Action and function of the neuropeptide gastrin-releasing peptide in stress and memory formation
Human Cognitive and Systems Neuroscience
Cognitive, Systems and Behavioural Neurobiology
Final Report Abstract
Learning and memory formation require plasticity of cortical and subcortical neuronal circuits. In the cortex, inhibitory cells exert powerful control over the excitability of principal cells and thus learning and memory. Vasoactive intestinal peptide expressing (VIP) cells are uniquely positioned to release direct inhibition from principal cells and thus disinhibit cortical circuits and increase plasticity. Interestingly, VIP cells are marked by a rich repertoire of neuromodulator and peptide receptors. However very little is known how VIP cell activity is regulated by these receptors. We aim to understand peptidergic regulation of VIP cells and its effects onto learning and memory. Based on RNA sequencing data we found a peptide receptor that is strongly enriched in VIP cells – the gastrin releasing peptide (GRP) receptor. GRP release in the amygdala and hippocampus have been implicated in the formation of fear memories. However, the function in the cortex is not yet known. We show that GRP depolarizes VIP cells leads to calcium release from internal stores and entry through voltage gated calcium channels and increases inhibition of pyramidal cell-targeting inhibitory neurons in vitro. We found that in anaesthetized mice, GRP infusion leads to increased c-Fos expression of superficial layer pyramidal cells, pointing to a layer specific disinhibitory effect of GRP. Importantly, the GRP receptor was also expressed in human visual cortex and a majority of GRP receptor-expressing cells was marked by the expression of VIP, suggesting that GRP is a neuropeptide with evolutionarily conserved neuronal and behavioral function and mechanisms of action. GRP is expressed in L2/3 and in L6 cortico-thalamic pyramidal cells as well as in subpopulations of thalamo- and amygdala-cortical projecting neurons. It is not known yet which of these cells lead to release of GRP in the cortex in vivo. We developed new CRISPR/Cas9 constructs to knockout the GRP receptor in defined brain areas through viral-mediated gene delivery and neuronal expression. We are currently using this tool to study the function of the GRP receptor in the formation of fear memories in various cortical areas. Moreover, we developed a new fluorescent sensor to detect the release of GRP. This sensor readily reveals the presence of bath-applied GRP in acute brain slices. We are optimizing the sensor currently for in vivo application and detection of endogenously released GRP. Lastly, we developed a tool for wireless intracerebral injection of drugs into freely moving mice. This device employs radiofrequency to trigger injection of drugs through microfluidic channels into two brain areas simultaneously. It is thus suited for bilateral manipulation of brain areas during the performance of behavioral tasks. We are currently optimizing the tool for reliable injection of low volumes required to specifically target cortical subregions. This tool is designed to replace conventional cannula for pharmacological investigation of defined brain areas in behavioral tasks. It will not only allow delivery of drugs while the mouse performs a task, but also reduce stress levels and acute damage to the brain that have been an issue with conventional cannula so far. In summary, we investigated mechanisms and functions of the neuropeptide GRP in the cortex of mice and by this created a platform for cellular, circuit-level and behavioral analysis of neuropeptides in vitro and in vivo.
Publications
- The long and short of it: a perspective on peptidergic regulation of circuits and behaviour. Journal of Experimental Biology, 2018, 221
Jekély G, Melzer S, Beets I, Grunwald Kadow IC, Koene J, Haddad S, Holden-Dye L
(See online at https://doi.org/10.1242/jeb.166710)
