Cholinergic mechanisms in scent marking behavior by Mongolian gerbils (Meriones unguiculatus)

The Mongolian gerbil reared in Japan manifested scent marking behavior in the similar behavioral topography as described by foreign researchers. The frequency of marking was affected by early isolation housing; isolated male gerbils exhibited a higher frequency of marking than aggregated males. The marking behavior was suppressed by scopolamine (1.5 mg/kg, IP), whereas methylscopolamine was ineffective. In order to elucidate the possible neural mechanisms, acetylcholinesterase (ACh-E) and choline acetyltransferase (Ch-Ac) activities were measured in 8 discrete areas of the brain (the cortex, striatum, amygdala, hypothalamus, midbrain, hippocampus, olfactory bulbs, and pons plus medulla oblongata). There was, however, no significant difference between isolated and aggregated gerbils in either ACh-E or Ch-Ac activity in any of the brain areas. These results suggest that other neural events, such as changes in the ACh turnover rate or in ACh release, may participate in the manifestation of scent marking behavior.