Involvement of brain tryptophan hydroxylase in the mechanism of hibernation

Gut Microbiota and Metabolites May Play a Crucial Role in Sea Cucumber Apostichopus japonicus Aestivation

The constant increase in temperatures under global warming has led to a prolonged aestivation period for Apostichopus japonicus, resulting in considerable losses in production and economic benefits. However, the specific mechanism of aestivation has not been fully elucidated. In this study, we first tried to illustrate the biological mechanisms of aestivation from the perspective of the gut microbiota and metabolites. Significant differences were found in the gut microbiota of aestivating adult A. japonicus (AAJSD group) compared with nonaestivating adult A. japonicus (AAJRT group) and young A. japonicus (YAJRT and YAJSD groups) based on 16S rRNA gene high-throughput sequencing analysis. The abundances of Desulfobacterota, Myxococcota, Bdellovibrionota, and Firmicutes (4 phyla) in the AAJSD group significantly increased. Moreover, the levels of Pseudoalteromonas, Fusibacter, Labilibacter, Litorilituus, Flammeovirga, Polaribacter, Ferrimonas, PB19, and Blfdi19 genera were significantly higher in the AAJSD group than in the other three groups. Further analysis of the LDA effect size showed that species with significant variation in abundance in the AAJSD group, including the phylum Firmicutes and the genera Litorilituus, Fusibacter, and Abilibacter, might be important biomarkers for aestivating adult A. japonicus. In addition, the results of metabolomics analysis showed that there were three distinct metabolic pathways, namely biosynthesis of secondary metabolites, tryptophan metabolism, and sesquiterpenoid and triterpenoid biosynthesis in the AAJSD group compared with the other three groups. Notably, 5-hydroxytryptophan was significantly upregulated in the AAJSD group in the tryptophan metabolism pathway. Moreover, the genera Labilibacter, Litorilituus, Ferrimonas, Flammeovirga, Blfdi19, Fusibacter, Pseudoalteromonas, and PB19 with high abundance in the gut of aestivating adult A. japonicus were positively correlated with the metabolite 5-HTP. These findings suggest that there may be potential biological associations among the gut microbiota, metabolites, and aestivation in A. japonicus. This work may provide a new perspective for further understanding the aestivation mechanism of A. japonicus.

Modification of glial response in hibernation: a patch-clamp study on glial cells acutely isolated from hibernating land snail

Hibernation is a dormant state of some animal species that enables them to survive harsh environmental conditions during the winter seasons. In the hibernating state, preservation of neuronal rhythmic activity at a low level is necessary for maintenance of suspended forms of behavior. As glial cells support rhythmic activity of neurons, preservation of brain function in the hibernating state implies accompanying modification of glial activity. A supportive role of glia in regulating neuronal activity is reflected through the activity of inwardly rectifying K+ channels (Kir). Therefore, we examined electrophysiological response, particularly Kir current response, of glial cells in mixture with neurons acutely isolated from active and hibernating land snail Helix pomatia. Our data show that hibernated glia have significantly lower inward current density, specific membrane conductance, and conductance density compared with active glia. The observed reduction could be attributed to the Kir currents, since the Ba2+-sensitive Kir current density was significantly lower in hibernated glia. Accordingly, a significant positive shift of the current reversal potential indicated a more depolarized state of hibernated glia. Data obtained show that modification of glial current response could be regulated by serotonin (5-HT) through an increase of cGMP as a secondary messenger, since extracellular addition of 5-HT or intracellular administration of cGMP to active glia induced a significant reduction of inward current density and thus mimicked the reduced response of hibernated glia. Lower Kir current density of hibernated glia accompanied the lower electrical activity of hibernated neurons, as revealed by a decrease in neuronal fast inward Na+ current density. Our findings reveal that glial response is reduced in the hibernating state and suggest seasonal modulation of glial activity. Maintenance of low glial activity in hibernation could be important for preservation of brain rhythmic activity and survival of the animal.

