Central blockage of nesfatin-1 has anxiolytic effects but does not prevent corticotropin-releasing factor-induced anxiety in male rats.

Nesfatin-1, a pleotropic peptide, was recently implicated in the regulation of anxiety and depression-like behavior in rats. However, the underlying mechanisms remain unclear so far. Thus, this study aimed to investigate the role of endogenous nesfatin-1 in the mediation of anxiety and depression-like behavior induced by corticotropin-releasing factor (CRF). Therefore, normal weight male intracerebroventricularly (icv) cannulated Sprague Dawley rats received two consecutive icv injections of anti-nesfatin-1 antibody or IgG control antibody followed by CRF or saline, before being exposed to a behavioral test. In the elevated zero maze test, assessing anxiety and explorative behavior, blockade of nesfatin-1 using an anti-nesfatin-1 antibody under basal conditions increased the number of entries into the open arms compared to control antibody/vehicle (1.6-fold, p < 0.05) and the time in open arms compared to the other groups (p < 0.05). Control antibody/CRF-treated animals tended to spend less time in the open arms compared to control antibody/vehicle (0.7-fold, p = 0.17), an effect not altered by the nesfatin-1 antibody (control antibody/CRF-treated animals vs. nesfatin-1 antibody/CRF group, p = 1.00). In the novelty-induced hypophagia test, assessing anhedonia as part of depression-like behavior, no significant differences were observed between the four groups for the latency to the first bout, number of bouts and the amount of palatable snack eaten (p > 0.05). In summary, CRF tended to increase anxiety and explorative behavior an effect not altered by blockade of nesfatin-1, whereas no significant effect of CRF on anhedonia was observed. Blockade of endogenous nesfatin-1 significantly decreased anxiety-like behavior giving rise to a physiological role of brain nesfatin-1 in the mediation of anxiety.

Physical activity sustains memory retrieval in dopamine-depleted mice previously treated with L-Dopa.

The neurodegenerative disorder Parkinson's disease affects motor abilities as well as cognition. The gold standard therapy is L-Dopa, which mainly restores motor skills. Therefore, we require additional interventions to sustain cognitive functions in Parkinson's disease. The lifestyle intervention "physical activity" improves adult hippocampal neurogenesis and memory but so far, its impact has not been investigated in rodent models for Parkinson's disease previously treated with the standard therapy. We hereby asked whether physical activity serves as a pro-neurogenic and -cognitive stimulus in dopamine-depleted mice previously treated with L-Dopa. Therefore, we injected dopamine-depleted mice with L-Dopa/Benserazide followed either by exercise or by a sedentary lifestyle. We analysed adult hippocampal neurogenesis histologically and assessed spatial memory in the Morris water maze. Furthermore, we investigated the hippocampal and striatal monoaminergic cross-talk. Physical activity prevented memory decline and was linked to a slower dopamine turnover but did not enhance neurogenesis in dopamine-depleted mice previously treated with L-Dopa. In conclusion, physical activity did not develop its full pro-neurogenic potential in mice previously treated with L-Dopa but sustained spatial cognition in Parkinson's disease.

Deep brain stimulation alters light phase food intake microstructure in rats.

Treatment of eating disorders like obesity or anorexia is challenging. Options are limited and new approaches desired. An interesting approach is the application of deep brain stimulation (DBS). The nucleus accumbens (NAcc) is part of the food reward system. A pilot study reported that DBS of the NAcc shell modulates food intake and body weight in rats. Underlying mechanisms such as the food intake microstructure are unknown so far. Normal weight female Sprague-Dawley rats were equipped with a custom-made DBS electrode placed unilaterally in the NAcc shell. Biphasic stimulation was performed for seven days. Body weight and food intake including the microstructure were assessed over the experimental period. Behavior was monitored manually. DBS tended to increase body weight gain (28.1 ± 5.4 g) compared to sham-stimulated controls (16.7 ± 3.4, P = 0.05) without affecting daily food intake (P > 0.05). Further analyses showed that light phase food intake was stimulated, whereas dark phase food intake was decreased in the DBS group (P < 0.05). During the light phase bout frequency (+50%), bout duration (+64%), meal duration (+71%) and overall time spent in meals (+92%) were increased in DBS rats (P < 0.05), while during the dark phase no alterations were observed (P > 0.05). Behavior did not show differences regarding overall eating and drinking behavior (including food/water approach), grooming or locomotion (P > 0.05). Summarized, although overall food intake was not changed by DBS, light phase food intake was stimulated likely via a reduction of satiation.

