Differential role of leptin receptors at the hypothalamic paraventricular nucleus in tonic regulation of food intake and cardiovascular functions

Leptin plays an important role in the central regulation of body weight and arterial pressure via activation of leptin receptors (Ob-Rs) in the hypothalamic area, including the hypothalamic paraventricular nucleus (PVN). The present study was undertaken to investigate whether endogenous leptin in the PVN plays a dual role in the tonic regulation of body weight and arterial pressure. Adult, male normal-weight Sprague-Dawley rats, which were anesthetized and maintained with propofol, were used. A direct bilateral microinjection into the PVN of an antisense oligonucleotide against Ob-R mRNA (ASON1, 50 pmol) significantly increased the daily food intake and body weight gain, effects which lasted for at least 14 days. The same treatment, on the other hand, had no appreciable effect on the basal mean systemic arterial pressure (SAP), heart rate (HR), or power density of the vasomotor components of SAP signals, the experimental index of neurogenic sympathetic vasomotor tone. ASON1 treatment also exerted an insignificant effect on the baroreceptor reflex control of HR. Western blot analysis revealed that a bilateral microinjection into the PVN of ASON1 (50 pmol) significantly decreased the expression of the Ob-R protein in the hypothalamus. The same treatment also attenuated hypertension, tachycardia, and the increase in the power density of the vasomotor components of the SAP signals induced by exogenous bilateral application of leptin (5 or 50 ng) into the PVN. Control application of sense (SON, 50 pmol) or a scrambled antisense Ob-R oligonucleotide (ASON2, 50 pmol) into the bilateral PVN promoted no discernible effect on Ob-R protein expression in the hypothalamus, on daily food intake, or on cardiovascular performance. Our results indicate that whereas the Ob-Rs in the PVN are involved in the tonic regulation of food intake, they might not be actively involved in the tonic regulation of cardiovascular functions.     

Central nervous system actions of growth hormone on brain monoamine levels and behavior of juvenile rainbow trout

Growth hormone (GH) has been demonstrated to alter the behavior of juvenile salmonids. However, the mechanisms behind this action are not yet understood. In mammals and birds, peripheral GH treatment has been shown to affect monoaminergic activity in the central nervous system, which may be a mechanism whereby GH alters behavior. To investigate if GH may influence behavior directly at the central nervous system, juvenile rainbow trout were injected with GH into the third ventricle of the brain, whereupon physical activity and food intake were observed during 2 h. Thereafter, brains were sampled and the content of serotonin, dopamine, and noradrenaline and their metabolites were measured in hypothalamus, telencephalon, optic tectum, and brainstem. The GH-treated fish increased their swimming activity relative to sham-injected controls, while appetite remained unchanged, compared with sham-injected controls. Analysis of brain content of monoamines revealed that the GH treatment caused a decrease in the dopamine metabolite homovanillic acid in the hypothalamus, indicating a lowered dopaminergic activity. It is concluded that GH may alter behavior by acting directly on the central nervous system in juvenile rainbow trout. Furthermore, GH seems to alter the dopaminergic activity in the hypothalamus. Whether this is a mechanism whereby GH affects swimming activity remains to be clarified.     

