Fetal and neonatal exposure to trimethylolpropane phosphate alters rat social behavior and emotional responsivity

Biological and Acoustic Sex Differences in Rat Ultrasonic Vocalization

The rat model is a useful tool for understanding peripheral and central mechanisms of laryngeal biology. Rats produce ultrasonic vocalizations (USVs) that have communicative intent and are altered by experimental conditions such as social environment, stress, diet, drugs, age, and neurological diseases, validating the rat model's utility for studying communication and related deficits. Sex differences are apparent in both the rat larynx and USV acoustics and are differentially affected by experimental conditions. Therefore, the purpose of this review paper is to highlight the known sex differences in rat USV production, acoustics, and laryngeal biology detailed in the literature across the lifespan.

Evaluation of the neutrophil-lymphocyte ratio as a measure of distress in rats

The ability to evaluate distress in laboratory animals is needed in order to ensure that husbandry and experimental procedures do not negatively impact animal welfare. Accurate measurement of acute stress and chronic stress, and distinguishing between stress that is harmful (distress) and stress that does no harm (eustress), can be challenging. Whereas corticosterone concentrations are commonly used to measure stress in laboratory animals, the neutrophil-lymphocyte ratio has been proposed as a potentially better indicator of chronic stress. Furthermore, an association between such measures of stress and concurrent behavioral indicators of negative welfare is required to determine their accuracy in evaluating distress. The authors compared serum corticosterone concentrations and neutrophil-lymphocyte ratios to assess acute or chronic stress in male Sprague Dawley rats. Elevated serum corticosterone concentrations, but not neutrophil-lymphocyte ratios, were associated with acute stress exposure, whereas elevated neutrophil-lymphocyte ratios, but not serum corticosterone concentrations, were associated with chronic stress exposure. Because the neutrophil-lymphocyte ratio differences corresponded with a behavioral indicator of distress in chronically stressed rats, it may serve as a valuable tool for the physiological assessment of distress in rats.

Evaluation of submarine atmospheres: effects of carbon monoxide, carbon dioxide and oxygen on general toxicology, neurobehavioral performance, reproduction and development in rats. II. Ninety-day study

Carbon monoxide (CO), carbon dioxide (CO2) and low-level oxygen (O2) (hypoxia) are submarine atmosphere components of highest concern because of a lack of toxicological data available to address the potential effects from long-duration, combined exposures on female reproductive and developmental health. In this study, subchronic toxicity of mixed atmospheres of these three submarine air components was evaluated in rats. Male and female rats were exposed via inhalation to clean air (0.4 ppm CO; 0.13% CO2; 20.6% O2) (control), a low-dose (5.0 ppm CO; 0.41% CO2; 17.1% O2), a mid-dose (13.9 ppm CO; 1.19 or 1.20% CO2; 16.1% O2) and a high-dose (89.9 ppm CO; 2.5% CO2; 15.0% O2) gas mixture for 23 h per day for 70 d premating and a 14-d mating period. Impregnated dams continued exposure to gestation day 19. Adverse reproductive effects were not identified in exposed parents (P0) or first (F1) and second generation (F2) offspring during mating, gestation or parturition. No adverse changes to the estrous cycle or in reproductive hormone concentrations were identified. The exposure-related effects were reduced weight gains and adaptive up-regulation of erythropoiesis in male rats from the high-dose group. No adverse, dose-related health effects on clinical data or physiological data were observed. Neurobehavioral tests identified no apparent developmental deficits at the tested levels of exposure. In summary, subchronic exposures to the submarine atmosphere gases did not affect the ability of the exposed rats or their offspring to reproduce and did not appear to have any significant adverse health effects.

Evaluation of submarine atmospheres: effects of carbon monoxide, carbon dioxide and oxygen on general toxicology, neurobehavioral performance, reproduction and development in rats. I. Subacute exposures

