Dissecting the mechanisms of fear formation: a pharmacological study with healthy volunteers

Traumatic events such as military combat, car accidents, or sexual assault can
lead to debilitating psychological disturbances, including posttraumatic stress
disorder (PTSD), a common and often chronic and disabling disorder. Its
uniqueness among psychiatric disorders resides in the fact that its etiology
can be pinpointed to a precise moment. This raises the possibility that
prevention of PTSD might be achieved through intervention in the consolidation
phase of the traumatic memory. In recent years, due to the advances in
neuroscience, namely with the extraordinary possibilities opened by molecular
genetics in animal models, knowledge of the mechanisms of memory formation has
progressed at a rapid pace. Fear conditioning plays a pivotal role in these
studies, as fear is well conserved throughout evolution, making it a near-ideal
model system to study the interplay between genetic factors, operating brain
circuits and behavior that modulate learning and memory besides presenting
itself as a reliable model of PTSD. Furthermore, decades of human psychological
studies conducted in normal and brain lesioned patients have provided unique
insights into the areas involved in the processing of each memory subtype.
Also, the progresses in clinical psychopharmacological drug discovery that
revolutionized modern-day Psychiatry have yielded a number of compounds that
can be used as psychopharmacological tools in order to probe the abovementioned
memory formation mechanisms.
We intend to capitalize on the knowledge and possibilities offered by these 3
areas for providing clues of what could be the appropriate pharmacological
interventions in the aftermath of a traumatic situation and also as a way to
probe and pharmacologically dissect the differential neurotransmitter and
circuitry underlying human memory formation. As a step towards these goals, a
study design is therefore proposed in order to address the influence of
pharmacological interventions in primary memory formation through the use of
CS-US (mild electrical shock) with SCR and startle response as fear
measurement. In order to probe the mechanisms of memory formation and the
putative pharmacological prevention strategies we propose the use of a specific
set of clinical drugs targeting the mechanisms known to be involved in memory
consolidation. Single clinically relevant oral doses of atomoxetine (the most
selective NA agonist), propranolol (a selective Beta-blocker) and placebo will
be used for targeting the effects of Noradrenaline in the mechanism of memory
consolidation. The safety of the proposed pharmacological interventions is
consubstantiated by its extensive use in the clinical setting as well as in
previous studies in healthy subjects, both in a single dose and multiple dose
interventions.
This will be achieved through the use of visual and auditory conditioned
stimulus (CS) paired with mild electrical shocks as unconditioned stimuli (US)
with skin conductance response and eye startle reflex as fear measures in
memory reassessment. A double-blind parallel-groups design will be used where
each group of participants will receive a psychopharmacological intervention
following CS-US pairing, thus acting upon the memory consolidation phase. The
fact that the pharmacological manipulations will be administered after learning
eliminates bias posed by any possible influence on attentional or motivational
processes occurring during encoding. By influencing in a precise way the
formation of non-subjective memories whose strength can be accessed reliably
and accurately, it is expected that insights into the mechanisms of memory
formation will be obtained and novel strategies for the prophylaxis of PTSD can
be developed.

• To elucidate the role of noradrenaline in the mechanisms involved in human
memory consolidation

• Evaluate the levels of cortisol and 3-methoxy-4-hydroxyphenylglycol in the
various points of a memory consolidation window

• Define pharmacological strategies for preventing fear formation

The study will develop in a randomized placebo controled double blind design.
The present study will employ a between-subject rather than within-subject
design, in order to avoid bias related to previous conditioning and practice
effects on neuropsychological tests that can make interpretation difficult in
studies employing cross-over designs.

In this study we will make use of the pharmacological agents atomoxetine,
propranolol and placebo in a randomized double blind design in order to probe
the effects of the differential neurotransmitters in the mechanisms of memory
formation.

Participants will have to undergo fear conditioning; like often used in
comparable experiments with human participants, the volunteers will receive
mild shocks during the fear conditioning. Like often used in comparable
experiments with human participants, the volunteers will receive mild shocks
during the fear conditioning. Also, at unexpected moments during these
experiments participants can receive mild but painless shocks to the wrist,
noises of high intensities through headphones and/or fear-relevant images on a
computer screen.
Venous punction will be performed on three occasions (3x10 ml).
The pharmacological compounds in a single dose administration at the intended
dosage may cause the following side effects: A) Atomoxetine: GI symptoms,
namely nausea, abdominal discomfort and dyspepsia. Somnolence and dizziness
have been reported to occur in fewer than 4 % of the subjects. B) Propranolol:
GI symptoms, namely nausea, abdominal discomfort and dyspepsia Dizziness and
hypotension are also reported to occur. Psychomotor disturbances such as
somnolence and agitation have been reported in less than 2% of the subjects.
Total duration of the experiment is about 5 hours (four hours on day 1 plus one
hour on day 2)
Overall there are negligible risks associated with this study.