Influence of electrical supramedullary stimulation on the plasma level of free fatty acids, blood pressure and heart rate in the dog

Melanocortin-4 receptor mRNA is expressed in sympathetic nervous system outflow neurons to white adipose tissue

Energy balance results from the coordination of multiple pathways affecting energy expenditure and food intake. Candidate neuropeptides involved in energy balance are the melanocortins. Several species, including Siberian hamsters studied here, decrease and increase food intake in response to stimulation and blockade of the melanocortin 4-receptor (MC4-R). In addition, central application of the MC3/4-R agonist melanotan-II decreases body fat (increases lipolysis) beyond that accounted for by its ability to decrease food intake. Because an increase in the sympathetic nervous system drive to white adipose tissue (WAT) is the principal initiator of lipolysis, we tested whether the sympathetic outflow circuitry from brain to WAT contained MC4-R mRNA expressing cells. This was accomplished by labeling the sympathetic outflow to inguinal WAT using the pseudorabies virus (PRV), a transneuronal retrograde viral tract tracer, and then processing the brain for colocalization of PRV immunoreactivity with MC4-R mRNA, the latter assessed by in situ hybridization. MC4-R mRNA was impressively colocalized in PRV-labeled cells (approximately greater than 60%) in many brain areas across the neuroaxis, including those typically implicated in lipid mobilization (e.g., hypothalamic paraventricular, suprachiasmatic, arcuate and dorsomedial nuclei, lateral hypothalamic area), as well as those not traditionally identified with lipolysis (e.g., preoptic area, subzona incerta of the lateral hypothalamus, periaqueductal gray, solitary nucleus). These data provide compelling neuroanatomical evidence that could underlie a direct central modulation of the sympathetic outflow to WAT by the melanocortins through the MC4-Rs resulting in changes in lipid mobilization and adiposity.

Sympathetic activation in adipose tissue and skeletal muscle of hypertensive rats

The activation of the sympathetic nervous system is a common feature of arterial hypertension and other cardiovascular diseases. This activation might be dependent on an altered baroreflex control of vascular resistance of which the inhibitory response on sympathetic activity appears impaired. The aim of the study was to monitor during the natural course of arterial hypertension in spontaneously hypertensive (SHR) and age-matched Wistar Kyoto (WKY) rats (5, 16, 30, and 54 weeks of age) the peripheral sympathetic activity expressed as interstitial norepinephrine (NE) release and as tyrosine hydroxylase (TH) activity, the rate-limiting enzyme of NE synthesis, in the differently baroreflex-controlled subcutaneous adipose tissues and skeletal muscles. Blood pressure and plasma NE in SHR were similar to WKY at 5 weeks of age but increased at all other ages. Body weight was similar in both 5-week-old rats but reduced in SHR at all other ages. The interstitial NE levels were greater in both SHR tissues at all ages as compared with WKY. In adipose tissue of SHR, TH activity was higher at all ages as compared with WKY, whereas TH activity in skeletal muscle was higher only after the development of hypertension. These data show that in both SHR tissues, an increase of interstitial NE release is always present during its lifespan. This suggests that increased sympathetic activation in the SHR model is not specific to baroreflex-controlled tissues such as skeletal muscle but involves also subcutaneous adipose tissue, the sympathetic efferents of which are independent from baroreflexes.

Innervation of mammalian white adipose tissue: implications for the regulation of total body fat

We review the extensive physiological and neuroanatomical evidence for the innervation of white adipose tissue (WAT) by the sympathetic nervous system (SNS) as well as what is known about the sensory innervation of this tissue. The SNS innervation of WAT appears to be a part of the general SNS outflow from the central nervous system, consisting of structures and connections throughout the neural axis. The innervation of WAT by the SNS could play a role in the regulation of total body fat in general, most likely plays an important role in regional differences in lipid mobilization specifically, and may have a trophic affect on WAT. The exact nature of the SNS innervation of WAT is not known but it may involve contact with adipocytes and/or their associated vasculature. We hypothesize that the SNS innervation of WAT is an important contributor to the apparent "regulation" of total body fat.

