Gerard P. Smith

Cholecystokinin elicits Satiety in Rats with Open Gastric Fistulas

WITHIN 10 min of starting to eat, a rat stops eating1, grooms for a short period, then usually sleeps. We define this behavioural sequence as satiety: its physiological basis is unknown. Beaumont2 presented the first evidence that the presence of food in the gut is important in generating satiety signals. In 1949, Janowitz and Grossman3 confirmed Pavlovs observation4 that oesophagostomized dogs, in which no food reached the stomach or intestines, ate prolonged meals.

Analysis of the microstructure of the rhythmic tongue movements of rats ingesting maltose and sucrose solutions.

The interlick interval distribution of rats while ingesting maltose under real and sham feeding conditions and while ingesting seven concentrations of sucrose under real feeding conditions was analyzed. The analysis revealed that the licking behavior of rats is organized into bursts of licking at a high rate. These bursts occurred in clusters that were separated by brief (250-500 ms) interruptions. The clusters were separated by intervals that ranged from 500 ms to many hundreds of seconds. Sham feeding increased the length of the meal by increasing the number but not the size of the clusters. Increasing the concentration of sucrose increased monotonically the size of the clusters but varied the number of clusters as an inverted-V-shaped function. This analysis revealed the details of the central nervous systems control over ingestive behavior.

Mesolimbicocortical dopamine terminal fields are necessary for normal locomotor and investigatory exploration in rats

Rats explore a novel open field or novel object less after denervation of mesolimbicocortical dopaminergic terminal fields produced by bilateral 6-hydroxydopamine (6-OHDA) microinjections into the anterolateral hypothalamus after pretreatment with desmethylimipramine (DMI). These behavioral deficits were correlated with complete or nearly complete loss of fluorescent dopaminergic (DA) terminals in the nucleus accumbens, olfactory tubercle, dorsal bed nucleus of the stria terminalis, lateral septal nucleus and the deep layers of the frontal and piriform cortices. There were also fewer A10, medial A9, and A8 DA fluorescent cells after the 6-OHDA-DMI injections; this suggests retrograde degeneration of the cells of origin of the mesolimbicocortical DA system. When the DMI pretreatment was omitted, identical bilateral 6-OHDA microinjections also produced severe loss of norepinephrine (NE) fibers in the neocortex, hippocampus, lateral hypothalamus and ventral bed nucleus of the stria terminalis. The addition of this noradrenergic damage did not change the exploratory deficits observed after mesolimbicocortical DA denervation alone. Systemic administration of the DA agonist apomorphine, but not the adrenergic agonist clonidine, to the 6-OHDA-DMI rats repaired the deficits in exploration of a novel open field or novel object. The increased locomotion in a novel open field and investigation of a novel object produced by apomorphine in 6-OHDA-DMI rats were blocked by the DA antagonist, pimozide. This is evidence that apomorphine restored exploratory responses by stimulating dopaminergic receptors. The exploratory responses produced by apomorphine were also blocked by testing rats in a familiar open field or with a familiar novel object. This is evidence that apomorphine facilitates exploratory responding to novel stimuli by 6-OHDA-DMI rats, but that the same dose of apomorphine does not increase activity when 6-OHDA-DMI rats are confronted by familiar stimuli. We conclude: (1) that mesolimbicocortical dopaminergic terminals are necessary for normal exploratory behavior in rats; and (2) that DA released by these terminals may facilitate optimal sensorimotor integration in these terminal fields during spontaneous exploratory behavior.

The direct and indirect controls of meal size

Meal size is a major determinant of energy intake and an important phenotype in animal models of obesity and in human eating disorders. Successful analysis of the controls of meal size is a fundamental goal of the science of ingestion. This paper proposes a new classification of the controls of meal size based on an unambiguous physical criterion. The criterion is food stimuli contacting preabsorptive receptors along the surface of the gut from the tip of the tongue to the end of the small intestine. Direct controls depend upon such contact. Indirect controls, e.g., rhythmic metabolic, cognitive, etc., do not have such contact. Instead, indirect controls change meal size by modulating the potency of direct controls. A method of measuring the potency of direct and indirect controls is described. The classification is unambiguous, comprehensive, and explicates the functional relationship between indirect and direct controls. Because the method of measurement is quantitative, this classification is heuristic foe mechanistic research and provides a common theoretical framework for diverse investigators interested in different aspects of the controls of eating and meal size.

