1. Electrophysiological Investigation of the Laterodorsal Tegmental in the Freely
Navigating Rat
Special
thanks
to
Yong
Sang
Jo
for
his
continued
help.
This
work
is
supported
by:
Grant
MH58755
Contact:
Chantelle
Kinzel
at
adamec@uw.edu
REFERENCES
• Long-Evans rats were tested on a differential
reward spatial working memory task. Animals
navigated to either small or large rewards on an 8-
arm radial maze.
• Each session was comprised of two blocks with 5
trials in each block. Each trial consisted of a forced
choice portion and a free choice portion.
• The first block was the control block and the second
block consisted of one of three manipulations:
darkness, reward omission or reward switch5.
• Electrodes were bilaterally implanted into the LDTg
to record single unit cellular activity.
The ventral tegmental area (VTA) and hippocampal
circuit processes rewarding and novel information,
which may play a role in the formation of spatial and
working memory, reinforcement learning and
decision making. VTA dopaminergic burst cell firing
encodes novel, unexpected-rewarding and reward-
predicting stimuli3. However the circuitry, which
modulates VTA activity, is not well known. A division
of the mesonpontine tegmentum, the laterodorsal
tegmental nucleus (LDTg) provides a cholinergic,
GABAergic and glutamatergic input into the VTA. It
has been shown that electrical excitation of the
LDTg modulates VTA activity and subsequent
increases in midbrain dopamine release1.
Inactivation of the LDTg greatly reduces VTA
dopaminergic burst firing, implicating the LDTg’s
role in permitting VTA activity2. In the current study
we sought to identify the information coded by LDTg
neurons in order to better understand the type of
information that regulates dopamine cell activity and
further the reward circuitry of the brain.
Complex
Pre-Reward (Short) Pre-Reward (Long)
Post-Reward
Velocity
• A large proportion of LDTg cells are
velocity and reward related. Therefore it
is likely that the LDTg helps to integrate
behavior with reward information.
• LDTg cells showed excitatory
responses to rewards, both before and
after reward. Responses prior to reward
clustered into three different types of
responses (complex, short term and
long term).
• The other portion of the mesponpontine
tegmentum, the PPTg is affected by
reward size but the LDTg was not,
although the LDTg did distinguish
rewards4.
• It is likely the LDTg sends information
about reward to the VTA and possibly
gates PPTg activity to affect VTA
dopaminergic burst activity.
1. Forster, G.L., Blaha, C.D., (2000). Laterodorsal tegmental
stimulation elicits dopamine efflux in the rat nucleus accumbens by
activation of acetylcholine and glutamate receptors in the ventral
tegmental area. European Journal of Neuroscience, 12,
3596-3604.
2. Lodge, D.J. & Grace, A.A. (2006). The laterodorsal tegmentum
is essential for burst firing of ventral tegmental are dopamine
neurons. Proc. Natl. Acad. Sci. U.S.A. 103, 5167–5172.
3. Martig, A.K., Jones, G.L., Smith, K.E., Mizumori, S.J.Y. (2009).
Context dependent effects of ventral tegmental area inactivation on
spatial working memory. Behavioral Brain Research, 203, 316-320.
4. Norton, A., Jo, Y.S., Clark, E.W., Taylor, C.A., Mizumori, S.J.
(2011). Independent neural coding of reward and movement by
pedunculopontine tegmental nucleus neurons in freely navigating
rats. European Journal of Neuroscience.
5. Puryear, C.B., Kim, M.J. & Mizumori, S.J.Y (2010). Conjunctive
encoding of movement and reward by ventral tegmental area
neurons in the freely navigating rodent. Behav Neurosci, 124,
234-247.
Chantelle Kinzel, Van Redila, Sheri J.Y. Mizumori.
Department of Psychology, University of Washington, Seattle, WA, USA
Forced Choice Portion Free Choice Portion
Population
activity
Single
Unit
Cell
Activity
Manipulations affect behavior as shown by differing
number of errors made, dependent on the manipulation.
Animals can distinguish reward magnitude shown by
their preference for large arms which is affected by
manipulations.
A large proportion of LDTg cells are correlated
with velocity and reward suggesting a role for
the LDTg in movement and reward processing.
Time (ms)
Cell WaveformAnimal’s Velocity
Firing rate (Hz)
LDTg
Velocity (cm/sec)
Velocity correlates were not affected by manipulations.
The LDTg may encode movement information as
shown by the large number of high R values that
reflect correlated firing rates with velocity.