Journal of Comparative Physiology B-Biochemical Systems and Environmental Physiology最新文献

Rest is a state of adaptive inactivity that increases the efficiency of activity by regulating its timing and reducing energy use when activity is not beneficial. Thus, animals can go without rest when specific demands, such as mating, favour being awake. Sexually active male blue wildebeest (bulls) are typically territorial, and it has been reported that when a bull is protecting a harem during the mating season (rut), he neither eats nor rests. We examined the daily activity and inactivity patterns of dominant bulls by means of actigraphy for 3 months, which included the rut. We also measured faecal androgen metabolite (fAM) levels and subcutaneous temperature, both of which have variances known to delineate the rut. During the rut, wildebeest bulls experienced higher levels of activity, fAM, and a greater daily range of subcutaneous temperature. Despite previous reports, the male blue wildebeest rested daily during the rut, and while the amount of rest was low, it was not substantially lower than prior to the rut. The amount of time spent inactive increased substantially after the rut. The timing of daily activity and inactivity patterns did not vary substantially across the recording period. Across the recording period, the average daily ambient temperatures decreased (seasonality), and the subcutaneous temperature followed this pattern, although it was not as marked. It appears that in the post-rut period a substantive increase in time spent at rest occurs, potentially allowing the wildebeest bulls time to recover following a period of intense activity.

Sleep pressure builds during wakefulness, but the mechanisms underlying this homeostatic process are poorly understood. One zebrafish model suggests that sleep pressure increases as a function of global neuronal activity, such as during sleep deprivation or acute exposure to drugs that induce widespread brain activation. Given that the arousal-promoting noradrenergic system is important for maintaining heightened neuronal activity during wakefulness, we hypothesised that genetic and pharmacological reduction of noradrenergic tone during drug-induced neuronal activation would dampen subsequent rebound sleep in zebrafish larvae. During stimulant drug treatment, dampening noradrenergic tone with the α₂-adrenoceptor agonist clonidine unexpectedly enhanced subsequent rebound sleep, whereas enhancing noradrenergic signalling with a cocktail of α₁- and β-adrenoceptor agonists did not enhance rebound sleep. Similarly, CRISPR/Cas9-mediated elimination of the dopamine β-hydroxylase (dbh) gene, which encodes an enzyme required for noradrenalin synthesis, enhanced baseline sleep in larvae but did not prevent additional rebound sleep following acute induction of neuronal activity. Across all drug conditions, c-fos expression immediately after drug exposure correlated strongly with the amount of induced rebound sleep, but was inversely related to the strength of noradrenergic modulatory tone. These results are consistent with a model in which increases in neuronal activity, as reflected by brain-wide levels of c-fos induction, drive a sleep pressure signal that promotes rebound sleep independently of noradrenergic tone.

While the majority of studies have concluded that sleep deprivation causes detrimental effects on various cognitive processes, some studies reported conflicting results. We examined the effects of a 108-h total sleep deprivation (TSD) on working memory in the northern fur seal, an animal with unusual sleep phenomenology and long-range annual migrations. The performance of fur seals was evaluated in a two-choice visual delayed matching to sample (DMTS) task, which is commonly used to evaluate working memory. In baseline conditions, the performance of fur seals in a DMTS task based on the percentage of errors was somewhat comparable with that in nonhuman primates at similar delays. We have determined that a 108-h TSD did not affect fur seals' performance in a visual DMTS task as measured by overall percentage of errors and response latencies. On the contrary, all fur seals improved task performance over the study, including the baseline, TSD and recovery conditions. In addition, TSD did not change the direction and strength of the pattern of behavioral lateralization in fur seals. We conclude that a 108-h TSD did not interfere with working memory in a DMTS test in northern fur seals.

