Somatic and metabolic responses of mature female rats with dietary obesity to dorsomedial hypothalamic lesions: effects of diet palatability

The dorsomedial hypothalamic nucleus and its role in ingestive behavior and body weight regulation: lessons learned from lesioning studies

This review article discusses the well-established role of the dorsomedial hypothalamic nucleus (DMN) in feeding, drinking and body weight (BW) regulation. DMN lesions (L) in both weanling and mature rats of both sexes produce hypophagia, hypodipsia and reduced ponderal and linear growth in the presence of normal body composition. The growth reduction is not due to a deficient secretion of growth hormone, insulin-like growth factor-1, thyroxine, triiodothyronine or insulin. DMNL rats actively defend their lower BW (BW settling point) by becoming either hyper- or hypophagic, depending on the experimental manipulation, thereby defending both lean and fat mass. They also regulate their 24-h caloric intake, but they may overeat during the first hour of refeeding following a fast, possibly due to a reduced ability to monitor blood glucose or to respond to cholecystokinin (CCK). 2-Deoxy-D-glucose (2DG) increases c-fos expression in orexin-A neurons in the DMN, and DMNL eliminated the orexigenic effect of 2DG. DMNL rats on high-fat diets do not get as obese as controls, which may be due to a reduction of DMN neuropeptide Y (NPY). Rats lacking DMN CCK-A receptors are obese and have increased expression of NPY in the DMN, supporting earlier data that CCK may act at the DMN to suppress food intake. Excitotoxin studies showed that loss of DMN cell somata, and not fibers of passage, is important in the development of the DMNL syndrome. The DMN is a site where opioids increase food intake and knife-cut studies have shown that fibers traveling to/from the DMN are important in this response. An interaction of glucose and opioids in DMN may also be involved in the control of food intake. DMN knife cuts interrupting fibers in the posterior and ventral directions additively produce the hypophagia and reduced linear and ponderal growth observed after DMNL. Ventral cuts may interrupt important connections with the arcuate nucleus. Lateral and posterior DMN cuts additively produce the hypodipsic effect seen after DMNL, but DMNL rats respond normally to all water-regulatory challenges, i.e., the hypophagia is not due to a primary hypodipsia. The DMN has been shown to be involved in the rat's feeding response to an imbalanced amino acid diet. These data show the DMN has an important role in many processes that control both food intake and BW regulation.

Effect of palatable diet on growth, caloric intake and endocrine-metabolic profile in weanling rats with dorsomedial hypothalamic lesions

Weanling male Sprague-Dawley rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats); sham-operated rats served as controls. All animals were fed lab chow for 15 postoperative days. At that time they were subdivided into two groups each. One DMNL and one control group continued to be fed lab chow until the termination of the experiment on postoperative day 116. A second DMNL and control group were fed a high-fat diet and 32% sucrose solution (HF/SS diet). All DMNL rats showed reduced body weight and linear growth, but the HF/SS diet depressed these parameters further below the levels of the chow-fed groups. Both DMNL and control rats fed HF/SS had more carcass fat, heavier epididymal fat pads, more carcass fat per calories eaten, higher plasma levels of glucose, glycerol and free fatty acids but lower insulin levels than chow-fed DMNL rats and controls. This occurred in the face of lower body weights and caloric intake. Neither growth hormone nor insulin showed lesion effects. Rats with DMNL exhibited the same inverse relationship between plasma insulin and free fatty acids as controls. The data indicate that DMNL rats respond to the HF/SS diet essentially like sham-operated controls, i.e., they develop dietary obesity. Although they do show some small deficits, their lipogenic capacity is actually significantly greater than that of HF/SS-diet fed controls.

Normal pancreatic and intestinal enzymes in hypophagic growth-retarded rats that received dorsomedial hypothalamic lesions shortly after weaning

Male weanling Sprague-Dawley rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats). Sham-operated rats served as controls. After being fed lab chow for two postoperative weeks, the animals were divided into four groups. One group of DMNL rats and controls received a high-caloric diet (high-fat diet, chocolate chip cookies, 32% sucrose solution, potato chips and marshmallows), whereas another group of DMNL rats and controls continued to receive lab chow. The experiment was terminated on the 185th postoperative day. In accordance with previous findings, DMNL rats, irrespective of diet, were lighter and shorter than controls. In addition, DMNL rats fed junk food were lighter than DMNL rats fed lab chow, and junk-fed controls weighed as much as chow-fed controls. Both DMNL rats and controls fed junk food were also shorter and showed higher carcass fat than their chow-fed counterparts. Also, DMNL rats fed junk food had less carcass fat than junk-fed sham-operated controls, whereas in accordance with previous findings, there was no difference between chow-fed DMNL rats and chow-fed sham-operated controls. Irrespective of diet, DMNL rats ate less calories than their respective sham-operated controls. Both absolute and percent pancreas weight and protein/pancreas were unaffected in DMNL rats but were reduced in both junk-fed groups in comparison with their chow-fed counterparts. Both concentrations and contents of pancreatic trypsinogen, amylase and lipase were unaffected in DMNL rats but total activities of all three enzymes were dramatically reduced in the junk-fed compared with the chow-fed DMNL rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Avian pancreatic polypeptide-like immunoreactivity in ground squirrel hypothalamus

The distribution of avian pancreatic polypeptide-like immunoreactivity (APP-LI) within the hypothalamus of the golden-mantled ground squirrel (Spermophilus lateralis) was analyzed using the indirect peroxidase-antiperoxidase immunocytochemical technique. Avian pancreatic polypeptide-LI is widely distributed within the hypothalamus of the golden-mantled ground squirrel and in general, the distribution of APP-LI containing neuronal fibers in this species is qualitatively similar to the distribution found in the laboratory rat. This similarity in APP-LI distribution in two rodents from different taxonomic Families suggests that the distribution of APP-LI containing neurons is probably very conservative within the Order Rodentia.