c-Fos Expression In Area Postrema Research Articles

The role of autonomic pathways in peripheral apelin-induced gastrointestinal dysmotility: involvement of the circumventricular organs.

What is the central question of this study? Are central autonomic pathways and circumventricular organs involved in apelin-induced inhibition of gut motility? What is the main finding and its importance? Peripherally administered apelin-13 inhibits gastric and colonic motor functions through sympathetic and parasympathetic autonomic pathways, which seems to be partly mediated by the apelin receptor in circumventricular organs. Peripheral administration of apelin-13 has been shown to inhibit gastrointestinal (GI) motility, but the relevant mechanisms are incompletely understood. This study aimed to investigate (i) whether the apelin receptor (APJ) is expressed in circumventricular structures involved in autonomic functions, (ii) whether they are activated by peripherally administered apelin, (iii) the role of autonomic pathways in peripheral exogenous apelin-induced GI dysmotility, and (iv) the changes in apelin levels in the extracellular environment of the brain following its peripheral application. Ninety minutes after apelin-13 administration (300μgkg-1 , i.p.), gastric emptying (GE) and colon transit (CT) were measured in rats that underwent parasympathectomy and/or sympathectomy. Plasma and cerebrospinal fluid (CSF) samples were also collected from another group of rats that received apelin-13 or vehicle injection. The immunoreactivities for APJ and c-Fos in circumventricular organs (CVOs) were evaluated by immunohistochemistry. Compared with vehicle-treated rats, GE and CT were inhibited significantly by apelin-13 treatment, and were completely restored in animals that underwent the combination of parasympathectomy and sympathectomy and sympathectomy alone, respectively. Apelin concentrations were elevated in both plasma and CSF following peripheral administration of apelin-13. APJ expression was detected in area postrema (AP), subfornical organ and organum vasculosum of lamina terminalis, and c-Fos expression was observed in response to apelin injection. Apelin-induced c-Fos expression in AP was partially attenuated by pretreatment with the cholecystokinin-1 receptor antagonist lorglumide, whereas it was completely abolished in vagotomized rats. The present data suggest that APJ in CVOs could indirectly contribute to the inhibitory action of peripheral apelin on GI motor functions.

Effect of electroacupuncture of "biaoben acupoint combination" on central sensitivity of cholecystokinin in obese rats with insulin resistance

To observe the effect of electroacupuncture (EA) of "biaoben acupoint combination" on appetite, body fat, insulin sensitivity and central sensitivity of cholecystokinin (CCK) in obese rats with insulin resistance (IR), and to explore the mechanism of EA on improving obesity with insulin resistance. Among the fifty 8-week-old healthy SPF male Wistar rats, 10 rats were randomly selected and fed with normal diet; after 8 weeks, 8 rats were randomly selected as a normal group. The remaining 40 rats were fed with high-fat diet to establish the model of obsesity IR; after 8 weeks, 24 rats with successful model of obsesity IR were randomly divided into a model group, an EA group and a sham EA group, 8 rats in each group. Eight weeks after model establishment, the rats in the EA group were intervened with EA at "Fenglong" (ST 40), "Zhongwan" (CV 12), "Guanyuan" (CV 4) and "Zusanli" (ST 36), with continuous wave, in frequency of 2 Hz, and current intensity of 1 mA, for 10 min each time. The rats in the sham EA group were intervened with EA at the points 5 mm next to the acupoints used in the EA group and no electricity was given; the sham EA was given for 10 min each time. Both the treatments were given once every other day for 8 weeks. The Lee's index and food intake were observed before the intervention as well as 2 weeks, 4 weeks, 6 weeks and 8 weeks into intervention; after the intervention, serum insulin (INS) and glucose infusion rate (GIR) were detected; serum cholecystokinin (CCK) level was detected by ELISA; c-fos expression in the area postrema (AP) and nucleus tractus solitarius (NTS) of medulla oblongata was detected by immunohistochemistry. Before the intervention as well as 2 weeks, 4 weeks, 6 weeks and 8 weeks into intervention, the Lee's index and food intake in the model group were higher than those in normal group (P<0.01). The Lee's index (6 weeks and 8 weeks into intervention) and food intake (4 weeks, 6 weeks and 8 weeks into intervention) in the EA group were lower than those in the model group and the sham EA group (P<0.05, P<0.01). After intervention, compared with the normal group, serum level of INS was increased (P<0.01), while GIR, serum CCK level, c-fos expression in AP and NTS in the model group were decreased (P<0.01, P<0.05). Compared with the model group and the sham EA group, serum level of INS in the EA group was decreased (P<0.01), and GIR, serum CCK level, c-fos expression in AP and NTS were increased (P<0.01, P<0.05). EA of "biaoben acupoint combination" could effectively reduce appetite, body fat and enhance insulin sensitivity in obese rats with IR. The mechanism may be related to the regulation of central sensitivity of CCK.

