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The autonomic nervous system (ANS) is implicated in maintaining homeostasis of the internal environment in mammals. Therefore, changes occurring in the ANS can cause alterations of physiological phenomena. Ethyl hexanoate (EH) is known as the aroma component of apples. To study the action of ethyl hexanoate on physiological phenomena, we examined the effect of an intragastric (IG) injection of 1 mL/kg body weight of 0.1 ppm EH solution on sympathetic nerve activity innervating the brown adipose tissue (BAT) and white adipose tissue (WAT) in anesthetized rats. Consequently, IG administration of EH increased activity of the sympathetic nerves innervating both the BAT and WAT. In addition, the effects of the IG injection on body temperature above the interscapular BAT and plasma free fatty acid (FFA) concentration were also examined in conscious rats. In this attempt IG injection of EH elevated both the body temperature and plasma FFA levels. Furthermore, subdiaphragmatic vagotomy eliminated the effects of EH on sympathetic nerves innervating BAT and WAT. These findings suggest that EH causes excitations of sympathetic nerves innervating BAT and WAT, and enhances thermogenesis and lipolysis via the afferent vagus nerve. Thus, these present findings also suggest the possibility that EH might have anti-obesity effects.

Splenic sympathetic nerve activity (SNA) modulates cellular immune functions such as splenic natural killer cell activity. Lactobacillus pentosus strain S-PT84 enhances splenic natural killer cell activity. Here, we examined whether S-PT84 affects splenic natural killer activity through splenic SNA in BALB/c mice. Splenic SNA was significantly decreased following the administration of S-PT84. This phenomenon was inhibited by pretreatment with thioperamide (histamine H3 receptor antagonist), suggesting that S-PT84 directly affected splenic SNA. Thioperamide also inhibited the increase in splenic natural killer activity by S-PT84. Thus, the change in splenic natural killer activity by S-PT84 may be partially modulated through SNA.

Changes in the activity of the autonomic nervous system are good indicators of alterations in physiological phenomena such as the body temperature, blood glucose, blood pressure. Hesperidin, a flavanone known as vitamin P, has been shown to reduce the levels of serum lipids, cholesterol, and blood pressure. However, hesperidin is not water-soluble and is not well absorbed from the intestine. G-hesperidin (4G-alpha-glucopyranosyl hesperidin) is more water-soluble and more rapidly absorbed than hesperidin. In order to clarify the functions of G-hesperidin, we examined the effects of oral administration of G-hesperidin on interscapular brown adipose tissue-sympathetic nerve activity (BAT-SNA) and cutaneous sympathetic nerve activity (CASNA) in rats weighing about 300 g. In this study, we found that oral administration of 60 mg of G-hesperidin increased the BAT-SNA but decreased the CASNA in urethane-anesthetized rats. Since an elevation in BAT-SNA increases heat production (i.e. body temperature (BT)) and a decrease in CASNA increases cutaneous perfusion, we examined whether oral administration of G-hesperidin had an effect on the peripheral BT in rats. Consequently, we observed that the subcutaneous BT at the caudal end of the back after oral administration of 60 mg of G-hesperidin was significantly higher than the subcutaneous BT after oral administration of water in conscious rats. These findings suggest that G-hesperidin enhances the BAT-SNA and suppresses the CASNA resulting in an increase in the peripheral BT, probably by an increase in the thermogenesis in the BAT and an elevation in the cutaneous blood flow.

Oral supplementations of L-arginine and L-lysine show tumor inhibition abilities. The splenic sympathetic nerve is involved in central modulation of cellular immunity and suppresses splenic natural killer cell activity in rats. An intravenous administration of a mixture of 10 mM L-arginine and L-lysine decreased splenic sympathetic nerve activity (splenic-SNA). We examined the effect of L-arginine and L-lysine mixtures on splenic-SNA in urethane-anesthetized rats by administration of 1 ml mixtures of 2 mM, 10 mM, and 50 mM L-arginine and L-lysine. We also studied the effect of the above mixtures on human colon cancer cell proliferation in athymic nude mice. An increase in splenic-SNA and tumor volume (2 mM), no effect (10 mM), and a decrease in both values (50 mM) were seen. Bivariate correlation analysis revealed a positive correlation between changes in splenic-SNA and tumor volume, indicating the tumor suppressing ability of weakened splenic-SNA.

