This study investigated the effects of repeated deep brain stimulation of the pedunculopontine tegmental nucleus (PPTg) in rats. Electrodes were implanted in the PPTg of rats which then received 6 days of stimulation. Behavioral responses and neural activation markers cFOS and GAP-43 were assessed on days 1 and 6. Results found that repeated stimulation increased the threshold current needed to elicit behavioral responses on day 6 compared to day 1, suggesting an inhibitory effect. Expression of cFOS and GAP-43 was also found near the stimulation site, indicating repeated stimulation triggers neural plasticity.

1. Effects of Repeated Deep Brain Stimulation of the Pedunculopontine Tegmental Nucleus on
Current Thresholds for Movement-Related Behavioral Responses and Neural Activity
Titus John1,2, Eduardo Chaparro MD/PhD1, Robert Pearlstein PhD1
1Department of Surgery/ Neurosurgery, Duke University School of Medicine, Durham, NC
2Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI
Introduction
The pedunculopontine nucleus (PPN) has been used
as a target for deep brain stimulation (DBS) in the
treatment of PSP and found to provide some benefits
in advanced stage PSP.
The PPN and cuneiform nucleus are components of
the mesencephalic locomotor center that has been
hypothesized to be linked to the development of gait
freezing, a common finding in patients with PSP.
The effects of repeated DBS of the pedunculopontine
tegmental nucleus (PPTg) in the rat on evoked
behavioral responses and cFOS (neural activation
marker) / GAP-43 (neural plasticity marker)
expression has been the focus of the current research.
Objectives
 Develop a model of PPN DBS in freely moving
rodents for behavioral analysis.
 Quantify changes in behavioral endpoints due to
repeated PPTg stimulation.
 Differentiate effects of the initial and repeated DBS
on neuronal activity around stimulation site using
c-FOS expression to identify activated neurons.
 Assess effects of repeated DBS on neuroplasticity
in the PPtg and the PAG using GAP-43.
Methods
1. A Bipolar electrode was implanted within the left
PPTg of male Wistar Rats (n=8). Stimulation was
performed in freely moving animals using
biphasic stimulation (25Hz, 100µsec pulses).
2. PPN DBS stimulation (n=4) for 6 days (12 hr/day)
3. Assessments of current threshold for evoking
behavioral responses were determined on Day 1
and Day 6 of stimulation period.
4. Day 7: 4 Hour normalization stimulation, for
immunohistochemistry analysis
• Hazrati LN, Wong JC, Hamani C, Lozano AM, Poon YY,
Dostrovsky JO, Hutchison WD, Zadikoff C and Moro E (2012)
Clinicopathological study in progressive supranuclear palsy with
pedunculopontine stimulation. Mov Disord.
• Saryyeva A, Nakamura M, Krauss JK, Schwabe K. (2011) c-Fos
expression after deep brain stimulation of the pedunculopontine
tegmental nucleus in the rat 6-hydroxydopamine Parkinson
model. J Chem Neuroanat.
• This work was supported by CurePSP Summer Student
Fellowship Program.
Discussion and Conclusions
 These initial findings are consistent with the
hypothesis that repeated stimulation triggers
neural plasticity.
 DBS animals required greater current flow on
the final day of stimulation compared to the
initial stimulation period suggesting that
repeated PPN DBS produces an inhibitory effect
on measured behavioral endpoints (Jumping
response/ increased exploratory activity)
 The effects of repeated DBS on the current
threshold for evoking behavioral responses may
be related to sprouting of inhibitory neurites and
associated synaptic changes within the PPTg or
secondary nuclei innervated by PPTg neurons.
 Current efforts are focused on quantifying c-Fos
& GAP-43 expression within the PPTg and
determining whether c-FOS and GAP-43 are
co-localized within the same cells.
 PPTg DBS can be applied to emerging models
of tauopathies.
References & Acknowledgements
Figure 4: Utilizing a non-parametric analysis
(Wilcoxon test), changes in current simulation
thresholds for evoking behavioral response
(jumping/exploration) on Day 1 and Day 6 were
compared for DBS and SHAM animals and found to
be statistically different. Error bar indicate SEM.
Figure 2: c-Fos expression
DBS group at electrode tract
Figure 3: GAP 43 expression
DBS animal at electrode tract
Results
Figure 1: Electrodes were coated
with a red dye, DiI, in order to
confirm electrode placement
within the PPTg.
Groups c-FOS GAP-43
DBS Positive Positive
SHAM Positive Negative
Table 1: Initial observations of c-Fos & GAP-43
expression in DBS vs. Sham animals.
0
100
200
300
400
500
StimulationCurrentµA
DBS (n=4) SHAM (n=4)
Average Increase in Stimulation Current