Prevalence of zinc deficiency in junior high school students of Tehran City

Zinc deficiency is a health problem in many communities especially among adolescents because of pubertal growth sprout. This investigation was carried out to determine the epidemiology of zinc deficiency in junior high school students in Tehran City in 1997. This cross-sectional study was performed on 881 students (452 males and 429 females) with the mean age of 13.2±1.0 yr, who were selected by multistage random sampling method. Plasma, erythrocyte, and hair zinc levels were assayed by flame atomic absorption spectrophotometry. Anthropometric and demographic characteristics were measured and recorded on a questionnaire. Dietary intakes were evaluated by a 24-h recall method. Zinc deficiency was defined as having at least two indices from indices of erythrocyte, plasma, and hair zinc below 10 μg/mL, 100 μg/dL, and 125 μg/g of hair, respectively. The results showed that zinc deficiency prevalence was 31.1% (confidence interval: 28–34.4%). Zinc deficiency was 65%, 49%, and 1.3% based on plasma, erythrocyte, and hair zinc levels, respectively. The mean ± SD for plasma, erythrocyte, and hair zinc concentration, height-for-age, as well as weight-for-age Z scores were 95.2±17.7 μg/dL, 10.3±2.3 μg/mL, 239.4±54.4 μg/g, −0.40±0.92, and 0.12±0.91, respectively. As for dietary intake compared with the RDA, 50% of the subjects consumed less than 50% of their requirement for zinc RDA based on a 24-h dietary recall. Zinc intake in subjects was 7.5±3.7 μg, that in boys was higher than in girls. Correlation coefficients between zinc status indices were very weak. There was neither a linear nor nonlinear relationship between biochemical parameters and nutritional zinc intake. It is concluded that almost one-third to one-half of the subjects would be considered zinc deficient.     

Urinary and serum electrolyte changes in athletes during periodic and continuous hypokinetic and ambulatory conditions

Hypokinesia (HK) (diminished movement) induces significant electrolyte changes, but little is known about the effect of periodic hypokinesia (PHK) on minerals. The aim of this study was to measure the effect of PHK and continuous hypokinesia (CHK) on urinary and serum electrolytes. Studies were done during a 30-d period of prehypokinesia (HK) and during 364 d of PHK and CHK periods. Thirty male athletes aged 24.6±7.7 yr were chosen as subjects. They were equally divided into three groups: unrestricted ambulatory control subjects (UACS), continuously hypokinetic subjects (CHKS), and periodically hypokinetic subjects (PHKS). The UACS group experienced no changes in the daily activities and regular training and they were maintained under an average running distance of 11.7 km/d. The CHKS group was limited to an average walking distance of 0.7 km/d; and the PHKS group was limited to an average walking distance of 0.7 and running distance of 11.7 km/d for 5 d and 2 d/wk, respectively, for a period of 364 d. Urinary and serum phosphate (P), calcium (Ca), sodium (Na) and potassium (K), serum intact parathyroid hormone (iPTH), calcitonin (CT), plasma renin activity (PRA) and aldosterone (PA) levels, food and water intakes, and physical characteristics were measured. Urinary P, Ca, Na, and K loss, serum Ca, P, Na, and K, and PRA and PA values increased significantly (p≤0.01), whereas serum iPTH and CT levels decreased significantly (p≤0.01) in the PHKS and CHKS groups when compared with the UACS group. However, significant (p≤0.01) differences were observed between PHKS and CHKS groups regarding urinary and serum electrolytes, serum and plasma hormones. Food and water intakes, body weight, body fat, and peak oxygen uptake decreased significantly (p ≤ 0.01) in the CHKS group when compared with PHKS and UACS groups. Food and fluid intakes, body fat, and body weight increased significantly (p≤0.01), whereas peak oxygen uptake remained significantly (p≤0.01) higher in the PHKS group when compared with the CHKS group. Serum and urinary minerals, serum hormones, food and fluid intakes, and physical characteristics did not change significantly (p>0.01) in the UACS group when compared with their baseline control values. It was shown that both PHK and CHK induce significant serum and urinary electrolyte changes. However, urinary and serum electrolyte changes were significantly (p≤0.01) greater during PHK than CHK. It was concluded that the greater the stability of muscular activity, the smaller the serum and urinary electrolyte changes during prolonged HK.     