The spleen is an important organ for tumor immunity, and the splenic sympathetic nerve has a suppressive effect on splenic natural killer (NK) cytotoxicity. On the basis of this and reports that Lentinus edodes (Shiitake mushroom) has tumor-inhibitory effects, the authors hypothesized that an extract of a mycelial culture of L. edodes grown in a solid medium of sugar-cane bagasse and defatted rice bran–L·E·M–might affect the sympathetic splenic sympathetic nerve activity (Splenic-SNA) and thus inhibit tumor proliferation. Thus, the effect of L·E·M on Splenic-SNA and human cancer cell proliferation was examined. Splenic-SNA was found to be suppressed by an intraduodenal L·E·M injection in urethane-anesthetized rats, which significantly inhibited increases in the tumor volume of human colon and breast cancer cells implanted in athymic nude mice. These findings suggest that L·E·M has an inhibitory effect on tumor proliferation possibly via a reduction in NK cytotoxicity through the suppression of Splenic-SNA.

L-Carnosine is synthesized in mammalian muscles and brain and affects autonomic neurotransmission and physiological phenomena. To clarify the role of l-carnosine, the effects of intraduodenal administration of l-carnosine on muscle sympathetic nerve activity (muscle-SNA) and blood flow (BF) were examined. The changes in muscle-SNA and BF were examined using electrophysiological and Doppler flowmeter in urethane-anesthetized rats. The effect of propranolol, a β-adrenergic antagonist, on the increase in muscle BF due to l-carnosine was also examined. Low dose (1μg/300g body weight [bw]) of l-carnosine increased both muscle-SNA and muscle BF, while high dese (100mg/300g bw) of l-carnosine decreased both muscle-SNA and muscle BF. Furthermore, propranolol eliminated the increase in muscle BF caused by a low dose of l-carnosine. These results suggest that l-carnosine has dose-dependent effects on muscle BF via changes in muscle-SNA, and the β-adrenergic receptor is implicated in the increase in muscle BF due to l-carnosine.

Lactobacilli provide several health benefits to mammals, including humans. We previously observed that in rats, intraduodenal injection of Lactobacillus johnsonii La1 elevated efferent gastric vagal nerve activity (efferent-GVNA), while Lactobacillus paracasei ST11 suppressed efferent-GVNA, and thereby increased or decreased food intake. To determine the function of Lactobacillus brevis (SBC8803), its effect on food intake was examined by providing food containing heat-killed SBC8803 to mice. We observed that administration of SBC8803 elevated food intake. Because the afferent intestinal vagal nerve (IVN) is hypothesized to be involved in efferent-GVNA changes, we examined the effect of intraduodenal administration of heat-killed SBC8803 on efferent-GVNA and afferent-IVN activity (IVNA) in rats. In this study, we found that intraduodenal administration of heat-killed SBC8803 increased both efferent-GVNA and afferent-IVNA in rats. Moreover, IV administration of the serotonin 3 receptor antagonist granisetron eliminated the effects of SBC8803 on efferent-GVNA and afferent-IVNA. These findings suggest that heat-killed SBC8803 enhances appetite by elevating digestion and absorption abilities via changes in autonomic neurotransmission that might be mediated by the serotonin 3 receptor.

Intestinal administration of various lactobacilli has been reported to affect autonomic neurotransmission, blood pressure, blood glucose, and body weight in rats, however, the mechanisms of action of the lactobacilli remain to be clarified. Therefore, the effect of the culture supernatant of Lactobacillus pentosus strain S-PT84 on the autonomic nerve activity in urethane-anesthetized rats was investigated. Intraduodenal injection of the low-molecular-weight (LMW) fraction (molecules less than 10,000 Da) of the S-PT84 culture supernatant elevated the brown adipose tissue sympathetic nerve activity and reduced the gastric vagal nerve activity. Moreover, intraoral administration of this LMW fraction increased the body temperature of rats above the interscapular brown adipose tissue. These results suggest that the LMW fraction of the S-PT84 culture supernatant affects the autonomic nerve activity and thermogenesis, and that the change in thermogenesis may be caused by the change in the sympathetic nerve activity of brown adipose tissue.

l-Carnosine (β-alanyl-l-histidine), a dipeptide of the amino acids β-alanine and histidine, is found in mammalian tissues including those in the central nervous system and in skeletal muscles. In the present study, we examined the effects of intraduodenal (ID) injection of l-carnosine on splenic sympathetic nerve activity (splenic-SNA) in urethane-anesthetized rats and found that ID injection of 3.3mg/kg of body weight of l-carnosine significantly suppressed splenic-SNA. Since it has been suggested that splenic-SNA reduction increases natural killer (NK) activity of splenic cells, which in turn elevates tumor immunity, we then investigated the effect of l-carnosine on the proliferation of human colon cancer cells transplanted into athymic nude mice. The findings of this study revealed that 1mg/mL of l-carnosine solution given as the only drinking water inhibited tumor proliferation. These results suggest that l-carnosine suppresses splenic-SNA and inhibits cancer cell proliferation, probably by elevating NK activity.