Neuroglobin in the rat brain (II): co-localisation with neurotransmitters

In an accompanying article, we found that neuroglobin (Ngb) was expressed in a few well-defined nuclei in the rat brain. Here, we show by use of immunohistochemistry and in situ hybridisation (ISH) that Ngb co-localise with several specific neurotransmitters. Ngb co-localise consistently with tyrosine hydroxylase (TH) in the noradrenergic/adrenergic A1/C1 and A2/C2; the noradrenergic A5, A6 and A7. Ngb were not observed to co-localise TH in the dopaminergic A8-A16 cell populations. Ngb were only seen to co-localise with choline acetyltransferase (ChAT) in the laterodorsal tegmental nucleus (LDTg) and in the pontine tegmental nucleus (PPTg). Many Ngb-ir neurones co-localised with neuronal nitric oxide synthase (nNOS) in the LDTg, whereas fewer Ngb-ir neurones co-localise nNOS in the anterior basomedial (BMA) and the posterodorsal medial (MePD) amygdaloid nucleus, in the medial preoptic area (MPA) and in part of the lateral hypothalamus (LH). Ngb-ir neurones co-localise heme oxygenase 1 (HO-1) in the LDTg and locus coeruleus. Ngb-ir neurones co-localise hypocretin-1 (Hcrt1) in the perifornical (PeF) and perifornical lateral hypothalamus (PeFLH). Within the LH, Ngb-ir neurones co-localised melanin concentration hormone (MCH). A few Ngb-ir perikarya in the paraventricular hypothalamic nucleus (PVN) co-localised arginine vasopressin (aVP). Ngb were not observed to co-localise with serotonin, vasointestinal peptide (VIP), or cocaine amphetamine-regulated transcript (CART) at any places. In the present study, we found no evidence that one or more particular neurotransmitters are coupled 100% to Ngb or that Ngb is coupled 100% to a specific neurotransmitter. Based on these findings, we suggest that Ngb could be involved in some sort of regulation of the sleep-wake cycle. Secondly, that Ngb in some neurones is involved in regulation of gaseous neurotransmission, and that this in any given case only involves a subset of neurones. To us this indicates that the cellular and physiological function of Ngb in different subsets of neurones might not be identical, or that all neurones containing Ngb has one thing in common that we at presently not are aware of.