Role of the cerebellum in survival circuits activated by fear.

Lead Research Organisation: University of Bristol
Department Name: Physiology and Pharmacology

Abstract

Our understanding of how disturbances in neural networks in the brain result in emotional disorders is limited, and many patients (animal and human) don't respond well to existing treatments. Fundamental research into the neural networks that underlie 'survival circuits' in animals will provide essential information that will inform the development of new therapeutic strategies.

There are two types of survival circuits that produce defensive responses to aversive or fearful events. One generates an UNCONDITIONED response, innate and hard wired, the other a CONDITIONED response, the result of activity in survival circuits modified by experience. Both co-ordinate adjustments to emotional state, cardiovascular activity and generate appropriate actions such as fight, flight or freezing. The sum of these activities constitutes a defensive response.

The neural networks involved can be likened to a postal service that 'knows' what's being posted and where it needs to go in order that the appropriate information informs the necessary outcome. A major gap in our understanding concerns how this postal service engages with motor systems of the brain to elicit distinct and behaviourally appropriate unconditioned and conditioned defensive responses to fearful events. It is also unknown if the motor system can feed back and modify activity in survival circuits.

We aim to provide new insights into the ANATOMY - which defines the 'postal address'; the PHYSIOLOGY - which determines the nature of the 'message' being transmitted; and the BEHAVIOUR- the effect the message has. The cerebellum is the largest motor controller in the brain and an emerging concept is that it plays a key role in this postal system. Recently we have shown that defensive freezing behaviour in rats, evoked by unconditioned and conditioned fearful events, is dependent on intact cerebellar circuitry. The cerebellum is a highly modular structure, so there is ample scope for different pathways to be involved in the range of defensive responses essential for survival.

We will focus on cerebellar interactions with key components of central survival circuits, namely the midbrain periaqueductal grey and the amygdala. Our key objectives are to:
(i) chart the chain of neural connections that link the cerebellum with the brain survival network;
(ii) test directly for a causal link between cerebellar function and survival circuit-related unconditioned and conditioned defensive responses.

We will use the combined power of anatomical, electrophysiological and behavioural techniques at the systems level of analysis to improve understanding of the structure and function of brain circuits involved in animal survival. If specific regions of the cerebellum (modules) are an essential part of the neural network by which survival circuits elicit particular aspects of a defensive response, then experimental inactivation of these different regions should lead to an altered emotional, motor and/or cardiovascular response.

Choice of experimental model: cerebellar and survival network architecture and patterns of connectivity are highly conserved across mammalian species, including human. However, rats are the experimental animal of choice because our understanding of the basic neuroanatomy and physiology is most complete in this species. Importantly, our experiments will include study of neural network interactions during behavioural situations that have been most thoroughly characterized in rats, namely: unconditioned and conditioned behaviours in response to exposure to an aversive or fearful stimulus e.g. predator (cat) odour and aversive footshock.

Our results should reveal general rules as to how brain circuit structure and information coding give rise to the well-defined behavioural responses that are so critical to animal welfare and survival.

Technical Summary

Understanding the anatomy and physiology of central survival circuits is an essential prerequisite to determining the neurobiological basis of emotional disorders. The neural network underpinning survival behaviours includes the amygdala and midbrain periaqueductal grey (PAG) which generate defensive responses to aversive or fearful stimuli. Different circuits within the network generate innate and conditioned responses. But how these survival circuits interact with supraspinal motor/cognitive systems to elicit appropriate behavioural responses remains poorly understood.

Building on preliminary data that demonstrate a potent link between the cerebellum and the PAG, we will test the hypothesis that cerebellar interaction with survival circuits is dependent on its modular organization. More specifically, that different parts of the cerebellar A module located in individual vermal lobules, are associated with cognitive, motor and/or autonomic aspects of defensive behaviours.

Three systems level approaches will be used in adult rats:
(i) anatomical/electrophysiological mapping, including use of transneuronal axonal tracers; ii) intervention experiments; and iii) behavioural studies in which cerebellar neuronal interactions with survival circuits will be studied during innate and associative fear conditioning.

