Maternal Separation and Its Effect on Parvalbumin-Expressing Interneuron Development and Behavior

Joey Low1,2, Shawn Tan Pang Hao2, Shawn Je Hyunsoo 21School of Biological Sciences, Nanyang Technological University, Singapore 637551

2Duke-National University of Singapore Graduate Medical School, 8 College Road, Singapore 169857

www.sbs.ntu.edu.sg

1. Introduction Early life stress induces vulnerability to psychiatric disorders in humans, but the underlying neurobiology remains unclear. Parvalbumin (PV)-interneurons are a subtype of inhibitory interneurons in the neural circuits of the brain that are implicated in behavioral disorders such as attention-deficit hyperactive disorder (ADHD), schizophrenia, and autism. Using maternal separation (MS) in a reporter mice line as a model to study stress-induced psychiatric disorders in humans, we hypothesized that early life stress leads to dysfunctional development of PV-interneurons, hence resulting in altered behavior.

MS

MC

CrawleyBox

FearConditioning

TailSuspension

Behavioral Assays

PND 0 2 14 28 49 50 71

Weaning

Generalhealthcheck Behavioral Assays

PND 0 28 49 50 71

Separation of pupsfrom dam 3hours daily

Weaning

Generalhealthcheck

PV

Stop tdTomato

LoxPLoxP

Cre Recombinase

A. Experiment timeline. Behavioral assays were carried out in the order shown.B. Two mice lines respectively carrying a PV-Cre and Rosa26tdTomato (RTM) construct were crossed to generate a PV-Cre RTM reporter mice line used for PV-interneuron quantification. Any changes in PV-interneuron numbers in MS mice could then be correlated with changes in behavior.

A

B

3. Results

3.1. MS Mice display Novelty-Induced Hyperlocomotion in the Open Field Test

3.2. MS Mice show Impulsivity and are More Likely to make Transitions in the Light/Dark Box

3.3. MS Mice show Stronger Learning and Retention of Fear Memory in the Contextual Fear Conditioning Test

3.4. MS Mice exhibit Depression-Like Behavior and show Less Struggling in the Tail Suspension Test

3.5. PV-Cre RTM Mice show Specific Staining for PV but not for Other Interneuron Markers

DAPI tdTomato PV Composite

DAPI tdTomato Calretinin Composite

DAPI tdTomato SST Composite

3.6. Interneuron Quantification shows No Change in Hippocampal PV-Interneuron Numbers in MS Mice

4. Conclusion

Fig 3.3.1 Day One fear conditioning

Fig 3.3.2 Day Two contextual fear recall

Our maternal separation paradigm produces a phenotype in mice resembling that of ADHD and depression in humans, as well as stronger fear memory and response. However, no change in PV-interneurons is observed possibly because interneuron dysfunction is more subtle. Further characterization of potential functional changes in PV-interneurons of MS mice needs to be done to explain the behavioral changes.

ElevatedZeroMaze

OpenField

LightDarkBox

1, 2, 3

FSohal, V.S., Zhang, F., Yizhar, O., Deisseroth, K., 2009. Parvalbumin neurons and gamma rhythms enhance cortical circuit performance. Nature 459, 698-702.Gandal, M.J., Nesbitt, A.M., McCurdy, R.M., Alter, M.D., 2012. Measuring the maturity of the fast-spiking interneuron transcriptional program in autism, schizophrenia, and bipolar disorder. PLoS ONE 7.

Karch, S., Segmiller, F., Hantschk, I., Cerovecki, A., Opgen-Rhein, M., Hock, B., Dargel, S., Leicht, G., Hennig-Fast, K., Riedel, M., Pogarell, O., 2012. Increased gamma oscillations during voluntary selection processes in adult patients with attention defi-cit/hyperactivity disorder. J Psychiatr Res 46, 1515-1523.

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2. Methodology

Behavioral Assays

PV-Interneuron Quantification