Periodic Reporting for period 1 - NeuroModSense (Peptidergic Neuromodulation of Sensory Representation in the Brain)
Berichtszeitraum: 2017-03-01 bis 2019-02-28
We interact with and respond to our environment by processing sensory inputs such as visual and auditory cues and touch, taste and smell. Neuromodulators constantly modulate these sensory representations in the brain to adapt our behaviour to changes in the internal (e.g. sleep, wakefulness, stress, fed or hungry conditions) and external (e.g. danger) environment. The main objective of this proposal is to investigate the role and mechanism of neuromodulatory neurons, GnRH/NPY secreting neurons, in chemosensory processing and behaviour.
Gonadotropin releasing hormone (GnRH) and neuropeptide Y (NPY) are neuropeptides that are conserved across vertebrates and modulate feeding and reproductive behaviours, respectively. They are produced by discrete population of neurons in the brain and are dispersed widely throughout the brain. Past studies have shown that GnRH promotes the release gonadotropin and is known to modulate reproductive behaviours in vertebrates. NPY is involved in an increased food intake in vertebrates and has been shown to modulate olfactory responses to food odour in hungry animals. However, it is not known how GnRH/NPY neurons influence the processing of chemosensory information in the olfactory bulb (OB) and ultimately odour driven behaviour.
We found that GnRH neurons respond to the chemosensory information. Their responses are sexually dimorphic and are modulated by satiety. Their activity is necessary for odour driven feeding and reproductive behaviours. Our result implies a central role of these neurons in mediating odour driven feeding and reproduction. Moreover, we continue to work towards understanding the role of NPY neurons in sensory processing and behaviour.
Gonadotropin releasing hormone (GnRH) and neuropeptide Y (NPY) are neuropeptides that are conserved across vertebrates and modulate feeding and reproductive behaviours, respectively. They are produced by discrete population of neurons in the brain and are dispersed widely throughout the brain. Past studies have shown that GnRH promotes the release gonadotropin and is known to modulate reproductive behaviours in vertebrates. NPY is involved in an increased food intake in vertebrates and has been shown to modulate olfactory responses to food odour in hungry animals. However, it is not known how GnRH/NPY neurons influence the processing of chemosensory information in the olfactory bulb (OB) and ultimately odour driven behaviour.
We found that GnRH neurons respond to the chemosensory information. Their responses are sexually dimorphic and are modulated by satiety. Their activity is necessary for odour driven feeding and reproductive behaviours. Our result implies a central role of these neurons in mediating odour driven feeding and reproduction. Moreover, we continue to work towards understanding the role of NPY neurons in sensory processing and behaviour.
The overall aim of this project is to understand how neuromodulators influence the processing of chemosensory information in the olfactory bulb (OB) and ultimately animal behaviour in response to odours. Specifically, we proposed to determine how chemosensory information influences the activity of terminal nerve (TN) GnRH/NPY neurons and how TN GnRH/NPY neurons affect olfactory processing and odour-driven behaviours in zebrafish.
We have completed most of the work packages and achieved the scientific objectives in understanding the role of terminal nerve GnRH neurons in chemosensory processing and behaviour. However, through the project, it was difficult to generate NPY transgenic zebrafish lines. Thanks to our collaborators, we have the NPY transgenic zebrafish. Since all our methods/tools are optimized, we continue to work on achieving the remaining objectives.
For workpackage(WP)-1, we investigated how chemosensory information modulates the activity of terminal nerve GnRH/NPY neurons. To address this, first, we used genetic approach and established transgenic zebrafish line to label the TN GnRH neurons specifically with the genetically encoded calcium indicator. Thanks to our collaborator, we received transgenic line that marks all the NPY neurons in the zebrafish brain. Next, we established the method to image neural activity using two-photon microscopy in brain explant preparation. This allowed us to observe the activity of these neurons in response to natural odours. Finally, we developed the quantitative analytical tools to analyse the neural data. We found that GnRH secreting neurons are spontaneously active. They respond to natural odorants with complex dynamics and have strong preference for food related odours. This odour representation in the GnRH neurons are sexually dimorphic and strongly modulated by physiological states (satiety/hungry) of animals.
In WP-2, we had hypothesised that GnRH/NPY neurons modulate odour representation in the olfactory bulb. To test this hypothesis, we perturbed (downregulate/upregulate) the basal activity of GnRH/NPY neurons. This required establishing transgenic lines that label these neurons with optogenetic transgenes, halorhodopsin and channel rhodopsin, and chemogenetic gene, nitroreductase. Optogentic tools allowed temporal control over modulation of neural activity and chemogentic tool provided a means to study the acute effect of this modulation. We successfully down regulated or silenced the GnRH neuron activity using these methods and imaged neural activity in the olfactory bulb for any change in olfactory processing. Our initial findings suggested that modulation by GnRH neuron in olfactory bulb is quite subtle. Moreover, these neurons project to multiple brain regions including dorsomedial telencephalon (amygdala), dorsolateral telencephalon (hippocampus), ventral telencephalon, habenula and hypothalamus. Hence, we expanded the scope of our work to observe neural activity in these regions and modified our analytical tools for analysis of the new data set. Initial findings suggest that changes in odour representation likely involve network involved in aversion, such as habenula and amygdala. Moreover, we have established the framework to modulate the activity of NPY neuron and observe change in odour representation in the brain.