The mapping studies will determine the spatial pattern of cerebellar efferents to survival circuits. The physiological and behavioural studies will characterize cerebellar-survival circuit functional links (with a focus on connections with PAG), and will provide direct evidence of a causal link between network interactions and function.

Overall, the project will provide new insights into the structure and function of survival circuits with the overarching goal of providing the foundations for understanding the neural mechanisms that underlie emotional disorders.

Planned Impact

The research will be of benefit to:
(i) Companion and farmed animals with anxiety-related behavioural disturbances.
(ii) Patients suffering from anxiety disorders; and their families, charities and organizations seeking to support patients with such disorders.
(iii) The research staff employed on the grant.
(iv) Members of the general public with an interest in anxiety disorders.
(v) Academia.

How will they benefit from this research?
(i) Companion and farmed animals with anxiety-related behavioural disturbances. These are common problems and can lead to behavioural (e.g. stereotypy, aggression), reproductive (e.g. infertility) and other issues. A greater understanding of the neural circuitry underpinning emotional behaviour could, in the longer term, lead to identification of novel brain targets for drug treatment without producing sedation. This would be hugely advantageous in a range of common veterinary problems such as managing fear aggression and separation anxiety in pet dogs. In the longer term our research hopes to improve treatment of such animals by identifying novel brain targets for drug treatment. Progress in understanding network dysfunction that leads to anxiety disorders requires a global perspective on brain function i.e. it is not sufficient to study one brain region in isolation. The network analysis we seek to provide will offer a more accurate picture of the neurobiology involved.

(ii) Patients suffering from anxiety-related disorders. At present there is no satisfactory treatment for mood related psychiatric diseases (e.g. anxiety disorders including post traumatic stress disorder and phobias). In large part this is because the underlying neurobiology of these disorders is unknown. The impact of the research on patient groups and their families will be in terms of identifying potential new targets for therapies and being able to provide a better understanding of the brain circuitry that underpins these distressing conditions. These types of disorder can also be very damaging to an individual's social life and well being, leading to a negative impact on carers, friends and family. By providing insights into normal and aberrant brain circuit function associated with anxiety disorders, the research will enable charities which support patients with such disorders to realize their mission of providing education and help to patients and their carers.

(iii) The named staff employed on the grant will develop expertise in highly novel and state-of-the-art research techniques that will aid their future careers. As indicated in the Academic Beneficiaries section, there is a worldwide skills shortage of researchers with experimental animal in vivo research expertise. By taking a lead role in the research programme (see work plan) the named postdoc will also develop her time/project management, communication, team working and other transferable skills.

(iv) Members of the general public. The findings from this project are applicable to understanding human anxiety disorders. Such knowledge is of wide interest to the general public. The findings will therefore be appropriate to disseminate through public engagement activities.

(v) Academia. International academia in the fields of preclinical and clinical psychiatry, as well as basic scientists in the fields of motor, cognitive and behavioural neuroscience are likely to benefit from the scientific progress made by this research (see 'Academic Beneficiaries').

Publications

10 25 50
 
Description Key findings to date include:
i) Anatomical connectivity between the medial cerebellar nuclei (MedCN) and the vlPAG. Anterograde and retrograde neural tracers and viruses have revealed a substantial bilateral projection from the cerebellum to PAG with a contralateral preponderance. Electrical microstimulation of the contralateral MedN provided complementary physiological evidence of a secure, short latency projection localised to the vlPAG (Figure 1, Objective 1).

ii) Physiological communication between vlPAG and MedCN. Simultaneous recording of single units and local field potential (LFP) activity in these two brain sites has been successfully achieved during an auditory cued fear conditioning paradigm. These experiments are, to the best of our knowledge, the first to investigate how these two brain regions interact and encode fear-related responses (Figure 2, 3 & 4, Objective 2).

a) We have classified PAG single unit activity patterns into 4 types and identified extinction resistant and extinction sensitive units1. More recent experiments have extended this to study of PAG activity during acquisition of the fear conditioned response, showing encoding of noxious input. A proportion of units (50%) respond to the conditioned tone which then demonstrate a pattern of extinction similar to behavioural extinction measured by freezing levels. (Figure 2, Objective 2 and 3)1.
b) We have classified cerebellar single unit recordings and LFP responses to a conditioned tone. Similar to the PAG a proportion of units respond to the unconditioned stimulus (34%), and importantly a small proportion (18%) of units also demonstrate a pattern of extinction similar to behavioural extinction measured by freezing levels (Figure 3, Objective 2 and 3).

