J. Manuel Herrera-Zamora, Fernando Osuna-Lopez, Miriam E. Reyes-Méndez, Ramon E. Valadez-Lemus, Enrique A. Sánchez-Pastor, Ricardo A. Navarro-Polanco, Eloy G. Moreno-Galindo, Javier Alamilla
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引用次数: 0
Abstract
Circadian rhythms synchronize to light through the retinohypothalamic tract (RHT), which is a bundle of axons coming from melanopsin retinal ganglion cells, whose synaptic terminals release glutamate to the ventral suprachiasmatic nucleus (SCN). Activation of AMPA–kainate and NMDA postsynaptic receptors elicits the increase in intracellular calcium required for triggering the signaling cascade that ends in phase shifts. During aging, there is a decline in the synchronization of circadian rhythms to light. With electrophysiological (whole-cell patch-clamp) and immunohistochemical assays, in this work, we studied pre- and postsynaptic properties between the RHT and ventral SCN neurons in young adult (P90–120) and old (P540–650) C57BL/6J mice. Incremental stimulation intensities (applied on the optic chiasm) induced much lesser AMPA–kainate postsynaptic responses in old animals, implying a lower recruitment of RHT fibers. Conversely, a higher proportion of old SCN neurons exhibited synaptic facilitation, and variance–mean analysis indicated an increase in the probability of release in RHT terminals. Moreover, both spontaneous and miniature postsynaptic events displayed larger amplitudes in neurons from aged mice, whereas analysis of the NMDA and AMPA–kainate components (evoked by RHT electrical stimulation) disclosed no difference between the two ages studied. Immunohistochemistry revealed a bigger size in the puncta of vGluT2, GluN2B, and GluN2A of elderly animals, and the number of immunopositive particles was increased, but that of PSD-95 was reduced. All these synaptic adaptations could be part of compensatory mechanisms in the glutamatergic signaling to ameliorate the loss of RHT terminals in old animals.
期刊介绍:
The Journal of Neuroscience Research (JNR) publishes novel research results that will advance our understanding of the development, function and pathophysiology of the nervous system, using molecular, cellular, systems, and translational approaches. JNR covers both basic research and clinical aspects of neurology, neuropathology, psychiatry or psychology.
The journal focuses on uncovering the intricacies of brain structure and function. Research published in JNR covers all species from invertebrates to humans, and the reports inform the readers about the function and organization of the nervous system, with emphasis on how disease modifies the function and organization.