Transport of cholecystokinin (CCK) binding sites in subdiaphragmatic vagal branches

In order to evaluate vagal cholecystokinin (CCK) binding sites as potential target sites for the satiety actions of CCK, their presence, axonal flow and pharmacological specificity in subdiaphragmatic vagal branches were examined by autoradiography utilizing 125I-Bolton Hunter CCK-33. Specific CCK binding and axonal transport were found in vagal trunks and all abdominal vagal branches. Binding was inhibited by unlabelled CCK-8, but not by desulfated CCK-8. The pharmacological specificity and transport of CCK binding sites to subdiaphragmatic branches indicate a potential role in mediating CCKs satiety effect.

The controls of eating: a shift from nutritional homeostasis to behavioral neuroscience

The experimental analysis of the controls of eating has undergone a paradigmatic shift in the past decade. Instead of seeing meals as a problem of how intake serves metabolism and nutritional homeostasis, meals are now seen as a problem in behavioral neuroscience. The major developments underlying this significant change are behavioral, neurological, and theoretical. Behavioral analysis has shown that a central pattern generator in the caudal brainstem organizes eating movements and that the size of a liquid meal is determined by the number and size of clusters of licking. Neurologic analysis has shown that eating is under orosensory positive-feedback control and postingestive, preabsorptive, negative-feedback control. These feedback controls are activated by food ingested during a meal. The sensory information of the feedbacks is carried by afferent fibers that project to the caudal brainstem. The new theory is based on the fact that the feedback controls are stimulated by food acting directly on mucosal receptors along the gastrointestinal tract, from the mouth to the end of the small intestine. Thus, they are referred to as direct controls, and the caudal brainstem is sufficient for organizing their action. All other controls, such as metabolic, rhythmic, and ecologic, that do not contact the mucosal receptors are indirect controls. Indirect controls act by modulating the potency of the central effects of the direct controls, and they require the forebrain and its reciprocal connections with the caudal brainstem for their control of eating and meal size.

Characterization of type A and type B CCK receptor binding sites in rat vagus nerve

We employed quantitative receptor autoradiography to analyze pharmacological properties of 125I-Bolton Hunter cholecystokinin (CCK-8)-labeled binding sites in sections of rat cervical vagus nerve that had been ligated 24 h prior to extraction. Binding densities were detected in segments of nerve proximal and distal to the ligature. Analysis was confined to proximal segments. Saturation and competitive binding studies were carried out using sulphated CCK-8 and two selective CCK receptor antagonists: MK-329, to define type-A (CCKA) binding sites; and, L-365,260, to define type-B (CCKB) binding sites. Sulphated CCK-8 was the most potent inhibitor of vagal 125I-CCK binding (IC50 = 2 nM). Nonlinear curve fitting analysis of the CCK binding data favored the presence of a single class of vagal CCK receptors (KDi = 1 nM). However, both MK-329 (IC50 = 18 nM) and L-365,260 (IC50 = 45 nM) competed for vagal 125I-CCK binding indicating the presence of CCKA and CCKB binding sites. Co-analysis of the antagonist binding data suggested that CCKA and CCKB receptors were transported in equal concentrations within the vagus. MK-329 bound with high affinity to CCKA sites (Ki = 3 nM) and low-affinity to CCKB sites (Ki = 462 nM) while L-365,260 bound with high affinity to CCKB sites (Ki = 10 nM) and low-affinity to CCKA sites (Ki = 775 nM). These same ligands were used to characterize the specificity of 125I-CCK binding in the medial and lateral divisions of the nucleus of the solitary tract (NTS), two regions innervated by primary vagal afferents carrying CCK receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Satiating Effect of Cholecystokinina

