Single trial nicotine conditioned place preference in pre-adolescent male and female rats.

The mean age of first voluntary tobacco inhalation is 12.3 years (DiFranza et al., 2004). 60% of smokers start smoking before the age of 14 and 90% are dependent before reaching the age of 19. Females are typically more sensitive to nicotine than males yet few studies examine the effects of nicotine on the reward systems in pre-adolescent female subjects. This study utilized the single trial conditioned place preference (CPP) test in very young (postnatal day 25-27) rats of both sexes. Latent effects on anxiety and amphetamine response were determined 5 and 7 days following a second nicotine exposure. Results show that 0.05 mg/kg nicotine induced CPP in females following a single trial while both sexes showed CPP following the 0.5 mg/kg dose. Five days later, rats dosed with 0.05 mg/kg show increased time on the open arm of the elevated plus maze, an anxiolytic response. While baseline activity was increased in nicotine-exposed males 7 days following dosing, amphetamine response was not affected by the treatments in either sex. Therefore, our data suggest that young females are more sensitive to nicotine reward than males supporting a heightened sensitivity of the mesolimbic dopamine system in very young females. However, alterations in baseline activity were only seen in males suggesting that different components of the system are affected by nicotine in each sex. An anxiolytic response to nicotine 5 days after dosing may suggest that this very young age group is uniquely affected by this very low nicotine dose. Clearly, nicotine has substantial acute and lasting effects during pre-adolescence at doses substantially lower than seen at older ages as reported by others. These effects, which could potentially result from cigarette or e-cigarette smoking by 11-12 year old children , focus attention on the vulnerability of this age group to nicotine.

Withdrawal from THC during adolescence: sex differences in locomotor activity and anxiety.

Research suggests that the use and abuse of marijuana can be especially harmful if it occurs during adolescence, a period of vast developmental changes throughout the brain. Due to the localization of cannabinoid receptors within the limbic system and the established effects of cannabinoids on emotional states and anxiety levels of rats and humans, we studied the sex- and dose-related effects of Δ9-tetrahydrocannabinol (THC, the main psychoactive component in marijuana) on behavior and anxiety during spontaneous withdrawal. Male and female Sprague Dawley rats were administered 2, 7.5 or 15 mg/kg THC or vehicle from postnatal day 35-41 (approximating mid-adolescence in humans). Locomotor activity and anxiety-related behaviors were measured during drug administration and abstinence. THC caused significant dose-dependent locomotor depression during drug administration. Locomotor depression initially abated upon drug cessation, but re-emerged by the end of the abstinence period and was greater in female than male rats. We found sensitization to the locomotor-depressing effects of THC in middle- and high-dose rats and the subsequent development of tolerance in high-dose rats. The high dose of THC increased anxiety-like behaviors while the low dose decreased anxiety-like behaviors during drug administration, with females more sensitive to the anxiogenic effects of THC than males. During abstinence, females were again especially sensitive to the anxiogenic effects of THC. This study demonstrates sexually-dimorphic effects of THC on anxiety-related behaviors and locomotor activity during and after THC administration during adolescence. This information may be useful in the development of therapeutic approaches for the treatment of marijuana withdrawal in adolescents.

Methylphenidate response in prenatal cocaine-exposed rats: a behavioral and brain functional study.

Prenatal cocaine exposure is associated with abnormal arousal and attention in children. Since methylphenidate (MPD) is widely used to treat attention disorders, we wanted to determine whether prenatal cocaine exposure affects brain function in response to MPD as measured by glucose metabolism in a rodent model. Pregnant rats received 60 mg/kg cocaine or vehicle from gestational days 8-22 by intragastric intubation. On a single day between postnatal days 41-45, offspring received 10mg/kg i.p. of MPD or saline. After 15 min, the quantified 2-deoxyglucose (2DG) method was carried out in freely behaving animals. Seventy nine brain regions were assessed but we focused on functional units such as the mesolimbic and motor circuits which were analyzed using mixed linear models. MPD increased glucose metabolism in most brain regions from 15% to 30% over saline regardless of the prenatal treatment. Prenatal cocaine produced insignificant effects on the rates of brain glucose metabolism overall but produced a reduced response to MPD in the nucleus accumbens in a rostral/caudal gradient compared to control. In addition, correlations of rates of metabolism in the mesolimbic and nigrostriatal systems with the amount of MPD-induced behavior (stereotypy and locomotion) show that prenatal cocaine alters the relationship between regional metabolism and behavior in sex-specific ways. In summary, prenatal cocaine has minimal effects on brain metabolic activity even under drug challenge conditions but has a major impact on the relationship between brain metabolism and behavior.