The inhalation toxicity of submarine contaminants is of concern to ensure the health of men and women aboard submarines during operational deployments. Due to a lack of adequate prior studies, potential general, neurobehavioral, reproductive and developmental toxicity was evaluated in male and female rats exposed to mixtures of three critical submarine atmospheric components: carbon monoxide (CO) and carbon dioxide (CO2; levels elevated above ambient), and oxygen (O2; levels decreased below ambient). In a 14-day, 23 h/day, whole-body inhalation study of exposure to clean air (0.4 ppm CO, 0.1% CO2 and 20.6% O2), low-dose, mid-dose and high-dose gas mixtures (high dose of 88.4 ppm CO, 2.5% CO2 and 15.0% O2), no adverse effects on survival, body weight or histopathology were observed. Reproductive, developmental and neurobehavioral performance were evaluated after a 28-day exposure in similar atmospheres. No adverse effects on estrus phase, mating, gestation or parturition were observed. No developmental or functional deficits were observed in either exposed parents or offspring related to motor activity, exploratory behavior or higher-level cognitive functions (learning and memory). Only minimal effects were discovered in parent-offspring emotionality tests. While statistically significant increases in hematological parameters were observed in the offspring of exposed parents compared to controls, these parameters remained within normal clinical ranges for blood cells and components and were not considered adverse. In summary, subacute exposures to elevated concentrations of the submarine atmosphere gases did not affect the ability of rats to reproduce and did not appear to have any significant adverse health effects.

Cannabidiol and clozapine reverse MK-801-induced deficits in social interaction and hyperactivity in Sprague-Dawley rats

Recently, a novel paradigm has been designed to assess social investigative behaviour in pairs of Sprague-Dawley rats, which involves physical separation whilst ensuring they are able to maintain contact through other social cues. We have modified this set-up in order to assess not just social behaviour but also locomotor activity of the rats. Results showed that the MK-801- (0.3 mg/kg) treated rats displayed reduced social investigative behaviour, hyperactivity as well as reduced attention span. Pretreatment with the phytocannabinoid cannabidiol (3 mg/kg) not only normalised social investigative behaviour but increased it beyond control levels. Pretreatment with clozapine (1, 3 mg/kg) also normalised social investigative behaviour. Both cannabidiol and clozapine inhibited MK-801-induced hyperactivity. However, there were no effects of pretreatment on impairments to attention span. Our findings reinforce several aspects of the validity of the MK-801-induced model of social withdrawal and hyperactivity and also support the use of this novel set-up for further investigations to assess the antipsychotic potential of novel compounds.

Acute illness-induced behavioral alterations are similar to those observed during withdrawal from acute alcohol exposure

Exposure to an immunogen results in a constellation of behavioral changes collectively referred to as "sickness behaviors," with alterations in cytokine expression previously shown to contribute to this sickness response. Since behaviors observed during ethanol withdrawal are strikingly similar to sickness behaviors, we hypothesized that behavioral manifestations of ethanol withdrawal might be an expression of sickness behaviors induced by ethanol-related changes in peripheral and/or central cytokine expression. Accordingly, behaviors exhibited during a modified social investigation test were first characterized in male rats following an acute injection of lipopolysaccharide (LPS; 100μg/kg). Subsequently, behavioral changes after either a high (4-g/kg; Experiment 2) or low dose (0.5g/kg; Experiment 3) of ethanol were also examined in the same social investigation test, as well as in the forced-swim test (FST; Experiment 4). Results from these experiments demonstrated similar reductions in both exploration and social investigatory behavior during acute illness and ethanol withdrawal, while a seemingly paradoxical decrease in immobility was observed in the FST during acute ethanol withdrawal. In follow-up studies, neither indomethacin (Experiment 5) nor interleukin-1 receptor antagonist (Experiment 6) pre-exposure reversed the ethanol withdrawal-induced behavioral changes observed in this social investigation test. Taken together, these studies demonstrate that the behavioral sequelae of acute illness and ethanol withdrawal are similar in nature, while antagonist studies suggest that these behavioral alterations are not reversed by blockade of IL-1 receptors or inhibition of prostaglandin synthesis. Though a direct mechanistic link between cytokines and the expression of acute ethanol withdrawal-related behaviors has yet to be found, future studies examining the involvement of brain cytokines as potential mediators of ethanol effects are greatly needed.

Perinatal exposure to polychlorinated biphenyls alters social behaviors in rats

Perinatal exposure to polychlorinated biphenyls (PCBs) leads to significant alterations of neural and hormonal systems. These alterations have been shown to impair motor and sensory development. Less is known about the influence of PCB exposure on developing emotional and motivational systems involved in social interactions and social learning. The present study examined the impact of perinatal PCB exposure (mixture of congeners 47 and 77) on social recognition in juvenile animals, conspecific-directed investigation in adults and on neural and hormonal systems involved in social functions. We used a standard habituation-dishabituation paradigm to evaluate juvenile recognition and a social port paradigm to monitor adult social investigation. Areal measures of the periventricular nucleus (PVN) of the hypothalamus were obtained to provide correlations with related hormone and brain systems. PCB exposed rats were significantly impaired in social recognition as indicated by persistent conspecific-directed exploration by juvenile animals regardless of social experience. As adults, PCB exposure led to a dampening of the isolation-induced enhancement of social investigation. There was not a concomitant alteration of social investigation in pair-housed PCB exposed animals at this stage of development. Interestingly, PVN area was significantly decreased in juvenile animals exposed to PCB during the perinatal period. Shifts in hypothalamic regulation of hormones involved in social behavior and stress could be involved in the behavioral changes observed. Overall, the results suggest that PCB exposure impairs context or experience-dependent modulation of social approach and investigation. These types of social-context deficits are similar to behavioral deficits observed in social disorders such as autism and other pervasive developmental disorders.

