Effects of intracerebroventricularly administered leptin on protein selection in the rat.

The effect of centrally administered rat leptin on selection of 5 and 30% protein diets was investigated in male Sprague-Dawley rats with indwelling i.c.v. cannulas. Leptin (0 vs 2.5 microg/day) was administered for 4 consecutive days, followed by an 8-day withdrawal period. Total intake was reduced to approximately 50% of that in the vehicle injected group during each day following leptin administration. Intake of both the 5 and 30% diets was reduced. Vehicle-treated rats selected a 13-15% CP diet. Diet selection in leptin-treated rats was not different during the first day, but on Days 2-4, leptin-treated rats selected a 10% CP diet. Intake began to normalize within 24-48 h after the last treatment, and was not different by Day 3 of the withdrawal period. Body weight was reduced by leptin treatment, and despite the normalization of food intake, did not recover during the withdrawal period. Rats were sacrificed at the end of the 8-day withdrawal period. Despite the reduction in body and carcass weights, liver, kidney, heart, and soleus muscle weights were not different between control and leptin-treated groups when expressed on an absolute or relative basis. However, epididymal and retroperitoneal fat pad weights were still reduced 56 and 78%, respectively, in rats that had been previously treated with leptin for 4 days and then not treated for 8 days. In addition, circulating T3 levels remained elevated in rats that had been treated with leptin. Centrally administered leptin has little effect on muscle mass, but had potent effects on intake of nonobese rats and a sustained effect on adipose tissue mass, thyroid hormone status, and body weight after withdrawal. Results from rats selecting between diets varying in protein content suggest that leptin may cause avoidance of protein.

Metabolic responses to intracerebroventricular leptin and restricted feeding.

Leptin is a hormone secreted by adipocytes, which plays an important role in the control of food intake and metabolic processes. In the current study, a dose-dependent relationship was shown between a bolus intracerebroventricular rat recombinant leptin administration and reductions in food intake and body weight in Sprague-Dawley rats. During the 24 h postinjection period, food intake was decreased by 24, 26, and 52% with 0.625, 2.5, and 10 microg of leptin, respectively. Body weight was reduced by 2, 3, and 5% at 24 h after leptin administration at the doses of 0.156, 2.5, and 10 microg, respectively. Furthermore, indirect calorimetry demonstrated that five daily i.c.v. injections of leptin resulted in an increase in heat production per unit of metabolic body size and fat oxidation by approximately 10 and 48%, respectively. In contrast, food-restricted rats that consumed the equivalent amount of food as leptin-treated rats for 5 days decreased their energy expenditure by 10%. Food restriction was found to decrease respiratory quotient in a similar pattern as the leptin administration. When ad lib feeding was resumed, food-restricted rats quickly recovered their normal food intakes, body weights, and metabolism. Conversely, leptin treatment has prolonged effects on body weight resulting from different metabolic responses than food restriction. Leptin not only suppresses food intake, but also enhances energy expenditure to reduce fat depots.

Intracerebroventricular administration of antisense oligodeoxynucleotide against GLUT2 glucose transporter mRNA reduces food intake, body weight change and glucoprivic feeding response in rats.

The GLUT2 glucose transporter, which may play a glucose-sensing role in hepatocyte and islet beta cells because of its low affinity and high Km for glucose, has been identified in some discrete brain areas that are related to feeding behavior and energy metabolism. We tested the hypothesis that brain GLUT2 may play a role in the control of food intake by antisense technology loss-of-function analysis. Antisense oligonucleotides directed against GLUT2 mRNA were administered intracerebroventricularly to eight rats daily for 13 days. Another eight rats were administered intracerebroventricularly with missense oligonucleotides as the control. Food intake was monitored by a computerized feeding system. Data were analyzed using a one-way general linear model or Mann-Whitney U test when appropriate. Cumulative food intake and body weight change in antisense-treated rats were significantly lower (18 and 160%, respectively) in the group treated with antisense oligonucleotides than in the group treated with missense control oligonucleotides. There was no increase in cumulative food intake in response to 2-deoxyglucose challenge in rats treated with antisense oligonucleotide, but in those treated with missense control oligonucleotide, cumulative food intake was fivefold greater in response to 2-deoxyglucose. These data suggest a possible role of brain GLUT2 in the regulation of food intake and body energy stores.

