2.5. Horizontal locomotor activity (HLA)
During the habituation phase (2 days), mice received an intraperitoneal
(i.p.) saline injection and placed into a black Plexiglass open field
arena (25x25x40 cm) under low-light conditions and white noise for 60
minutes. On the test day, horizontal locomotor activity (HLA) was
measured as described by (Duart-Castells et al., 2019), with minor
modifications. Briefly, the animals were given their corresponding i.p.
injection (saline (5 ml/kg), pentedrone (3, 10 or 30 mg
kg-1), N-ethyl-pentedrone (1, 3 or 10 mg
kg-1), N,N-diethyl-pentedrone (3.5, 12.5 or 35 mg
kg-1), α-PVP (1, 3 or 10 mg kg-1) or
α-PpVP (7.5, 25 or 75 mg kg-1) and immediately placed
in the open field arena. HLA was video-monitored for 60 min using a
tracking software (Smart 3.0 Panlab, Barcelona, Spain) and their total
travelled distance (in cm) was measured. All HLA experiments were
performed between 8:00 am and 3:00 pm. On one hand, pentedrone and α-PVP
doses were chosen following the results reported by Hwang et al., 2017
and Wojcieszak et al., 2018. On the other hand, there is no data
available about the doses of N-ethyl-pentedrone, N,N-diethyl-pentedrone
and α-PpVP used in animal research. Therefore, these doses were chosen
in pilot experiments and according to the psychostimulant effect induced
by pentedrone or α-PVP in our experiments at the medium doses tested in
order to have, at least, one dose of N-ethyl-pentedrone,
N,N-diethyl-pentedrone and α-PpVP equally effective (similar distance
travelled after injection). Moreover, all the highest doses used were
always 10-fold higher than the lowest dose tested, a protocol also used
by the same authors when injecting pentedrone or α-PVP (Hwang et al.,
2017; Wojcieszak et al., 2018).