Award details

Functional organisation of a corollary discharge mechanism

Reference	BB/F008783/1
Principal Investigator / Supervisor	Professor Berthold Hedwig
Co-Investigators / Co-Supervisors
Institution	University of Cambridge
Department	Zoology
Funding type	Research
Value (£)	317,446
Status	Completed
Type	Research Grant
Start date	01/06/2008
End date	31/05/2011
Duration	36 months

Abstract

Experiments are based on our substantial experience to evoke singing behaviour in crickets by pharmacological brain stimulation and to expose their nervous system to intracellularly record from primary afferents or central interneurons in semi-intact and de-efferented preparations. 1. SYNAPTIC LINK BETWEEN THE SINGING CPG AND CDI: Intracellular recordings will be obtained from metathoracic interneurons involved in motor pattern generation. We will identify the neurons and test their functional significance by current injection and reset experiments. Motor activity will be monitored by recording wing movements with an opto-electronic camera (custom made) and activity of mesothoracic motor nerves or muscles (AM 1700 amplifier). CPG neurons will be stained with Lucifer yellow and confocal microscopy will be used to demonstrate their structure. Simultaneous recordings of CDI and CPG wing closer interneurons will reveal the synaptic connections between the motor network and the corollary discharge pathway. The two amplifiers (NPI, BA-1S) will be used for these recordings. 2. GLOBAL OR LOCAL FUNCTION OF CDI? In an approach similar to our protocol for the analysis of auditory processing we will explore processing in the wind-sensitive cercal pathway and vibration-sensitive leg chordotonal organs. Wind puffs (Picopump PV820) and/or vibration stimuli (B&K exciter) will be used for stimulation. Intracellular recordings of afferents and sensory interneurons will reveal any central impact on sensory processing during singing. The synaptic link between CDI and these sensory pathways will be revealed with double intracellular recordings. 3. STRUCTURE AND NEUROTRANSMITTER OF CDI: Staining of CDI will be obtained with Lucifer yellow or Neurobiotin. Stained neurons will be embedded and sectioned on a microtom. Immunohistochemistry using GABA or histamine anitibodies will be used to identify the transmitter candidate. Picrotoxin may be used to block GABA receptors.

Summary

A fundamental problem in sensory neuroscience is the processing of self-generated sensory information and information from the environment that occurs in the same pathway. For example how can animals like crickets, which repetitively generate very loud acoustic signals for intraspecific communication, prevent their auditory pathways from desensitisation or distinguish their own sound signals from the sound of singing rivals? As a solution to this problem neuroscientists proposed a corollary discharge mechanism that is activated by the animals own motor activity and that is mediated to sensory areas to interfere with the processing of self-generated signals. The evidence for corollary discharges is compelling but the cellular basis of this principle of neural processing has been demonstrated only in weakly electric fish, tadpole swimming, crayfish escape behaviour and in singing crickets. In crickets we recently identified a corollary discharge interneurone (CDI), that is activated in the phase of sound production and that inhibits auditory afferents and interneurons, whenever the animals produce a sound pulse during singing. As a consequence their responses to self-generated sound pulses are distinctly reduced and the sensitivity of the auditory pathway is maintained. To complement this picture of the corollary discharge mechanism we now want to progress in three areas. 1. How is CDI activated? Evidence points towards the motor network that generates the singing activity. This network however, has not yet been studied in any detail. We will therefore identify the interneurons of this motor network by intracellular recordings, dye injection and current injection experiments, which demonstrate the functional importance of neurons for pattern recognition. Then we will use simultaneous recordings of the motor network interneurons and of CDI to analyse any synaptic connections between them. These experiments will tell how the corollary discharge is generated in the firstplace. We expect that interneurons of the motor network, which are active in phase with sound production, drive CDI with excitatory postsynaptic potentials. This would lead to a comprehensive cellular understanding of the corollary discharge mechanisms. 2. Furthermore we want to analyse if CDI affects sensory pathways other than the auditory pathway. This is important for our understanding of the organisation of corollary discharge pathways. CDI has profuse axonal output arborisation in the auditory neuropil but other axonal collaterals project into the mechanosensory neuropils of all ganglia. The arborisation pattern of CDI is therefore suited to modulate other sensory pathways as well - so is it a local or a global corollary discharge pathway? We will analyse neural processing in a wind-sensitive and vibration-sensitive pathway. These pathways are activated by self-generated stimuli during singing but at the same time also have to mediate escape responses. A problem of sensory processing that is most similar to the processing of auditory signals. We will stimulate these pathways with wind puffs or vibration stimuli and we will record the activity of the primary afferents and interneurons to reveal any signs of inhibition during singing. If the experiments demonstrate that sensory processing is modulated by a corollary discharge we will again use double intracellular recordings to analyse the synaptic interaction between CDI and afferents and interneurons of these pathways. Our experiments will reveal, if CDI globally modulates sensory processing during singing, as it is indicated by its structure. 3. Finally, we will analyse the details of CDI's arborisation pattern with histological sections. This will show the overlap of its axonal arborisations with mechanosensory neuropils. We also will use immunohistochemistry to demonstrate if GABA is the transmitter of the interneurone that mediates the inhibitory postsynaptic synaptic potentials.

Committee	Closed Committee - Animal Sciences (AS)
Research Topics	Neuroscience and Behaviour
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

I accept the terms and conditions of use (opens in new window)

export PDF file

back to list new search