Day-night difference in thermoregulatory responses to olfactory stimulation.

Previously, we observed that olfactory stimulation with scent of grapefruit oil (SGFO) or scent of lavender oil (SLVO) affected, elevated or lowered brown adipose tissue temperature (BAT-T) in conscious mice, respectively. In the present study, to test the day-night difference in the actions of olfactory stimulations, we examined the responses of BAT-T and body temperature (BT) measured as the abdominal temperature to SGFO or SLVO during day-time at 14:00 and night-time at 2:00 in conscious rats. In the light period, BAT-T and BT were suppressed after SLVO and elevated after SGFO whereas in the dark period, these parameters remained unchanged with olfactory stimulations. Bilateral lesions of the hypothalamic suprachiasmatic nucleus (SCN) eliminated the effects of olfactory stimulations with SGFO and SVLO on BAT-T and BT. Moreover, sympathetic nerve activity innervating brown adipose tissue (BAT-SNA) changes after SGFO or SLVO were abolished in SCN-lesioned rats. Thus, we concluded that there is day-night difference in the effects of SGFO or SLVO on BAT-T and BT, and that the SCN might be involved in these effects.

Effects of olfactory stimulations with scents of grapefruit and lavender oils on renal sympathetic nerve and blood pressure in Clock mutant mice.

Previously, we observed that in mice, olfactory stimulation with scent of grapefruit oil elevates renal sympathetic nerve activity and blood pressure. In contrast, olfactory stimulation with scent of lavender oil has opposite effects in mice. Moreover, electrolytic lesions of the mouse hypothalamic suprachiasmatic nucleus eliminated changes in renal sympathetic nerve activity and blood pressure induced by either scent of grapefruit oil or scent of lavender oil. Here, we show that grapefruit oil-induced elevations in renal sympathetic nerve activity and blood pressure were not observed in Clock mutant mice, which harbor mutations in Clock and lack normal circadian rhythms, whereas lavender oil-suppressions were preserved in Clock mutant mice. In addition, responses of c-Fos inductions in the suprachiasmatic nucleus and paraventricular nucleus of the hypothalamus to scent of grapefruit oil observed in wild-type mice were not observed in Clock mutant mice. These findings suggest that the Clock gene might be implicated in elevating responses of autonomic and cardiovascular functions to olfactory stimulation with scent of grapefruit oil.

Mechanism of changes induced in plasma glycerol by scent stimulation with grapefruit and lavender essential oils.

In a previous study, we found that stimulation with scent of grapefruit oil (SGFO) elevated plasma glycerol levels in rats. However, stimulation with scent of lavender oil (SLVO) triggered a negative effect. To identify the mechanism of these changes during lipolysis, we examined the role of autonomic blockers and bilateral lesions of the hypothalamic suprachiasmatic nucleus (SCN) in the modification of plasma glycerol in rats exposed to SGFO and SLVO. We found that intraperitoneal injection of propranolol hydrochloride and atropine sulfate eliminated the changes in plasma glycerol levels induced by SGFO and SLVO, respectively. Bilateral lesions of the SCN completely abolished the effects of SGFO and SLVO on lipolysis. In addition, we investigated tyrosine phosphorylation of the transmembrane glycoprotein BIT (a brain immunoglobulin-like molecule with tyrosine-based activation motifs, a member of the signal-regulator protein family), which was found to be involved in the activation of renal sympathetic nerves and increase in body temperature on cold exposure. SGFO was found to enhance the immunoreactivity of BIT to the 4G10 anti-phosphotyrosine antibody in the SCN, whereas SLVO decreased the immunoreactivity. The changes in BIT phosphorylation resulting from the exposure to SGFO and SLVO were eliminated by the corresponding histamine receptor antagonists, which eliminated the changes in plasma glycerol concentration. The results suggest that SGFO and SLVO affect the autonomic neurotransmission and lipolysis. The SCN and histamine neurons are involved in the lipolytic responses to SGFO and SLVO, and tyrosine phosphorylation of BIT is implicated in the relevant signaling pathways.

Restoration of circadian behavior by anterior hypothalamic heterografts.

The suprachiasmatic nucleus (SCN) of the anterior hypothalamus (AH) is a circadian oscillator and an important component of the mammalian circadian system. To determine whether the SCN is the dominant circadian pacemaker responsible for generating a species-typical characteristic of circadian rhythms [i.e., period length (tau)], neural transplantation was conducted using fetal AH donors of different species and SCN-lesioned (SCNx) hosts. The circadian behavior of each of the three donor species is clearly distinguishable by its species-typical tau. The extent of SCN pacemaker autonomy was assessed by noting whether the period of the restored circadian rhythm following heterograft transplantation was characteristic of the donor or the host, or whether an atypical circadian period was established. Hamsters rendered arhythmic by SCN ablation were implanted with AH tissue from fetal hamsters (E13-E14, homograft controls) or fetal mice or rats (E15-E17). The AH homografts restored circadian activity rhythms with a tau similar to that of intact hamsters, and fetal mouse AH heterografts restored circadian rhythmicity with a tau similar to that of the donor mouse strain. However, fetal rat AH tissue implanted into SCNx hamsters renewed circadian rhythmicity with a period significantly shorter than either the species-typical tau of the rat donor or the hamster host. In both the mouse and rat AH heterograft experiments, immunocytochemical analysis performed with species-specific monoclonal antibodies revealed extensive fiber outgrowth from the implant into the host hypothalamus, evident up to 7 months postimplantation. The rat implants were consistently larger, more fully vascularized and exhibited less necrosis than the implanted mouse tissue. The histological appearance of the grafts, thus, provides no explantation for the difference in efficacy of the grafts to restore species-typical behavior. However, several interpretations are considered that are consistent with the combined behavioral results observed.