The multifaceted effects of oral administration of methylphenidate in juvenile rats: anxiety, activity, and attention.

In previous studies, acutely administered oral methylphenidate (MPD, 3mg/kg) prior to testing improved performance on the radial arm maze in juvenile rats. In order to examine the mechanisms producing this improvement we administered MPD once prior to each test of anxiety, locomotor activity and attention. On postnatal day (PND) 22 on an elevated plus maze, rats spent more time beyond the rails on the open arms and showed altered risk-assessment behaviors suggesting an anxiolytic-like effect of MPD. Grid crossings on the plus maze indicated that MPD increased locomotor activity, as did activity recording on PND 23. In another group of juveniles, MPD improved performance in a multi-trial attention task in an age-dependent fashion. These data suggest that oral MPD has multifaceted effects on juvenile rats that together improve performance on cognitive tests such as the radial arm maze. In addition, our data support human studies finding multifaceted effects of MPD.

Methylphenidate improves performance on the radial arm maze in periadolescent rats.

Methylphenidate (Ritalin; MPD) is one of the most commonly prescribed drugs in childhood and adolescence and many clinical studies have documented its efficacy. Due to the limitations of conducting invasive research in humans, animal models can be beneficial for studying drug effects. However, few animal studies have demonstrated the effects of methylphenidate on cognitive processes. The objective of this study was to find a dose of methylphenidate that was effective in improving performance on a spatial working memory cognitive task when administered orally to periadolescent rats. Therefore, we dosed subjects with methylphenidate at 1 or 3 mg/kg/day via gastric intubation from postnatal day 22 to 59 and assessed the effects of the drug on performance on the radial arm maze each day. To enhance performance overall, a second experiment was conducted where the subjects were moderately food restricted (to 90% of the free-feeding weight). Results of Experiment 1 show that during the first week of testing only the 3 mg/kg MPD-treated males showed improved performance (entries prior to repeated entry) when ad lib fed and housed in pairs while the same dose significantly improved performance in both males and females under conditions of food-restriction and individual housing in Experiment 2. MPD also produced a pattern of increased errors and arms entered during the first week, especially in Experiment 2. MPD increased locomotor activity when tested at postnatal day 60 in both experiments. The data suggest that 3 mg/kg oral methylphenidate improves performance on a spatial cognitive task only early in treatment in the rat. While males show improvement under conditions of both high and low motivation, females only show MPD effects when highly motivated. Hypothetically, methylphenidate may improve radial arm maze performance through increased attention and improved spatial working memory and/or alterations in locomotion, reactivity to novelty or anxiety. Regardless, the study supports the utility of the rat as a suitable model to examine the effects of low dose oral MPD.

Oral methylphenidate improves spatial learning and memory in pre- and periadolescent rats.

Methylphenidate (MPD) is widely prescribed for attention-deficit/hyperactivity disorder in the United States. Patients, mostly school-age children, are taking the drug orally. To simulate the human condition, the authors used a cracker to administer methylphenidate orally (without the stress of handling) from Postnatal Day (PND) 22 to PND 40 and determined the effects of daily low-dose administration on the learning and performance of a radial arm maze win-shift task with all 8 arms baited. Number of entries to repeat, time to finish 8 entries, and days to reach criterion (at least 7 entries without errors for 4 out of 5 consecutive trials) were evaluated. An improvement during the first 7 days was revealed in both male and female rats treated with 3.0 mg/kg of oral methylphenidate compared with the controls. On PND 40, locomotor activity levels were not significantly different in the 3.0 mg/kg treated group compared with the controls during the initial 5 min or during the full 1 hr of recording. These data suggest that oral administration of low-dose MPD improves spatial learning and memory in both male and female preadolescent rats.

Gender differences in prodynorphin but not proenkephalin mRNA expression in the striatum of adolescent rats exposed to prenatal cocaine.

The objective of this study was to determine if prenatal cocaine affects the levels of prodynorphin and proenkephalin mRNA in male and female adolescent rats. Pregnant dams received cocaine or vehicle from gestational days 8-22 and upon delivery, the pups were fostered. At postnatal days 42-44, pups were killed and brains removed and frozen. Sections of striatum and nucleus accumbens were processed for prodynorphin and proenkephalin mRNA expression. Prenatal cocaine did not affect the expression of proenkephalin mRNA, but males showed higher expression than females. However, prodynorphin mRNA was lower in female rats exposed to cocaine compared to controls. Prenatal cocaine appears to have unique effects on neuropeptides during adolescence.

Prenatal cocaine dampened behavioral responses to methylphenidate in male and female adolescent rats.

