Assessment of depression-like behavior in rats
Depression-like behavior was assessed in the FST, originally proposed as
a model of stress-induced depression-like behavior
(Porsolt, Le Pichon, & Jalfre, 1977).
FST is broadly used for the early screening of novel molecules with
putative antidepressant-like (AD) effects since immobility is commonly
qualified as “despair” and considered to reflect depression-like
states. Remarkably, the immobility response in the FST can be prevented
by various types of AD treatments, including tricyclic antidepressants,
monoamine oxidase inhibitors, SSRIs, and NA reuptake inhibitors
(Planchez et al., 2019).
Behavioral experiments were performed between 09:00 and 14:00 hours.
Animals were adapted to handling and were taken into the experimental
room (80-90 lux) for at least 1 hour to reach habituation and assigned
randomly to the experimental groups. Peptides were freshly prepared and
intranasal treatments were administered 24 hours before the test phase
(20 μl total volume). Doses for Galanin receptor 2 agonist (M1145), Y1R
receptor agonist [Leu31,
Pro34]NPY, GALR2 Antagonist M871 and ANA-12 were
chosen based on previous published protocols
(Borroto-Escuela et al., 2022;
Ribeiro et al., 2020;
Serova et al., 2017). We performed
dose-response curves to determine effective doses. Separate group of
rats were randomly allocated into six experimental groups: (1) Control:
distilled water; (2) M1145- treated group (132 µg); (3) Y1R
agonist-treated group receiving the Y1R agonist
[Leu31- Pro34]NPY (132 µg); (4)
M1145+Y1R: group administered with both substances; (5) M1145+Y1R+M871:
group treated with M1145, [Leu31-
Pro34]NPY and the GALR2 antagonist (M871; 132 µg);
(6) M1145+Y1R+ANA-12: group treated with M1145,
[Leu31- Pro34]NPY and the TrkB
antagonist (ANA-12, 5.06304, Sigma, St. Louis, MO, USA; 0.5 mg/kg,
i.p.) (N=6 in each group).
Swimming sessions were conducted by placing individually the rats in
cylinders containing water (25±0.2°C), 30 cm deep. Two sessions were
conducted: an initial 15 min pretest followed 48 h later by a 5-min
test. The water in the cylinders was changed after every trial. The FST
was performed according to previously reported methods
(Borroto-Escuela et al., 2021;
Koike & Chaki, 2014). The total duration
of floating (immobility) and swimming periods were scored during the 5
min test and analyzed using the Raton Time 1.0 software (Fixma S.L.,
Valencia, Spain). Floating in the water without struggling and only
making movements necessary to keep its head above the water was regarded
as immobility. Swimming was scored when they actively swam around the
cylinder. Following swimming sessions, the rats were removed from the
tank, carefully dried in heated cages, and then returned to their home
cages. Behavioral experiments were carried out by observers blinded to
all experimental conditions.