S sulpiride

Dopamine hydrochloride, (S)-(−)-sulpiride, dimethyl sulfoxide (DMSO), and droperidol were all acquired from Sigma-Aldrich. Haloperidol and piribedil were both acquired from TCI Chemicals. Bromocriptine mesylate was acquired from VWR. Apomorphine hydrochloride was kindly provided by EVERPharma AT GmbH within the context of a different project. Tested compounds (shown in Table S9) were acquired either from SPECS (https://www.specs.net/, accessed in April 2021) or Maybridge (https://www.thermofisher.com/at/en/home/industrial/pharma-biopharma/drug-discovery-development/screening-compounds-libraries-hit-identification.html, accessed in April 2021). All the compounds were dissolved in DMSO, aliquoted, and stored at −80 °C until further use.

We injected SCH23390 (5 mM × 69 nL; Sigma-Aldrich, USA), a specific antagonist of D1-like receptor (Kokay and Mercer, 1996 (link); Titlow et al., 2013 (link)) in the brains of gregarious locusts before behavioral assay was performed to determine the role of Dop1 in gregarization of solitary locusts. After the antagonist was injected, fourth-stadium gregarious locusts were reared with other gregarious locusts for 1 h before behavioral assay was conducted.
To evaluate the role of Dop2 in the solitarization of gregarious locusts, S(-)-sulpiride (5 mM × 69 nL; Sigma-Aldrich, USA), a specific antagonist of Dop2 (Feng et al., 1996 (link)), was injected in the brains of gregarious locusts before behavioral assay was performed. After the antagonist was injected, fourth-stadium gregarious locusts were placed in separate solitary-rearing cages to live individually for 15, 30, or 60 min before behavioral assay was conducted. All of the control groups received the same volume of saline before behavioral assay was carried out.

The NT (Sigma–Aldrich Co., St. Louis, MO, USA, N 6383) and the D1-like DA receptor antagonist (R)-(+)-SCH23390-hydrochloride (Sigma-Aldrich Co., St. Louis, MO, USA, D054) were dissolved in a 0.15 M sterile saline solution containing 0.01 M Na-acetate and 0.01 M phosphate-buffered saline. The D2-like DA receptor antagonist (S)-(-)-sulpiride (Sigma–Aldrich Co., S7771) was dissolved in 0.1 N HCl, and after the addition of the phosphate buffer (pH 6.9) it was titrated with 0.1 N NaOH. NT was microinjected at a dose of 100 ng, SCH23390 at 1 μg and sulpiride at a dose of 4 μg. The dose of NT was determined based on the effective dose of NT in the VP in the earlier behavioural experiments conducted by our research group [31 (link),32 (link)]. The doses of the DA receptor antagonists were determined based on pilot experiments and on effective dose ranges blocking the effect of NT in other brain areas [27 (link)]. Control rats received the corresponding vehicle solution in the same volume (0.4 μL). All mentioned doses were applied per side.