Project Outline

A key function of the brain is to monitor our environment – both our surroundings as well as our internal state. As an example, as we eat our stomach distends. The stretch in the stomach wall is sensed by the vagus nerve, which transmits the signal to the brain – primarily to the nucleus of the solitary tract (NTS). Here, neurons use that information to drive changes in behaviour and to limit further food intake.

Within the NTS a small group of neurons express the neuropeptide corticotropin-releasing hormone (NTS^CRH neurons). CRH is the perhaps most important neuropeptide in controlling behavioural and physiological responses to stress and CRH is a potent suppressor of food intake when injected directly into the brain. However, the role of NTS^CRH neurons has not been investigated. In fact, beyond their placement in the NTS, nothing is known about these cells. Our research has now revealed that NTS^CRH neurons send projections to the cerebellum – a region of the brain increasingly recognised to play an important role in feeding behaviour. In humans, parts of the cerebellum are active following stomach distension or food intake.

The overall objective of this research project is to characterise in detail the neuroanatomy, cellular physiology and function of NTS^CRH neurons.

We have three aims:

1. Map the neuroanatomy of NTS^CRH neurons and their connections
2. Characterise the cellular and electrical properties of NTS^CRH neurons and determine if they make functional connections with cerebellar neurons
3. Determine if NTS^CRH neurons are necessary for control of food intake

To address these aims, we use transgenic mice expressing Cre recombinase under the control of the Crh promoter (Crh-Cre mice) to selectively and efficiently target these cells in vivo. Mice will be stereotaxically injected with viruses to label or manipulate NTS^CRH neurons. Using immunolabelling and fluorescence microscopy, we will map the neuroanatomical profile of NTS^CRH neurons¹. Whole cell patch-clamp electrophysiology and ex vivo calcium imaging will be conducted under the supervision of Dr Emily Lane-Hill and Professor Mark Wall. This will allow us to monitor the cellular responses to stimulation of the vagus nerve and application of appetite-related signalling molecules (e.g. leptin)². Using optogenetics in acute brain slices we will determine if there is a direct connection between NTS^CRH and cerebellar neurons. Finally, using pharmacology and chemo- and optogenetics, we will determine the role of NTS CRH neurons in food intake control³.

This project will reveal a novel population of neurons in the NTS responsible for food intake.

References

References below are examples of our previous studies using similar ideas and approaches as those described above.

1. Holt, M. K. et al. Synaptic inputs to the mouse dorsal vagal complex and its resident preproglucagon neurons. J. Neurosci. Off. J. Soc. Neurosci. 39, 9767–9781 (2019).
2. Hisadome, K., Reimann, F., Gribble, F. M. & Trapp, S. Leptin directly depolarizes preproglucagon neurons in the nucleus tractus solitarius: electrical properties of glucagon-like Peptide 1 neurons. Diabetes 59, 1890–1898 (2010).
3. Brierley, D. I. et al. Central and peripheral GLP-1 systems independently suppress eating. Nat. Metab. 3, 258–273 (2021).

Techniques

• Whole cell patch-clamp electrophysiology
• Advanced mouse surgery including stereotaxic brain injections
• Chemo- and optogenetics
• Viral tracing
• Mouse behavioural analysis
• Use of open-source devices for food intake analysis
• Immunolabelling and RNAscope in situ hybridisation on mouse tissue
• Fluorescence microscopy