Constraints on the evolution of phenotypic plasticity: limits and costs of phenotype and plasticity

Phenotypic plasticity is ubiquitous and generally regarded as a key mechanism for enabling organisms to survive in the face of environmental change. Because no organism is infinitely or ideally plastic, theory suggests that there must be limits (for example, the lack of ability to produce an optimal trait) to the evolution of phenotypic plasticity, or that plasticity may have inherent significant costs. Yet numerous experimental studies have not detected widespread costs. Explicitly differentiating plasticity costs from phenotype costs, we re-evaluate fundamental questions of the limits to the evolution of plasticity and of generalists vs specialists. We advocate for the view that relaxed selection and variable selection intensities are likely more important constraints to the evolution of plasticity than the costs of plasticity. Some forms of plasticity, such as learning, may be inherently costly. In addition, we examine opportunities to offset costs of phenotypes through ontogeny, amelioration of phenotypic costs across environments, and the condition-dependent hypothesis. We propose avenues of further inquiry in the limits of plasticity using new and classic methods of ecological parameterization, phylogenetics and omics in the context of answering questions on the constraints of plasticity. Given plasticity's key role in coping with environmental change, approaches spanning the spectrum from applied to basic will greatly enrich our understanding of the evolution of plasticity and resolve our understanding of limits.

Adrafinil: effects on behavior and cognition in aged canines

1. Adrafmil is a novel vigilance promoting agent developed in France by Louis Lafon Laboratories. 2. Adrafinil causes increased locomotion without producing stereotypical activity in canines tested in an open field. 3. The effectiveness of a single treatment is long-lasting, and the effectiveness persists over repeated treatments. 4. Acquisition of a size discrimination problem is enhanced by adrafinil. This may be linked to performance motivation. 5. Adrafinil causes a long-lasting increase in high frequency electroencephalographic activity recorded from cortical electrodes. 6. These results indicate that adrafinil is novel behavioral stimulant with cognitive enhancing potential. The underlying mechanisms of action are still unknown.

The canine as a model of human cognitive aging: recent developments

1. Aged dogs display many of the cognitive impairments associated with aging and dementia. 2. Aged dogs, like humans, display a wide range of individual variability in cognitive functioning (i.e., different cognitive functions decline at different rates in aged dogs). 3. Different categories of aged canines can be identified on the basis of neuropsychological test performance, and these categories can be used to model different subgroups of aged humans (i.e., dementia, mild cognitive impairment and successful aging). 4. Additional research is required to further validate the dog as a model of human cognitive aging and dementia.

Development of a protocol for studying object recognition memory in the dog

1. Dogs had considerable difficulty learning a delayed-non-matching-to sample task at a short delay (approximately 5 seconds) for an extended period (900 trials). Only 3 of 19 dogs met the learning criterion. 2. Acquisition on the DNMS task was markedly improved when a pause was introduced on presentation of the stimulus objects, when the objects were approximately 30 cm from the dog; eleven of 16 dogs learned the task within 600 trials. 3. Dogs learned the task more rapidly at 20 and 30 second delays than at 10-second delays. This indicates a transfer of learning. 4. Dogs that did learn the task were able to perform at accuracy greater than 85% at delays of 150 and 200 seconds. At a 5-minute delay, performance was at 75%. 5. When the animals were switched to a repeated object paradigm, accuracy markedly declined. 6. The improved performance produced by introduction of the pause is attributable to: (1) presenting the object at a distance longer than the dogs' near point, and (2) allowing increased processing time.

Behavioral activating effects of adrafinil in aged canines

Adrafinil, a vigilance enhancing pharmaceutical, was administered to aged dogs for 14 consecutive days at doses of 10, 20, 30, or 40 mg/kg using a crossover design. The effects on spontaneous behavior in a 10-min canine open-field test were systematically recorded every fourth day, starting with day 1 of treatment. The open field tests were given 2 or 10 h following oral administration of capsules containing either adrafinil or lactose, the placebo control. Adrafinil caused an increase in locomotor activity at the three highest doses at both the 2- and 10-h intervals and during both the first (days 1 and 5) and second treatment week (days 9 and 13). Adrafinil also caused a transient increase in directed sniffing. At the highest dose level, adrafinil caused a decrease in urination frequency. The increased locomotion was generally unaccompanied by stereotypical behavior in the test session. There was some variability; a subpopulation of animals showed either no effect, or decreased locomotion. The individual differences were correlated with changes in serum levels of adrafinil 10 h following treatment.

