Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “REINFORCEMENT”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37Linked to original sources
PubMed1989

Interactions between the amygdala and ventral striatum in stimulus-reward associations: studies using a second-order schedule of sexual reinforcement.

Bilateral, N-methyl-D-aspartate-induced lesions of the basolateral region of the amygdaloid complex in male rats resulted in a marked decrease in instrumental responses maintained by a visual conditioned reinforcer in a paradigm in which sexual reinforcement was presented under a second-order schedule. There were no effects of lesions of the amygdala on the unconditioned sexual behaviour of the males, i.e. on behaviour elicited by primary reinforcers. Infusion of D-amphetamine bilaterally into the nucleus accumbens region of the ventral striatum resulted in a dose-dependent amelioration of the decrease in instrumental behaviour maintained by a conditioned reinforcer which followed lesions of the amygdala. This effect of D-amphetamine critically depended upon the presentation of the conditioned reinforcer (a previously neutral light which had gained reinforcing properties through its prior association with sexual interaction). The results indicate that the basolateral region of the amygdala may interact with dopamine-dependent processes in the ventral striatum in mediating the control by conditioned reinforcers over instrumental behaviour.

Amphetamines↗
PubMed2006

Processing and tensile properties of hydroxyapatite-whisker-reinforced polyetheretherketone.

Polyetheretherketone (PEEK) was reinforced with 0-50 vol% hydroxyapatite (HA) whiskers using a novel powder processing and compression molding technique which enabled uniform mixing at high whisker content. Texture analysis showed that viscous flow during compression molding produced a preferred orientation of whiskers along the specimen tensile axis. Consequently, the elastic modulus or ultimate tensile strength of HA-whisker-reinforced PEEK was able to be tailored to mimic human cortical bone. PEEK reinforced with 40 and 50 vol% HA whiskers exhibited elastic moduli of 17 and 23 GPa, respectively. Elastic constants were measured using ultrasonic wave propagation and revealed an orthotropic anisotropy also similar to that measured in human cortical bone. PEEK reinforced with 10 and 20 vol% HA whiskers exhibited an ultimate tensile strength of 90 and 75 MPa, respectively. Tensile specimen fracture surfaces showed evidence of brittle failure in both reinforced and un-reinforced PEEK. Whisker pullout was observed with PEEK adhered to HA whiskers, suggesting a relatively strong interface between the PEEK matrix and HA whisker reinforcements.

Benzophenones↗
PubMed2004

Flexural properties of denture base polymers reinforced with a glass cloth-urethane polymer composite.

OBJECTIVES: A newly designed light-cured reinforcement made from urethanemethacrylate oligomer and woven glass cloth has orthotropic anisotropy. This is produced for incorporation into the outermost position under the greatest tension in denture base resins. In this study, the flexural properties of self-, heat-, and light-curing reinforced resins were determined. METHODS: The silanized glass cloth was soaked in urethanemethacrylate oligomer containing camphorquinone and 2-(dimethylamino)ethylmethacrylate. It was sandwiched between two pieces of polyethylene film and pressed to form a reinforcement sheet 0.3 mm in thickness, which was light-cured and prepared using four different surface conditions: with or without the polyethylene film and with or without a bonding agent. The reinforcement sheet was fixed in a fluorocarbon resin mold 3 mm in thickness, which was filled with self-, heat-, or light-curing resin and cured. The cured laminated plate was cut for flexural testing (40 x 7 x 3 mm3). A three-point flexural test was carried out at a crosshead speed of 2 mm/min and a span length of 30 mm. In this study, the glass fiber content was measured at percentages by weight because it was not possible to determine accurately the volume of the various polymers. RESULTS: The baseline flexural strengths of the self-, heat-, and light-curing resins were 76.2, 68.6, and 55.6 MPa, respectively, and these values were increased to 271.7, 216.4, and 266.5 MPa by the reinforcement sheet. The baseline flexural moduli of self-, heat-, and light-curing resins were 2.0, 2.4, and 2.1 GPa, respectively. These values were increased to 7.2, 5.1, and 6.6 GPa by the reinforcement sheet. SEM photographs revealed good impregnation of the glass fiber within the polymer matrix. SIGNIFICANCE: The differences in the flexural strengths and flexural moduli of the control and reinforced specimens were significant (p < 0.01).