Outcomes of the research to date have been presented at national and international meetings4,5,6,7 and, so far, one major publication1 and two consensus paper contributions2,3 have been published. The work continues to progress well and it is fully anticipated that further publications will be completed within the term of the grant and beyond. Ongoing work includes analysis of LFP coherence between the two brain regions and modulation of MedN outputs to the PAG to effect patterns of unit activity during the auditory cued fear conditioning task. We also organised an international workshop (funded by a BBSRC International Partnering Award8) as a direct result of this grant. This workshop was co-organized and chaired by the named postdoctoral researcher8 and has led to new collaborations for future grant proposals.

Outcomes
1Watson TC, Cerminara NL, Lumb, BM, Apps R. Neural Correlates of fear in the Periaqueductal Gray. J Neurosci (2016) 14;36(50) 12707-12719
2Lawrenson C, Bares, M., Kamondi, A., Kovács, A., Lumb, B., Apps, R., Filip, P. & Manto, M. (2018) The mystery of the cerebellum: clues from experimental and clinical observations. Cerebellum Ataxias. 5:8
3Apps, R., Hawkes, R., Aoki, S., Bengtsson, F., Brown, A. M., Chen, G., Ebner, T. J., Isope, P., Jörntell, H., Lackey, E. P., Lawrenson, C., Lumb, B., Schonewille, M., Sillitoe, R. V., Spaeth, L., Sugihara, I., Valera, A., Voogd, J., Wylie, D. R. & Ruigrok, T. J. H. (2018) Cerebellar Modules and Their Role as Operational Cerebellar Processing Units. From neurons to clinical applications. Cerebellum. P1-21
4Lawrenson CL (2017) - 'Cerebellar-periaqueductal grey contributions to fear behaviour'. Symposium at the British Neuroscience Association. Birmingham.
5Lawrenson CL (2017) 'Cerebellar and periaqueductal grey contributions to fear behaviour'. Symposium at The 16thEuropean Congress of European Neurophysiology. Budapest.
6Lawrenson CL, Jenkins G, Drake R, Lumb B, Apps RA. 'Cerebellar-periaqueductal grey contributions to fear behaviour'. Cerebellum: Gordon Research Conference, Lewiston.
7Lawrenson CL, Drake R, Lumb B, Apps RA. Cerebellar-periaqueductal grey contributions to freezing behaviour. Symposium at the UK Sensory-Motor Conference, Bristol.
8Lawrenson CL. Apps R. (2017) BBSRC International Partnering Award: An Anglo-French-German consortium to understand cerebellar contributions to emotional behaviour.
Exploitation Route International collaboration
Sectors Healthcare

 
Description An Anglo-French-German consortium to understand cerebellar contributions to emotional behaviour.
Amount £16,835 (GBP)
Funding ID BB/R02135X/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 05/2018 
End 07/2019
 
Description International Strategic Fund
Amount £3,814 (GBP)
Organisation University of Bristol 
Sector Academic/University
Country United Kingdom
Start 06/2018 
End 07/2018
 
Description Travel Award Scheme
Amount £650 (GBP)
Organisation Physiological Society 
Sector Charity/Non Profit
Country Global
Start 07/2017 
End 07/2017
 
Description Bristol Neuroscience Festival 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact A 3 day event attended by primary, secondary school children and open to the public to provide engagement relating to Neuroscience
Year(s) Of Engagement Activity 2020
URL https://www.bristol.ac.uk/neuroscience/bnf/2020-event/
 
Description Invited speaker: Essen 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Oral communication on current work
Year(s) Of Engagement Activity 2020
 
Description Research Without Borders 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Pioneering work of the University of Bristol's postgraduate researchers open to the public
Year(s) Of Engagement Activity 2018
URL https://www.bristol.ac.uk/doctoral-college/current-research-students/events-and-opportunities/resear...
 
Description Snapshots: Bristol University seminar series 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Oral communication within School about current research
Year(s) Of Engagement Activity 2019