Exercise prevents high-fat diet-induced impairment of flexible memory expression in the water maze and modulates adult hippocampal neurogenesis in mice.

Obesity is currently one of the most serious threats to human health in the western civilization. A growing body of evidence suggests that obesity is associated with cognitive dysfunction. Physical exercise not only improves fitness but it has also been shown in human and animal studies to increase hippocampus-dependent learning and memory. High-fat diet (HFD)-induced obesity and physical exercise both modulate adult hippocampal neurogenesis. Adult neurogenesis has been demonstrated to play a role in hippocampus-dependent learning and memory, particularly flexible memory expression. Here, we investigated the effects of twelve weeks of HFD vs. control diet (CD) and voluntary physical activity (wheel running; -R) vs. inactivity (sedentary; -S) on hippocampal neurogenesis and spatial learning and flexible memory function in female C57Bl/6 mice assessed in the Morris water maze. HFD was initiated either in adolescent mice combined with long-term concurrent exercise (preventive approach) or in young adult mice with 14days of subsequent exercise (therapeutic approach). HFD resulted in impaired flexible memory expression only when initiated in adolescent (HFD-S) but not in young adult mice, which was successfully prevented by concurrent exercise (HFD-R). Histological analysis revealed a reduction of immature neurons in the hippocampus of the memory-impaired HFD-S mice of the preventive approach. Long-term physical exercise also led to accelerated spatial learning during the acquisition period, which was accompanied by increased numbers of newborn mature neurons (HFD-R and CD-R). Short-term exercise of 14days in the therapeutic group was not effective in improving spatial learning or memory. We show that (1) alterations in learning and flexible memory expression are accompanied by changes in the number of neuronal cells at different maturation stages; (2) these neuronal cells are in turn differently affected by HFD; (3) adolescent mice are specifically susceptible to the negative effects of HFD. Thus, physical exercise, by modulating adult neurogenesis in the hippocampus, might represent a potential preventive approach for treating cognitive impairments associated with adolescent obesity.

Physical exercise counteracts MPTP-induced changes in neural precursor cell proliferation in the hippocampus and restores spatial learning but not memory performance in the water maze.

Parkinson's disease (PD) is characterized by a continuous loss of dopaminergic neurons in the substantia nigra, which not only leads to characteristic motor symptoms but also to cognitive impairments. Physical exercise has been shown to improve hippocampus-dependent cognitive functions in PD patients. Animal studies have demonstrated the involvement of adult hippocampal neurogenesis in exercise-induced improvements of visuo-spatial learning and memory. Here, we investigated the direct impact of voluntary wheel running on hippocampal neurogenesis and spatial learning and memory in the Morris water maze (MWM) using the1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. We also analyzed striatal and hippocampal dopamine transmission and mRNA expression levels of dopamine receptors. We show that MPTP-induced spatial learning deficits were alleviated by short-term physical exercise but not MPTP-induced spatial memory impairments in either exercise intervention group. Neural precursor proliferation was transiently altered in MPTP-treated mice, while the cell survival was increased by exercise. Dopamine was progressively depleted by MPTP and its turnover altered by exercise. In addition, gene expression of dopamine receptor D1/D5 was transiently upregulated following MPTP treatment but not affected by physical exercise. Our findings suggest that physical exercise benefits spatial learning but not memory performance in the MWM after MPTP-induced dopamine depletion by restoring precursor cell proliferation in the hippocampus and influencing dopamine transmission. This adds to the understanding of cognitive decline and mechanisms for potential improvements by physical exercise in PD patients.

NOMA-GAP/ARHGAP33 regulates synapse development and autistic-like behavior in the mouse.