Composite Resins↗
PubMed2004

Survival of ceramic onlays placed with and without metal reinforcement.

STATEMENT OF PROBLEM: All-ceramic molar onlays continue to have higher failures from bulk fracture than similar cast metal onlays. PURPOSE: The purpose of this retrospective study was to compare long-term failure rates and causes for posterior sintered feldspathic ceramic (Mirage) onlays placed with and without metal substructure reinforcement. MATERIAL AND METHODS: Nineteen onlays were placed with and 78 without metal reinforcement in 50 older adolescent and adult patients treated by 2 prosthodontists in a private practice. All onlays opposed occluding tooth surfaces. Clinical judgment determined the type of onlay placed. Observational factors included patients, clinicians, onlay sites, and failure modes. Acrylic resin maxillary splints were generally provided for patients with multiple onlays or parafunctional habits. Thirty-six dies were also available for comparison of the occlusal thickness and taper of intact and failed molar onlays. The chi-square test or Fisher exact test, Student t test, and life table survival statistics were used to evaluate the data (alpha=.05). RESULTS: Over 6 years, failures occurred in 21.1% of onlays placed with metal reinforcement and in 26.9% without metal reinforcement. Cumulative survival estimates (+/- standard error) were 62.4% +/- 14.7% and 60.5% +/- 6.3%, respectively (P=.84). Bulk fracture occurred in 16.5% of molars, independent of metal reinforcement (P=1.00). Overall, 11.4% of premolar and 33.9% of molar onlays failed. Irreversible pulpitis occurred in 6.2% of all teeth. From the dies, there were no clear relationships between either the thickness of occlusal ceramic material or the internal preparation taper and molar onlay failures, for onlays placed with or without metal reinforcement. CONCLUSION: Sintered ceramic onlays placed with and without metal reinforcement showed a similar incidence of bulk fracture in molars. Preparations for both types of onlays were similar.

Adolescent↗
PubMed1998

Development and clinical applications of a light-polymerized fiber-reinforced composite.

STATEMENT OF PROBLEM: After 0 years of intermittent reports in the literature, the use of fiber reinforcement is just now experiencing rapid expansion in dentistry. PURPOSE: This article describes the development and use of a continuous, unidirectional fiber reinforced composite as a framework for the fabrication of fixed prostheses. METHODS: By using various matrix materials and fibers, a number of fiber-reinforced composite formulations were evaluated with the goal of creating a system with optimized mechanical properties and handling characteristics. Fiber-reinforced composite based on a light polymerized BIS-GMA matrix has been used clinically to make 2-phase prostheses comprised of an internal glass fiber-reinforced composite substructure covered by a particulate composite. The clinical and laboratory procedures required for the fabrication and use of reinforced composite fixed prostheses are described for laboratory-fabricated complete or partial coverage fixed prosthesis and chairside prosthesis. RESULTS: Although additional clinical experience is needed, fiber-reinforced composite materials can be used to make metal-free prostheses with excellent esthetic qualities.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1997

Aneurysm reinforcement in the anterior circulation.

