Quantitative imaging of proteoglycan in cartilage using a gadolinium probe and microCT.

OBJECTIVE: Micro-computed tomography (microCT) imaging has the potential to allow the three-dimensional (3D) visualization of cartilage morphology. However, cartilage intensity on a microCT image is weak because cartilage does not strongly attenuate X-rays. This work was designed to demonstrate that exposure of cartilage to charged gadolinium compounds modifies the intensity to allow an improved visualization of cartilage morphology and the determination of proteoglycan content. DESIGN: Trypsin was used to deplete proteoglycan in bovine nasal cartilage disks. Disks were then exposed to Gd(3+), gadopentetate (Gd-DTPA(2-)), or gadoteridol (Gd-HP-DO3A), and imaged with microCT. The intensities of the disks were measured from the images and compared to the actual proteoglycan content determined with a dimethylmethylene blue assay. RESULTS: Treatment of naïve disks with 200 mM Gd(3+) for 24h at room temperature produced a 2.8-fold increase in intensity on microCT images. Similar treatment with 200 mM Gd-DTPA(2-) produced a 1.4-fold increase. After 2h of trypsin treatment at room temperature, the intensities of cartilage disks exposed to 20 0mM Gd(3+) decreased by 12%. Conversely, the intensities of trypsin-treated disks exposed to 200 mM Gd-DPTA(2-) increased by 15%. Trypsin treatment caused a 4% increase in the intensities of disks exposed to neutral Gd-HP-DO3A. The correlation between proteoglycan content and the microCT intensity of cartilage treated with Gd(3+) was very good (r(2)=0.81). CONCLUSIONS: Gadolinium and microCT allow an improved 3D visualization of cartilage and quantification of its proteoglycan content.

Reduced feeding response to neuropeptide Y in senescent Fischer 344 rats.

The anorexia of aging syndrome in humans is characterized by spontaneous body weight loss reflecting diminished food intake. We reported previously that old rats undergoing a similar phenomenon of progressive weight loss (i.e., senescent rats) also display altered feeding behavior, including reduced meal size and duration. Here, we tested the hypothesis that blunted responsiveness to neuropeptide Y (NPY), a feeding stimulant, occurs concurrently with senescence-associated anorexia/hypophagia. Young (8 mo old, n = 9) and old (24-30 mo old, n = 11) male Fischer 344 rats received intracerebroventricular NPY or artificial cerbrospinal fluid injections. In response to a maximum effective NPY dose (10 microg), the net increase in size of the first meal after injection was similar in old weight-stable (presenescent) and young rats (10.85 +/- 1.73 and 12.63 +/- 2.52 g/kg body wt (0.67), respectively). In contrast, senescent rats that had spontaneously lost approximately 10% of body weight had significantly lower net increases at their first post-NPY meal (1.33 +/- 0.33 g/kg body wt (0.67)) than before they began losing weight. Thus altered feeding responses to NPY occur in aging rats concomitantly with spontaneous decrements in food intake and body weight near the end of life.

Neurochemical alterations during age-related anorexia.

Unexplained weight loss during the latter stages of aging is commonly preceded by a spontaneous diminution in food intake. Multiple etiologies of age-related anorexia in humans, ranging from social isolation to impaired gastrointestinal function, have been proposed. The observation of this phenomenon in older laboratory animals suggests that physiological changes play a significant causal role. A continually expanding body of information on the neurochemical control of food intake supports a contribution of altered neurochemistry to dysregulated feeding behavior. This review provides an update on the relationship between declining food intake during advanced age and physiological (specifically neurochemical) function. The complexity of the control of food intake as well as the variety of investigative methods used in this field of study render the identification of definitive causes difficult. Evidence presented here is evaluated and possible etiologic factors are suggested.

Meal patterns associated with the age-related decline in food intake in the Fischer 344 rat.

We previously reported that aging Fischer 344 (F344) rats display a spontaneous, rapid loss in body weight associated with decreased food intake near the end of life. Here, we describe the specific changes in feeding patterns underlying this reduced intake. Nine male F344 rats, aged 25 mo, were monitored continuously until 7 days after the onset of spontaneous rapid weight loss (i.e., senescence). Regardless of age at death (25.5-32.5 mo), all senescent rats demonstrated a similar pattern of decreased food intake. They ate significantly smaller meals (g/meal) of shorter duration during spontaneous rapid weight loss compared with their period of weight stability (presenescence). However, no differences occurred in the number of meals eaten per day. Rapid weight loss had no effect on the rats' selection of preferred diets. Serum levels of the hormone leptin were not higher in the senescent vs. age-matched presenescent rats, nor was the incidence of common disease different in senescent animals. Moreover, the area of the pituitary-hypothalamus interface, measured to identify possible hypothalamic compression, was similar in the senescent rats and an age-matched, presenescent control group despite significantly greater pituitary size in the former. Our data show that simultaneous with rapid spontaneous weight loss, aging rats demonstrate significant changes in feeding patterns suggestive of earlier satiation. These feeding alterations do not result from loss of ability to select for palatable food, elevated serum leptin levels, specific pathology, or hypothalamic compression.