Two-generation reproductive toxicity study of implanted depleted uranium (DU) in CD rats

Depleted uranium (DU) munitions and armor plating have been used in several conflicts over the last 17 yr, including the Persian Gulf War and the Iraq War. Because of its effectiveness and availability, DU will continue to be used in military applications into the foreseeable future. There is much controversy over the use of DU in weapons and equipment because of its potential radiological and toxic hazards, and there is concern over the chronic adverse health effects of embedded DU shrapnel in war veterans and bystanders. This study evaluated the effects of long-term implantation of DU on the reproductive success of F0 generation adults and development and survival of subsequent F1 and F2 generations in a two-generation reproductive toxicity study. F0 generation Sprague-Dawley rats, 8 wk of age, were surgically implanted with 0, 4, 8, 12, or 20 DU pellets (1 x 2 mm). Inert implant control animals were implanted with 12 or 20 tantallum (Ta) pellets. The F0 generation was then mated at 120 d post DU implantation. In the F0 generation, when measured on postimplantation d 27 and 117, uranium was present in the urine of DU-implanted animals in a dose-dependent manner. F0 reproductive success was similar across treatment groups and the maternal retrieval test revealed no changes in maternal behavior. DU implantation exerted no effect on the survival, health, or well-being of the F0 generation. Necropsy results of F0 animals were negative with the exception of a marked inflammatory response surrounding the implanted DU pellets. For the F1 generation, measures of F1 development through postnatal day (PND) 20 were unremarkable and no gross abnormalities were observed in F1 offspring. No uranium was detected in whole-body homogenates of PND 4 or PND 20 pups. Necropsy findings of F1 PND 20 pups were negative and no instances of ribcage malformation were observed in F1 PND 20 pups. Body weight and body weight gain of F1 rats through PND 120 were similar across treatment groups. Eight of 414 F1 animals observed from PND 20 to 120 died of unknown causes; 7 were from litters of DU-implanted F0 mating pairs. F1 mating success at 10 wk of age was an overall 70% compared with 91% for F0 mating pairs. Mating success was similar between F1 animals derived from DU-implanted F0 adults and those derived from F0 implant control adults suggesting that the comparatively low mating success was not due to F1 DU exposure. The gestational index of F1 animals derived from mid-dose F0 mating pairs was found to be lower compared with F1 controls. The average gestation duration of F1 animals derived from high-dose F0 mating pairs was found to be significantly longer than F1 controls. F1 sperm motility analyses did not differ among experimental groups and no gross abnormalities were identified at necropsy among surviving F1 animals at PND 120. Histopathology of kidneys, spleen, thymus, bone marrow, ovaries, and testes of F1 high-dose animals did not differ from F1 controls. F1 high-dose females had significantly higher mean relative liver and heart weights compared with F1 controls; the biological relevance of this finding could not be determined. For the F2 generation, measures of F2 development through PND 20 were unremarkable and no gross abnormalities were observed in F2 offspring. Necropsy findings of F2 PND 20 pups were negative and no instances of ribcage malformation were observed in F2 PND 20 pups. Body weight and body weight gain of F2 rats through PND 90 were similar across treatment groups. Mean relative heart weights of males derived from high-dose F0 parents were significantly lower compared with F2 controls. Sperm motility and concentration analysis of F2 males at PND 90 were similar across F2 groups. Overall, the consistent absence of positive findings in this study seems to suggest that DU is not a significant reproductive or developmental hazard, particularly when one considers that mid- and high-dose rats were implanted with the equivalent of 0.3 and 0.5 lb of DU in a 70-kg human, respectively. However, the findings that seven of eight F1 adults that died postweaning were from DU-implanted F0 mating pairs, and that mean relative heart weights were elevated in high-dose F1 and F2 pups, suggest conservatism is warranted in characterizing the reproductive and teratogenic hazards of embedded DU until further studies are completed.