Sleep is an important behavioural and physiological state that is ubiquitous throughout the animal kingdom. Birds are an interesting group to study sleep since they share similar sleep features with mammals. Interestingly, sleep time in birds has been shown to vary greatly amongst seasons. To understand the mechanisms behind these variations in sleep time, we did an electro-encephalogram (EEG) study in eight European jackdaws (Coloeus monedula) in winter and summer under outdoor seminatural conditions. To assess whether the amount and pattern of sleep is determined by the outdoor seasonal state of the animals or directly determined by the indoor light-dark cycle, we individually housed them indoors where we manipulated the light-dark (LD) cycles to mimic long winter nights (8:16 LD) and short summer nights (16:8 LD) within both seasons. Jackdaws showed under seminatural outdoor conditions 5 h less sleep in summer compared to winter. During the indoor conditions, the birds rapidly adjusted their sleep time to the new LD cycle. Although they swiftly increased or decreased their sleep time, sleep intensity did not vary. The results indicate that the strong seasonal differences in sleep time are largely and directly driven by the available dark time, rather than an endogenous annual clock. Importantly, these findings confirm that sleep in birds is not a rigid phenomenon but highly sensitive to environmental factors.

Neuronal Tau protein hyperphosphorylation (PPtau) is a hallmark of tauopathic neurodegeneration. However, a reversible brain PPtau occurs in mammals during either natural or "synthetic" torpor (ST), a transient deep hypothermic state that can be pharmacologically induced in rats. Since in both conditions a high sleep pressure builds up during the regaining of euthermia, the aim of this work was to assess the possible role of post-ST sleep in PPtau dephosphorylation. Male rats were studied at the hypothermic nadir of ST, and 3-6 h after the recovery of euthermia, after either normal sleep (NS) or total sleep deprivation (SD). The effects of SD were studied by assessing: (i) deep brain temperature (Tb); (ii) immunofluorescent staining for AT8 (phosphorylated Tau) and Tau-1 (non-phosphorylated Tau), assessed in 19 brain structures; (iii) different phosphorylated forms of Tau and the main cellular factors involved in Tau phospho-regulation, including pro- and anti-apoptotic markers, assessed through western blot in the parietal cortex and hippocampus; (iv) systemic factors which are involved in natural torpor; (v) microglia activation state, by considering morphometric variations. Unexpectedly, the reversibility of PPtau was more efficient in SD than in NS animals, and was concomitant with a higher Tb, higher melatonin plasma levels, and a higher frequency of the microglia resting phenotype. Since the reversibility of ST-induced PPtau was previously shown to be driven by a latent physiological molecular mechanism triggered by deep hypothermia, short-term SD soon after the regaining of euthermia seems to boost the possible neuroprotective effects of this mechanism.

Embryonic development is one of the most sensitive and critical stages when maternal effects may influence the offspring's phenotype. In birds and other oviparous species, embryonic development is confined to the eggs, therefore females must deposit resources into the eggs to prepare the offspring for the prevailing post-natal conditions. However, the mechanisms of such phenotypic adjustments remain poorly understood. We simulated a maternal nutritional transfer by injecting 1 mg of L-methionine solution into Japanese quail eggs before the onset of incubation. The increase in early methionine concentration in eggs activated the insulin/insulin-like signalling and mechanistic target of rapamycin (IIS/mTOR) signalling pathways and affected post-natal developmental trajectories. Chicks from methionine-supplemented eggs had higher expression of liver IGF1 and mTOR genes at hatching but were similar in size, and the phenotypic effects of increased growth became apparent only a week later and remained up to three weeks. Circulating levels of insulin-like growth factor-1 (IGF-1) and expression of ribosomal protein serine 6 kinase 1 (RPS6K1), the mTOR downstream effector, were elevated only three weeks after hatching. These results show that specific nutritional cues may have phenotypic programming effects by sequentially activating specific nutrient-sensing pathways and achieving transgenerational phenotypic plasticity.

