Vasopressin and oxytocin expression in hypothalamic supraoptic nucleus and plasma electrolytes changes in water-deprived male Meriones libycus.

In mammals, plasmatic osmolality needs to be stable, and it is highly related to the hydric state of the animals which depends on the activity of the hypothalamic neurohypophysial system and more particularly by vasopressin secretion. Meriones, a desert rodent, can survive even without drinking for more than one month. The mechanism(s) by which they survive under these conditions remains poorly understood. In this study, we examine the water's deprivation consequences on the: (1) anatomy, morphology, and physiology of the hypothalamic supraoptic nucleus, (2) body mass and plasma electrolytes changes in male desert rodents 'Meriones libycus' subjected to water deprivation for 30 days. The effect of water deprivation was evaluated on the structural and cellular organization of the supraoptic nucleus by morphological observations and immunohistochemical approaches, allowing the labeling of AVP but also oxytocin. Our finding demonstrated that upon water deprivation (1) the body weight decreased and reached a plateau after a month of water restriction. (2) The plasmatic osmolality began to decrease and return to values similar to control animals at day 30. (3) The SON, both in hydrated and water-deprived animals, is highly developed.(4) The AVP labeling in the SON increased upon dehydration at variance with OT. These changes observed in body mass and plasma osmolality reveal an important adaptive process of male Meriones in response to prolonged water deprivation. Overall, this animal represents an interesting model for the study of water body homeostasis and the mechanisms underlying the survival of desert rodents to xeric environments.

Effects of prolonged night-time light exposure and traffic noise on the behavior and body temperature rhythmicity of the wild desert rodent, Gerbillus tarabuli.

The aim of this study was to demonstrate for the first time in Tarabul's gerbils (Gerbillus tarabuli), the effects of simultaneous exposure to two major environmental stressors - light and noise pollutions - on the body temperature rhythm and anxious behavior. Seven groups, each consisting of 6 adult male gerbils, were subjected to a standard LD cycle (12 L:12D) with lights on at 08:00 h and off at 20:00 h, constant conditions (total darkness, DD), prolonged nighttime exposure to light (PEL: 18 L:6D) with lights on at 08:00 h and off at 02:00 h, mimicking prolonged exposure to light pollution in peri-urban areas, exposure to auditory stress (TNS) of 80 dB, and conditions combining PEL&TNS. The body temperature circadian rhythm was recorded, and behavioral tests were performed at the end of experimental phases. The results revealed the existence, for the first time in Gerbilus tarabuli, of an endogenous circadian rhythm of body temperature with a period of 23.8 ± 0.04 h. Prolonged exposure to light at night (PEL) induced a significant phase delay (02 h 09 min ± 0.16 h) of the rhythm, with an acrophase (peak time) occurring at 04:42 ± 0.13 h instead of 02:33 ± 0.21 h. Exposure to TNS for 4 hours per night induced a significant increase of the amplitude of the rhythm and a decrease of the rhythm regularity (robustness of 73.26% in TNS vs. 82.32 in control condition). While combining TNS and PEL significantly delayed the phase of the Tb rhythm by 3 h 10 min (acrophase at 06:39 ± 0.37 h instead of 02:33 ± 0.21 h), increased the amplitude, and significantly reduced the stability of the rhythm (robustness of 67.25% in PEL&TNS vs. 82.32 in control condition). PEL&TNS and TNS environments induce an important stress in gerbils highlighted by a significant decrease of the number of line crossings and time spent in the center area of the open field test. Furthermore, elevated plus maze test revealed gerbils of the PEL&TNS and TNS conditions significantly visited the lowest number of open arms and spent a shorter amount of time in it. In addition, these conditions were responsible for less activity (total number of entries in arms) than in the control and PEL conditions. These results indicate clearly that in the desert area, peri-urban light and noise pollutions disturb the circadian rhythm components and alter the behavior of Tarabul's gerbils inducing an anxious state.

The Light/Dark cycle disruption affects hepatic function both in metabolic parameters and tissue structure in a nocturnal desert rodent: Gerbillus tarabuli.