Intracerebroventricular (i.c.v.) administration of mouse leptin in rats: behavioral specificity and effects on meal patterns.

Leptin is a protein that is produced primarily in fat tissue and is thought to be a lipostatic feedback signal for the regulation of body fat stores. The purpose of this study was to determine the behavioral specificity of i.c.v.-administered mouse leptin in rats and to assess the effects on meal patterns. Using a modified two-bottle paradigm we examined the putative aversive response to i.c.v. doses of 1, 5, 7, 10, and 30 microg of mouse leptin. Artificial CSF and intraperitoneal lithium chloride served as negative and positive controls, respectively. Saccharin consumption in all leptin treatments was not significantly different from the negative control. Following a recovery period, rats from the same group were used to assess the effects of a 30-microg i.c.v. dose on cumulative food intake and meal patterns using a computer-based system for acquisition of feeding data. Leptin (i.c.v.) significantly increased intermeal interval and decreased meal size. We, therefore, conclude that mouse leptin, at doses up to 30 microg i.c.v., is not aversive in the rat, and that leptin has a multiphasic effect on meal patterns.

ICV administration of anti-NPY antisense oligonucleotide: effects on feeding behavior, body weight, peptide content and peptide release.

Neuropeptide-Y (NPY) is a potent stimulator of feeding, and chronic administration of the peptide has been shown to increase body weight. This study determined the chronic effects of repeated daily injections of an antisense phosphorothioate oligonucleotide complementary to the rat mRNA for NPY (aNPY) on food intake, feeding behavior and body weight change in rats. Five micrograms of the aNPY oligonucleotide in ten microliters of vehicle or a missense control oligonucleotide were administered intracerebroventricularly (ICV) for seven consecutive days. Cumulative food intake, meal size and meal duration were significantly lowered in aNPY-treated animals. Body weight change of aNPY-injected animals was significantly lower than controls, and the effect was reversed after treatments ceased. A two-bottle taste aversion paradigm was employed to determine the behavioral specificity of the anorectic effect, and the phosphorothioate oligonucleotide was found not to be aversive at the dosage used. Following an additional five day injection period, animals were killed and paraventricular nuclei (PVN) were dissected. In vitro release and tissue content of NPY from this brain area were evaluated by heterologous radioimmunoassay. Content of NPY was unchanged in this brain area. Paradoxically, in vitro release of NPY was increased in aNPY-treated animals.

ICV administration of anti-corticotropin-releasing factor antisense oligonucleotide: effects on feeding behavior and body weight.

Corticotropin-releasing factor (CRF) has been reported to reduce food intake and body weight, and numerous studies suggest a role for CRF in putative mechanisms for the regulation of body energy. This study investigated the effects of ICV-administered antisense phosphorothioate oligonucleotides, directed against the CRF mRNA, on feeding behavior and body weight in rats. Sixteen male HSD rats were cannulated in the lateral ventricle, and given ad libitum access to tap water and a ground chow diet. Feeding behavior was recorded by computer, and meal patterns were assessed. Rats were given 3 micrograms each of two anti-CRF oligonucleotides (aCRF) or two control oligos in the hour before the onset of the nocturnal cycle for ten consecutive days. Cumulative food intake was assessed at 3, 6, 12 and 24 h after each injection, as well as over the 10-day injection period. Compared to missense controls, rats receiving the antisense oligonucleotides ate significantly more at 6 h (P = 0.01), but not at 3, 12, 24 h, or during the entire 10-day injection period (P > 0.05). There was no effect on body weight change, meal size, or meal interval (P > 0.05). These data indicate that daily administration of anti-CRF oligonucleotides has a significant short-term stimulatory effect on feeding behavior, but does not have a long-term effect on feeding or body weight gain.