Neuropsychiatric developmental disorders, such as autism spectrum disorders (ASDs) and schizophrenia, are typically characterized by alterations in social behavior and have been linked to aberrant dendritic spine and synapse development. Here we show, using genetically engineered mice, that the Cdc42 GTPase-activating multiadaptor protein, NOMA-GAP, regulates autism-like social behavior in the mouse, as well as dendritic spine and synapse development. Surprisingly, we were unable to restore spine morphology or autism-associated social behavior in NOMA-GAP-deficient animals by Cre-mediated deletion of Cdc42 alone. Spine morphology can be restored in vivo by re-expression of wild-type NOMA-GAP or a mutant of NOMA-GAP that lacks the RhoGAP domain, suggesting that other signaling functions are involved. Indeed, we show that NOMA-GAP directly interacts with several MAGUK (membrane-associated guanylate kinase) proteins, and that this modulates NOMA-GAP activity toward Cdc42. Moreover, we demonstrate that NOMA-GAP is a major regulator of PSD-95 in the neocortex. Loss of NOMA-GAP leads to strong upregulation of serine 295 phosphorylation of PSD-95 and moreover to its subcellular mislocalization. This is associated with marked loss of surface α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor and defective synaptic transmission, thereby providing a molecular basis for autism-like social behavior in the absence of NOMA-GAP.

Estudio de cohortes sobre la carga socioeconómica de la enfermedad de Parkinson en Portugal / Health-economic burden of Parkinson’s disease in Portugal: a cohort study

Introducción. La enfermedad de Parkinson (EP) es un trastorno neurodegenerativo frecuente que acarrea una considerable carga socioeconómica. Las evaluaciones económicas de la EP en los países del sur de Europa son escasas. Objetivo. Valorar los costes de la EP en una cohorte de pacientes ambulatorios de Portugal. Pacientes y métodos. Se reclutó a 49 pacientes consecutivos con EP en un centro ambulatorio de neurología adscrito a la Universidad de Lisboa entre octubre de 2004 y diciembre de 2005. El estado clínico se evaluó con la escala unificada de evaluación de la EP y la escala de Hoehn y Yahr. Los costes se evaluaron desde la perspectiva social mediante cuestionarios de economía de la salud. El cálculo de los costes indirectos se llevó a cabo aplicando el criterio del capital humano. La calidad de vida relacionada con la salud se valoró por medio del cuestionario EuroQoL (EQ-5D). Resultados. Los costes directos ascendieron a 2.717 euros (intervalo de confianza al 95%, IC 95% = 1.147-3.351) por paciente a lo largo de un semestre. Los principales contribuyentes a los costes directos fueron los medicamentos, con 544 euros (IC 95% = 426-6.940), y los ingresos hospitalarios, con 690 euros (IC 95% = 229-1.944). Los costes indirectos totalizaron 850 euros (IC 95% = 397-1.529), mientras que los gastos sufragados por el paciente constituyeron el 12% de los costes directos. La asistencia facilitada por la familia y otros allegados tuvo un papel destacado. En general, los costes resultaron inferiores a los de otros países occidentales. Conclusiones. La EP acarrea una considerable carga económica en Portugal. Entre los principales componentes del coste se encuentran la medicación y los gastos de hospitalización. Es preciso proseguir las investigaciones para describir unos patrones detallados de la utilización de los servicios sanitarios en Portugal y orientar las decisiones de política sanitaria de manera más efectiva (AU)

Introduction. Parkinson’s disease (PD) is a common neurodegenerative disorder with a considerable socioeconomic burden. Health-economic evaluations of PD in the Southern European countries are limited. Aim. To evaluate the costs of PD in an outpatient cohort in Portugal. Patients and methods. 49 consecutive PD patients were recruited at the neurological outpatient clinic of the University of Lisbon between October 2004 and December 2005. Clinical status was evaluated using the Unified Parkinson’s Disease Rating Scale and the Hoehn & Yahr stages. Costs were assessed from the societal perspective using health-economic questionnaires. Human capital approach was used to estimate indirect costs. Health-related quality of life was evaluated by means of the EQ-5D. Results. Direct costs were 2,717 euros (95% CI = 1,147-3,351) per patient for a six-month period. Main contributors to the direct costs included drugs (544 euros; 95% CI = 426-6,940) and hospitalizations (690 euros; 95% CI = 229-1,944). Indirect costs amounted to 850 euros (95% CI = 397-1,529), whereas patient expenditures constituted 12% of direct costs. Assistance by family and other relatives played a major role. In general, costs were lower than in other Western countries. Conclusions. The economic burden of PD in Portugal is considerable. Important cost components include medications and hospitalizations. More research is needed in order to describe a comprehensive health service patterns in Portugal and to guide health policy decisions more effectively (AU)

[Health-economic burden of Parkinson's disease in Portugal: a cohort study]. / Estudio de cohortes sobre la carga socioeconomica de la enfermedad de Parkinson en Portugal.