Clinical and animal data point toward deficits in attention and arousal after prenatal cocaine exposure. Since methylphenidate (MPD) is widely used to treat attention disorders, we wanted to determine whether prenatal cocaine (PC) exposure affects the behavioral response to MPD in young rats of both sexes. Pregnant dams received 60 mg/kg of cocaine or vehicle from gestational days 8-22 by intragastric intubations. After delivery, litters were culled to 10 (5 males, 5 females) and fostered. On a single day between PND 41-44 locomotion was recorded in a Plexiglas box within an Accuscan activity monitor after receiving a single injection of 10 mg/kg intraperitoneally of MPD or saline. Rats were also videotaped for analysis of stereotyped behavior. Results showed that MPD administration enhanced locomotion compared to saline injected groups. PC exposure in male rats did not have any effect on the locomotor response to MPD compared to prenatal controls. However, PC-exposed males showed a lower amount of time spent in low intensity stereotypy compared to prenatal control males and both groups of females that received MPD. PC exposure in female rats that received MPD dampened the locomotor response compared to prenatal control females that also received MPD. In conclusion PC exposure dampens the behavioral response to MPD differentially in males and females with an apparent selectivity of locomotion in females and stereotyped behavior in males.

Standardization of a novel blood-sampling method through the jugular vein for use in the quantified [14C] 2-deoxyglucose method.

In the traditional [14C] deoxyglucose (2DG) method for the measurement of local cerebral glucose utilization (LCGU), blood samples are collected from the femoral artery. However, the placement of a femoral catheter can affect locomotor activity of the animal. We wanted to develop a new technique for blood sampling that would not interfere with the ongoing behavior. Therefore, the present report establishes a method of collecting blood samples for the 2DG method through the jugular vein. To calibrate this method, catheters were inserted in both the femoral artery and jugular vein of adult male Sprague Dawley rats. The next day, rats were injected with 2DG (125 microCi/kg) through the jugular vein. To quantify 14C in plasma, the standard method of blood collection was used for the femoral artery while syringes were used to extract blood samples from the jugular vein. We calculated the integrated specific activity of the plasma and final tissue 2DG concentrations based on Sokoloff's original equation using blood samples derived from both vessels. LCGU determined in selected brain regions was equivalent using both sampling methods. In conclusion, sampling from the jugular vein is appropriate for the quantified 2DG method and does not disrupt locomotor activity of the rat.

Perinatal AZT exposure alters the acoustic and tactile startle response to 8-OH-DPAT and apomorphine in adult rats.

The present study was designed to assess the dopaminergic and serotonergic contributions of the acoustic startle response (ASR) and the tactile startle response (TSR) in adult rats that had been perinatally exposed to AZT (azidothymidine, zidovudine; an antiretroviral agent). Each dam was randomly assigned to a treatment group: non-treated, AZT0, 100 or 150 mg/kg. Once daily gastric intubation began prenatally on gestational day (G) 19 and continued to G22 and then the pups were intubated between postnatal day (PND) 2-20. On PND60, animals were tested for responses to both acoustic and tactile stimuli following a challenge of vehicle, 0.25 or 0.5 mg/kg 8-OH-DPAT, a 5-HT(1A) agonist, or 0.75 or 2.0 mg/kg apomorphine (APO, a dopaminergic agonist) IP. Both DPAT and APO increased startle magnitude as expected. Additionally, perinatal AZT exposure enhanced startle responses following both DPAT and APO, an effect not due to perinatal handling or intubation. Similarly, perinatal AZT increased tactile responses following drug challenge in a gender-specific manner. Perinatal AZT also prolonged startle latencies, a change which may indicate that perinatal AZT alters conduction velocity. Therefore, the administration of AZT during the perinatal period results in long-term functional alterations within the startle reflex pathways.

Repeated administration of methylphenidate in young, adolescent, and mature rats affects the response to cocaine later in adulthood.

RATIONALE: Previous studies have shown that the expression of behavioral sensitization to psychostimulants depends on the age and gender of the animal. OBJECTIVE: This study was conducted to determine the pattern of behavioral sensitization to repeated administration of methylphenidate (MPD) at three different developmental ages and to assess the response to a cocaine challenge in adulthood. METHODS: We gave five daily i.p. injections of 10 or 20 mg kg(-1) of MPD (10 MPD, 20 MPD) or saline to male and female rats beginning on postnatal days (PND) 21, 45, or 60. When all groups reached PND 90, rats were challenged with 10 mg kg(-1) cocaine. For both MPD administration and cocaine challenge, locomotion and stereotyped behaviors were assessed for 1 h. RESULTS: The 10 MPD dose produced increased locomotion over the other two treatments at all ages. Rats that received 20 MPD showed a decline in locomotion across days with an increase in the time spent in high intensity stereotypy by day 5. Animals treated with 10 MPD showed diverse behavioral responses with adolescents showing somewhat dampened stereotypy than the other two age groups. In response to cocaine, pretreatment with MPD at all ages enhanced the cocaine response and produced qualitatively different patterns of stereotyped behavior for each gender and pretreatment age group. CONCLUSION: MPD produced clear age-specific sensitization of behavior in rats. Furthermore, exposure to MPD cross-sensitized with cocaine regardless of the age at which MPD exposure occurred with each pretreatment age group showing a unique pattern of responses.

