Orexin neurons in the hypothalamus regulate energy homeostasis by coordinating various physiological responses. Past studies have shown the role of the orexin peptide itself; however, orexin neurons contain not only orexin but also other neurotransmitters such as glutamate and dynorphin. In this study, we examined the physiological role of orexin neurons in feeding behavior and metabolism by pharmacogenetic activation and chronic ablation. We generated novel orexin-Cre mice and utilized Cre-dependent adeno-associated virus vectors to express Gq-coupled modified GPCR, hM3Dq or diphtheria toxin fragment A in orexin neurons. By intraperitoneal injection of clozapine-N oxide in orexin-Cre mice expressing hM3Dq in orexin neurons, we could selectively manipulate the activity of orexin neurons. Pharmacogenetic stimulation of orexin neurons simultaneously increased locomotive activity, food intake, water intake and the respiratory exchange ratio (RER). Elevation of blood glucose levels and RER persisted even after locomotion and feeding behaviors returned to basal levels. Accordantly, 83% ablation of orexin neurons resulted in decreased food and water intake, while 70% ablation had almost no effect on these parameters. Our results indicate that orexin neurons play an integral role in regulation of both feeding behavior and metabolism. This regulation is so robust that greater than 80% of orexin neurons were ablated before significant changes in feeding behavior emerged.

ABSTRACT. Bone mineral density (BMD), distribution of its density and bone histomorphometric parameters were evaluated in lumbar vertebra of normally growing miniature pigs. The fourth lumbar vertebra (L4) of the Göttingen miniature pig were used in this cross-sectional study in vitro. The BMD of the miniature pig was similar to that of humans in tendency of gender differences and some growth patterns during puberty. In these regards this animal appears useful as a model for human bone study. However, the trabecular and cortical BMDs of lumbar spine were extremely high value (399.43 ± 26.36 mg/cm 3 in female trabeculae; 973.06 ± 69.55 mg/cm 3 in female cortical bone; 419.04 ± 34.84 mg/cm 3 in male trabeculae; 1038.81 ± 125.72 mg/cm 3 in male cortical bone in pigs 30 months or more). Furthermore, histomorphometric analysis yielded values that were remarkably different from those found in humans. From these results, it was revealed that miniature pig had a higher bone mass and denser trabecular network than human, indicating that its bone is probably stronger. Therefore, care should be taken in choosing the miniature pig as a bone study model. KEY WORDS: bone mineral density, histomorphometric analyses, lumbar spine, miniature pig.J. Vet. Med. Sci. 66(6): 599-609, 2004 Metabolic bone diseases such as osteoporosis are becoming more important because of an aging society in human medicine. These diseases increase the risk of fragility fracture as bone mineral levels decrease, and also reduces their quality of life. Previous studies have reported that bone strength and fracture risk are closely related to bone mineral density (BMD) [6,9,27]. In contrast, several studies have suggested that changes in bone architecture increase fracture risk [29,31,33,34,43]. Therefore, it is necessary to study the changes in both BMD and architecture for more sensitive investigation of the bone disease.Quantitative computed tomography (QCT) has been widely investigated and applied in recent years as a means of non-invasive quantification of BMD. It has been reported that QCT might be most sensitive to changes in bone density caused by rapid bone turnover, such as in menopausal immobilization or hyperthyroidism [9]. QCT can selectively measure both trabecular and cortical bone [9,13,22,38], and the BMD is expressed in milligrams per cubic centimeter (volumetric density) [9]. Ebbesen et al. showed highly correlation between BMD by QCT and compressive strength in the lumbar vertebrae [9].Several studies have reported that bone disorders such as osteoporosis lead to trabecular and cortical bone alterations in humans. These alterations are characterized not only by a reduction of bone mass but also by structural changes in microarchitecture which is measured by histomorphometry of bone [29,31,33]. Therefore, it has been considered that histomorphometric analysis have an important role as contributor to bone strength, in addition to BMD.Recently, miniature pig has been noticed as for experimental animal of bone study. The pig is an excel...

The secretion of pancreatic polypeptide (PP) is regulated by fluctuations in blood glucose concentrations and food intake, in which vagal-cholinergic mechanisms play an important role, especially for the cephalic phase of PP secretion. In this study, we examined whether central cholinergic mechanisms are also important for PP secretion by relaying information in the brain to the vagus nerve and the muscarinic cholinergic receptors in the pancreas. Atropine sulfate (20-200 micrograms) was administered into the lateral cerebral ventricle and its effects on the basal secretion of PP as well as the secretions stimulated by insulin-induced hypoglycemia (Actrapid MC, 0.25 U/kg) and a mixed meal (243 kcal) were studied in seven dogs. Intralateral cerebroventricular (ILV) atropine (100 and 200 micrograms) abolished the fluctuations in basal PP secretion without appearing in the plasma. Pretreatment with 20, 100, and 200 micrograms ILV atropine significantly decreased the PP response to insulin-induced hypoglycemia, with the integrated PP response to 58, 32, and 26% of that of controls respectively. Atropine (100 micrograms ILV) significantly reduced the postprandial PP secretion in both the cephalic and the gastrointestinal phases, whereas increased insulin and glucose levels were unaffected. Centrally administered atropine was able to suppress the basal secretion of PP as well as the secretions stimulated by hypoglycemia and food intake. These findings suggest that (1) the spontaneous release of PP is governed by an oscillating, central cholinergic tone, and (2) the stimulating PP secretion is, at least in part, regulated by the central cholinergic system.