Oral administration of adrafinil improves discrimination learning in aged beagle dogs

Aged beagle dogs were trained on either a size or intensity discrimination task 2 h following treatment with either 20 mg/kg of adrafinil or a placebo control. Training continued until the dogs reached a predetermined criterion level of performance, or failed to acquire the task after 40 sessions. The treatments and tasks were then reversed, with both the test order and treatment order counterbalanced. Thus, half of the animals were first tested on the intensity discrimination, and half of these were first tested under adrafinil. Treatment with adrafinil produced significant improvement in learning, as indicated by a decrease in both errors and trials to criterion. An effect of adrafinil on motivation may partially account for these findings; however, adrafinil did not significantly affect response latency. Adrafinil is believed to serve as an alpha-1 adrenoceptor agonist. The improved learning may also result from enhancement of vigilance due to facilitation of noradrenergic transmission in the central nervous system.

Use of a delayed non-matching to position task to model age-dependent cognitive decline in the dog

Spatial learning and memory in young and old dogs was studied in a series of experiments using a delayed non-matching to position (DNMP) paradigm. Past research from our laboratory has suggested that aged dogs perform more poorly on a version of the DNMP task compared to young dogs [Head et al., Spatial learning and memory as a function of age in the dog, Behav. Neurosci. 1995;109(5):851-585]. We have now extended these findings by testing a large number of dogs on three different variations of the DNMP paradigm to evaluate different aspects of spatial learning and memory. Our results indicate that: (1) aged dogs show impaired spatial learning compared to young dogs, (2) aged dogs display spatial working memory deficits compared to young dogs, (3) young dogs have a greater maximum working spatial memory capacity than old dogs and (4) we can use the DNMP paradigm to cognitively categorize different subsets of aged dogs. These data indicate that the DNMP paradigm can serve as a valuable tool to evaluate age-dependent cognitive dysfunction in the canine.

Landmark discrimination learning in the dog

Allocentric spatial memory was studied in dogs of varying ages and sources using a landmark discrimination task. The primary goal of this study was to develop a protocol to test landmark discrimination learning in the dog. Using a modified version of a landmark test developed for use in monkeys, we successfully trained dogs to make a spatial discrimination on the basis of the position of a visual landmark relative to two identical discriminanda. Task performance decreased, however, as the distance between the landmark and the "discriminandum" was increased. A subgroup of these dogs was also tested on a delayed nonmatching to position spatial memory task (DNMP), which relies on egocentric spatial cues. These findings suggest that dogs can acquire both allocentric and egocentric spatial tasks. These data provide a useful tool for evaluating the ability of canines to use allocentric cues in spatial learning.

Visual-discrimination learning ability and beta-amyloid accumulation in the dog

Young, middle-aged, and old beagle dogs were tested on several visual-discrimination tasks: reward- and object-approach learning, object discrimination and reversal, long-term retention of a reversal problem, and a size-discrimination task. Beta-amyloid accumulation in the entorhinal, prefrontal, parietal, and occipital cortices was quantified using immunohistochemical and imaging techniques at the conclusion of cognitive testing. Middle-aged and old dogs were impaired in size-discrimination learning. In each task, a subset of aged dogs was impaired relative to age-matched peers. Beta-amyloid accumulation was age-dependent. However, not all middle-aged and old dogs showed beta-amyloid accumulation in the entorhinal cortex. The error scores from dogs tested with a nonpreferred object during visual discrimination learning and from reversal learning were correlated with beta-amyloid in the prefrontal but not entorhinal cortex. Size-discrimination and reward and object-approach learning error scores were correlated with beta-amyloid accumulation in the entorhinal but not prefrontal cortex. The results of these studies support an association between cognitive test and the location and extent of beta-amyloid pathology.

Open field activity and human interaction as a function of age and breed in dogs

Open field (OF) activity was studied in kennel reared purebred beagles from two separate colonies (2-13 years in age) and pound source mixed breed dogs (9 months to 10 years in age). Dogs were observed for 10 min sessions and records were taken of: locomotion, urination, sniffing, grooming, rearing, vocalizing, jumping frequencies and inactivity (16). Since dogs are uniquely social towards people, we also measured human interaction (HI), which recorded the same behaviors as during OF when a person was present in the room. Measures of exploratory behavior decreased as a function of age in pound source dogs in the OF test, but not in beagles from either colony. No breed differences were found between the young dogs. In the HI test, age effects were found in beagles but not pound source dogs. OF activity correlated with tests of cognitive function, but differences were found between the three groups. These findings indicate that OF activity is age-sensitive in dogs, but that breed and test conditions are also essential factors.