In 1937, MacLaganl reported that a duodenal extract obtained from Lim inhibited food intake in rabbits. The inhibitory effect was achieved after subcutaneous or intravenous administration and lasted 1 hour. This extract was obtained after the duodenum had been exposed to olive oil. Kosaka and Lim2 had named the active principle in the extract enterogastrone, because it inhibited gastric acid secretion. Because Kosaka and Lim2 found that another extract (gift of A. C. Ivy) that had cholecystokinetic activity also inhibited gastric acid secretion under their conditions, it is probable that they thought their preparation of enterogastrone also had cholecystokinetic activity. (See Gregory3 for discussion of the history of enterogastrone preparations.) MacLagans observation was not followed up until 1960 when Ugoleg reported that extracts of rat duodenum decreased food intake in mildly deprived rats. This effect was limited to the first 30 minutes after intraperitoneal administration. Ugolevs extract was specific in the sense that similarly prepared extracts of stomach and spleen did not inhibit intake. It was the purification of cholecystokinin (CCK) from duodenal and upper jejunal porcine extracts by Jorpes et aL5 and the synthesis of the carboxy-terminal octapeptide of CCK (CCK-8) by Ondetti et al.,6 however, that made the modern attack on the problem of the satiating effect of CCK possible. This began with the 1973 paper of Gibbs el aL7 which showed that intraperitoneal administration of an impure extract of cholecystokinin, synthetic CCK-8, or ceruletide (an amphibian peptide of similar structure and with potent cholecystokinetic activity) produced inhibition of food intake in rats. The effect was dose-related and lasted 15-30 minutes. The effect was behaviorally specific because doses that inhibited food intake in food-deprived rats did not inhibit water intake in water-deprived rats. Furthermore, there were no signs of toxicity. Because the inhibitory effect was apparently specific and did not occur in the initial phase of the test meals, we interpreted the inhibition of food intake as a satiating effect of CCK and hypothesized that endogenous CCK released by ingested nutrients entering the duodenum and upper jejunum during a meal participated in the satiating process that terminated eating. In this review, we describe the current status of the hypothesis and indicate the important problems associated with it that require further investigation.

Effects of peripheral and central bombesin on feeding behavior of rats

Intraperitoneal injections of tetradecapeptide bombesin (BBS) produced large, dose-related suppressions of liquid and solid food intake in rats, with threshold doses of 1--2 micrograms-kg-1. The feeding-associated behaviors of rats receiving BBS by this route at a test meal were normally sequenced, and several other observations suggested that the effect of BBS was specific and not due to malaise. The structurally related amphibian peptide litorin and the structurally related mammalian gastrin-releasing peptide (GRP) produced similar suppressions of food intake. The satiety effect of BBS administered intraperitoneally did not require the accumulation of food in the gut, the presence of intact adrenals, the abdominal vagus, or the release of cholecystokinin. When BBS and cholecystokinin were administered simultaneous, the suppressive effects on food intake were additive. Lateral cerebroventricular injections of BBS also produced large, dose-related suppressions of food intake, with a threshold dose of 100 ng per rat. The effect by this route, however, was not behaviorally specific: BBS produced equivalent inhibitions of food and water intake at every point on the dose-response curve, and produced a marked increase in grooming which dominated the behavioral display. Thus, (1) peripheral BBS is a putative satiety signal in the rat; (2) the class (endocrine, paracrine, or neural) and mechanism of this satiety action is not established; and (3) the differences in specificity and behavior following intraperitoneal and cerebroventricular routes indicate that peripheral BBS does not act solely via the cerebrospinal fluid to elicity satiety.

Behavioral effects of bombesin administration in rats

Bombesin (BBS, 0.1-4.0 micrograms) administered to the lateral cerebral ventricle (IVT) of rats decreased food intake and feeding behavior. Grooming behavior increased and resting behavior decreased as doses greater than or equal to 0.01 microgram. IVT BBS (4.0 micrograms) caused greater suppression of food-deprivation-induced food intake and feeding behavior than the same dose and volume administered intraperitoneally (IP). After IVT BBS, rats displayed more grooming and less resting than normal, but after IP BBS, rats displayed a normal frequency of grooming and more resting. IVT BBS (greater than or equal to 0.01 microgram) also decreased drinking behavior, and drinking-associated feeding, and suppressed (greater than or equal to 0.1 microgram) water-deprivation-induced water intake. When neither food nor water was present, non-deprived rats displayed increased grooming and decreased resting after IVT BBS (1.0 microgram). The results show that IVT BBS inhibits feeding markedly, but the inhibition of feeding by IVT BBS does not resemble normal satiety or the effect of IP BBS because the central inhibition of feeding is always accompanied by excessive grooming and little resting. Furthermore, since IVT BBS decreases drinking at a dose lower than that required to reduce food intake, and IP BBS does not, the specific satiety effect of IP BBS on feeding cannot be mediated solely by increasing bombesin in the cerebrospinal fluid.