Participation of the autonomic nervous system in lipolysis induced by intraventricular injection of carbachol in the pigeon

The possible involvement of central cholinergic neurotransmission in lipomobilization in avian species was investigated by injecting carbachol into the brain lateral ventricle (i.c.v.) of conscious pigeons (N = 9 per experimental group). I.c.v. injections of carbachol (27 nmol in 1 microliter) induced an intense increase (nearly 91% above baseline levels) in the concentration of plasma free fatty acids (FFA). Previous intraperitoneal administration of hexamethonium (10 mg/kg) completely blocked the lipomobilizing effect of i.c.v. injections of carbachol. These results suggest that cholinergic neurons may be involved in central mechanisms controlling FFA mobilization in pigeons, and that this response is mainly mediated by activation of autonomic nervous system.

Results of stimulation and destruction of the posterior hypothalamus in man

✓ Autonomic and somatomotor responses to electrical stimulation of the posterior hypothalamus are reported in 51 patients with pathologically aggressive behavior. The stimulated area causing rise in blood pressure, tachycardia, and maximal pupillary dilatation lies in the posteromedial hypothalamus, more than 1 mm and less than 5 mm lateral to the lateral wall of the third ventricle, occupying a triangle formed by the midpoint of the intercommissural line, the rostral end of the aqueduct, and the anterior border of the mammillary body. Electrical stimulation of this (ergotropic) triangle resulted in desynchronization of the electroencephalogram (EEG) with hippocampal theta waves, or diffuse irregular delta waves of high voltage.

Cases with violent behavior showed higher plasma levels of non-esterified fatty acids (NEFA) in the fasting stage; these were markedly elevated by electrical stimulation of the ergotropic triangle.

Points in the ergotropic triangle where signs of sympathetic discharge were most marked were electrocauterized bilaterally. This procedure produced marked calming effects (95% of the cases) during the follow-up period of more than 2 years. Postoperatively there was a tendency to a decrease in sympathicotonia or an increase in parasympathicotonia. The follow-up plasma level of NEFA was found to have decreased to approximately the normal value.

Blood flow, oxygen consumption, and free fatty acid release in subcutaneous adipose tissue during hemorrhagic shock in control and phenoxybenzamine-treated dogs

Dogs were anesthetized with α-D (+)-glucochloralose. After bleeding to a mean arterial pressure of 55 mm Hg, blood flow in subcutaneous adipose tissue decreased from 6 ± 0.9 (mean ± SE) to 0.6 ± 0.21 ml/min/100 g (P < 0.001), and remained at that low level during bleeding to 35 mm Hg for an additional 90-minute period. In five out of nine experiments the blood flow ceased completely. Sixty minutes after reinfusion, the blood flow was significantly lower than control, and in two there was no blood flow after reinfusion. In animals previously treated with phenoxybenzamine (5 mg/kg), the decrease in blood flow was significant only at 35 mm Hg arterial pressure (2.6 ± 0.67 ml/min/100 g). After reinfusion blood flow increased to a mean above 10 ml/min/100 g, significantly higher than resting blood flow (P < 0.05). There was no significant change in arterial FFA concentration or FFA release in subcutaneous adipose tissue during bleeding and after reinfusion. In phenoxybenzamine-treated animals there was a tendency to have higher arterial FFA concentration and FFA release. The oxygen uptake fell from 0.47 ± 0.07 to 0.13 ± 0.05 ml/min/100 g (P<0.01) during 55 mm Hg arterial pressure and remained significantly lower also during 35 mm Hg arterial pressure. Previous treatment with phenoxybenzamine prevented a fall in O 2 uptake in subcutaneous adipose tissue. The decrease in blood flow in subcutaneous adipose tissue during bleeding was more pronounced than found in other organs with same hemorrhagic shock procedure. After reinfusion, flow in subcutaneous adipose tissue could not be restored, indicating irreversible vascular damage, α-receptor activity seems to play a significant part in the development of vascular and metabolic changes in subcutaneous adipose tissue during bleeding.