Abstract
In Parkinson's disease, there is degeneration of dopamine-producing cells in the brain, and a
subsequent loss of dopamine in target brain areas (the striatum) responsible for motor control.
Pharmacological treatments aim to ameliorate the dopamine depletion that underpins the
disease, by supplementing with the dopamine pro-drug, Levodopa, or dopamine receptor
agonists (e.g., D2 agonist ropinirole). However, oral administration of these drugs results in
non-physiological dopaminergic stimulation in the striatum, and subsequent off-target effects,
leading to suboptimal drug efficacy and adverse side effects.
To address these challenges, our lab (the Reynolds lab) is developing a novel drug delivery
system that utilises transcranial ultrasound to trigger the release of the dopamine agonist
ropinirole from ultrasound-sensitive liposomes at targeted brain regions, specifically the
striatum. The Reynolds lab has successfully demonstrated in vivo drug release using this system
by observing contralateral turning in hemiparkinsonian rats after administering ropinirole-
loaded liposomes (ropinisomes) and applying transcranial ultrasound to the striatum. However,
we hypothesise that a large dose is needed to induce the turning behaviour – therefore, for my
thesis, we set out to investigate the effects of ropinirole on neuronal circuits below the level
driving motor activity, by looking at the impact on striatal neurons. To examine this, we used
fibre photometry to record the calcium activity in striatal neurons of rats under isoflurane
anaesthesia, as a measure of spontaneous neural activity. First, we recorded the effects of
subcutaneous injection of ropinirole and raclopride (D2 antagonist). Subsequently, we
investigated ultrasound-only application, and combined ultrasound and ropinisome application
to assess targeted release of ropinirole from circulating liposomes.
Subcutaneous injection of ropinirole reduced spontaneous neural activity, indicated by a
decrease in the fibre photometry calcium signal, and this effect was reversed by administration
of subcutaneous raclopride. The decrease in calcium activity was later used as a marker to
identify ultrasound-induced ropinirole release. Transcranial ultrasound application alone did
not produce a significant change in neural activity, likely because the parameters used were not
optimised for neuromodulation but instead for triggering drug release from liposomes. When
transcranial ultrasound was applied following the administration of ropinirole-loadediii
liposomes, the results were variable, with the in vivo stability of the ropinisomes influencing
the outcome. Two primary effects were observed on ropinisome administration: either the
ropinisomes remained intact, or there was spontaneous release of the drug. In the experiments
where the ropinisomes had remained intact, we observed ultrasound-mediated ropinirole
release evidenced by a decrease in calcium activity following ultrasound stimulation, however
this difference did not reach statistical significance (P>0.05).
In summary, our study demonstrates the ability to record neural activity in response to a novel
ultrasound-mediated drug delivery system. We also show the potential of this system to
successfully release ropinirole from loaded liposomes upon application of transcranial
ultrasound, while identifying areas for future refinement.