Neuroactive steroids modulate crustacean locomotor activity

We examined the effects of neuroactive steroids known to modulate gamma-aminobutyric acid A (GABA) A receptor activity, on locomotor activity in a submerged circular open-field apparatus. Juvenile male lobsters, Homarus americanus, were treated with a single administration of an agonist, 3α-hydroxy-5α-pregnan-20-one (allopregnanolone, 3α,5α-TH PROG), an antagonist, pregnenolone sulfate (PREGS), or vehicle alone. 3α,5α-TH PROG treatment (125 and 250 μg) significantly reduced while PREGS significantly elevated locomotor activity in a dose-dependent manner similar to diazepam. PREGS increased locomotor activity at 30 and 60 μg, while diminishing such activity and altering locomotor patterns at 120 μg. These results suggest that neuroactive steroids may affect crustacean GABA receptors in a fashion similar to the GABA A type found in the vertebrates, and that they may be involved in the regulation of locomotor behavior.