Daily rhythms of emergence of small invertebrates inhabiting shallow subtidal zones: A comparative investigation at four locations in Japan

Many small invertebrates inhabit the shallow subtidal zone and some of them emerge at times into the water column. The daily timing of their emergence is affected by the day/night and tidal cycles, and shows various patterns of synchrony with these cyclical factors, depending on the species. To detect possible regional differences in their emergence patterns, sampling was carried out at four locations in Japan: a boreal sea (Akkeshi), a temperate sea (Sugashima), an inland sea (Ushimado) and a subtropical sea (Iriomote-jima). The emergence patterns of major taxa were examined by visual inspection and by two statistical methods (periodogram and autocorrelogram). The composition of the taxa collected by the pump system, mostly crustaceans, was similar in each location. The number of taxa that emerged revealed a day/night rhythm in every location. This characteristic was clearest at Iriomote-jima and least clear at Sugashima. The daily fluctuation in the number of individuals in each taxon varied widely, from very clearly nocturnal to weakly diurnal patterns. In Iriomote-jima, the major taxa all showed well-demarcated nocturnal patterns, so these patterns were classified as either level N₂ or N₃ with regard to the degree of synchrony with the day/night cycle. With regard to the synchrony with the tide, the majority of patterns in all locations showed a double-tidal interval. Many patterns were slightly modified by the tidal cycle. These patterns were classified as level T₁ or T₂ with regard to the degree of synchrony with the tidal cycle. The synchrony with the tide was comparatively strong at Ushimado. The synchrony with day/night and tidal cycles varied even within the same species or closely related species. In benthic invertebrates, hiding or resting in the bottom substrates and swimming in the water column would occur alternatively. In planktonic animals, aggregation near the bottom and dispersal in the water column would occur alternatively. The daily timing of such activities may be synchronized with the day/night and tidal cycles to various degrees among species or populations, resulting in a wide variety of emergence patterns in subtidal small invertebrates. This type of behavior is not daily (diel) vertical migration; it should rather be called daily emergence/dispersal. Strong winds, rough waves and unknown seasonal factors would also affect emergence patterns. Furthermore, the transparency of the seawater may also strongly affect these patterns. Nocturnal patterns may be an adaptation to avoid vulnerability to sighted predators. Variation of synchrony with the tide indicates that by definition, the tidal rhythm can only be distinguished from the day/night rhythm. Hence, the daily patterns that are weakly modified by the tides (levels T₁ and T₂) should be called the tidal rhythms. As the period of such rhythms cannot be determined exactly by using statistical methods, lengthy field investigations and visual inspection of each pattern is essential to assess the influence of tides.     

Chronic neuropeptide Y infusion during lactation suppresses pup growth and reduces the length of lactational infertility in rats

In lactating rats, food restriction potentiates the already high levels of hypothalamic neuropeptide Y (NPY). To investigate the role that high levels of NPY might play in the prolongation of lactational infertility that typically accompanies a food restricted lactation we investigated the effects of chronic central infusions of NPY in ad libitum-fed lactating females. First, we compared the effects of intracerebroventricular (icv) infusion of NPY from Days 12-19 postpartum at a dose of 14.4 microg/day with a similar treatment in nonlactating females. In subsequent experiments we examined the effects of NPY infusions into the lateral ventricle at doses of 6 or 20 mug/day or unilaterally into the medial preoptic area at a dose of 1 microg/day from either Days 12-19 or 7-21 postpartum. Effects on food intake; female body weight; and, where appropriate, litter weight and length of lactational diestrus were compared between NPY and vehicle-treated females. As expected NPY infusion produced a robust increase in body weight and food intake in nonlactating females that was accompanied by a suppression of cyclicity. By contrast NPY treatment in lactating rats resulted in a marked decrease in litter growth and an earlier termination of lactational diestrus.     

The seasonal daily travel in a group of Sichuan snub-nosed monkey (Pygathrix roxellana) in Shennongjia Nature Reserve,China

The seasonal daily travel of a group of snub-nosed monkey (Pygathrix roxellana) was investigated using the group’s straight-line distance method. The group was followed from dawn to dusk for 30 consecutive days during each season to encompass all aspects of daily travel patterns. The results showed that in Summer and Autumn, the mean daily travel distance (m) was significantly longer than in Winter and Spring. There was no significant difference in the mean daily travel distance between Summer and Autumn or between Winter and Autumn. The mean travel distance (m/hr) during daytime was significantly higher in Summer and Autumn than in Spring, and in Autumn than in Winter. The travel of the group in all seasons had similar patterns. Traveling showed morning and afternoon peaks, with a rest period at the noon in a day. Seasonal food availability, length of daytime, and mean travel distance (m/hr) during daytime might have contributed to the different daily travel distances in different seasons.     