BACKGROUND: Aneurysms are primarily treated with surgical clipping. Unclippable aneurysms are at risk of recurrent bleeding similar to the natural history of ruptured aneurysms. Aneurysm reinforcement with muslin and ethyl 2-cyanoacrylate may provide a safe and useful alternative to reduce the rebleeding rate in those aneurysms found to be unclippable at surgical exploration. METHODS: We examined a population of 19 patients with aneurysms treated by reinforcement with muslin and ethyl 2-cyanoacrylate. One patient was lost to follow-up. Patients had a mean follow-up of 60 months. The yearly risk of rebleeding was calculated and compared to the natural history of the disease. RESULTS: Most of the aneurysms were located in the middle cerebral artery or the anterior communicating artery. The two main causes for reinforcement were a wide base aneurysm or the presence of arterial branches originating from or intimately adherent to the dome. Those patients with aneurysms in which reinforcement was used as the primary and only treatment had a risk of rebleeding of 2.95% per year. The group of patients with ruptured aneurysms in which the reinforcement was used to supplement a clip had no rebleeding. When all the patients with ruptured aneurysms are combined, there is a risk of rebleeding of 1.94% per year. Unruptured aneurysms treated with reinforcement had not shown hemorrhage. No complications related to the use of muslin or ethyl 2-cyanoacrylate were found in this study. CONCLUSION: The reinforcement with muslin and ethyl 2-cyanoacrylate provides some protection in patients with aneurysms for which direct clipping cannot be done and in those clipped cases in which there is a residual neck or dome. This protection is inferior to clipping, but reduces the risk of rebleeding during the first 6 months after the initial hemorrhage. A longer follow-up is needed to determine if it provides better protection for late rebleeding than the natural history of ruptured aneurysms.

Adult↗
PubMed2001

Comparison of intra-accumbens injection of histamine with histamine H1-receptor antagonist chlorpheniramine in effects on reinforcement and memory parameters.

Histaminergic neurons are located exclusively in the tuberomammillary nuclei (TM) of the hypothalamus from where they project to many regions of the brain including the basal ganglia. Earlier experiments led to the hypothesis that neuronal histamine (HA), particularly in relation to the H1 receptor, has an inhibitory role in learning and reward-related processes. Based on this premise, the objective of the present study was to compare HA with the H1-receptor antagonist d-chlorpheniramine (CPR) in effects on reinforcement and memory parameters after injection into different subregions of the rat nucleus accumbens (NAcc). In the first experiment, mnemoactive effects of CPR (0.1-10 microg) were assessed after injection into the caudal or rostral part of the NAcc with the one-trial uphill avoidance task as a measure of learning. The data show that intra-NAcc injection of CPR (10 microg) facilitated retention of the task, when the compound was administered immediately after training. This effect was evident only when CPR was administered into the caudal-shell but not into the rostral pole of the NAcc providing evidence for anatomical specificity of the intra-NAcc induced promotion of memory. In the second experiment, possible mnemonic and reinforcing effects of HA (0.001-1 microg) were gauged after injection of the amine into the caudal NAcc, using post-trial application in the uphill avoidance task to assess effects on learning and place preference as an index of reinforcing properties. The data show that caudal-NAcc injection of HA (0.1 microg) improved retention of the avoidance task and produced place preference indicative of a reinforcing action. The finding that intra-NAcc injection of HA can facilitate learning and has reinforcing effects is at variance with the proposed inhibitory nature of neuronal HA in reward-related processes. Thus, the disinhibition of reinforcement and facilitation of learning found earlier after partial destruction of TM-intrinsic neurons might not necessarily be related to a lesion-induced reduction of the HAergic tone. The observation that CPR has behavioral effects quite similar to HA suggests that the mnemoactive and reinforcing action of this compound might involve pharmacodynamic aspects beyond its antagonistic activity at H1-receptive sites.

Animals↗
PubMed1997

A neuroendocrine role in cocaine reinforcement.