Efficacy of the herbicide trifluralin against four P-glycoprotein-expressing strains of Leishmania

Drug resistance has emerged as a major obstacle to chemotherapy for many infectious diseases. Trifluralin, an antimicrotubule herbicide, is a new experimental drug for treatment of leishmaniasis. Here, we found that it was effective against two strains of Leishmania that express the multidrug-resistant genes ldmdr1 and lmpgpA and two strains that express proteins that are immunologically cross-reactive with mammalian P glycoproteins. These results suggest that trifluralin is not subject to counteractions of these multidrug resistance mechanisms of Leishmania species.

Interferometric atmospheric refractive-index environmental monitor

Long, open-path, outdoor interferometric measurement of the index of refraction as a function of wavelength (spectral refractivity) requires a number of innovations. These include active compensation for vibration and turbulence. The use of electronic compensation produces an electronic signal that is ideal for extracting data. This allows the appropriate interpretation of those data and the systematic and fast scanning of the spectrum by the use of bandwidths that are intermediate between lasers (narrow bandwidth) and white light (broad bandwidth). An Environmental Interferometer that incorporates these features should be extremely valuable in both pollutant detection and pollutant identification. Spectral refractivity measurements complement the information available from spectral absorption instruments (e.g., a Fourier-transform infrared spectrometer). The Environmental Interferometer currently uses an electronic compensating device with a 1-kHz response time, and therefore rapid spectral scans are feasibe so that it is possible to monitor the time evolution of pollutant events.

Bladder surface glycosaminoglycans: an epithelial permeability barrier

Sulfated polysaccharide's ability to modulate the movement of small molecules was examined both in vivo and in vitro. For the in vivo test, the rabbit bladder was utilized and C-14 labeled urea 45-Ca, or 3H2O was placed into the lumen of control bladders, bladders pretreated with protamine sulfate (20 mg./cc) and bladders pretreated with protamine sulfate (20 mg./cc) plus pentosanpoly-sulfate (PPS), 10 mg./cc. After 45 minutes, the controls absorbed 21% of the urea, 16% of the calcium, and 38% of the 3H2O; the protamine treated group 40% urea, 23% calcium, and 51% H2O; the PPS only group 22% urea and the protamine plus PPS group absorbed 24% of urea, 18% calcium, and 44% water. Differences between the control and protamine groups were statistically significant, p less than 0.01 for urea 45-Ca and 3H2O. The bladder mucosa contained a significantly higher concentration of urea and calcium after protamine treatment which were both reversed by PPS (p less than 0.01) while 3H2O content went down significantly (p = 0.03), reflecting a loss of the hydrophilic effect of bladder GAG. The control mucosas had 250 cpm/mg. tissue urea for Ca 64 cpm/mg. and water 262 cpm/mg., the protamine group urea 498 cpm/mg., Ca 190 cpm/mg., and H2O 139 cpm/mg.; the protamine plus PPS group urea 344 cpm/mg., Ca 129 cpm/mg., and water 168 cpm/mg. For the in vitro studies, an Ussing chamber was employed. Normal rabbit bladder membranes were placed in the chambers and the potential difference was zeroed across the membrane. There were three groups, membranes that were treated only with the irrigating solution, membranes pretreated with protamine, and membranes pretreated with protamine plus PPS. At the end of 40 minutes, there was an approximately 1.2% movement of urea across the control membrane, a 3.5% movement across the protamine treated membrane (a significant increase p less than 0.001) and a 1.1% movement across the protamine plus PPS treated membrane. It would appear that the surface polysaccharide may play an important role as a bladder permeability barrier in modulating both charged and uncharged small molecule movement in that its ability to impair such movement can be inhibited by protamine and this protamine effect can be reversed by a treatment with an exogenous sulfated polysaccharide.

Decrease in rabbit bladder mucosal glycoprotein after oophorectomy

Hormonal manipulation has been shown to result in less efficient bladder clearance of bacteria. We describe the use of a double antibody technique to semiquantitatively demonstrate the diminution of bladder glycoproteins from the transitional epithelium in oophorectomized rabbits. Rabbit bladder glycoprotein was isolated and used to immunize Swiss-Webster mice. Bladders of normal and oophorectomized rabbits were sequentially stained with mouse antirabbit sera and fluoresceinated goat antimouse antibody. A significant loss of bladder epithelial glycoprotein was evident in oophorectomized rabbits as compared to controls. This study, utilizing a semiquantitative immunologic staining technique, suggests an intact glycoprotein layer is important in the bladder defense mechanism.