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Rats were trained to respond under a cyclic-ratio schedule of reinforcement composed of an ascending, followed by a descending, sequence of ratio values. Subjects were trained while exposed to 70 dB white noise, then tested while exposed to 70 or 90 dB white noise. Exposure to 90 dB white noise elevated the response function (p < .02). Naloxone was then administered intraperitoneally at 0.3, 1.0, and 3.0 mg/kg under 70 dB and 90 dB white noise. Naloxone administration (1.0 and 3.0 mg/kg) significantly depressed the response function obtained under 90 dB white noise (ps < .01) but did not affect the function obtained under 70 dB white noise. These findings suggest that mild stress increases food intake through a mechanism affecting palatability enhanced by the release of endogenous opioids.

We have used a simian virus 40 (SV40)‐based shuttle vector, pZ189, to analyze the sequence specificity of spontaneous point mutations that arise after transfection of this vector into monkey cells. The majority of the mutants which we studied had multiple base substitutions (mostly G‐C‐‐‐‐A‐T transitions and G‐C‐‐‐‐T‐A transversions) within the 160‐bp region sequenced. Almost all of the mutations occurred in the right‐hand G‐C bp of one of the two following sequences, 5′‐TC‐3′:3′‐AG‐5′ or 5′‐CC‐3′:3′‐GG‐5′. We postulate that these mutations result from DNA replication infidelity occurring during repair of the transfected DNA which has been damaged by cellular nucleases. The sequence specificity of the mutations suggests an effect of the following nucleotide on misincorporation wherein A (or less frequently T) is preferentially misincorporated opposite C when the next nucleotide inserted is A (or less frequently G). Our results support the utility of the shuttle vector as a model in studies on gene transfer and document the extreme plasticity of DNA transfected into mammalian cells.

We have examined the effect on feeding of opioid blockade with naloxone in two species which demonstrate a marked seasonality in their feeding patterns, the racoon (Procyon lotor)and the woodchuck (Marmota monax). Naloxone suppressed food intake in the woodchuck which is a true hibernator. Naloxone failed to suppress food intake in the racoon and, in fact, enhanced intake of a preferred sucrose solution. In the racoon, ir-dynorphine concentrations were extremely high in the hypothalamus compared to the values obtained in rats and woodchucks. We suggest that possible explanations for the lack of responsiveness to opiates in racoons may be (1) their extremely high daily food intake relatively to body mass when compared to woodchucks and rats and (2) the high levels of ir-dynorphin may be sufficient to overcome the inhibitory effect of naloxone. These studies stress the occurrence of species diversity in the response to opioid antagonism.

Malabsorption of fermentable material in a variety of foods was assessed by measurement of breath H2excretion. Breath H2increased well above that observed in fasting subjects after ingestion of 100 g of carbohydrate in oats, whole wheat, potatoes, corn, and baked beans. Rice caused only a minimal increase in H2excretion and hamburger was associated with no increase. We estimated the malabsorption of fermentable material by comparing the H2excretion for 9 h after ingestion of various complex carbohydrates with that after 10 g of lactulose. The mean malabsorption of fermented material after 100-g carbohydrate meals was 20 g for baked beans; 7–10 g for wheat, oats, potatoes, and corn; and 0.9 g for rice. Whole oats or whole wheat resulted in 2–5 times more H2than did the refined flours. As purified fiber appeared to be a poor substrate for H2production by fecal homogenates, we conclude that most complex carbohydrates, with the exception of rice, contain a good deal of fermentable material that escapes small bowel absorption and it seems likely that this fermentable material is malabsorbed starch.

Opiate systems in the brain are thought to play a major, though not exclusive, role in the regulation of intake. The rough correspondence of feeding and pineal activity rhythms in the rat offers the possibility that the pineal may also modulate ingestive behavior. In these studies we measured the possibility that pineal manipulations would influence feeding responses to opiate agonists and the antagonist naloxone. Male rats received one of four treatments (or a corresponding control treatment): pinealectomy, removal of the superior cervical ganglia (SCG), transection of the optic nerves or chronic melatonin treatment (1 mg/kg daily). Pinealectomy and melatonin treatment reduced intake during the first half of the dark period, and removal of the SCG reduced intake during the second half of the light period. The most striking effect was seen after optic nerve transection, which reduced nocturnal and increased diurnal intake. Pinealectomy, but no other manipulation, caused a slight decrease in sensitivity to the inhibitory effects of naloxone on intake. None of the treatments affected daytime feeding responses to morphine, ketocyclazocine, or butorphanol. These results suggest that the pineal gland has a minimal role in modulating the opioid regulation of food intake.

The control of ingestive behavior involves a variety of neurotransmitters, including monoamines, peptides and amino acids. For the past decade many investigators have focused their research on the role that regulatory peptides play in eating behavior. Many peptides, including cholecystokinin, bombesin, calcitonin, corticotropin-releasing factor, neurotensin and somatostatin, have been reported to decrease the amount of food ingested by laboratory animals. In contrast, a relatively small number of peptides increase food intake. The present review describes the effects of these peptides on consummatory behaviors in various species and their sites of action.