Validation of a novel social investigation task that may dissociate social motivation from exploratory activity

The present series of studies provide validation of a new paradigm that uniquely combines the assessment of the propensity to engage in social investigation with measures of (nonsocial) exploratory activity in rats. Assessment of this social investigation paradigm indicated that (a) rats showed a robust preference for social investigation over nonsocial exploratory activity, (b) female rats showed a greater preference for social investigation than male rats, (c) no signs of habituation in these responses were observed when rats were tested once daily for 4 consecutive days, (d) the preference for social investigation was stable and robust in both the dark and light periods of the daily light cycle for 5 consecutive days, and (e) testing under bright light conditions suppressed social investigation. In addition, acute administration of opiate drugs, low dose morphine (1.0 mg/kg) and naltrexone (1.0 mg/kg) produced a more robust attenuation of social investigation than nonsocial exploratory activity. Amphetamine increased both forms of investigation and haloperidol had the opposite effect, but the overall preference for social investigation over exploratory activity remained largely intact after both amphetamine and haloperidol injection. Together, these findings validate the use of this behavioral task to assess changes in social-motivation and general exploratory activity. Importantly, the task is bi-directionally sensitive to subject characteristics (i.e., sex), drug manipulations which modulate social motivation, and environmental manipulations.

Evaluation of the effect of implanted depleted uranium (DU) on adult rat behavior and toxicological endpoints

In 2002, the Naval Health Research Center Toxicology Detachment began a study to determine the effects of surgically implanted depleted uranium (DU) pellets on adult rat (e.g., P1 generation) health and reproduction. In this report, the effect of implanted DU on adult rat behavior and health is described. Adult Sprague-Dawley (SD) rats, 8 wk of age, were surgically implanted with 0, 4, 8, 12, or 20 DU pellets (1 x 2 mm); 20 DU pellets of size 1 x 2 mm approximates to 0.22 kg (0.5 lb) of DU in a 70-kg (154 lb) person. Control animals were implanted with 12 or 20 tantallum (Ta) pellets. The animals were then housed for up to 150 d postimplantation or 20% of an assumed 2-yr life span for rats. The concentration of uranium in urine directly correlated with the number of implanted DU pellets, indicating that DU was migrating into the body from the implanted pellets. Three male and 4 female animals died during the 150-d period of causes apparently not related to DU implantation. Behavioral testing found no definitive evidence of neurobehavioral perturbations associated with DU implantation. Uranium translocated to tissues known to sequester uranium (bone, teeth, and kidneys), but uranium concentrations varied considerably within each dose group and did not follow a dose-response pattern as anticipated. Serum chemistry values were within normal ranges for the SD rat. However, alanine aminotransferase measurements were significantly lower for rats implanted with 20 DU pellets as compared to sham surgery controls but not when compared to animals implanted with Ta pellets only. Phosphate measurements were significantly lower for female rats implanted with 20 DU pellets as compared to both sham surgery controls and animals implanted with Ta pellets only. Monocyte ratios were higher in adult rats implanted with 20 DU pellets as compared to sham surgery controls but not when compared to animals implanted with 20 Ta pellets. Mean platelet volume was found to be significantly lower for rats implanted with 20 DU pellets as compared to sham surgery controls but not when compared to animals implanted with 20 Ta pellets. Gross necropsy found no obvious tissue abnormalities in implanted rats, and the weights of major tissues did not differ between Ta- and DU-implanted animals. Histopathologic analysis of major tissues from animals implanted with 0 pellets, 20 Ta pellets, or 20 DU pellets found no differences between treatment groups. The findings of this study indicate that implantation of up to 20 DU pellets in adult rats did not have a significant negative impact on their general health and neurobehavioral capacities when assessed after 150 d of pellet implantation. However, the growing body of data on the potential health effects associated with DU exposure warrants further studies involving higher embedded DU body burdens in conjunction with longer surveillance periods postimplantation.

