Enhanced Expression of Heme Oxygenase‐1 and Carbon Monoxide Excitatory Effects in Oxytocin and Vasopressin Neurones During Water Deprivation

Abstract

A growing body of evidence supports carbon monoxide (CO) as a gas neurotransmitter within the central nervous system. While CO has been shown to affect neurohypophyseal hormone release in response to osmotic stimuli, the precise sources, targets and mechanisms underlying CO actions within the magnocellular neurosecretory system remain largely unknown. In this study, we combined immunohistochemistry and patch-clamp electrophysiology to study the cellular distribution of the CO-synthase enzyme heme oxygenase type 1 (HO-1), as well as CO actions on oxytocin (OT) and vasopressin (VP) magnocellular neurosecretory cells (MNCs) in euhydrated (EU) and 48h water-deprived rats (48WD). Our results show expression of HO-1 immunoreactivity both in OT and VP neurones, as well as in a small proportion of astrocytes, both in the supraoptic (SON) and paraventricular (PVN) nuclei. HO-1 expression, and its colocalization with OT and VP neurones within SON and PVN were significantly enhanced in 48WD rats. Inhibition of HO activity (CrMP 20μM) resulted in a slight membrane hyperpolarization in SON neurones from EU rats, without significantly affecting their firing activity. In 48WD rats, on the other hand, CrMP resulted in a more robust membrane hyperpolarization, significantly decreasing neuronal firing discharge. Taken together, our results indicate that magnocellular SON and PVN neurones express HO-1, and that CO acts as an excitatory gas neurotransmitter in this system. Moreover, we found the expression and actions of CO to be enhanced in water-deprived rats, suggesting that the state-dependent up-regulation of the HO-1/CO signalling pathway contributes to enhance MNCs firing activity during an osmotic challenge.

Bidirectional neuro-glial signaling modalities in the hypothalamus: Role in neurohumoral regulation

“…This is in agreement with previous studies showing HO-1 presence in astrocytes and their ability to contribute to CO bioavailability in other brain regions (Li et al, 2008; Mancuso, 2004; Schipper et al, 2009). Importantly, we found CO to tonically stimulate SON neuronal activity, having thus opposite effects to NO (Reis et al, 2012). Thus, astrocytes in the SON/PVN are important cellular sources of two opposingly acting gas gliotransmitters, NO and CO.…”

“…In fact, a growing body of evidence supports a modulatory role for CO on OT and VP release (Gomes et al, 2010; Mancuso et al, 1999). In a recent study, we reported HO1 to be expressed not only on SON/PVN magnocellular neurons, but also in astrocytes within these nuclei (Reis et al, 2012). This is in agreement with previous studies showing HO-1 presence in astrocytes and their ability to contribute to CO bioavailability in other brain regions (Li et al, 2008; Mancuso, 2004; Schipper et al, 2009).…”

Mapping and signaling of neural pathways involved in the regulation of hydromineral homeostasis

“…Accordingly, inhibition of HO was shown to decrease the hyperosmolality-induced release of OT and ANP by the medial basal hypothalamus in vitro 56. Similarly, inhibition of this enzyme also induced a strong hyperpolarization and a decrease in the firing rate of magnocellular neurosecretory cells in water-deprived animals 55. In addition to acting individually, CO has also been shown to interact with the nitrergic system to control hydromineral homeostasis.…”

The Endocannabinoid System and the Neuroendocrine Control of Hydromineral Balance

“…The higher magnification shows the anatomical relationship between CB 1R‐positive terminals (in green) and oxytocinergic magnocellular neurones (in red) of the SON ( c ) or PVN ( d ). Free‐floating sections of 30 μm were obtained on a cryostat and submitted to the procedures for fluorescent staining, as described previously . The primary and secondary antibodies used were: anti‐cannabinoid receptor 1 (dilution 1 : 1000, rabbit, #ab23703; Abcam, Cambridge, MA, USA) and anti‐ OT (dilution 1 : 20 000, guinea pig, #T‐4084; Bachem, Torrance, CA, USA), f luorescein isothiocyanate ‐conjugated donkey‐anti‐rabbit (dilution 1 : 250, #711‐095‐152; Jackson ImmunoResearch, Newmarket, UK) and Cy5‐conjugated donkey anti‐guinea pig (dilution 1 : 250, #706‐175‐148; Jackson ImmunoResearch).…”