Melatonin, consciousness, and traumatic stress

Abstract

: Descartes intuitively anticipated the so‐called ‘binding problem’ of consciousness and thought that the pineal gland enables spatio‐temporal integration in cognitive processing. Recent findings indicate that a major role in the process of temporal integration and binding involve neurons in suprachiasmatic nuclei, specifically targeting the pineal gland and other structures, and control the neuroendocrine rhythms. Melatonin is an endocrine output signal of the clock and provides circadian information as an endogenous synchronizer which stabilizes and reinforces circadian rhythms. This integrative process occurs at the different levels of the circadian network via gene expression in some brain regions and peripheral structures that enables integration of circadian, hormonal, and metabolic information and creating temporal order of bodily and mental experience. This specific temporal order is reflected in associative sequentiality that is necessary for cognition, behavior and all processes of memory consolidation that must preserve all information in the temporal causal order and synchrony. In this context, recent findings suggest that melatonin could be a potential regulator in the processes that contribute to memory formation, long‐term potentiation, and synaptic plasticity in the hippocampus and other brain regions. There is evidence that stress disrupts normal activity and memory consolidation in the hippocampus and prefrontal cortex, and this process leads to memories that are stored without a contextual or spatiotemporal frame. These findings emphasize a specific role of melatonin in mechanisms of consciousness, memory and stress and are also consistent with reported studies that indicate melatonin alterations under stressful conditions and in mental disorders.

Unveiling the role of melatonin MT2 receptors in sleep, anxiety and other neuropsychiatric diseases: a novel target in psychopharmacology

“…128 Long-term potentiation is a measure that results from simultaneous activity between 2 neurons, enhancing the signal neurotransmission after electrical stimulation. 128 As reviewed by Bob and Fedor-Freybergh, 129 MLT regulates memory formation, acting directly on hippocampal neur ons, 29,130 which are involved in the processes of memory acquisition and consolidation. [131][132][133] In particular, MLT enhances the firing rate of action potentials in CA 1 neurons of hippocampal slices 29 and promotes synaptic transmission.…”

Protective Effect of Melatonin upon Neuropathology, Striatal Function, and Memory Ability after Intracerebral Hemorrhage in Rats

“…Hippocampal neurons have receptors for melatonin (Morgan et al, 1994;Musshoff et al, 2002), and the administration of this hormone is known to alter excitability and synaptic transmission within the hippocampus (Hogan et al, 2001;Musshoff et al, 2002;Wan et al, 1999), and melatonin has been shown to alter hippocampal synaptic plasticity through the MT2-mediated regulation of the adenylate cyclase-protein kinase A (AC-PKA) pathway (Wang et al, 2005). The synaptic plasticity in the hippocampus and other brain regions has recently gained attention as an important means by which melatonin may augment its neuroprotective effects beyond reductions in oxidative stress alone (Baydas et al, 2005;Bob and Fedor-Freybergh, 2008;Fukunaga et al, 2002;Gorfine and Zisapel, 2007;Larson et al, 2006;Talaei et al, 2009;Wang et al, 2005). In light of these findings, and those of this study, there is an urgent need for more high-quality mechanistic studies to further investigate these plasticity processes as a possible means of improving outcomes after ICH.…”

Circadian Synchronization of Cognitive Functions

“…The SCN comprises individual neuronal oscillators coupled into a neural network. First it was thought that the SCN was composed of identical resettable oscillators, however, more recent investigations have shown that circadian rhythmicity in the SCN is the product of a highly organized network of heterogeneous cells [ 4 ].…”