The overt expression of circadian rhythms is a manifestation of the suprachiasmatic nucleus (SCN). This integrated complex function based on the transcriptional/translational feedback loops (TFFLs), neurotransmitters, genes, networking, and synchronization is essential for this molecular mechanism to operate effectively. Neurotransmitters by participating in the entrainment to the environmental light conditions and synchronization contribute to the robustness of the rhythm. Neurotransmitter signaling is the hallmark of circadian rhythm expression. Even during development, neuropeptides contribute to the dramatic cellular, genetic, and network circuit changes. Participating neurotransmitters are seen in afferent inputs, efferent output, and the SCN. There are numerous neurotransmitters involved in SCN function. Astrocytes co-exist with neurons in the SCN. Autonomous clocks seen in astrocytes can drive circadian behavior like neurons. Astrocytes and neurons are acting as two arms of the clock. Coupling through glutamate released from astrocytes gives additional evidence for the role of astrocytes. Glutaminergic signaling from astrocytes may also be responsible for timekeeping. The neurotransmitters can independently and in combination execute the functions making SCN a unique pacemaker for the overt expression of circadian rhythms. This reassessment also highlights its role in underlying molecular mechanisms, genetic linkage, and the recently known role of astrocytes.

For more than a decade now, research studies, proof of concept work, and clinical trials have endeavored to understand how mesenchymal stem cells might be used to help protect, repair, and/or regenerate damaged brain tissue following stroke. To date, the majority of studies have not demonstrated significant improvements in either morbidity or medium-long-term outcome, although safety has been relatively well proven. Limitations are likely to be linked to the pathobiological complexity and seriousness of stroke tissue damage, low efficacy of treatment, and short half-life of bio-active proteins released by stem cells. This article will highlight the heterogeneity and limitation of completed studies and the current status of ongoing work. At the same time, the potential of other combinational type treatments, such as drug-loading and targeting, and the use of hydrogels is discussed.

Exposure to stressful conditions plays a critical role in brain processes, including neural plasticity, synaptic transmission, and cognitive functions. Since memory-related brain regions, the hippocampus (Hip), the amygdala, and the prefrontal cortex, express high glucocorticoid receptors (GRs), these areas are the potential targets of stress hormones. Stress affects memory encoding, consolidation, and retrieval, which may depend on many factors such as the type, duration, the intensity of the stressor or the brain region. Here, this review mainly focused on the mechanisms involved in stress-induced memory impairment. Acute/chronic stress induces structural and functional changes in neurons and glial cells. Dendritic arborization, reduction of dendritic spine density, and alteration in glutamatergic-mediated synaptic transmission via N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors are mechanisms that stress affect long-term memory formation. Exposure to acute or chronic stress could interplay with multiple neurotransmitter signaling, modulating the neuronal circuits involved in memory impairment or state-dependent learning. Stress hormones also modulate the expression of microRNAs in the specific brain regions responsible for stress-induced behaviors. Because of expressing GRs in astrocytes and microglial cells, stress could affect the morphology, structure, and functions of these glial cells in memory-related brain regions. Astrocytes play a crucial role in stress-induced aversive or fear memory formation. Over-activation of the microglial cells enhances the release of inflammatory cytokines, which results in neuronal injury. Stress has a prominent role in cognitive decline to induces memory problems, particularly in older adults. Due to the issue’s importance, here the provided overview attempted to address the question of how stress alters neuronal epigenetic regulators, synaptic transmissions, and glial activity in the brain.