5HT 7 Receptors in the Rodent Suprachiasmatic Nucleus

Serotonergic modulation of circadian rhythms in rodent model preparations has received considerable attention over the past decade. Investigators have also been trying to determine which of the many serotonin receptor subtypes may be mediating the effects of serotonin in the suprachiasmatic nucleus, the location of the biological clock that generates the circadian rhythms. Asingle study in 1993 using the in vitro rat hypothalamic slice preparation suggested that serotonergic modulation of circadian rhythms at the level of the suprachiasmatic nucleus was acting via the newly discovered 5HT₇ receptor subtype. Since that initial claim, serotonin modulation of circadian rhythms at the level of the suprachiasmatic nucleus has generally been attributed to 5HT₇ receptor activation. However, when trying to cite relevant literature in support of 5HT₇ involvement, it becomes evident that attributing rhythm-related serotonin activity in the suprachiasmatic nucleus to 5HT₇ receptors may be somewhat premature. There are issues related to pharmacological specificity, species-specific results, and significant knowledge gaps that necessitate a careful review of the literature to make a judgment as to whether 5HT₇ receptors are responsible for serotonergic activity in the rodent suprachiasmatic nucleus. In addition, there is sufficient data available at present to make an initial determination as to the degree of 5HT₇receptor involvement at any level in the generation or modulation of circadian rhythms in rodent species.