating respiratory airflow in mammals

This article reviews recent studies on the importance of glycine receptors for both the spontaneous and the reflex respiratory modulation of the laryngeal abductors and adductors. Our findings show that strychnine blockade of glycine receptors within the brainstem changes the eupneic three-phase respiratory pattern into two phases. This has major implications for glottal control: (i) the inspiratory glottic abduction and early expiratory adduction were both compromised--a finding mimicked by 5% hypoxia; (ii) closure of the glottis during defensive upper airway reflexes became intermittent and the reflex apnoea reversed to sustained inspiratory discharge. Based on these data, we predict that periods of prolonged hypoxia, such as those that occur during sleep apnoeas, will constrain inspiratory glottic abduction thereby impeding inhalation.     

Strain differences of the light-dark preference in inbred rats

he present study examined strain differences in the light-dark preference among four strains of rats. The test was done in the home-cage situation under 12L:12D cycles. Data from four strains were compared: BN/Kyo, BDIX/Nem, Wistar/Nu, and F344/NSlc. These strains differed in the light-dark preference measured by the ratio of the time spent in the field area of the home cage during the light period. BN/Kyo and BDIX/Nem spent the most time (approx. 23%) in the field during the light period, while F344/NSlc spent the least time (approx. 5%). Wistar/Nu fell between the two (approx. 12%).This study was conducted as partial fulfillment for the master's degree, submitted to Nagoya University by the first author. It was presented at the 47th Annual Conference of the Japanese Society of Animal Psychology.     

Circadian and age-related modulation of thermoreception and temperature regulation: mechanisms and functional implications

At older ages, the circadian rhythm of body temperature shows a decreased amplitude, an advanced phase, and decreased stability. The present review evaluates to what extent these changes may result from age-related deficiencies at several levels of the thermoregulatory system, including thermoreception, thermogenesis and conservation, heat loss, and central regulation. Whereas some changes are related to the aging process per se, others appear to be secondary to other factors, for which the risk increases with aging, notably a decreased level of fitness and physical activity. Moreover, functional implications of the body temperature rhythm are discussed. For example, the relation between circadian rhythm and thermoregulation has hardly been investigated, while evidence showed that sleep quality is dependent on both aspects. It is proposed that the circadian rhythm in temperature in homeotherms should not be regarded as a leftover of ectothermy in early evolution, but appears to be of functional significance for physiology from the level of molecules to cognition. A new view on the functional significance of the circadian rhythm in peripheral vasodilation and the consequent out-of-phase rhythms in skin and core temperature is presented. It is unlikely that the strong, daily occurring, peripheral vasodilation primarily represents heat loss in response to a lowering of set point, since behavioral measures are simultaneously taken in order to prevent heat loss. Several indications rather point towards a supportive role in immunological host defense mechanisms. Given the functional significance of the temperature rhythm, research should focus on the feasibility and effectiveness of methods that can in principle be applied in order to enhance the weakened circadian temperature rhythm in the elderly.     

Adrenalectomy increases local cerebral blood flow in the rat hippocampus

The present study examined the effect of glucocorticoid manipulations on local cerebral blood flow in the hippocampus. We measured local cerebral blood flow in the hippocampus at 1-h intervals over a 1-day period in freely moving rats, by means of the H₂ clearance method, before and after sham adrenalectomy, adrenalectomy or adrenalectomy with corticosterone replacement. We also measured local cerebral blood flow in the prefrontal cortex before and after adrenalectomy. Four weeks after the adrenalectomy, hippocampal blood flow at each time of day was an average of 47% greater than before the operation, showing diurnal variation as before. After the sham adrenalectomy or adrenalectomy with corticosterone replacement, hippocampal blood flow did not change significantly with respect to either its level or its diurnal variation. Local cerebral blood flow in the prefrontal cortex increased by only 19% after adrenalectomy. The present study demonstrates that adrenalectomy causes a remarkable increase in hippocampal blood flow, probably due to a lack of corticosterone.     

Changes in hypothalamic temperature of rats after daily exposure to heat at a fixed time

Rats were subjected to an ambient temperature (T_a) of 33°C for ca. 5 h during the last half of the dark phase for 5, 14 or 28 consecutive days (heat-exposed rats, HE), while control rats were kept at a constant T_a of 24°C. After the heat exposure schedule, the levels of hypothalamic temperature (T_hy) as an index of body core temperature in the HE were significantly lower than those of the controls for 2–4 h in the last half of the dark phase. The low levels of T_hy persisted during the specific period for 1, 3 and 6 days after the end of the 5-, 14- and 28-day heat exposure schedules, respectively. These results confirm that, in rats subjected to daily heat exposure for ca. 5 h at a fixed time per day, their T_hy falls during the period when the rats were previously exposed to heat, and suggest that the duration of the specific T_hy change observed after completing the heat exposure schedule depends on the length of the heat exposure schedule.     