INTRODUCTION: Parkinson's disease (PD) is a common neurodegenerative disorder with a considerable socioeconomic burden. Health-economic evaluations of PD in the Southern European countries are limited. AIM: To evaluate the costs of PD in an outpatient cohort in Portugal. PATIENTS AND METHODS: 49 consecutive PD patients were recruited at the neurological outpatient clinic of the University of Lisbon between October 2004 and December 2005. Clinical status was evaluated using the Unified Parkinson's Disease Rating Scale and the Hoehn and Yahr stages. Costs were assessed from the societal perspective using health-economic questionnaires. Human capital approach was used to estimate indirect costs. Health-related quality of life was evaluated by means of the EQ-5D. RESULTS: Direct costs were 2,717 euros (95% CI = 1,147-3,351) per patient for a six-month period. Main contributors to the direct costs included drugs (544 euros; 95% CI = 426-6,940) and hospitalizations (690 euros; 95% CI = 229-1,944). Indirect costs amounted to 850 euros (95% CI = 397-1,529), whereas patient expenditures constituted 12% of direct costs. Assistance by family and other relatives played a major role. In general, costs were lower than in other Western countries. CONCLUSIONS: The economic burden of PD in Portugal is considerable. Important cost components include medications and hospitalizations. More research is needed in order to describe a comprehensive health service patterns in Portugal and to guide health policy decisions more effectively.

[Parkinson's disease: cost-of-illness in an outpatient cohort]. / Morbus Parkinson: Krankheitskosten einer ambulanten Patientenkohorte.

OBJECTIVE: The aim of this study was to evaluate the direct and indirect costs in a cohort of German outpatients with Parkinson's disease (PD) and to identify major cost drivers in PD. METHODS: 91 PD patients were consecutively enrolled in the outpatient department of the neurological clinic at the University of Marburg, Germany. Patients had to fill out a standardised questionnaire at baseline and at a 3-month follow-up and report their health service resource utilisation for the past three months, retrospectively. In addition, information on clinical parameters of PD (UPDRS, Hoehn and Yahr stage) were assessed. For 86 patients, the direct and indirect cost data were analysed. Indirect costs were calculated by the human capital approach. RESULTS: Total costs per patient and 6-month period amounted to € 8,400 [95%CI 6,768-10,302]. Of these, 30% were indirect costs (€ 2,505 [95%CI 1,541-4,047]) and 70% were direct costs (€ 5,895 [95%CI 4,846-7,376]). The major parts of the direct costs were triggered by antiparkinsonian medication (€ 2,889 [95%CI 2,392-3,655]) and inpatient stays (hospital und rehabilitation, € 1,556 [95%CI 865-2,892]). A linear multivariate model with disease severity, disease duration, sleep disorders, psychosis and dystonia explained 24% of the variance of total costs and 33% of variance of direct costs, respectively. CONCLUSION: Parkinson's disease imposes a high financial burden on both patient and society. A reduced health-related quality of life reflects the individual patient's impairment by PD.

Longitudinal study of the socioeconomic burden of Parkinson's disease in Germany.

OBJECTIVE: To determine the health economic burden on patients with Parkinson's disease (PD) in Germany over a 12-month observation period and provide a comprehensive analysis of cost-driving factors. METHODS AND PATIENTS: Patients with PD (n = 145) were recruited from two clinical departments, two office-based neurologists and 12 GPs. Clinical evaluations were performed at baseline, 3, 6 and 12 months. Disease severity was measured using the Unified Parkinson's Disease Rating Scale (UPDRS). Cost data were assessed based on a patient diary and via personal structured interviews at the respective time-points. Costs were calculated from the societal perspective (2009 euro). Cost-driving factors were identified by multivariate regression analysis. RESULTS: Mean annual costs totalled euro20 095 per patient. Amongst direct costs, the highest expenditures (euro13 158) were for drugs (euro3526) and inpatient care including nursing homes (euro3789). Indirect costs accounted for 34.5% (euro6937) of total costs. Costs of home care provided by family accounted for 20% of direct costs. Cost-driving factors were identified for total costs (UPDRS, fluctuations, dyskinesia and younger age), direct costs (UPDRS, fluctuations), patient expenditures (UPDRS, depression) and drug costs (younger age). CONCLUSION: Parkinson's disease has a chronic course with growing disability and considerable socioeconomic burden. Disease progression leads to an increasing number of patients who require costly institutionalized care. Home care is a major factor influencing patients' families. Healthcare programmes aimed at reducing the burden of PD on society and individuals should consider cost-driving factors of PD.