In WP-3, we investigated the impact of modulation of activity GnRH/NPY neuron on olfactory perception and odour driven feeding and reproductive behaviours. First, we established transgenic tools to modulate the activity of GnRH/NPY neurons in the olfactory bulb of freely behaving animals. Next, we developed and refined the behavioural assays to measure feeding rate, courtship intensity, reproductive success and olfactory behaviour assay. Finally, we optimized the quantitative analysis tools and parameters and analysed the behavioural data. Previously, hypothalamic GnRH has been shown to promote reproductive behaviour and suppress feeding behaviour. However, we found that TN GnRH neurons are essential for both feeding and reproduction. Thus, we found differential role of hypothalamic and terminal nerve GnRH in feeding behaviour.
As described in the proposal, we have presented our findings in seminars at our institute and at several conferences/meetings and venues(The 10th European Zebrafish Meeting 2017; The 11th FENS forum of Neurosciences 2018; The European Chemoreception Research Organization 2018; The XXXVI Annual conference of Indian Academy of Neurosciences 2018.). We are now preparing our first manuscript on the modulation of chemosensory representation in the zebrafish brain by GnRH neurons. It will be submitted to high quality peer-reviewed international scientific journal.
We have completed most of the work packages and achieved the scientific objectives in understanding the role of terminal nerve GnRH neurons in chemosensory processing and behaviour. However, through the project, it was difficult to generate NPY transgenic zebrafish lines. Thanks to our collaborators, we have the NPY transgenic zebrafish. Since all our methods/tools are optimized, we continue to work on achieving the remaining objectives.
For workpackage(WP)-1, we investigated how chemosensory information modulates the activity of terminal nerve GnRH/NPY neurons. To address this, first, we used genetic approach and established transgenic zebrafish line to label the TN GnRH neurons specifically with the genetically encoded calcium indicator. Thanks to our collaborator, we received transgenic line that marks all the NPY neurons in the zebrafish brain. Next, we established the method to image neural activity using two-photon microscopy in brain explant preparation. This allowed us to observe the activity of these neurons in response to natural odours. Finally, we developed the quantitative analytical tools to analyse the neural data. We found that GnRH secreting neurons are spontaneously active. They respond to natural odorants with complex dynamics and have strong preference for food related odours. This odour representation in the GnRH neurons are sexually dimorphic and strongly modulated by physiological states (satiety/hungry) of animals.
In WP-2, we had hypothesised that GnRH/NPY neurons modulate odour representation in the olfactory bulb. To test this hypothesis, we perturbed (downregulate/upregulate) the basal activity of GnRH/NPY neurons. This required establishing transgenic lines that label these neurons with optogenetic transgenes, halorhodopsin and channel rhodopsin, and chemogenetic gene, nitroreductase. Optogentic tools allowed temporal control over modulation of neural activity and chemogentic tool provided a means to study the acute effect of this modulation. We successfully down regulated or silenced the GnRH neuron activity using these methods and imaged neural activity in the olfactory bulb for any change in olfactory processing. Our initial findings suggested that modulation by GnRH neuron in olfactory bulb is quite subtle. Moreover, these neurons project to multiple brain regions including dorsomedial telencephalon (amygdala), dorsolateral telencephalon (hippocampus), ventral telencephalon, habenula and hypothalamus. Hence, we expanded the scope of our work to observe neural activity in these regions and modified our analytical tools for analysis of the new data set. Initial findings suggest that changes in odour representation likely involve network involved in aversion, such as habenula and amygdala. Moreover, we have established the framework to modulate the activity of NPY neuron and observe change in odour representation in the brain.
In WP-3, we investigated the impact of modulation of activity GnRH/NPY neuron on olfactory perception and odour driven feeding and reproductive behaviours. First, we established transgenic tools to modulate the activity of GnRH/NPY neurons in the olfactory bulb of freely behaving animals. Next, we developed and refined the behavioural assays to measure feeding rate, courtship intensity, reproductive success and olfactory behaviour assay. Finally, we optimized the quantitative analysis tools and parameters and analysed the behavioural data. Previously, hypothalamic GnRH has been shown to promote reproductive behaviour and suppress feeding behaviour. However, we found that TN GnRH neurons are essential for both feeding and reproduction. Thus, we found differential role of hypothalamic and terminal nerve GnRH in feeding behaviour.
As described in the proposal, we have presented our findings in seminars at our institute and at several conferences/meetings and venues(The 10th European Zebrafish Meeting 2017; The 11th FENS forum of Neurosciences 2018; The European Chemoreception Research Organization 2018; The XXXVI Annual conference of Indian Academy of Neurosciences 2018.). We are now preparing our first manuscript on the modulation of chemosensory representation in the zebrafish brain by GnRH neurons. It will be submitted to high quality peer-reviewed international scientific journal.
Our study provides insight into role of GnRH/NPY neurons in sensory induced feeding and reproductive behavior and how feeding and reproductive behaviors can be altered through the use of neuromodulators. We believe these findings will inspire novel therapeutic approaches for neurological diseases in humans associated with eating habits (e.g. obesity/anorexia) as well as reproduction (e.g. infertility associated with hormonal imbalance). Broadly, neuromodulatory imbalance have been associated with several neuropsychiatric disorder such as attention-deficit/hyperactivity disorder (ADHD), obsessive compulsive disorders (OCD), post-traumatic stress disorder (PTSD), schizophrenia, and depression. Understanding the function of neuromodulatory neurons will further help to develop treatments for neurological disorders. Furthermore, GnRH/NPY are conserved across species and hence it has large implication both in developing novel feeding strategies in fishery/aquaculture/ meat industry.