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EN
The intergeniculate leaflet (IGL) is a small but important structure of the mammalian biological clock located in the thalamus. It has been previously classified as an integral part of lateral geniculate nucleus (LGN) but there are many histochemical and functional differences. In this study we have characterized the diversity of low-threshold ionic currents what helped us to distinguish different IGL neuronal subpopulations. The in vitro patch clamp recordings in voltage and current clamp mode were performed on the brain slices from Wistar rats. After each experiment, the immunohistochemical study was carried out to verify the location and the biochemical nature of the recorded cell. Our results show a group of IGL neurons expressing inward calcium currents, similar to the ones recorded from LGN interneurons, but characterized by much lower amplitude. Moreover, some IGL neurons show low-threshold outward currents what is unique feature among LGN cells.
EN
The intergeniculate leaflet (IGL) is a small part of the biological clock mechanism. The well known IGL function is the integration of photic and non-photic information and then such integrated message is delivered to the master biological clock – suprachiasmatic nuclei. IGL consists of two main neuronal populations: enkephalinergic (ENK) and neuropeptide Y (NPY) positive neurons. In both populations GABA is expressed. During our study using patch clamp technique we investigated how the two kinds of IGL non-photic inputs: orexin and serotonin, can modulate the functioning of this structure. Moreover, we checked how local neurotransmitter (GABA) can affect IGL neuronal network. We observed that both orexin and serotonin can mainly activate target IGL neurons. In case of GABA we observed both inhibition and depolarization. Our data indicates that various IGL neurons can differently respond to non-photic signals what probably leads to modulation of output information.
EN
The intergeniculate leaflet (IGL) of the thalamus is an important structure of the circadian timing system. Its primary role is the integration of both photic and non-photic stimuli relevant for the regulation of the sleep-wake cycle. The consolidated information is then transmitted to the main generator of circadian rhythms – the suprachiasmatic nuclei (SCN). As the non-photic cues are delivered to the IGL via non-specific projections of the brainstem, we chose to investigate how one projec‑ tion, the norepinephrine (NE) system from the locus coe‑ ruleus (LC), influences IGL neuronal activity. Moreover, we divided recorded cells into two groups, anticipating that they reflect two different projections arising from the IGL. The first group, expressing T-type calcium cur‑ rent (T-type cells), putatively comprises the connection between the leaflets located in both hemispheres, while A-type potassium current expressing neurons (or A-type cells) most likely transmit information to the SCN. The influence of NE on IGL neurons was tested by patch clamp recordings in the current clamp mode on 250 μm brain slices from 2/3-week-old male Wistar rats. In each instance NE (20 μM) was applied twice, the second ap‑ plication in the presence of tetrodotoxin (TTX, 0.5 μM), to determine if the observed effect was postsynaptic or presynaptic. Both substances were applied by bath per‑ fusion. After the experiment, slices were immunostained against the neuropeptide Y to confirm that the recorded cell was within the borders of the IGL. For this purpose, ExtrAvidinCy3 (1:250) and anti-NPY antibodies (1:8000) were used. NE was shown to elicit a direct effect on a ma‑ jority of IGL neurons. The effects were diverse; however, all A-type cells, and most T-type cells, responded with depolarization. Some neurons within the T-type group showed no response and, interestingly, a few neurons were hyperpolarized. Our study shows for the first time the electrophysiological effects of NE on the neuronal activity of single IGL neurons. The variety of respons‑ es, probably through activation of different receptors, requires further study. We predict that the diverse re‑ sponses reflect the differential impact of NE on neurons foming different projections, but the variety of respons‑ es from the T-type cells indicate that this group may be more complex and consist of additional subpopulations.
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EN
The lateral geniculate nucleus (LGN) is a retinorecipient thalamic structure serving both vision and non-vision forming functions. Subpopulation of LGN neurons is characterised by isoperiodic, infra slow oscillation (ISO; <0.01 Hz) in the rate of action potential firing. This ISO is common in the subcortical visual system and is synchronised among nuclei innervated by the same eye. Recently a new feature of light responsive neurons in the suprachiasmatic nuclei (SCN) has been described – harmonic distribution pattern (HDP) of interspike intervals (ISI), revealing fundamental frequency of ca. 30 Hz. The aim of this study was to determine the existence of HDP in the firing of the rat LGN. Single- or 32-channel extracellular recordings of neuronal firing were performed on in vivo (urethane anaesthesia) and in vitro preparations of Wistar rat brain. In vivo recordings were performed in experimentally controlled lighting conditions and during alternating brain states determined by EEG monitoring. We have discovered harmonic distribution pattern (HDP) of interspike intervals (fundamental ISI ~25–30 ms) in half of the in vivo recorded LGN and OPN neurons that were characterised by ISOs, but not in vitro. HPD was resistant to sustained light changes, although altered by transient (5 s) light pulses. Inactivation of contralateral retina (TTX injection) abolished HDP observed in LGN. HDP was correlated within each LGN and OPN and also between ipsilateral nuclei. For the first time we show that in LGN and OPN there is a subpopulation of neurons that fires in synchrony, governed by common HDP. Our results, combined with observation in SCN, allow as to propose the retina as a common source of HDP in light-responsive neurons and bring us closer to understanding the function of widespread retinal innervation of the mammalian brain. FINANCIAL SUPPORT: Supported by MSHE grant: 0001/ DIA/2014/43
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