Neuroscience
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Hyperpolarization-activated currents (I(h)) affect multiple neuronal functions including membrane potential, intrinsic firing properties, synaptic integration and frequency-dependent resonance behavior. Consistently, I(h) plays a key role for oscillations at the cellular and network level, including theta and gamma oscillations in rodent hippocampal circuits. Little is known, however, about the contribution of I(h) to a prominent memory-related pattern of network activity called sharp-wave-ripple complexes (SPW-R). ⋯ Likewise, coupling between field oscillations and units was unchanged, showing unaltered recruitment of neurons into oscillating assemblies. Control experiments exclude a contribution of T-type calcium channels to the observed effects. Together, we report a specific contribution of hyperpolarization-activated cation currents to the generation of sharp waves in the hippocampus.
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To investigate neurofilament (NF) dynamics during the cytoskeleton reorganization in regenerating axons, and their electrophysiological and histological consequences, we used two transgenic lines of mice: neurofilament high (NFH)-LacZ and NFH-green fluorescent protein (GFP). In NFH-LacZ mice, NFs are retained in cell bodies and deficient in axons (Eyer and Peterson, 1994), while in NFH-GFP mice the fluorescent fusion protein is normally transported along axons (Letournel et al., 2006). ⋯ Finally, the axonal transport of NFH-GFP fusion protein and NFs is re-initiated after the crush as evidenced by the fluorescent and immunolabelling of axons distal from the crushed point, but NFs and the fusion protein are not transported along axons during regeneration in NFH-LacZ mice. Together, these results argue that the absence of axonal NFs in NFH-LacZ mice compromises the axonal regeneration, and that the NFH-GFP reporter fusion protein represents an efficient model to evaluate the NF dynamics during axonal regeneration.
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Previous anatomical and physiological studies suggest that the superior colliculus sends integrated sensory information to the multimodal cortical areas via the thalamic suprageniculate nucleus (SG). However, the detailed distribution of rat tecto-SG axon terminals and SG neurons projecting to the multimodal cortex, as well as synaptic connections between these tectal axons and SG neurons, remains unclear. In this study, the organization of the tecto-thalamo-cortical pathway was investigated via combined injections of anterograde and retrograde tracers followed by light and electron microscopic observations. ⋯ CTB-labeled neurons were also found in other cortical areas such as the visual cortex, the auditory cortex, the parietal association cortex, and the perirhinal cortex. (2) Anterogradely BDA-labeled axons and their terminals were also observed throughout SG. Dual visualization of BDA and CTB showed that retrogradely labeled SG neurons and anterogradely labeled tectal axon terminal boutons overlapped considerably in the rostral part of SG, and their direct synaptic contacts were also confirmed via electron microscopy. These findings suggest that multimodal information from the superior colliculus can be processed directly in SG neurons projecting to Te2D.
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The intergeniculate leaflet (IGL) of the lateral geniculate body in the rat is a population of GABAergic neurons that can be divided into two, anatomically and neurochemically distinct populations. One population comprises neuropeptide-Y (NPY)-positive neurons that form the geniculohypothalamic tract innervating the suprachiasmatic nuclei (SCN) and the other population comprises enkephalin-positive (ENK) neurons giving rise to the geniculo-geniculate tract innervating the contralateral IGL (cIGL). Previous electrophysiological studies have observed various patterns of firing and different responses to changes in lighting conditions of IGL neurons in vitro and in vivo. ⋯ In contrast, all IGL neurons identified as projecting to the SCN displayed a low level of firing in the light and a majority of these cells increased firing in the darkness. All IGL neurons projecting to the SCN were characterised by an irregular pattern of firing in the light and dark. These data are the first to demonstrate that differentially projecting rat intergeniculate leaflet neurons are characterised by distinct firing patterns and opposite responses to light and dark conditions.
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Neonatal hypoxia-ischemic encephalopathy (HIE) remains a major cause of brain damage, leading to high disability and mortality rates in neonates. In vitro studies have shown that hesperidin, a flavanone glycoside found abundantly in citrus fruits, acts as an antioxidant. Although hesperidin has been considered as a potential treatment for HIE, its effects have not been fully evaluated. ⋯ The neuroprotective effects of hesperidin are likely the results of preventing an increase in intracellular reactive oxygen species and lipid peroxide levels. Hesperidin treatment also activated a key survival signaling kinase, Akt, and suppressed the P-FoxO3 level. Hesperidin pretreatment protected neonatal HIE by reducing free radicals and activating phosphorylated Akt.