Cocaine stimulates the secretion of corticosterone and ACTH, probably through a CRF-related mechanism, indicating that the drug activates the HPA axis. Indeed, cocaine has been reported to produce anxiety and to precipitate episodes of panic attack during chronic use and withdrawal in humans and to induce anxiogenic behavior in animals. Cocaine also alters benzodiazepine receptor binding in discrete regions of the rat brain. Some of these changes in binding are obviously related to the convulsions and seizures which are often observed in an acute cocaine overdose. However, data from behavioral studies have suggested that some of these effects may be related directly to cocaine reinforcement since receptor changes also were observed when binding in the brains of rats that self-administered cocaine was compared with that from animals that had received identical yoked, but non-contingent infusions of the drug. In this regard, pretreatment with the benzodiazepine receptor agonists chlordiazepoxide and alprazolam decreased cocaine self-administration without decreasing food-reinforced responding, suggesting that these effects were specific for cocaine. Since this attenuation of self-administration was reversed by increasing the unit dose of cocaine, it is likely that these drugs were decreasing cocaine reinforcement. In contrast, exposure to stress increases vulnerability to self-administer psychostimulants. In these experiments, low-dose cocaine self-administration was related directly to stress-induced increases in plasma corticosterone, such that plasma corticosterone was always greater than 150 ng/ml for rats which subsequently self-administered cocaine at doses of 0.125 mg/kg/infusion or lower, suggesting a threshold for the hormone in cocaine reinforcement. In other experiments, bilateral adrenalectomy completely abolished the acquisition of intravenous cocaine self-administration in naive rats, while metyrapone decreased ongoing self-administration. In addition, ketoconazole pretreatment resulted in patterns of self-administration that were virtually indistinguishable from that observed during saline extinction, suggesting that plasma corticosterone is not only important, but may even be necessary for cocaine reinforcement. The mechanisms through which adrenocorticosteroids alter cocaine reinforcement remain to be determined, but there is increasing evidence that the mesocorticolimbic dopaminergic system is involved. In particular, the medial prefrontal cortex appears to be at least one brain region where dopamine and adrenocorticosteroids may interact to affect cocaine reinforcement.

Adrenocorticotropic Hormone↗
PubMed2000

The effect of second-half reinforcer type on responding for sucrose in the first half of the session.

The present study investigated whether the sucrose-reinforced lever pressing of rats in the first half of a 50-min session would be sensitive to upcoming food-pellet reinforcement in the second half. In Experiment 1, the type of reinforcer in the first half of the session was always liquid sucrose and type of reinforcer in the second half (liquid sucrose or food pellets) varied across conditions. Sucrose concentration varied across groups (1, 5, or 25%). Results showed that rates and patterns of responding for 1%, and sometimes for 5%, sucrose reinforcers in the first half of the session were higher and steeper, respectively, when food-pellet, rather than sucrose, reinforcement occurred in the second half. Responding for 25% sucrose was not similarly affected. Experiment 2 replicated the results of Experiment 1 using a within-subjects design. Although the present results represent induction (i.e. the opposite of contrast), they are consistent with some results on consummatory contrast. They also further demonstrate that responding on interval schedules of reinforcement can be altered prospectively. By doing so, however, they pose potential problems for current theories for why operant response rates change within the session.

Journal Article↗
PubMed2001

The critical dimensions of the response-reinforcer contingency.

Two major dimensions of any contingency of reinforcement are the temporal relation between a response and its reinforcer, and the relative frequency of the reinforcer given the response versus when the response has not occurred. Previous data demonstrate that time, per se, is not sufficient to explain the effects of delay-of-reinforcement procedures; needed in addition is some account of the events occurring in the delay interval. Moreover, the effects of the same absolute time values vary greatly across situations, such that any notion of a standard delay-of-reinforcement gradient is simplistic. The effects of reinforcers occurring in the absence of a response depend critically upon the stimulus conditions paired with those reinforcers, in much the same manner as has been shown with Pavlovian contingency effects. However, it is unclear whether the underlying basis of such effects is response competition or changes in the calculus of causation.

Journal Article↗
PubMed2003

The effect of non-contingent negative and positive reinforcement operations on the acquisition of superstitious behaviors.