Co-administration of dopamine D1 and D2 agonists additively decreases daily food intake, body weight and hypothalamic neuropeptide Y level in rats

This study investigated whether co-administration of dopamine D1 and D2 agonists might additively inhibit the feeding effect and whether this effect was mediated by the action on hypothalamic neuropeptide Y (NPY). The D1 agonist SKF 38393 (SKF) and D2 agonists apomorphine (APO) or quinpirole (QNP) were administered, alone or in combination, to examine this possibility. In single administration, decreases of daily food intake were observed only in rats treated twice a day with a higher dose of SKF, APO or QNP. However, combined administration of D1 and D2 agonists, with each agent at a dose that alone did not induce anorexia in one daily treatment, exerted a significant effect. These results reveal that co-activation of D1 and D2 receptors can additively reduce daily food intake and body weight. The same treatment also decreased the level of hypothalamic NPY 24 h post-treatment. These results suggest an additive effect during combined activation of D1 and D2 receptor subtypes to decrease food intake and body weight that are mediated by the action of hypothalamic NPY. Similar to the effects seen in healthy rats, combined D1/D2 administration was also effective in the reduction of food intake in diabetic rats, revealing the efficiency of D1/D2 agonist in the improvement of hyperphasia in diabetic animals.     

Intraventricular insulin decreases kappa opioid-mediated sucrose intake in rats

The hormone insulin acts in the central nervous system (CNS) as a regulator of body adiposity and food intake. Recent work from our laboratory has provided evidence that one way by which insulin may decrease food intake is by decreasing the rewarding properties of food. Evidence from others suggests that endogenous opioids may mediate the palatable properties of foods, and insulin may decrease nonfood-related reward via interaction with some CNS kappa opioid systems. In the present study we examined the ability of insulin to interact with exogenous or endogenous kappa opioids to modulate feeding of palatable sucrose pellets by nondeprived rats. Insulin (5 mU intracerebroventricular (i.c.v.), t=−3 h) completely reversed the ability of the exogenous kappa agonist U50,488 (26 μg, i.c.v., t=−15 min) to stimulate 90-min sucrose feeding (211±32% reduced to 125±23% of 90-min baseline intake). Further, i.c.v. insulin (5 mU, t=−3 h) interacted with a subthreshold dose of the kappa receptor antagonist norbinaltorphimine (5 μg, i.c.v., t=−15 min) to decrease the 90-min sucrose intake baseline (77±11% versus 109±10% of 90 min baseline intake, insulin/norbinaltorphimine versus norbinaltorphimine). Together these studies provide new evidence that insulin in the CNS may decrease the action of CNS kappa opioid system(s) that mediate palatable feeding.     

The effects of centrally administered apelin-13 on food intake, water intake and pituitary hormone release in rats

Apelin is the recently identified endogenous ligand for the G-protein-coupled receptor, APJ. Preproapelin and APJ mRNA are found in hypothalamic regions known to be important in the regulation of food and water intake, and pituitary hormone release. The effects of intracerebroventricular (ICV) administration of pyroglutamylated apelin-13 on food and water intake and pituitary hormone release in rats were investigated. Apelin-13 had little effect on food intake, but dose-dependently increased drinking behaviour and water intake at 1 h. Apelin-13 (10 nmol) increased water intake by up to sixfold compared to saline. Compared to saline control, apelin-13 (10 nmol) significantly increased plasma ACTH and corticosterone and decreased plasma prolactin, LH and FSH at 30 min. In vitro, apelin-13 stimulated the release of CRH and AVP from hypothalamic explants, but had no effect on NPY release. These results suggest that apelin may play an important role in the hypothalamic regulation of water intake and endocrine axes.