Neurodevelopmental effects of perinatal fenarimol exposure on rats

Knowledge about the potential toxic effects of fenarimol, a widely used fungicide, is still limited. Fenarimol is an aromatase inhibitor and therefore can affect estrogen/androgen levels in vivo in rodents. In view of these facts, the aim of the present work was to study the effects of fenarimol maternal exposure during different critical phases in the development of central nervous system in rat pups, on early physical and neurobehavioral endpoints essential to their development. For that, the effects of the fungicide fenarimol (150 and 300 mg/kg) were examined at three different developmental stages in the rat: during the first 6 days of gestation, prenatal (15-21 days), or first 6 days of lactation. Three categories of the impact of fenarimol on neonatal growth and neurobehavioral development of offspring were assessed: (1) physical, (2) reflex and strength, and (3) motor coordination. Findings on the pups' physical development did not indicate any significant alterations of the postnatal age at which specific developmental milestones were observed (pinna detachment, development of the fur, eruption of the incisor teeth, opening of the ears and eyes and testes descent). However, there was a reduced rate of weight gain in pups of mothers treated during lactation related to the earlier testing time periods (1-23 days of life). The study of the functional state of the rat pup nervous systems at different stages of postnatal development revealed some neurodevelopmental delays in righting reflex, climbing and grip response and locomotion (20-90 days of life) in the treated groups. Taken together, findings of this study emphasize that, as a result of fenarimol maternal exposure, some neuromuscular and behavioral deficits in nursing pups may occur principally during the last gestational period and lactation. These results could be the basis for further studies on molecular actions of fenarimol in order to predict better the biological consequences of this fungicide.

Affective consciousness: Core emotional feelings in animals and humans

The position advanced in this paper is that the bedrock of emotional feelings is contained within the evolved emotional action apparatus of mammalian brains. This dual-aspect monism approach to brain-mind functions, which asserts that emotional feelings may reflect the neurodynamics of brain systems that generate instinctual emotional behaviors, saves us from various conceptual conundrums. In coarse form, primary process affective consciousness seems to be fundamentally an unconditional "gift of nature" rather than an acquired skill, even though those systems facilitate skill acquisition via various felt reinforcements. Affective consciousness, being a comparatively intrinsic function of the brain, shared homologously by all mammalian species, should be the easiest variant of consciousness to study in animals. This is not to deny that some secondary processes (e.g., awareness of feelings in the generation of behavioral choices) cannot be evaluated in animals with sufficiently clever behavioral learning procedures, as with place-preference procedures and the analysis of changes in learned behaviors after one has induced re-valuation of incentives. Rather, the claim is that a direct neuroscientific study of primary process emotional/affective states is best achieved through the study of the intrinsic ("instinctual"), albeit experientially refined, emotional action tendencies of other animals. In this view, core emotional feelings may reflect the neurodynamic attractor landscapes of a variety of extended trans-diencephalic, limbic emotional action systems-including SEEKING, FEAR, RAGE, LUST, CARE, PANIC, and PLAY. Through a study of these brain systems, the neural infrastructure of human and animal affective consciousness may be revealed. Emotional feelings are instantiated in large-scale neurodynamics that can be most effectively monitored via the ethological analysis of emotional action tendencies and the accompanying brain neurochemical/electrical changes. The intrinsic coherence of such emotional responses is demonstrated by the fact that they can be provoked by electrical and chemical stimulation of specific brain zones-effects that are affectively laden. For substantive progress in this emerging research arena, animal brain researchers need to discuss affective brain functions more openly. Secondary awareness processes, because of their more conditional, contextually situated nature, are more difficult to understand in any neuroscientific detail. In other words, the information-processing brain functions, critical for cognitive consciousness, are harder to study in other animals than the more homologous emotional/motivational affective state functions of the brain.

Study of the reproductive effects in rats surgically implanted with depleted uranium for up to 90 days

In 2001, the Naval Health Research Center Toxicology Detachment was funded by the U.S. Army Medical Research Acquisition Activity (USAMRAA) to conduct a study of the effects of surgically implanted depleted uranium (DU) pellets on adult rat reproductive success and development across two successive generations. This article presents some of the findings for the group of offspring from adult rats mated at 30 d post surgical implantation of DU pellets. Adult male and female Sprague-Dawley rats (P1 generation) were surgically implanted with 0, 4, 8, or 12 DU pellets (1 x 2 mm). The P1 generation was then cross-mated at 30 d post surgical implantation. Urine collected from P1 animals at 27 d post surgical implantation showed that DU was excreted in the urine of DU-implanted animals in a dose-dependent manner. DU surgical implantation did not have a negative impact on P1 reproductive success, survival, or body weight gain through post surgical implantation d 90. There were no statistically significant differences in F1 birth weight, survival, and litter size at postnatal day (PND) 0, 5, and 20. No gross physical abnormalities identified in the offspring were attributable to neonatal DU exposure. A series of neurodevelopment and immune function assessments were also conducted on F1 offspring. No group differences were observed that were related to parental DU exposure. Studies are ongoing on the impact of leaving DU embedded in soft tissue for 120 d on rat reproduction and subsequent offspring survival and development.