[Long-term disease-related costs 4 years after stroke or TIA in Germany]. / Langzeitkrankheitskosten 4 Jahre nach Schlaganfall oder TIA in Deutschland.

BACKGROUND: The economic burden of stroke is considerable. While studies on the costs of acute stroke treatment have been undertaken in Germany, thorough analysis of direct and indirect long-term costs is lacking. PATIENTS AND METHODS: A hospital-based cohort of 151 consecutive patients with stroke or transient ischemic attacks (TIA) was followed up (medical examination and interview) at the end of the 4th year following the cerebrovascular event. Costs were calculated using a bottom-up approach and classified into direct medical and nonmedical costs, indirect costs, and patients' costs. RESULTS: Non-stroke-related costs (mean +/- standard deviation 4,610+/-9,310 Euros/person) were separated from total costs. Total stroke-related costs of the 4th year after stroke/TIA amounted to 7,670+/-10,250 Euros per person. The cost components were as follows: direct costs 56% (4,320+/-5,740 Euros), indirect costs 31% (2,350+/-2,710 Euros), and patients' payments 13% (1,000+/-4,100 Euros). The annual nationwide costs for the 4th year following stroke or TIA amounted to approximately 3 billion Euros. CONCLUSION: The considerable size of long-term costs after stroke/TIA is mainly due to direct costs and poses an economic challenge to the German health care system. Patients contribute in a relevant way by their own payments.

Bat flight generates complex aerodynamic tracks.

The flapping flight of animals generates an aerodynamic footprint as a time-varying vortex wake in which the rate of momentum change represents the aerodynamic force. We showed that the wakes of a small bat species differ from those of birds in some important respects. In our bats, each wing generated its own vortex loop. Also, at moderate and high flight speeds, the circulation on the outer (hand) wing and the arm wing differed in sign during the upstroke, resulting in negative lift on the hand wing and positive lift on the arm wing. Our interpretations of the unsteady aerodynamic performance and function of membranous-winged, flapping flight should change modeling strategies for the study of equivalent natural and engineered flying devices.

Stress and coping of Hong Kong Chinese family members during a critical illness.

AIM: The present study aimed to investigate the stress and coping strategies of Hong Kong Chinese families during a critical illness and to examine the relationships between stress and coping. BACKGROUND: Admissions to intensive care unit are usually an unanticipated event, which imposes stress on the family. Family's wellness is one of the significant factors affecting patient's well-beings. Much work has been conducted in Western societies. Stress and coping in Chinese families of critically ill patients have rarely been discussed. METHOD: Structured face-to-face interviews were conducted, using the Impact of Events Scale and the Family Crisis Oriented Personal Evaluation Scales. A convenience sample of 133 participants was recruited from a regional hospital in Hong Kong. Many were patients' children with age between 30 and 49. A total of 39.1% (n = 52) of the participants were males and 60.9% (n = 81) were females. RESULTS: The participants experienced high level of stress (mean = 25.1, SD = 8.3). Higher level of stress were experienced by female (t = -4.6; d.f. = 1, 131; P = 0.00), those with lower educational attainment (F = 3.0; d.f. = 2, 130; P = 0.05) and those whose relatives were admitted to the intensive care unit unexpectedly (t = -2.2; d.f. = 1; P = 0.03). Patients' length of stay in the unit was significantly correlated with levels of stress (r = 0.5, P < 0.00). Level of stress had significant correlation with coping strategies utilization (r = 0.5, P < 0.00). Reframing strategies were frequently used whereas the passive appraisal strategies were least used. Family members used positive-coping strategies, which concurred with the Chinese stress-coping pattern 'fatalistic voluntarism'. RELEVANCE TO CLINICAL PRACTICE: This study contributes to the understanding of Hong Kong Chinese families' stress and coping during a critical illness. Comprehensive assessments of family members' psychosocial needs are important to plan appropriate interventions to alleviate their stress and strengthen their coping skills. The findings will serve as guidance for nurses in delivering culturally sensitive and competent interventions.