The brain 5-HT1Areceptor gene expression in hibernation

Hibernation is a unique physiological state characterized by profound reversible sleep-like state, depression in body temperature and metabolism. The serotonin 5-hydroxytryptamine(1A) (5-HT(1A)) receptor gene sequence in typical seasonal hibernator, ground squirrel (Spermophilus undulatus), was specified. It was found that the fragment encoding the fifth transmembrane domain showed 93.6% of homology with the analogous fragment of the mouse and rat genes and displayed 88.5% homology with the human 5-HT(1A) receptor gene. Using primers designed on the basis of obtained sequence, the expression of 5-HT(1A) receptor gene in the brain regions in active, entering into hibernation, hibernating and coming out of hibernation ground squirrels was investigated. Significant structure-specific changes were revealed in the 5-HT(1A) messenger RNA (mRNA) level in entry into hibernation and in arousal. An increase in the 5-HT(1A) gene expression was found in the hippocampus during the prehibernation period and in ground squirrels coming out of hibernation, thus confirming the idea of the hippocampus trigger role in the hibernation. Significant decrease in 5-HT(1A) receptor mRNA level in the midbrain was found in animals coming out of hibernation. There was no considerable changes in 5-HT(1A) receptor mRNA level in different stages of sleep-wake cycle in the frontal cortex. Despite drastically decreased body temperature in hibernating animals (about 37 degrees C in active and 4-5 degrees C in hibernation), 5-HT(1A) receptor mRNA level in all examined brain regions remained relatively high, suggesting the essential role of this 5-HT receptor subtype in the regulation of hibernation and associated hypothermia.

Seasonal effects of Selank on the behavior of hibernating animals

We studied the seasonal effects of peptide preparation Selank on orientation and exploratory activity in 36 arctic ground squirrels Citellus undulatus in the open-field and hole-board tests. Selank most significantly increased behavioral activity of hibernating animals in the spring and fall. The test peptide had no effect on locomotor activity of animals. The selective stimulatory effect of Selank on exploratory behavior of hibernating animals was season-dependent. The maximum effect was observed under conditions of seasonal depression-like state.

Seasonal peculiarities of behavior of ground squirrel Citellus undulatus in holeboard and open field tests

Seasonal changes in the behavior of ground squirrels Citellus undulatus (n=35) in holeboard and open field tests were studied. It was found that the number of head dips and rearings in the holeboard and the number of crossed squares, rearings, and runs across the field center in the open field in ground squirrels during arousal between bouts at the end of the hibernation period, in the middle of March, were lower than these indices in active summer animals. A rapid restoration of all behavioral parameters after the arousal of animals from hibernation in mid-April was shown. In some cases, the behavioral parameters of activity in the holeboard and open field tests and the habituation reaction reached the values characteristic of active summer animals in a very short period of time, sometime within 1 day. By contrast, the locomotory and exploratory activities of animals tested in autumn (at the beginning of September and in the middle of October) were significantly lower than in summer animals, i.e. these indices decreased to minimum values 1.5-2 months prior to their entry into hibernation. The results of behavioral experiments indicate that the preparation of the CNS of hibernators for seasonal changes in the functional states is under the control of endogenous regulators.

The neuroendocrine system in hibernating mammals: present knowledge and open questions

The present review describes the distribution and the function-dependent reactivity pattern of those peptidergic and aminergic components of the neuroendocrine system of hibernating mammals that have been studied by histological, pharmacological and physiological techniques. Particular attention has been paid to the intrinsic connectivity of the peptidergic apparatus and its input systems. Since the reactivity patterns of the neuroendocrine system show remarkable fluctuations in relation to the various stages of hibernation and euthermia, these fluctuations have been analyzed with respect to (1) their causative role in the regulation of hibernation and (2) their secondary response to physiological changes during hibernation. The author's investigations described in this review have mainly been performed in European hedgehogs (Erinaceus europaeus), European and golden hamsters (Cricetus cricetus, Mesocricetus auratus), dormice (Glis glis), and in Richardson's and Columbian ground squirrels (Spermophilus richardsonii, Spermophilus columbianus), by the use of light- and electron-microscopic immunocytochemistry and histochemistry, in situ hybridization, radioimmunoassays and stereotaxically guided application techniques. These experiments were also performed in hypothermic animals. The (partially published) results obtained by the author and his associates are reviewed with reference to the body of evidence found in the recent literature. With respect to their reactivity patterns, several neuropeptide and transmitter systems can be regarded as candidates for control systems of hibernation. Neuronal complexes immunoreactive for endogenous opiates, in particular enkephalin, and also for vasopressin, somatostatin, substance P, corticotropin-releasing factor and serotonin are probably involved in the neuroendocrine control of hibernation.