Neuroanatomical characterization of a growth hormone secretagogue receptor‐green fluorescent protein reporter mouse

Abstract

Growth hormone secretagogue receptor (GHSR) 1a is the only molecularly identified receptor for ghrelin, mediating ghrelin-related effects on eating, body weight and blood glucose control, among others. The expression pattern of GHSR within the brain has been assessed previously using several neuroanatomical techniques. However, inherent limitations to these techniques and the lack of reliable anti-GHSR antibodies and reporter rodent models that identify GHSR-containing neurons have prevented a more comprehensive functional characterization of ghrelin-responsive neurons. Here, we have systematically characterized the brain expression of an enhanced green fluorescence protein (eGFP) transgene controlled by the Ghsr promoter in a recently-reported GHSR reporter mouse. Expression of eGFP in coronal brain sections was compared with GHSR mRNA expression detected in the same sections by in situ hybridization histochemistry. eGFP-immunoreactivity was detected in several areas including the prefrontal cortex, insular cortex, olfactory bulb, amygdala and hippocampus, which showed no or low GHSR mRNA expression. In contrast, eGFP expression was low in several midbrain regions and in several hypothalamic nuclei – particularly the arcuate nucleus– where robust GHSR mRNA expression has been well-characterized. eGFP expression in several brainstem nuclei showed high to moderate degrees of co-localization with GHSR mRNA labeling. Further quantitative PCR and electrophysiological analyses of eGFP-labeled hippocampal cells confirmed faithful expression of eGFP within GHSR-containing, ghrelin-responsive neurons. In summary, the GHSR-eGFP reporter mouse model may be a useful tool to study GHSR function – particularly within the brainstem and hippocampus– however, it underrepresents GHSR expression in nuclei within the hypothalamus and midbrain.

Palatability Can Drive Feeding Independent of AgRP Neurons

“…We reasoned that in the absence of AgRP neurons, orexigenic drive might rely on dopamine tone because the ghrelin receptor is expressed in the VTA (Mani et al, 2014) where its activation has been shown to trigger feeding (Abizaid et al, 2006; Egecioglu et al, 2010; Jerlhag et al, 2007; Naleid et al, 2005). Control and AgRP-ablated mice were implanted with ICV and intra-VTA cannulas and feeding responses to ghrelin were monitored on chow or HFHS diet in presence or absence of [D-Lys3]-GHRP-6, a selective antagonist of the ghrelin receptor (Traebert et al, 2002) that is known to reduce food intake (Ishii et al, 2002).…”

Constitutive activity of the Ghrelin receptor reduces surface expression of voltage-gated Ca2+ channels in a CaVβ-dependent manner

“…GHSRs are widely expressed in the brain (Zigman et al, 2006;Mani et al, 2014). On the basis of our current and previous data; we propose that this receptor controls Ca V density in neurons.…”

Neuroanatomical and functional characterization of CRF neurons of the amygdala using a novel transgenic mouse model

“…In particular, the amygdala has been suggested to mediate ghrelin’s roles on in the modulation of food reward and learning (Alvarez-Crespo et al, 2012). Indeed, a human functional MRI study showed that ghrelin activates the amygdala upon exposure to images of appealing foods (Malik et al, 2008), and ghrelin receptor is expressed in the amygdala (Mani et al, 2014). Despite that a significant increase of c-Fos was detected in the amygdala of ghrelin-treated mice, no c-Fos was detected in the CRF neurons of this brain region also suggesting that other neuronal populations of the amygdala mediate ghrelin’s effects.…”