Flight speed and body mass of nectar-feeding bats (Glossophaginae) during foraging.

Aerodynamic theory predicts that minimum power (Vmp) and maximum range (Vmr) flight speeds increase when the body mass of an individual animal increases. To evaluate whether foraging bats regulate their flight speed within a fixed speed category relative to Vmp or Vmr, I investigated how the natural daily changes in body mass caused by feeding affected the flight speed of neotropical nectar-feeding bats (Phyllostomidae: Glossophaginae) within a strictly defined, stereotyped behavioural context. Individual bats were maintained in a flight tunnel (lengths of five different types 14-50 m) with a fully automated feeding, weighing (using an electronic balance at the roost) and flight speed measuring system. Flight speeds were measured during normal nocturnal foraging activity by an undisturbed bat while it flew between the two ends of the flight tunnel to obtain food from two computer-controlled nectar-feeders. For a comparison of flight enclosure measurements with field data, flight speeds were also obtained from unrestrained bats foraging in their natural environment (Costa Rica). Foraging flight speeds spanned a range of at least a factor 3 within a single species, which demonstrates the wide range of speeds possible to these animals. Significant, positive correlations between flight speed and the natural individual variability in body mass were found in nearly all cases, with body mass exponents ranging between 0.44 and 2.1. Bats flying at normal speeds were therefore not near their upper limit of muscle power. The most reliable measurements of speed increase with mass (with individual mass changes of up to 30%) were close to the increase theoretically predicted for Vmp and Vmr for an individual bat (with constant wing span and area), which should vary as M0.42, where M is mass. This provides evidence that the glossophagine bats attemped to maintain their flight speed within a fixed speed category relative to Vmp or Vmr during foraging. Among differently sized species of glossophagine bat (N=4), flight speeds V varied with V=20M0.23, in agreement with the mass exponent of 0.21 expected from aerodynamic models for interspecific variation. In addition to the mass effect, at least five other variables significantly influenced flight speed. (1) Both mean and maximum flight speeds increased with the length and the cross-sectional area of the flight tunnel. Mean (maximum) flight speeds of 11-12 g Glossophaga soricina bats (in m s-1) were 4.6 (5.3) over a 7 m and 7. 3 (10.5) over a 50 m flight path. (2) The flight speed range adopted by a bat during one night could vary significantly between nights, independently of body mass and the effect of the size of the flight enclosure. (3) Bats flew significantly faster under illumination than in darkness. This effect was shown (i) by bats kept under natural ambient illumination that initiated foraging during the twilight phase of the evening, (ii) when bats continued to feed into the light phase directly after the dark-light transition in the laboratory and (iii) during foraging under constant, artificial illumination. (4) After a period of rest, the initial flight speed during a foraging bout was significantly increased by 25%, but declined to the mean level within 20 s of activity. (5) Flight speed could differ significantly between foraging (flight from feeder to feeder) versus non-foraging (flight from end to end of the enclosure without visiting the feeders) flights. The results of this study demonstrate a clear ability of bats to regulate their flight speed in response to small natural changes in body mass as predicted by aerodynamic theory for Vmp and Vmr. The set point in flight speed regulation, however, was influenced by multiple additional variables.

ZOO-FISH analysis in a species of the order Chiroptera: Glossophaga soricina (Phyllostomidae).

Glossophaga soricina is a flower-visiting bat which lives in the neotropics. The diploid chromosome number is 2n = 32 with a fundamental number of autosomal arms, FN, of 60. G. soricina belongs to the Microchiroptera which have a lower diploid DNA content and a higher AT composition in their DNA compared with other mammals. By ZOO-FISH analysis with human chromosome-specific DNA probes, the human autosomes were found conserved in 41 segments. This is an arrangement similar to other mammals which have been analyzed. Several chromosomal associations already known from ZOO-FISH studies in other species were also present in G. soricina.

Energetic cost of hovering flight in nectar-feeding bats (Phyllostomidae: Glossophaginae) and its scaling in moths, birds and bats.