Circadian variation of blood clotting time and circulating vitamin K in the athletic horse

In equine sport medicine, blood clotting and fibrinolysis variations are well investigated, given the practical implications of several pathophysiological conditions affecting the athlete horse such as exercise-induced pulmonary haemorrhage (EIPH) and other bleeding disorders whose etiology and pathogenesis mechanisms are not yet clearly understood. The purpose of the present investigation was to gain evidence of a daily rhythm of several blood clotting indices such as prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), plasma fibrinogen concentration and serum vitamin K concentration in the athletic horses. Blood samples from five thoroughbred mares were collected at 4-h intervals for 48 h (starting at 08:00 h on day 1 and finishing at 4:00 on day 2 via an intravenous catheter inserted into the jugular vein. Prothrombin time, activated partial thromboplastin time, thrombin time and plasma fibrinogen concentration were assessed by means of a Seac Clot 2 coagulometer (SEAC, Italy), while serum vitamin K concentration was measured by HPLC. Data analysis was conducted by one-way repeated analysis of variance (ANOVA) and by the single cosinor method. ANOVA showed a significant influence of time on all parameters investigated, in all horses, on either day. Cosinor analysis defined the periodic parameters and their acrophases (expressed in hours) during the 2 days of monitoring. PT showed a nocturnal acrophase, whereas serum vitamin K concentration acrophase occurred during the evening. The results of this study reflect the physiological peculiarities of the horse that is subjected to a number of exogenous (environmental, nutritional, physical) and endogenous stimuli capable of entraining the circadian rhythm specifically and thus producing time-dependent variations not always comparable with those observed in humans or laboratory animals.     

高血压病血压昼夜节律与心肌缺血的关系

目的 探讨高血压病患者血压昼夜节律改变与心肌缺血之间的关系及临床意义。方法对90例高血压病患者,根据动态心电图上有无心肌缺血(MI)分为MI组(40例)和无MI组(50例),并与20例健康体检者进行对照,观察3组的动态血压变化,同时分析血压昼夜节律正常组和异常组的心肌缺血的发生情况。结果 高血压病伴有MI的患者中,除dSBP、24hDBPL、dSBPL、dDBPL与无MI组比较无统计学差异外,其余各项动态血压指标均明显高于无MI组(P<0.01);高血压病血压昼夜节律异常组发生MI者明显高于血压昼夜节律正常组(P<0.05)。结论 高血压病患者中伴有血压昼夜节律异常者更易导致心肌缺血的发生。对高血压病患者的治疗,除积极控制血压外,还应注意检测和逆转异常的昼夜血压节律,对减少心肌缺血的发生和靶器官损害具有重要意义。     

The adrenergic modulation of firings of respiratory rhythm-generating neurons in medulla-spinal cord preparation from newborn rat

We analysed the modulation of respiratory neurons by adrenaline or noradrenaline (NA) in a newborn rat brainstem-spinal cord preparation. Adrenaline or NA caused a dose-dependent depression of the respiratory rhythm and induced C4 spinal tonic discharges. The inhibitory effect of adrenaline (ED₅₀=0.5 μM) on the respiratory rhythm was stronger than NA (ED₅₀=5 μM). The adrenaline respiratory rhythm depression was partially blocked by the α₁-antagonist prazosin or by the α₂-antagonist yohimbine. The C4 tonic discharge elicited by adrenaline was blocked by the α₁-antagonist prazosin. The direct effects of adrenaline on pre-inspiratory (Pre-I) neurons were examined in a synaptic blockade solution (low Ca), and fifty-six percent of Pre-I neurons were found to continue firing. In low-Ca solution, Pre-I neurons were excited (n=29 of 39) or depressed (n=5 of 39) by adrenaline, and excited by α₁-agonist phenylephrine or depressed by α₂-agonist clonidine. These results suggest that the respiratory rhythm depression under intact network conditions is mediated by some other inhibitory system. The inhibitory effect of adrenaline on the respiratory rhythm was partially blocked by the GABA_A-antagonists bicuculline or picrotoxin, but not by the GABA_B-antagonist phaclofen. The present results suggest that: (1) respiratory rhythm generation is more sensitive to adrenaline than NA through α-adrenergic action of adrenaline; (2) the activity of Pre-I neurons could be directly regulated by excitation via α₁-receptors and inhibition via α₂-receptors; and (3) the depression of the respiratory rhythm by adrenaline is partly mediated by GABA_Aergic neurons. Received: 8 April 1997 / Accepted: 6 October 1997     

Genetic variation in locomotor activity rhythm among populations ofLeptopilina heterotoma (Hymenoptera: Eucoilidae), a larval parasitoid ofDrosophila species

The locomotor activity rhythm ofLeptopilina heterotoma, a parasitoid insect ofDrosophila larvae, was investigated under laboratory conditions. Under LD 1212, the locomotor activity of females shows a clear rhythm which persists under continuous darkness (circadian rhythm). However, comparative study of five populations indicates that both the rate of activity and the profile of the rhythm vary according to the origin of females. The Mediterranean populations (Tunisia and Antibes) show two peaks of activity, at the beginning and at the end of the photophase, whereas more northern populations (Lyon and the Netherlands) are mostly active during the afternoon. Females originating from the area of Lyon have a very low level of activity. Reciprocal crosses (F₁ hybrids and backcrosses) between the French and the Tunisian strains demonstrated the genetic basis of these variations and the biparental inheritance of the trait. This genetic variability is interpreted as a consequence of selective pressures and suggests a local adaptation of natural populations in host foraging behavior. The selective factors which could act on the daily organization of parasitoid behaviors are discussed.