The differential effects of non-contingent positive and negative reinforcement operations on the acquisition of superstitious behaviors and rules were investigated in two experiments. College students were instructed to try to produce and/or keep the word "GOOD" on a computer screen (positive reinforcement), or to try to prevent and/or remove the word "BAD" from the screen (negative reinforcement) using response keys. Data from both experiments indicated that participants exposed to lean schedules of negative reinforcers believed that they had greater control over non-contingent stimulus events than participants exposed to either rich or lean schedules of positive reinforcers. These findings and results from research investigating everyday superstitious activities suggest that, relative to positive reinforcement, negative reinforcement operations may provide a more fertile condition for the development and maintenance of superstitious behaviors.

Journal Article↗
PubMed1999

The effect of delayed light exposure on bond strength: light-cured resin-reinforced glass ionomer cement vs light-cured resin.

Under clinical situations, the intervals between material mixing and light exposure during bracket bonding using light-cured resin-reinforced glass ionomer cement may vary for each individual bracket. This study evaluates the bond strength of light-cured resin-reinforced glass ionomer cement subjected to various time intervals between material mixing and subsequent light exposure. This investigation was conducted in two parts. The first part consisted of measuring the enamel surface temperature to define the conditions under which the second part of the study was carried out. One hundred fifteen subjects, 63 males and 52 females, participated in this study. The over-all mean temperature as measured with a noncontact infrared thermometer was 31.9 degrees C. The second part of this study assessed tensile and shear bond strengths of light-cured resin-reinforced glass ionomer cement subjected to immediate light exposure (time interval, 5 minutes) and bond strengths subjected to light exposure at 10, 20, and 40 minutes after material mixing. Light-cured resin-reinforced glass ionomer cement was then compared with light-cured composite resin. Mean tensile and shear bond strengths of light-cured resin-reinforced glass ionomer cement exposed after 40 minutes were 4.5 MPa and 20.5 MPa, respectively. This represented a reduction of approximately 20% when compared with the 5-minute group. Scheffé test showed no statistically significant differences between any two time intervals. Mean bond strengths of the light-cured resin decreased with time. Tensile and shear bond strengths of light-cured resin indicated high statistical significance within groups across time. It could therefore be concluded that the bond strength of light-cured resin-reinforced glass ionomer cement was not affected by the timing of visible light exposure; whereas, the bond strength of light-cured resin decreased as time intervals increased. Light-cured resin-reinforced glass ionomer cement may thus serve as an advantageous alternative to composite resin for bracket bonding.

Adolescent↗
PubMed2001

Glass fiber-reinforced abutments for dental implants. A pilot study.

Titanium abutments in dental implants shine through all-ceramic crowns and therefore limit excellent esthetic results. Prototypes of tooth-colored fiber-reinforced abutments were investigated to avoid the shining-through effect. In vitro, the fracture strength was determined after thermal cycling and mechanical loading of all-ceramic single crowns and four-unit bridges made of a fiber-reinforced composite. The suprastructures were adhesively fixed onto fiber-reinforced implant abutments and compared with those fixed on standard titanium abutments. The median of the fracture strength of the titanium-supported all-ceramic crowns was significantly higher than the median of crowns fixed onto the prototypes. But this value was still more than twice as high as the maximum loading force under oral conditions. No statistical difference was found between four-unit bridges made by fiber-reinforced composite inserted onto titanium abutments and those inserted onto fiber-reinforced abutments. Fiber-reinforced abutment prototypes for dental implants avoided the shining-through effect associated with metal abutments. Their load-bearing capacity after in vitro stress simulation was higher than the maximum oral loading force. With some improvements, the fiber-reinforced implant abutments are therefore a promising alternative to titanium abutments.

Composite Resins↗
PubMed1989

Prefrontal cortex lesions differentially disrupt cocaine-reinforced conditioned place preference but not conditioned taste aversion.