Three groups of specialist nectar-feeders covering a continuous size range from insects, birds and bats have evolved the ability for hovering flight. Among birds and bats these groups generally comprise small species, suggesting a relationship between hovering ability and size. In this study we established the scaling relationship of hovering power with body mass for nectar-feeding glossophagine bats (Phyllostomidae). Employing both standard and fast-response respirometry, we determined rates of gas exchange in Hylonycteris underwoodi (7 g) and Choeronycteris mexicana (13-18 g) during hover-feeding flights at an artificial flower that served as a respirometric mask to estimate metabolic power input. The O2 uptake rate (VO2) in ml g-1 h-1 (and derived power input) was 27.3 (1.12 W or 160 W kg-1) in 7-g Hylonycteris and 27.3 (2.63 W or 160 W kg-1) in 16.5-g Choeronycteris and thus consistent with measurements in 11.9-g Glossophaga soricina (158 W kg-1, Winter 1998). VO2 at the onset of hovering was also used to estimate power during forward flight, because after a transition from level forward to hovering flight gas exchange rates initially still reflect forward flight rates. VO2 during short hovering events (< 1.5 s) was 19.0 ml g-1 h-1 (1.8 W) in 16-g Choeronycteris, which was not significantly different from a previous, indirect estimate of the cost of level forward flight (2.1 W, Winter and von Helversen 1998). Our estimates suggest that power input during hovering flight Ph(W) increased with body mass M (kg) within 13-18-g Choeronycteris (n = 4) as Ph = 3544 (+/- 2057 SE) M1.76 (+/- 0.21 SE) and between different glossophagine bat species (n = 3) as Ph = 128 (+/- 2.4 SE) M0.95 (+/- 0.034 SE). The slopes of three scaling functions for flight power (hovering, level forward flight at intermediate speed and submaximal flight power) indicate that: 1. The relationship between flight power to flight speed may change with body mass in the 6-30-g bats from a J- towards a U-shaped curve. 2. A metabolic constraint (hovering flight power equal maximal flight power) may influence the upper size limit of 30-35 g for this group of flower specialists. Mass-specific power input (W kg-1) during hovering flight appeared constant with regard to body size (for the mass ranges considered), but differed significantly (P < 0.001) between groups. Group means were 393 W kg-1 (sphingid moths), 261 W kg-1 (hummingbirds) and 159 W kg-1 (glossophagine bats). Thus, glossophagine bats expend the least metabolic power per unit of body mass supported during hovering flight. At a metabolic power input of 1.1 W a glossophagine bat can generate the lift forces necessary for balancing 7 g against gravitation, whereas a hummingbird can support 4 g and a sphingid moth only 3 g of body mass with the same amount of metabolic energy. These differences in power input were not fully explained by differences in induced power output estimated from Rankine-Froude momentum-jet theory.

Energetic cost of hovering flight in a nectar-feeding bat measured with fast-response respirometry.

Hover-feeding glossophagine bats provide, in addition to the hummingbirds, a second vertebrate model for the analysis of hovering flight based on metabolic measurement and aerodynamic theory. In this study, the power input of hovering Glossophaga soricina bats (11.9 g) was measured by standard respirometry and fast-response (< 0.2 s) oxygen analysis. Bats needed 5-7 s after a rest-to-flight transition to return to a respiratory steady state. Therefore, only hovering events preceeded by a 7-s flight interval were evaluated. VO2 during hovering fluctuated with a frequency of 3-5 Hz, which corresponded in frequency to the licking movement of the tongue. During hovering, bats often may have hypoventilated as indicated by reduced VO2 and a respiratory exchange ratio (RER) well below the steady-state value of 1. Steady-state oxygen consumption (and derived power input) during hovering was estimated to be 27 (25-29) ml O2 g-1 h-1 (158 W kg-1 or 1.88 W) in the 11.9-g bats as indicated by three independent findings: (1) VO2 was 26 ml O2 g-1 h-1 after 6.5 s of hovering, (2) the mean RER during single hovering events was at its steady-state level of 1 only at oxygen uptake rates of 25-29 ml g-1 h-1, and (3) when the oxygen potentially released from estimated oxygen stores was added to the measured oxygen uptake, the upper limit for oxygen consumption during hovering was found to be 29 ml O2 g-1 h-1. Hovering power input was about 1.2 times the value of minimum flight power input (Winter and von Helversen 1998) and thus well below the 1.7-2.6 difference in power output postulated by aerodynamic theory (Norberg et al. 1993). Mass specific power input was 40% less than in hummingbirds. Thus, within the possible modes of hovering flight, Glossophaga bats seem to operate at the high-efficiency end of the spectrum.