INTRODUCTION: Biological rhythms, such as Light/Dark (LD) cycles, are an integral component of virtually all aspects of life. These rhythms are controlled in large part by circadian clocks, allowing the organism to adapt its internal rhythmic metabolism to changes in the external environment created by daily fluctuations in the LD cycle. Therefore, changes in the daily duration of the lighting could lead to adverse health consequences. The aim of the study was to investigate, in a nocturnal desert rodent, Gerbillus tarabuli, the effects of the LD cycle disruption on the structure of the hepatic tissue and the content of carbohydrate and lipid parameters as indicators of metabolic state. MATERIAL AND METHODS: The present study was conducted on two gerbil groups: control group was exposed to a standard lighting cycle (LD: 12:12), and the shifted group was subjected to a chronic disrupted LD cycle, alternating a standard cycle (LD: 12:12) with a modified cycle (LD: 20:4), i.e., the light phase of 24-h cycle was prolonged by 8 h on every second day during a period of 12 weeks. We used: (i) routine histology and histochemical staining for tissue analysis; (ii) immunohistochemistry (IHC) for MPO detection; (iii) biochemical methods for hepatic glycogen and lipids extraction and quantification. Blood metabolic parameters were assessed by enzymatic methods. RESULTS: Our structural results indicate in the shifted group an alteration of tissue architecture, showing widely scattered inflammatory foci with many dilated sinusoids and prominent leukocyte infiltration with connective fibrotic extension. IHC revealed also increased hepatic myeloperoxidase (MPO) expression confirming neutrophils' presence. In parallel, the histochemical study revealed a strong depletion of hepatocytic glycogen and lipid inclusions; these observations were also supported by the measurements of glycogen and total lipids in extracted tissue indicating a reduction in liver content. These results were accompanied by a decrease in body weight relative to the reduction of food intake, as well as hyperglycemia and some alterations in serum lipid parameters (triglycerides and cholesterol) suggesting a metabolic disturbance. CONCLUSION: We conclude that a phase difference between the endogenous activity rhythm of the species and the daily cycle of illumination has a strong impact on the liver morphology as well as on the metabolic activity of liver cells.

Diet-induced insulin resistance state disturbs brain clock processes and alters tuning of clock outputs in the Sand rat, Psammomys obesus.

Reciprocal interactions closely connect energy metabolism with circadian rhythmicity. Altered clockwork and circadian desynchronization are often linked with impaired energy regulation. Conversely, metabolic disturbances have been associated with altered autonomic and hormonal rhythms. The effects of high-energy (HE) diet on the master clock in the suprachiasmatic nuclei (SCN) remain unclear.This question was addressed in the Sand rat (Psammomys obesus), a non-insulin-dependent diabetes mellitus (NIDDM) animal model. The aim of this work was to determine whether enriched diet in Psammomys affects locomotor activity rhythm, as well as daily oscillations in the master clock of the SCN and in an extra-SCN brain oscillator, the piriform cortex. Sand rats were fed during 3 months with either low or HE diet. Vasoactive intestinal peptide (VIP), vasopressin (AVP) and CLOCK protein cycling were studied by immunohistochemistry and running wheel protocol was used for behavioral analysis. High energy feeding dietary triggered hyperinsulinemia, impaired insulin/glucose ratio and disruption in pancreatic hormonal rhythms. Circadian disturbances in hyper-insulinemic animals include a lengthened rest/activity rhythm in constant darkness, as well as disappearance of daily rhythmicity of VIP, AVP and the circadian transcription factor CLOCK within the suprachiasmatic clock. In addition, daily rhythmicity of VIP and CLOCK was abolished by HE diet in a secondary brain oscillator, the piriform cortex. Our findings highlight a major impact of diabetogenic diet on central and peripheral rhythmicity. The Psammomys model will be instrumental to better understand the functional links between circadian clocks, glucose intolerance and insulin resistance state.

[Cellular aspects of aging in the pineal gland of the shrew, Crocidura russula]. / Aspects cellulaires du vieillissement de la glande pinéale chez la musaraigne, Crocidura russula.

The Greater White-toothed shrew Crocidura russula is short-lived species and the phase of senescence is greatly elongated in captivity. The loss of rhythmicity of biological functions that accompanies its aging is also well documented. C. russula is thus an excellent model to test the effects of aging on biological clocks. Melatonin is a key hormone in the synchronization of behaviors, metabolisms and physiological regulations with environmental factors. In the present work we want to know if the loss of rhythmicity and the reduced melatonin levels registered by the second year of life in this species could be associated to modified ultrastructural features of the pineal parenchyma, site of melatonin synthesis. Transmission electron microscopy (TEM) analysis of young (1-4 months) and old (25-28 months) shrew's pineals show that in older individuals, the parenchyma undergoes alterations affecting mainly nucleus, mitochondria and endoplasmic reticulum cisternae, with increased numbers of dense bodies and the formation of many concretions as well as a depletion of secretory products. These changes suggest a process of slowing pinealocytes metabolism which could explain the gradual reduction of melatonin levels registered during aging in C. russula.