The reinforcing efficacy of cocaine is thought to involve, at least in part, mesocortical dopaminergic (DA) neurons. Rats will self-administer cocaine applied directly into the medial prefrontal cortex but not into nucleus accumbens or the ventral tegmental area (Goeders & Smith, 1983). The present experiments were conducted to assess whether lesions of prefrontal cortex (mesocortical DA target regions) attenuate the reinforcing properties of systemically administered cocaine. Male Sprague-Dawley rats were anesthetized, and one of three subfields (medial, orbital, or precentral) of the prefrontal cortex was removed by aspiration or no brain injury was done (sham operates). In four experiments the rats were tested on conditioned place preference (CPP), conditioned taste aversion (saccharin conditioned stimulus, cocaine unconditioned stimulus), general activity in the running wheel and open field, and food-reinforced spatial alternation in the T-maze. Sham operates demonstrated a cocaine-induced place preference, rats with medial frontal lesions showed a cocaine-induced place aversion, and other operates showed neither a conditioned place preference nor an aversion. The results of this experiment suggest that lesions of the DA projection fields of the prefrontal cortex in the rat reduce the positive reinforcing properties of systemically injected cocaine. In the second experiment, all subjects showed a conditioned taste aversion of equal magnitude. This suggests that whereas the positive reinforcing properties were affected differentially by prefrontal cortex lesions, the aversive properties were not affected. In Experiment 3 there were no lesion-induced differences in activity in either the running wheel or the open field. Therefore, changes in motor activity cannot account for the CPP data. In the final experiment, the medial frontal operates were impaired relative to the precentral and sham operates on learning to alternate choices in the T-maze, but the orbital frontal operates' performance was not different from that of any other group. This suggests that a general disruption of all reinforcement mechanisms did not occur following these lesions. Instead, these results indicate that mesocortical DA projection regions are involved with mediating the reinforcing properties of cocaine and that there is a separate system mediating the aversive properties of cocaine.

Animals↗
PubMed2005

Reinforcement of pre-zygotic isolation and karyotype evolution in Agrodiaetus butterflies.

The reinforcement model of evolution argues that natural selection enhances pre-zygotic isolation between divergent populations or species by selecting against unfit hybrids or costly interspecific matings. Reinforcement is distinguished from other models that consider the formation of reproductive isolation to be a by-product of divergent evolution. Although theory has shown that reinforcement is a possible mechanism that can lead to speciation, empirical evidence has been sufficiently scarce to raise doubts about the importance of reinforcement in nature. Agrodiaetus butterflies (Lepidoptera: Lycaenidae) exhibit unusual variability in chromosome number. Whereas their genitalia and other morphological characteristics are largely uniform, different species vary considerably in male wing colour, and provide a model system to study the role of reinforcement in speciation. Using comparative phylogenetic methods, we show that the sympatric distribution of 15 relatively young sister taxa of Agrodiaetus strongly correlates with differences in male wing colour, and that this pattern is most likely the result of reinforcement. We find little evidence supporting sympatric speciation: rather, in Agrodiaetus, karyotypic changes accumulate gradually in allopatry, prompting reinforcement when karyotypically divergent races come into contact.

Animals↗
PubMed2000

Effect of altering the type of enamel conditioner on the shear bond strength of a resin-reinforced glass ionomer adhesive.

The purpose of this study was to determine the effects of changing the type of enamel conditioner on the shear bond strength of a resin-reinforced glass ionomer within half an hour after bonding the bracket to the tooth. Freshly extracted human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were cleaned and polished. The teeth were randomly separated into 4 groups according to the enamel conditioner/etchant and adhesive used: group I, teeth were conditioned with 10% polyacrylic acid and brackets were bonded with a resin-reinforced glass ionomer adhesive; group II, teeth were conditioned with 20% polyacrylic acid and brackets were bonded with a resin-reinforced glass ionomer adhesive; group III, teeth were etched with 37% phosphoric acid and the brackets were bonded with a resin-reinforced glass ionomer adhesive; group IV, teeth were etched with 37% phosphoric acid and the brackets were bonded with a composite adhesive. The results of the analysis of variance comparing the 4 experimental groups (F = 24.87) indicated the presence of significant differences between the groups (P =.0001). In general, the shear bond strengths were significantly greater in the 2 groups etched with 37% phosphoric acid. This was true for both the resin-reinforced glass ionomer (X = 6.1 +/- 2.7 MPa) and the composite (X = 5.2 +/- 2.9 MPa) adhesives. On the other hand, the shear bond strengths were significantly lower in the two groups conditioned with polyacrylic acid. The bond strength of the resin-reinforced glass ionomer adhesive conditioned with 10% polyacrylic acid (X = 0.4 +/- 1.0 MPa) was significantly lower than the group conditioned with 20% polyacrylic acid (&xmacr; = 3.3 +/- 2.6 MPa). The present findings indicated that the bond strength of the resin-reinforced glass ionomer adhesive can be significantly increased in the initial half hour after bonding if the enamel is etched with 37% phosphoric acid instead of being conditioned with either 10% or 20% polyacrylic acid. The clinician needs to take these properties into consideration when ligating the initial archwires.