In vivo measurement of near maximal rates of nutrient absorption in a mammal.

The central limitation hypothesis postulates that energy budgets are limited by the capacity for energy assimilation. Contradictory evidence from in vitro studies of nutrient uptake capacity of intestinal tissues indicates a margin, however, that could allow a higher rate of energy acquisition than actually measured. As a more direct test, I measured nutrient uptake capacity in vivo. This is possible in animals such as the neotropical nectar-feeding bats (Glossophaginae: Phyllostomidae) that have both rapid gut transit times and high daily metabolic needs. Here, during the steady-state period of feeding, the rate of food intake is equal to the rate of food processing and food egestion. Therefore, the rate of food absorption can be determined directly from the rate of food ingestion. Maximal feeding rates were elicited by limiting the time period available for feeding during the 24-hr day through manipulation of the light/dark (LD) cycle. During 4-hr nights (LD 20:4), sugar intake averaged 488 J/g/hr and was 73% higher than during 12-hr nights (LD12:12). A 16.4-g bat would assimilate 96 kJ/day if feeding at this maximal rate during a regular 12-hr foraging period. This would be sufficient for maintaining a positive energy balance even during extreme physical activity under the natural conditions of its tropical environment. Nutrient assimilation capacity could thus not be identified as the single central factor setting the metabolic ceiling.

The energy cost of flight: do small bats fly more cheaply than birds?

Flapping flight is one of the most expensive activities in terms of metabolic cost and this cost has previously been considered equal for the two extant vertebrate groups which evolved flapping flight. Owing to the difficulty of obtaining accurate measurements without disturbing flight performance, current estimates of flight cost within the group of small birds and bats differ by more than a factor of five for given body masses. To minimize the potential problem that flight behaviour may be affected by the measurements, we developed an indirect method of measuring flight energy expenditure based on time budget analysis in which small nectar-feeding bats (Glossophaginae) could continue their natural rhythm of flying and resting entirely undisturbed. Estimates of metabolic flight power based on 172 24-h time and energy budget measurements were obtained for nine individual bats from six species (mass 7-28 g). Metabolic flight power (PF) of small bats was found to increase with body mass following the relation PF = 50.2 M0.771 (r2 = 0.96, n = 13, PF in W, M in kg). This is about 20-25% below the majority of current predictions of metabolic flight cost for small birds. Thus, either the flight cost of small birds is significantly lower than has previously been thought or, contrary to current opinion, small bats require less energy to fly than birds.

Gas exchange during hovering flight in a nectar-feeding bat Glossophaga soricina.

Glossophagine nectar-feeding bats exploit flowers while hovering in front of them. Aerodynamic theory predicts that power output for hovering flight in Glossophaga soricina is 2.6 times higher than during horizontal flight. We tested this prediction by measuring rates of gas exchange during hover-feeding. Five individuals of Glossophaga soricina (mean mass 11.7 g) were trained to feed from a nectar dispenser designed as a flow-through respirometry mask. Single hover-feeding events lasted for up to 4.5 s. Measured rates of gas exchange varied as a function of hovering duration. O2 and CO2 during short hovering events (up to 1 s) were 20.5+/-6.7 ml g-1 h-1 (N=55) and 21.6+/-5.6 ml g-1 h-1 (N=39) (means +/- S.D.), respectively. These values are in the range of a previous estimate of the metabolic power input for level forward flight (23.8 ml O2 g-1 h-1). However, during hovering events lasting longer than 3 s, oxygen uptake was only 16.7+/-3.5 ml g-1 h-1 (N=73), which is only 70 % of the value expected for forward flight. Thus, bats reduced their rate of oxygen uptake during longer periods of hovering compared with level forward flight. This result is in contrast to the predicted hovering cost derived from aerodynamic theory. The exact metabolic power input during hovering remains uncertain. During longer hovering events, bats were probably not in respiratory steady state, as indicated by the deviation of the respiratory exchange ratio from the expected value of 1 (oxidization of nectar sugar) to the measured value of 0.8.