Connexin30 and Connexin43 show a time-of-day dependent expression in the mouse suprachiasmatic nucleus and modulate rhythmic locomotor activity in the context of chronodisruption

Abstract

Background The astroglial connexins Cx30 and Cx43 contribute to many important CNS functions including cognitive behaviour, motoric capacity and regulation of the sleep-wake cycle. The sleep wake cycle, is controlled by the circadian system. The central circadian rhythm generator resides in the suprachiasmatic nucleus (SCN). SCN neurons are tightly coupled in order to generate a coherent circadian rhythm. The SCN receives excitatory glutamatergic input from the retina which mediates entrainment of the circadian system to the environmental light-dark cycle. Connexins play an important role in electric coupling of SCN neurons and astrocytic-neuronal signalling that regulates rhythmic SCN neuronal activity. However, little is known about the regulation of Cx30 and Cx43 expression in the SCN, and the role of these connexins in light entrainment of the circadian system and in circadian rhythm generation. Methods We analysed time-of-day dependent as well as circadian expression of Cx30 and Cx43 mRNA and protein in the mouse SCN by means of qPCR and immunohistochemistry. Moreover, we analysed rhythmic spontaneous locomotor activity in mice with a targeted deletion of Cx30 and astrocyte specific deletion of Cx43 (DKO) in different light regimes by means of on-cage infrared detectors. Results Fluctuation of Cx30 protein expression is strongly dependent on the light-dark cycle whereas fluctuation of Cx43 protein expression persisted in constant darkness. DKO mice entrained to the light-dark cycle. However, re-entrainment after a phase delay was slightly impaired in DKO mice. Surprisingly, DKO mice were more resilient to chronodisruption. Conclusion Circadian fluctuation of Cx30 and Cx43 protein expression in the SCN is differently regulated. Cx30 and astroglial Cx43 play a role in rhythm stability and re-entrainment under challenging conditions. Electronic supplementary material The online version of this article (10.1186/s12964-019-0370-2) contains supplementary material, which is available to authorized users.

Endogenous circadian time genes expressions in the liver of mice under constant darkness

“…Oscillation genes under LD, S-DD and L-DD were enriched in different biological process respectively, which was caused by an altered light cycle. As shown in Venn Diagram, more than 60% of oscillation genes kept rhythmicity only in their unique light cycle, once the light cycle changed, their oscillation [44]. Therefore, the oscillation of some genes depends on the entrainment of light while the others are endogenous.…”

Analysis of Spatial and Temporal Distribution of Purinergic P2 Receptors in the Mouse Hippocampus

“…However, P2Y 2 , which is sensitive for both ATP and UTP, shows the long-lasting increase. The temporal profile of P2Y 2 and P2Y 6 (increased during early-mid light phase) and P2X3, P2X4 and P2Y 12 (increased during the mid-late dark phase) in hippocampal layers (this study) was similar as in the SCN [ 19 ], suggesting a general regulatory mechanism and might also implicate a general role of these receptors in modulating glio-/neurotransmission during these temporal domains across brain regions. However, as the temporal profile of extracellular ATP is in antiphase in hippocampus [ 59 ] and SCN [ 21 ] a general regulation of these P2 receptors by their ligands is unlikely.…”

“…Brain preparation and immunohistochemistry were performed as described earlier [ 19 ]. Briefly, mice were deeply anaesthetized using ketamine:xylazine (100 mg:10 mg/kg body weight) and transcardially perfused with 0.9% NaCl followed by 4% paraformaldehyde.…”

“…After washing with PBS/0.2% Triton-X 100, slices were preincubated for 1 h with normal rabbit or goat sera. The sections were incubated with primary antibodies against different purinergic receptors ([ 19 ] ( Table 4 ) overnight at 4 °C, in addition to parallel negative control sections ( Supplementary Figure S4 ). Sections were rinsed again, and then incubated with the corresponding biotinylated anti-rabbit or anti-goat secondary antibodies for 2 h at RT.…”

“…Importantly, to fully understand P2 receptor signaling not only spatial but also temporal distribution should be considered [ 18 ]. We could show earlier, that P2 receptors show a time-of-day-dependent variation in the mouse suprachiasmatic nucleus (SCN) [ 19 ], the circadian rhythm generator [ 20 , 21 , 22 ]. Here, we focus on the spatial and temporal distribution of various P2 receptors in the hippocampus, the brain region of fundamental importance for learning and memory [ 23 ], processes which are strongly controlled by the circadian system [ 24 ].…”