The pattern of c-Fos immunoreactivity in the hindbrain of the rat following stomach distension.

It has been previously shown that the walls of the stomach contain vagal and splanchnic afferents, connected to low and high threshold (LT and HT) gastric receptors, that convey physiological and noxious information to areas of the hindbrain involved mainly in the control of gastrointestinal function. Because distension of the stomach also reflexly increases the sympathetic drive to the cardiovascular system, the present study was planned to examine the pattern of activation of all nuclei encountered throughout the hindbrain in response to gastric distension. In anaesthetized rats, the stimulus was controlled by employing different transmural pressures and frequencies of distension, and c-Fos immunohistochemistry was used to characterize neuronal activation. Low intensity stimulation induced c-Fos expression in the cranial part of nucleus of solitary tract (NTS), the nucleus ambiguus (NA), the lateral reticular area (LRt) and the ventrolateral medulla (RVL/CVL). At low frequency of stimulation c-Fos positive nuclei (p.n.) were found in NTS only. At high frequency of stimulation an increase in c-Fos immunoreactivity was found. High intensity stimulation induced c-Fos expression in area postrema (AP), the lateral vestibular nucleus (LVe) and the caudal part of the NTS. At low frequency, only the number of c-Fos p.n. was increased. Increasing the frequency of stimulation induced c-Fos expression in further nuclei such as the parabrachial nucleus (PBN), the inferior olive subnuclei (IOn), the oral part of spinal trigeminal nucleus (Sp5O) and locus coeruleus (LC). At higher frequencies c-Fos immunoreactivity decreased in NTS and LRt, disappeared in VLM and increased in NA. Thus stomach distension activated several neuronal excitatory and inhibitory circuits that are involved in the control of gastrointestinal function as well as in cardiovascular, respiratory and pain regulation. The differences in c-Fos immunoreactivity induced by changing the distension patterns suggested interactions between groups of vagal and splanchnic afferents.

The anorectic hormone amylin contributes to feeding-related changes of neuronal activity in key structures of the gut-brain axis.

Amylin is a peptide hormone that is cosecreted with insulin from the pancreas during and after food intake. Peripherally injected amylin potently inhibits feeding by acting on the area postrema (AP), a circumventricular organ lacking a functional blood-brain barrier. We recently demonstrated that AP neurons are excited by a near physiological concentration of amylin. However, the subsequent neuronal mechanisms and the relevance of endogenously released amylin for the regulation of food intake are poorly understood. Therefore, we investigated 1) amylin's contribution to feeding-induced c-Fos expression in the rat AP and its ascending projection sites, and 2) amylin's ability to reverse fasting-induced c-Fos expression in the lateral hypothalamic area (LHA). Similar to amylin (20 microg/kg sc), refeeding of 24-h food-deprived rats induced c-Fos expression in the AP, the nucleus of the solitary tract, the lateral parabrachial nucleus, and the central nucleus of the amygdala. In AP-lesioned rats, the amylin-induced c-Fos expression in each of these sites was blunted, indicating an AP-mediated activation of these structures. Pretreatment with the amylin antagonist AC-187 (1 mg/kg sc) inhibited feeding-induced c-Fos expression in the AP. Food deprivation activated LHA neurons, a response known to be associated with hunger. This effect was reversed within 2 h after refeeding and also in nonrefed animals that received amylin. In summary, our data provide the first evidence that feeding-induced amylin release activates AP neurons projecting to subsequent relay stations known to transmit meal-related signals to the forebrain. Activation of this pathway seems to coincide with an inhibition of LHA neurons.

C-Fos induction in rat brainstem in response to ethanol- and lithium chloride-induced conditioned taste aversions.

When consumption of a novel taste (conditioned stimulus; CS) is followed by exposure to a toxin, organisms will avoid consumption of that taste in the future. This learned response, known as a conditioned taste aversion (CTA), can be demonstrated using a variety of drugs, including lithium chloride (LiCl) and ethanol. c-Fos immunohistochemistry was used to examine neural activation in the rat brainstem associated with drug administration and with a CS taste previously paired with these drugs. Relative to saline controls, animals injected with either LiCl (76 mg/kg) or ethanol (3.5 g/kg) displayed greater c-Fos expression in area postrema, nucleus of the solitary tract (NTS), and lateral parabrachial nucleus. At these doses, LiCl- and ethanol-injected groups did not differ from each other. For establishing a CTA, intraoral infusion of a 0.15% saccharin solution was followed by injection of either LiCl or ethanol. Both LiCl and ethanol produced quantitatively similar CTAs. Relative to unpaired control groups, saccharin paired with either drug induced significant c-Fos expression in NTS. Thus, like LiCl, ethanol and tastes that have become aversive by virtue of their association with ethanol activate brainstem regions hypothesized to play a role in CTA learning.