Acid Etching, Dental↗
PubMed1999

The reinforcement of mating preferences on an island.

We develop a haploid model for the reinforcement of female mating preferences on an island that receives migrants from a continent. We find that preferences will evolve to favor island males under a broad range of conditions: when the average male display trait on the island and continent differ, when the preference acts on that difference, and when there is standing genetic variance for the preference. A difference between the mean display trait on the continent and on the island is sufficient to drive reinforcement of preferences. Additional postzygotic isolation, caused, for example, by either epistatic incompatibility or ecological selection against hybrids, will amplify reinforcement but is not necessary. Under some conditions, the degree of preference reinforcement is a simple function of quantities that can be estimated entirely from phenotypic data. We go on to study how postzygotic isolation caused by epistatic incompatibilities affects reinforcement of the preference. With only one pair of epistatic loci, reinforcement is enhanced by tighter linkage between the preference genes and the genes causing hybrid incompatibility. Reinforcement of the preference is also affected by the number of epistatically interacting genes involved in incompatibility, independent of the overall intensity of selection against hybrids.

Animals↗
PubMed1990

Models of relative reinforcing efficacy of drugs and their predictive utility.

Studies of drugs as reinforcers in animals have indicated a close agreement between the drugs that function as reinforcers in animals and those that are abused by humans. This agreement has prompted the use of results of studies in animals as a model to predict the abuse of newly synthesized drugs. While this model has widely accepted nominal predictive utility, there have been attempts to extend its predictive capability to assess the relative reinforcing efficacy of drugs. This concept implies that the reinforcing effects of drugs can be compared on ordinal, interval or ratio scales. Relative reinforcing efficacy has been assessed in studies of performances under progressive-ratio schedules and choice procedures, and it has been suggested that results of these studies might be used to predict the extent to which a drug will be abused. In order to use these data for prediction, scaling issues need to be addressed. With progressive-ratio schedules, it is unclear whether the results represent interval or ordinal data. Development and analysis of choice procedures must to occur before each study will yield more than a pair of ordered data points. In order to assess the predictive utility of models of relative reinforcing efficacy, laboratory data from assessments of known drugs of abuse need to be validated with data on the actual abuse of the compounds. There are significant issues in determining what data on "actual abuse" (e.g. epidemiologic results) should be used in attempts to validate the experimental results. Results of epidemiological surveys are influenced by non-pharmacological variables, such as social, marketing and legal factors, that can affect the degree to which results of laboratory studies agree with those from the surveys. Differential influences of these factors on particular drugs may render results of epidemiologic surveys unsuitable for validation of laboratory results. Other types of data, such as laboratory reports of subjective effects or reinforcing effects of drugs in humans subjects, may be influenced less by those factors but are not themselves reflective of "actual abuse." Currently nominal scaling may represent the best information that can be provided for predicting abuse of drugs. However, there are clear paths to take to overcome these shortcomings. More directed laboratory studies that concentrate on scaling issues as well as more pharmacological specificity of epidemiologic studies will undoubtedly increase our predictive ability.

Journal Article↗