Overwintering insects are facing energetic challenges because of food shortage, low temperature, and desiccation stress. Paper wasps of the genus Polistes overwinter as mated adults (gynes) in hibernacula protecting them from predation, snow, and rain but barely from low environmental temperature. In different climates, they face differing overwintering temperature regimes, and therefore they may differ in their energy use. We investigated how much of energy resources built up until autumn is used during diapause dormancy in natural hibernacula by measuring lipid, glycogen, and free carbohydrate content in autumn and early spring in Polistes dominula from temperate European (Austrian) and warm Mediterranean (Italian) climate and Polistes gallicus from Mediterranean climate. Winter energy consumption amounted to ~ 339 and ~ 310 J per wasp in the Austrian and Italian Polistes dominula populations. The smaller Italian Polistes gallicus consumed ~ 247 J. This amounts to 2.62, 2.35, and 1.79 J per day. Of this, the energy demand was mainly fuelled by lipids (84%, 93%, and 90%, respectively), but glycogen stores contributed also considerably (16%, 6%, and 9%). Free carbohydrates decreased only by 0.7%, 1%, and 0.8%. While fat stores seem still sufficient in spring, the wasps depleted most of their carbohydrates. The energy reserves of 396, 400, and 147 J per wasp remaining in spring in the three populations seem sufficient to fuel rest or simple brood care activities for a whole summer but restrict foraging flights to a few hours (~ 3.5-6 h). Results suggest that energy supply might become challenging in expected future climate scenarios.

Many teleosts possess a unique set of respiratory characteristics allowing enhanced oxygen unloading to the tissues during stress. This system comprises three major components: highly pH sensitive haemoglobins (large Bohr and Root effects), rapid red blood cell (RBC) intracellular pH (pHi) protection, and a heterogeneous distribution of membrane-bound plasma-accessible carbonic anhydrase (paCA; absence in the gills). The first two components have received considerable research effort; however, the evolutionary loss of branchial paCA has received little attention. In the current study, we investigated the availability of branchial membrane-bound CA, along with several other CA-related characteristics in species belonging to three basal actinopterygian groups: the Lepisosteiformes, Acipenseriformes and Polypteriformes to assess the earlier hypothesis that Root effect haemoglobins constrain branchial paCA availability. We present the first evidence suggesting branchial membrane-bound CA presence in a basal actinopterygian species: the Senegal bichir (Polypterus senegalus) and show that like the teleosts, white sturgeon (Acipenser transmontanus) and alligator gar (Atractosteus spatula) do not possess branchial membrane-bound CA. We discuss the varying respiratory strategies for these species and propose that branchial paCA may have been lost much earlier than previously thought, likely in relation to the changes in haemoglobin buffer capacity associated with the increasing magnitude of the Bohr effect. The findings described here represent an important advancement in our understanding of the evolution of the unique system of enhanced oxygen unloading thought to be present in most teleosts, a group that encompasses half of all vertebrates.

The freshwater sponge, Ephydatia muelleri, lacks a nervous or endocrine system and yet it exhibits a coordinated whole-body action known as a "sneeze" that can be triggered by exposure to L-glutamate. It is not known how L-glutamate is obtained by E. muelleri in sufficient quantities (i.e., 70 µM) to mediate this response endogenously. The present study tested the hypothesis that L-glutamate can be directly acquired from the environment across the body surface of E. muelleri. We demonstrate carrier mediated uptake of two distinct saturable systems with maximal transport rates (J_max) of 64.27 ± 4.98 and 25.12 ± 1.87 pmols mg^-1 min^-1, respectively. The latter system has a higher calculated substrate affinity (K_m) of 2.87 ± 0.38 µM compared to the former (8.75 ± 1.00 µM), indicative of distinct systems that can acquire L-glutamate at variable environmental concentrations. Further characterization revealed potential shared pathways of L-glutamate uptake with other negatively charged amino acids, namely D-glutamate and L-aspartate, as well as the neutral amino acid L-alanine. We demonstrate that L-glutamate uptake does not appear to rely on exogenous sodium or proton concentrations as removal of these ions from the bathing media did not significantly alter uptake. Likewise, L-glutamate uptake does not seem to rely on internal proton motive forces driven by VHA as application of 100 nM of the VHA inhibitor bafilomycin did not alter uptake rates within E. muelleri tissues. Whether the acquired amino acid is used to supplement feeding or is stored and accumulated to mediate the sneeze response remains to be determined.