Suppression of spontaneous scratching in hairless XXXX by sedatives but not by antipruritics.

@entity5403 @entity8765 @entity5404 @entity3303 @entity9090 @entity35 @entity1363
Experimental scratching in animals has hitherto been provoked by substances injected into the skin or central nervous system. We aimed to investigate if spontaneous scratching in the @entity35 can be reduced by sedatives and antipruritics, and to assess if spontaneous scratching is elicited from the skin or the central nervous system. It may also be a complex behaviour related to the @entity35 species, different from clinical itch. Eight male hairless @entity35 were studied for 6 weeks. The animals were recorded on videotape in the middle of the day and at night, and the scratching activity was counted. The following substances were tested sequentially: @entity1363 , @entity8765 , a eutectic mixture of @entity3303 and @entity5403 ( @entity5404 , @entity9090 and a vehicle. On days 1-3 of each sequence, the test material was applied to a 42-cm(2) area on the rostral part of the back. Subsequent treatment of the whole body was made on day 4. @entity1363 was injected intraperitoneally from day 1 to day 4. After 4 days of treatment, there was a wash-out phase of 3 days until the next sequence. We found a positive correlation between minutes awake and number of scratch episodes. Spontaneous scratching was lower after @entity8765 on day 4 (p = 0.046) and after @entity1363 injections on days 1-3 (p = 0.009) and day 4 (p = 0.003). The local anaesthetic, @entity5404 , did not significantly influence spontaneous scratching. In conclusion, only the drugs with sedative properties suppressed spontaneous scratching, which is probably a cerebral phenomenon or otherwise explained general behaviour, rather than a reaction to skin stimuli. Thus, for testing of topically applied antipruritics, spontaneous scratching cannot be used as an animal model. Furthermore, evaluation of provocative scratching should eliminate/exclude spontaneous scratching.
