Abstract
Similar to psychostimulants, the peripheral administration of menthol promotes mouse motor activity, and the neurotransmitter dopamine has been suggested to be involved in this effect. The present study aimed to elucidate the effects of l-menthol on parts of the central nervous system that are involved in motor effects. The subcutaneous administration of l-menthol significantly increased the number of c-Fos-like immunoreactive nuclei in the dorsal striatum of the mice, and motor activity was promoted. It also increased the extracellular dopamine level in the dorsal striatum of the mice. These observations indicated that after subcutaneous administration, l-menthol enhances dopamine-mediated neurotransmission, and activates neuronal activity in the dorsal striatum, thereby promoting motor activity in mice.
Highlights
Menthol, which is known as mint camphor, is a monocyclic terpene alcohol that is found naturally in more than 100 essential oils, and it is a major constituent of the essential oils of spearmint and peppermint
The acclimation procedure was conducted for 3 consecutive days to reduce stress in the mice, the experimental environment and handling still stimulated ambulatory activity on the 4th day
L-menthol administration had a much larger effect on the ambulatory activity: it significantly increased the ambulatory activity immediately after administration, and the effect persisted for almost 60 min (2-way analysis of variance (ANOVA): dose (F(1, 16) = 12.8583, P = 0.0025; time (F(5, 12) = 3.6462918, P = 0.0011; Fig 2), consistent with the results of a previous study [8]
Summary
Menthol, which is known as mint camphor, is a monocyclic terpene alcohol that is found naturally in more than 100 essential oils, and it is a major constituent of the essential oils of spearmint and peppermint. An experiment using a tilting-cage method, that is more sensitive to horizontal movement such as locomotion than to vertical movement, revealed that the peripheral administration of dl-menthol promotes motor activity, i.e., ambulatory activity, in mice [3]. Given that this behavior-activating effect is similar to that of known psychostimulants but distinct from that of nicotine and CNS depressants [4,5,6], the ambulatory effect of dlmenthol has been suggested to result from the activation of some part of the CNS.
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