• Neuropharmacology · Dec 2015

    Excitatory orexinergic innervation of rat nucleus incertus--Implications for ascending arousal, motivation and feeding control.

    • Anna Blasiak, Marcin Siwiec, Agnieszka Grabowiecka, Tomasz Blasiak, Anna Czerw, Ewa Blasiak, Alan Kania, Zenon Rajfur, Marian H Lewandowski, and Andrew L Gundlach.
    • Department of Neurophysiology and Chronobiology, Institute of Zoology, Jagiellonian University, 30-387 Krakow, Poland. Electronic address: anna.blasiak@uj.edu.pl.
    • Neuropharmacology. 2015 Dec 1; 99: 432-47.

    AbstractOrexin/hypocretin peptides play a central role in the integrated control of feeding/reward and behavioural activation, principally via interactions with other neural systems. A brainstem area involved in behavioural activation is the nucleus incertus (NI), located in the posterior ventromedial central grey. Several studies have implicated NI in control of arousal/stress and reward/feeding responses. Orexin receptor mRNA expression identifies NI as a putative target of orexin modulation. Therefore, in this study we performed neural tract-tracing and immunofluorescence staining to characterise the orexinergic innervation of NI. Our results indicate a convergent innervation of the NI area by different orexin neuron populations, with an abundance of orexin-A-containing axons making putative synaptic contacts with relaxin-3-positive NI neurons. The influence of orexin-A on NI neuron activity was investigated using patch-clamp recordings. Orexin-A depolarised the majority (64%) of recorded neurons and this effect was maintained in the presence of tetrodotoxin and glutamate and GABA receptor antagonists, indicating a likely postsynaptic action. Voltage-clamp experiments revealed that in 'type I' NI neurons comprising relaxin-3-positive cells, orexin-A acted via L-type calcium channels, whereas in 'type II' relaxin-3-negative neurons, activation of a sodium/calcium exchanger was involved. A majority of the orexin-A sensitive neurons tested for the presence of orexin receptor mRNA, were OX2 mRNA-positive. Immunohistochemical staining for putative orexin receptors on NI neurons, confirmed stronger expression of OX2 than OX1 receptors. Our data demonstrate a strong influence of orexin-A on NI neurons, consistent with an important role for this hypothalamic/tegmental circuit in the regulation of arousal/vigilance and motivated behaviours. Copyright © 2015 Elsevier Ltd. All rights reserved.

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