Eating Behavior is Associated to Sympathetic Activation Induced by ICV Injection of Prostaglandin E1in the Rat

Role of Autonomic Nervous System and Orexinergic System on Adipose Tissue

Adipose tissue, defined as white adipose tissue (WAT) and brown adipose tissue (BAT), is a biological caloric reservoir; in response to over-nutrition it expands and, in response to energy deficit, it releases lipids. The WAT primarily stores energy as triglycerides, whereas BAT dissipates chemical energy as heat. In mammals, the BAT is a key site for heat production and an attractive target to promote weight loss. The autonomic nervous system (ANS) exerts a direct control at the cellular and molecular levels in adiposity. The sympathetic nervous system (SNS) provides a complex homeostatic control to specifically coordinate function and crosstalk of both fat pads, as indicated by the increase of the sympathetic outflow to BAT, in response to cold and high-fat diet, but also by the increase or decrease of the sympathetic outflow to selected WAT depots, in response to different lipolytic requirements of these two conditions. More recently, a role has been attributed to the parasympathetic nervous system (PNS) in modulating both adipose tissue insulin-mediated glucose uptake and fatty free acid (FFA) metabolism in an anabolic way and its endocrine function. The regulation of adipose tissue is unlikely to be limited to the autonomic control, since a number of signaling cytokines and neuropeptides play an important role, as well. In this review, we report some experimental evidences about the role played by both the ANS and orexins into different fat pads, related to food intake and energy expenditure, with a special emphasis on body weight status and fat mass (FM) content.

Espresso coffee increases parasympathetic activity in young, healthy people

Caffeine induces modifications of activity of the autonomic nervous system. This study analyzed the effect of a cup of espresso coffee on the heart rate variability (HRV) power spectral analysis, which is a method providing evaluation of the sympathetic and parasympathetic discharge. In young, healthy sedentary subjects (10 male, 10 female; aged 25-30 years), the HRV-power spectrum was evaluated over a period of 150 min after the administration of espresso coffee (caffeine, 75 mg) or decaffeinated coffee (caffeine, < 18 mg) in supine and seated position. Absolute values of the spectrum were summed in low (LF) and high frequencies (HF). The LF and HF spectra were used to estimate the sympathetic and parasympathetic activity, respectively. In the supine position, coffee increases HF, while decaffeinated coffee causes little modifications of HF. In the seated position, HF is not modified by coffee or decaffeinated coffee. Coffee and decaffeinated coffee do not induce any modification of LF in both positions. This experiment indicates that espresso coffee influences parasympathetic activity in the supine position.

Procaine into the VMH inhibits IBAT activation caused by frontal cortex stimulation in urethane-anesthetized rats

This experiment tested the effect of procaine injection into the ventromedial hypothalamus on the sympathetic and thermogenic activation induced by frontal cortex stimulation. Oxygen consumption, firing rate of the sympathetic nerves to interscapular brown adipose tissue (IBAT), along with IBAT and colonic temperatures were monitored in fasted male Sprague-Dawley rats before and during 25 min after an electrical stimulation of the frontal cortex. The same variables were monitored in rats with administration of procaine into the ventromedial hypothalamus. The results show that cortical stimulation increases oxygen consumption, sympathetic firing rate, IBAT and colonic temperatures. The increase in sympathetic firing rate was reduced by procaine injection, and the increase in IBAT and colonic temperatures as well as oxygen consumption was fully inhibited by procaine. These findings suggest that the ventromedial nucleus plays an important role in the sympathetic and thermogenic changes induced by cortical stimulation.

Inhibition of prostaglandin synthesis reduces hyperthermic reactions induced by hypocretin-1/orexin A

This experiment tested (i) the effect of orexin A injected into a lateral cerebral ventricle on sympathetic and thermogenic activity and (ii) the involvement of prostaglandins in these phenomena. The firing rates of the sympathetic nerves to interscapular brown adipose tissue (IBAT), along with IBAT and colonic temperatures and heart rate were monitored in urethane-anesthetized male Sprague-Dawley rats before and 6 h after an injection of orexin A (1.5 nmol) into the lateral cerebral ventricle. The same variables were monitored in rats with an intraperitoneal administration of lysine acetylsalicylate (100 mg/kg bw), an inhibitor of prostaglandins synthesis. The results show that orexin A increases the sympathetic firing rate, IBAT and colonic temperatures and heart rate. This increase is reduced by lysine acetylsalicylate. These findings suggest that orexin A affects sympathetic activity, which controls body temperature. Prostaglandins are involved in this control.

Administration of muscimol into the posterior hypothalamus reduces hyperthermia induced by hippocampal neostigmine injection

The firing rate of the sympathetic nerves innervating interscapular brown adipose tissue (IBAT), IBAT and colonic temperatures (T(IBAT) and T(C)) and oxygen (O(2)) consumption were monitored in urethane-anesthetized male Sprague-Dawley rats. These variables were measured for 40 min before (baseline values) and 40 min after an injection of neostigmine (5 x 10(-7) mol in 1 microl of saline) into the hippocampus and a bilateral administration of a GABA(a)-agonist, muscimol (28 ng in 0.5 microl of saline, per side) into the posterior hypothalamus. The same variables were recorded in other rats, but the muscimol was replaced by saline. Control animals were used with muscimol or saline alone. The results show an increase of sympathetic firing rate, T(IBAT), T(C) and O(2) consumption after neostigmine injection. Muscimol significantly reduces this enhancement. The findings suggest that hippocampus controls the sympathetic and thermogenic activation induced by neostigmine through an influence on GABAergic tone of the posterior hypothalamus.