Preweaning cocaine exposure alters brain glucose metabolic rates following repeated amphetamine administration in the adult rat.

Developmental cocaine exposure produces long-term alterations in function of many neuronal circuits. This study examined glucose metabolic rates following repeated amphetamine administration in adult male and female rats pretreated with cocaine during postnatal days (PND) 11-20. PND11-20 cocaine increased the response to amphetamine in many components of the motor system and the dorsal caudate-putamen, in particular, and decreased the metabolic response in the hypothalamus. While amphetamine alone produced widespread increases in metabolism, there were no cocaine-related effects in the mesolimbic, limbic or sensory structures. These data suggest that a brief cocaine exposure during development can alter ontogeny and result in abnormal neuronal responses to repeated psychostimulant administration in adulthood.

Correlating brain metabolism with stereotypic and locomotor behavior.

Many studies have shown that developmental cocaine exposure alters brain function and behavior, the present study examined the relationship between brain metabolism and behavioral responses to drug challenge. SKF 82958, a selective D1 dopamine agonist, was administered to preweaning cocaine-exposed (50 mg/kg/day) rats and controls at 60 days of age. Deoxyglucose was administered 30 min later, during the peak behavioral response, to measure brain functional activity. Pearsonproduct-moment correlations of behavior (locomotor activity and stereotypic behavior) with rates of glucose metabolism in components of the nigrostriatal and mesolimbic circuits were analyzed. The analysis revealed that under saline-challenge conditions in control animals, rates of metabolism in mesolimbic regions are positively correlated to rates of locomotor activity, whereas in cocaine-treated rats, these correlations were absent. Following SKF challenge, a different pattern was seen; locomotor activity or stereotypic behavior was not correlated with mesolimbic or nigrostriatal metabolism, respectively, in controls but was positively correlated in cocaine-treated rats. Therefore, cocaine exposure during development enhances the coupling of metabolism in components of the mesolimbic and nigrostriatal dopamine systems with the behavioral output associated with these systems under drug-challenge conditions. This may be due to loss of inhibitory influences within the mesolimbic and nigrostriatal systems. Thus, the correlation of behavior and cerebral glucose metabolism provides a unique way of examining the effect of developmental cocaine exposure.

Blunted metabolic response to SKF 82958 in the mesolimbic system following preweaning cocaine treatment.

This study examined glucose metabolic rates following dopamine D(1) agonist challenge in adult male rats pretreated with cocaine during postnatal days 11-20. Water-pretreated control rats showed a reliable decrease in glucose metabolism of rostral mesolimbic structures when challenged with SKF 82958 while cocaine-pretreated males did not. These data support the notion that cocaine exposure during the preweaning period dampens D(1) receptor-mediated function and that the mesolimbic system exhibits a selective vulnerability to early cocaine exposure.

The effects of perinatal AZT exposure on the acoustic startle response in adult rats.

AZT (azidothymidine, zidovudine, ZDV) has become the standard medication to prevent the transmission of the human immunodeficiency virus from mother to fetus. The present study was designed to assess the acoustic startle response (ASR) in adult rats that had been perinatally exposed to AZT. Each litter was randomly assigned to a treatment group: nontreated, AZT 0, 50, 100 or 150 mg/kg. Once daily gastric intubation began prenatally between gestational day (G) 19 and 22 and then continued postnatally between postnatal day (PND) 2 and 20. Between PND75 and PND80, animals were tested for habituation to the acoustic stimuli and prepulse inhibition following a challenge of either saline or 1.0 mg/kg amphetamine (AMP) intraperitoneally. Amphetamine increased ASR and startle latencies throughout the session. The AZT100 dose increased ASR habituation. AZT treatment did not affect prepulse inhibition. Females treated with AZT150 continued to show high ASRs at the end of the startle session. AZT-treated animals showed a dose-dependent increase in peak latency, suggesting a possible abnormal conduction velocity. These effects are independent of handling and intubation effects. Therefore, perinatal AZT treatment results in long-term changes within the primary acoustic startle pathway.