From genotype to phenotype: computer-based modeling of gene expression with STELLA II.

STELLA II is a microcomputer program that is designed to simulate and animate the dynamics generated by biological systems in a quantitative fashion. The program employs the Macintosh user interface and includes a tool kit for assembling models, plus menus for setting parameters and selecting input or output. Quantitative relationships among components may be expressed with user-defined equations, graphical functions or data from spreadsheets. System dynamics are simulated by running the program after defining initial conditions, and results may be viewed immediately using windows for graphical or tabular plots. The present article describes how STELLA II may be used to simulate gene expression as an adjunct to experimentation or student-directed learning.

An anorectic agent from adipose tissue of overfed rats: effects on feeding behavior.

Parabiosis and blood-transfer studies with rodents suggest the existence of humoral factors capable of affecting energy balance. The nature and origin of these factors is undetermined. Aqueous extracts of adipose tissue from overfed rats significantly reduce food intake when administered intraperitoneally (IP) or intracerebroventricularly (ICV). We term the agent(s) responsible for this effect adipose satiety factor (ASF). A single IP dose of ASF, equivalent to 44 mg crude protein, suppresses cumulative food intake for over 12 h. ASF, prepared using a combination of adipose tissue from obese Zucker rats and overfed rats, is more potent per unit of protein than ASF prepared exclusively using adipose tissue from overfed rats. A single ICV dose of this hybrid preparation, equivalent to 14.6 micrograms of crude protein, suppresses cumulative food intake by 40% for up to 48 h. By ultrafiltration, the molecular weight associated with maximal ASF activity is between 30 and 100 kilodaltons (kDa). The behavioral specificity of ASF-induced anorexia is demonstrated using meal pattern, taste aversion, and differential starvation paradigms.

The kinetics of mammalian gene expression.

When rates of transcription from specific genes change, delays of variable length intervene before the corresponding mRNAs and proteins attain new levels. For most mammalian genes, the time required to complete transcription, processing, and transport of mRNA is much shorter than the period needed to achieve a new, steady-state level of protein. Studies of inducible genes have shown that the period required to attain new levels of individual mRNAs and proteins is related to their unique half-lives. The basis for this is a physical principle that predicts rates of accumulation of particles in compartmental systems. The minimum period required to achieve a new level is directly proportional to product half-lives because rates of decay control the ratio between the rate of synthesis and the concentration of gene products at steady state. This kinetic model suggests that sensitivity of gene products to degradation by ribonucleases and proteinases is an important determinant of the time scale of gene expression.

A system for automated recording and analysis of feeding behavior.

We have designed and implemented a system that utilizes a network of top-loading balances digitally interfaced to a Macintosh computer. The system simultaneously collects two forms of data which allow the evaluation of the animal's biting and/or licking behavior in addition to cumulative food intake and meal patterns. The system is capable of resuming data acquisition following a power failure without user intervention. Plexiglas cages utilized with the system features adjustable tunnel feeders and are appropriate for use with small rodents. Given appropriate caging, the system may be utilized to evaluate the feeding behavior of other species.

A computer program for modeling the kinetics of gene expression.

Enzyme induction may be modeled on the basis of four, quantifiable processes that control the rates at which specific gene products accumulate and decay. These processes include synthesis of functional mRNA, translation and degradation of mRNA, and degradation of the protein product. We present a simple computer program that permits mathematical simulation of gene expression on the basis of experimentally determined rates of synthesis and degradation. The program was implemented as a spreadsheet using Microsoft Excel for Macintosh and MS-DOS operating systems and also was adapted for HyperCard on the Macintosh. It contains a formula to account for growth of tissue or cell populations. The program predicts amounts of individual mRNAs and proteins (or enzyme activities) in cells as a function of time after a stimulus alters their rates of synthesis or degradation.