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Papers of the Week


Papers: 20 Jun 2020 - 26 Jun 2020


Animal Studies


2020 Jun 22


J Neurosci

The rostral agranular insular cortex, a new site of oxytocin to induce antinociception.

Authors

Gamal-Eltrabily M, Espinosa de Los Monteros-Zúñiga A, Manzano-García A, Martínez-Lorenzana G, Condés-Lara M, González-Hernández A
J Neurosci. 2020 Jun 22.
PMID: 32571836.

Abstract

The rostral agranular insular cortex (RAIC) is a relevant structure in nociception. Indeed, recruitment of GABAergic activity in RAIC promotes the disinhibition of the locus coeruleus (LC), which in turn inhibits (by noradrenergic action) the peripheral nociceptive input at the spinal cord level. In this regard, at the cortical level, oxytocin can modulate the GABAergic transmission; consequently, an interaction modulating nociception could exist between oxytocin and GABA at RAIC. Here, we tested in male Wistar rats the effect of oxytocin microinjection into RAIC during an inflammatory (by subcutaneous peripheral injection of formalin) nociceptive input. Oxytocin microinjection produces a diminution of (i) flinches induced by formalin and (ii) spontaneous firing of spinal wide dynamic range cells. The above antinociceptive effect was abolished by microinjection (at RAIC) of (i) L-368,899 (an oxytocin receptor -OTR- antagonist) or by (ii) bicuculline (a preferent GABA receptor blocker), suggesting a GABAergic activation induced by OTR. Since intrathecal injection of an α-adrenoceptor antagonist (BRL 44408) partially reversed the oxytocin effect, a descending noradrenergic antinociception is suggested. Besides, injection of L-368,899 induces a pronociceptive behavioral effect, suggesting a tonic endogenous oxytocin release during inflammatory nociceptive input. Accordingly, we found bilateral projections from the paraventricular nucleus of the hypothalamus (PVN) to RAIC. Some of the PVN-projecting cells are oxytocinergic and destinate GABAergic and OTR-expressing cells inside RAIC. Aside from the direct anatomical link between PVN and RAIC, our findings provide evidence about the role of oxytocinergic mechanisms modulating the pain process at the RAIC level.Oxytocin is a neuropeptide involved in several functions ranging from lactation to social attachment. Over the years, the role of this molecule in pain processing has emerged, showing that at the spinal level, oxytocin blocks pain transmission. The present work suggests that oxytocin also modulates pain at the cortical insular level by favoring cortical GABAergic transmission and activating descending spinal noradrenergic mechanisms. Indeed, we show that the paraventricular hypothalamic nucleus sends direct oxytocinergic projections to the rostral agranular insular cortex on GABAergic and oxytocin receptor expressing neurons. Together, our data support the notion that the oxytocinergic system could act as an orchestrator of pain modulation.