Characterization of Neuropeptide S (NPS) in view of its potential as a novel anxiolytic therapy for anxiety disorders

Anxiety disorders, such as posttraumatic stress disorder (PTSD),
are characterized by a high prevalence and debilitating symptoms.
However, the current first-line treatment for these conditions,
which consists of selective serotonin reuptake inhibitors (SSRIs)
and cognitive behavioral therapy, alongside symptomatic treatment
with benzodiazepines, does not represent by far a functional
solution for all affected patients. Therefore, identifying and
characterizing novel candidates for alternative anxiolytic
therapies are a crucial focus of psychiatric and neurobiological
research. This study focuses on Neuropeptide S (NPS), a newly
identified endogenous neuropeptide that has been shown to exert
strong anxiolytic effects upon intracerebral injection in rodents.
In an approach that combines basic research with incipient
clinically relevant application, novel mechanisms and brain targets
of NPS-mediated anxiolytic effects were identified, and a
noninvasive application procedure also applicable in patients,
namely the intranasal administration, was established for the first
time for NPS in mouse models. In a first step, the feasibility of
intranasal NPS delivery was established in mice using
fluorophore-coupled NPS to allow intracerebral tracking. This
method permitted for the first time tracking of intranasally
applied substances within the brain at a single-cell resolution.
These results not only proved the applicability of intranasal NPS
administration in the mouse, but also allowed identification and
characterization of hitherto undescribed cerebral NPS target cells,
which were shown to be most likely exclusively neurons. Moreover,
specific uptake of fluorescently labeled NPS in the hippocampus
provided the first direct evidence linking this brain region, a
well-known major player in the regulation of fear expression, to
the NPS circuitry. Further investigation into the functional role
of the hippocampus in NPS-elicited anxiolytic effects revealed that
local microinjections of NPS into the ventral CA1 (vCA1) region are
sufficient to elicit anxiolysis in C57BL6/N mice on the elevated
plus maze (EPM). In a second step, behavioral and molecular effects
of intranasal NPS treatment were characterized in C57BL/6N mice.
Intranasal application of NPS was shown here to produce anxiolytic
effects similar to those described by others after intracerebral
injection. This finding represents the basis for the implementation
of a future NPS-based therapy via nasal sprays in patients
suffering from anxiety disorders. Furthermore, the molecular
effects of NPS treatment on cerebral protein expression were
examined here for the first time. This research led to
identification of novel downstream targets of NPS-mediated
regulation in the hippocampus and the prefrontal cortex. These new
targets include proteins involved in the glutamatergic system and
in synaptic plasticity, both of which are known to be dysregulated
in anxiety disorders. Finally, the effects of intranasal NPS
treatment, hitherto described only in non-pathological animal
models, were examined for the first time in mouse models of anxiety
disorders, namely the high anxiety behavior (HAB) mice and a mouse
model of PTSD. In HAB mice, NPS treatment elicited anxiolytic
effects similar to those observed in C57BL/6N mice. In the mouse
model of PTSD, NPS counteracted disease-related changes in
expression levels of hippocampal synaptic proteins. To sum up, this
work expands the current state-of-knowledge concerning the
molecular and mechanistic background of NPS-mediated anxiolysis by
characterizing the role of the hippocampus in the NPS circuitry and
by identifying novel downstream targets of NPS. The data on
anxiolytic effects of intranasal NPS treatment especially in mouse
models of anxiety disorders furthermore establishes the therapeutic
potential of NPS as a novel anxiolytic treatment.