Developmental toxicity potential of paclobutrazol in the rat

Paclobutrazol is used as a fungicide and as a plant growth regulator, but there are few studies about its potential toxic effects. Experiments were conducted to determine whether this compound has adverse effects on the reproduction and development of offspring. The influence of 1.0 mg/kg paclobutrazol (10 x the acceptable daily intake-ADI), by oral exposure during gestational organogenesis of rats, was evaluated on maturational and behavioural aspects of offspring development. This dose did not promote evidence of maternal toxicity and the weight of gravid uterus, fetus, and ovary on days 16 and 20 of pregnancy were not affected. Also, the pesticide did not affect body weight gain of the dams and offspring. However, the pups' survival at weaning was impaired by paclobutrazol. Beyond that, study of the functional state of rat pups' nervous system at different stages of postnatal development revealed some differences in treated ones. Damage was observed in the expression of acoustic startle reflex and altered locomotion and/or rearing in an open-field apparatus in treated pups depending on their age. There were no observed alterations in swimming behaviour. The data support further studies of the potentially toxic effects that exposing mothers to this pesticide may have on their litters.

Reduction of motor seizures in rats induced by the ethyl bicyclophosphate trimethylolpropane phosphate (TMPP)

1. Trimethylolpropane phosphate (TMPP) is a potent cage convulsant, reported to act through binding to the picrotoxinin and/or benzodiazepine receptor sites of the gamma-aminobutyricA (GABA(A)) ionophore complex. 2. Adult male Fischer-344 rats were pretreated by intraperitoneal (i.p.) injection with either diazepam (DZP) [0.5-5.0 mg/kg], Phenobarbital (PB) [5-20 mg/kg], dizocilpine maleate (MK-801) [0.5-3.0 mg/kg], Tiagabine (TGB) [0.5-5.0 mg/kg], 6,7-dinitro-quinoxaline-2,3-dione (DNQX), [5-20 mg/kg], or scopolamine [SCP] (0.25-1.0 mg/kg) 30 min prior to i.p. injection with a convulsive dose of TMPP (0.6 mg/kg). 3. Rats were rated for occurrence of convulsive activity for 120 min post-injection. Time from TMPP injection to observation of subclinical seizures, generalized (tonic-clonic) seizures, and lethality was rated for each pretreatment group. 4. In general, DZP = PB > TGB in reduction of TMPP subclinical and/or clinical seizures. MK-801, at dose levels inducing near sedation, was also effective in modulation of TMPP-induced seizures. SCP or DNQX were generally ineffective in reducing or eliminating TMPP-induced seizures.

Behavioral sensitization following exposure to low doses of trimethylolpropane phosphate

Behavioral sensitization is commonly studied within the context of drugs known to directly increase activity in the brain's dopamine system, particularly drugs of abuse. However, the present research suggests such behavioral changes can also be observed following exposure to other compounds that indirectly affect the dopamine system. One such compound is trimethylolpropane phosphate (TMPP), a bridged organophosphate that can be produced by the partial pyrolysis of certain synthetic lubricants used on military ships and aircraft. Although TMPP is a potent convulsant, it has been demonstrated that treatment with doses below seizure threshold results in long-term behavioral sensitization. The effect has been demonstrated with a number of neurobehavioral endpoints, particularly those assessing appetitive responding. More specifically, sensitization has been observed in acquisition of schedule-induced polydipsia (SIP), appetitive reinforcer approach sensitization (ARAS) and social interaction as measured in neonatal ultrasonic vocalizations, juvenile play and adult conspecific approach. Overall, the rats demonstrated a heightened appetitive response pattern. More specifically, TMPP reliably reduced the number of SIP sessions necessary to induce asymptotic drinking level and increased the time spent investigating (sniffing) a food reinforcer as measured in the ARAS task. Specific effects of TMPP on social interaction were an increase in ultrasonic vocalizations when the neonate was isolated from the dam and littermates and an increase in both measures of juvenile play (pins and dorsal contacts). A complex set of interactions emerged for the measures of adult social investigation where the drug effect was modulated by such factors as sex and neutral vs. stress-inducing experiences coincident with the drug treatment. In contrast to the above results, no behavioral changes were recorded for measures in the elevated plus maze and open field exploration. These results suggest that TMPP produces neurophysiological changes that persist much longer than the pharmacological effect of the compound, particularly in the neural correlates for appetitive behavior.