Genetic alterations or early environmental challenges
typically lead to many neurobiological changes. While it is certainly possible
to predict some of these, the complexity of the brain and the neuronal
connectivity make it necessary to use special techniques that go beyond the
standard “hypothesis-driven” approach. Over the last decades the research field
has developed numerous so-called “hypothesis-free” techniques, such as genome
wide association studies, RNA sequencing and proteomics. Together with our
collaborators Drs Rob Keijzers and Bill Jordan, we are using two of these
techniques: Maldi and metabolomics.
Maldi (Matrix Assisted Laser Desorption/Ionization) is a
technique that allows the detection and distribution of many different
compounds in biological tissues. The idea is that a brain section is coated
with a specific matrix (a chemical coating) and subsequently exposed to a laser
beam. This laser created heat which vaporises the top layer of both the matrix
and the brain section. The resulting ions can then be detected with mass
spectroscopy. The great benefit of Maldi for neuroscience is that the laser can
be targeted to a very small region (in the order to 50 micrometers). By moving
the laser across a brain slice, we can get a detailed map of the distribution
of different neurobiological compounds. By adjusting the matrix, we can assess
many different components of the brain (neurotransmitters, lipids etc).
Metabolomics refers to the “systematic study of the
unique chemical fingerprints that specific cellular processes leave
behind”. As such it can be considered the final consequence of the
genomics -> transcriptomics -> proteomics -> metabolomics process.
There are several different methods that allow us to identify the metabolome of
a biological sample (such as brain region or blood plasma), including mass
spectroscopy, gas chromatography and nuclear magnetic resonance. Each of these
methods have their own advantages and disadvantages in terms of ease of sample
preparation, sensitivity and data interpretation. We therefore aim to use and
compare all three detection methods while assessing the metabolome changes seen
in SERT knock-out rats and in rats expose to maternal immune activation.
This project is in part supported by a grant from “Research
for Life” (formerly the Wellington Medical Research Foundation).
One of the major technological breakthroughs in human
neuroscience research has been the development of functional magnetic resonance
imaging (fMRI). This technique, for the first time allowed us to measure
changes in blood oxygen levels (and by extension brain activity) while subjects
were performing a specific task. Over the years, this technique has been
improved and refined especially in spatial, which can now be as small as 1 mm.
While structural MRI has also been developed for rats and
mice, fMRI is technically very challenging, mainly because of the risk of
movement artefact. fMRI requires subjects to be completely still, and thus
animals have to be either sedated or anesthetised, which obviously precludes
any behavioural studies. One potential alternative to fMRI is Near Infrared
Spectroscopy (NIRS). NIRS is based on the principle that while most biological
tissues are virtually transparent to infrared light, haemoglobin and oxygenated
haemoglobin both absorb infrared light. Thus like fMRI, NIRS can be used to
measure blood oxygen levels in the brain. Moreover, compared to fMRI, this can
be done at a fraction of the co st.
In the project, we aim to develop a wireless NIRS system to
measure brain blood oxygenation in freely moving animals. This project is a collaboration with Professor
Bor Shyh Lin from the National Chiao Tung University in Taiwan. Prof Lin is
working a miniaturizing a prototype NIRS system that sends data via Bluetooth
to a computer. Within our group, we will test the system in freely moving rats,
which will help us to further refine the system. This project is supported by a
Catalyst: Seeding grant.
One of the main challenges in behavioural neuroscience is to
improve the translational validity of the animal models for the human condition.
The lack of success in the development of new drugs for psychiatric disorders
has led many pharmaceutical companies to abandon research in the area
completely, despite the substantial need for better drugs for mental disorders.
To improve the chances of identifying more successful
psychoactive drugs, we are evaluating the usefulness of heart rate variability
(HRV). HRV refers to the beat-to-beat variation in individual heartbeats. Studies
in healthy volunteers have found that low HRV is typically associated with low
emotional stability and with low cognitive flexibility. As a result of this,
reductions in HRV are often reported in clinical populations, such as patients
suffering from schizophrenia, major depressive disorder or autism spectrum
One of the major benefits of HRV is that it can be assessed
in humans and rat with virtually identical methods. In our rat studies, we use
an implantable probe system which allows continuous recording in freely moving
animals. However, there are many different components to HRV. For instance, HRV
can be assessed using linear methods in either the time or the frequency domain.
While this represents the most often used methodology, they actually are a
simplification of the real process of HRV, which iss more accurately described
as a non-linear system.
In this project, we investigate the neurobiological
mechanisms underlying HRV in order to assess its potential applicability as a biomarker
for specific mental disorders. One of the aspects of the project to investigate
how HRV in rats is affected by specific drugs, or genetic alterations. In
addition to assessing the standard linear parameters, we also investigate
several non-linear methods. This will allow us to investigate the exact
contribution of different neurotransmitter system and brain regions in the
regulation of HRV.
Although rats do make audible sounds, most communication,
particularly between rats takes places at a frequency beyond our human hearing.
These so-called ultrasonic vocalizations (USVs) in rats range from roughly 22
to 90 kHz. Traditionally, USV research has shown that rat calls in the 20 – 25
kHz range are typically associated with negative affect, while calls in the 40
– 90 kHz range are typically associated with positive affect. Rat pups, when
separated from their mothers usually make calls in the 30 – 45 kHz range.
While this subdivision in three bands is still largely
correct, recent research focusses more on the classification of individual calls
within each of these ranges. We aim to investigate the specific language rats
use to communicate their emotional state. For that purpose, we expose rats to
different conditions (play behaviour, anticipatory pleasure, social
interaction, tickling) and record USV. Using Deepsqueak we categorize these
calls into different types to see whether rats use different types of calls
under different circumstances. Additionally, we will investigate whether
pharmacological and/or genetic manipulations alter the USV characteristics. In
the long run, we expect that this will give us a better understanding of the
emotional state of rats.