Neuroanatomical Basis for the Effects of Cocaine on Ontogeny of Dopamine Systems.
The effects of cocaine on the functional development of specific forebrain dopaminergic circuits are examined using functional imaging techniques, behavioral assessments and molecular markers for specific cell types using ISHH. Through collaborations with Dr. Yasmin Hurd at Mt. Sinai School of Medicine, molecular studies have shown that cocaine administered to preweaning males decreased the expression of the mRNA for prodynorphin, a neuropeptide localized in the GABAergic efferent projections of the striatal complex. Behavioral measures are correlated with in vivo imaging of the brain to determine the relationship between alterations in dopaminergic activity and the behavioral manifestations. The approach has been to administer cocaine during vulnerable periods of development and to examine exposed adults for brain metabolic and behavioral alterations. The lab has demonstrated that the effects of cocaine exposure depend on the time of drug administration as well as on the gender of the animal (Fig. 1).
Figure 1. shows autoradiographs of in vivo glucose imaging of the relationship between cocaine and gonad status with gonadectomy reducing metabolism in the controls and cocaine increasing metabolism primarily in components of the motor system.
Several other projects are ongoing in the lab, including the examining of spatial learning and performance using the Radial 8-arm maze and amphetamine sensitization, and the coupling of the dopamine receptor with second messenger systems (a collaboration with Hoau-Yan Wang, of CCNY, CUNY). The data from the Radial arm maze suggest that while postnatal cocaine treatment does not alter the rate of acquisition of a spatial learning task, it does impair performance when there has been a shift in the extra-maze cue profile. In addition, cocaine-treated females were not able to rapidly reacquire the performance as the other groups were. These data are particularly interesting since they are similar to clinical findings that also demonstrate gender differences in cocaine's effects on cognitive function. The results from the amphetamine sensitization project suggest that postnatal cocaine treatment dampens amphetamine-induced sensitization behaviors in males, while in females cocaine treatment affected the circuits mediating locomotor activity and stereotypy differently such that stereotypy was increased and locomotor activity was relatively decreased with repeated amphetamine administration. These changes in behavior may be due to a selective uncoupling of the dopamine receptor from its second messenger system in the cortex of exposed rats.
Recent studies by Annelyn Torres-Reveron, PhD, (a recent graduate student in the lab) show that prenatal cocaine dampens the behavioral response to methylphenidate in sex-specific ways and alters the relationships between metabolism in specific brain regions with the behaviors observed. Since methylphenidate (Ritalin®) is used to treat attention disorders and prenatal cocaine has been found to increase the incidence of this disorder in humans, our findings may suggest that children exposed to cocaine prenatally may require larger doses of methylphenidate to obtain improved function. However, we have yet to examine the effects of prenatal cocaine exposure on methylphenidate responses in an attention test.
We are also studying the effects of gonadectomy in females on the behavioral and metabolic response to cocaine. These results suggest that gonadectomy reduces metabolism but that cocaine administration to a gonadectomized female still produces increased metabolism (see Fig. 1).
THC (the primary psycho-active component on marijuana) alters the development of executive function.
The overall goal of this project is to identify which specific domains of executive function (EF) [which we will define as the coordination and control of cognitive operations to attain specific goals] are affected by marijuana exposure during different phases of development. Marijuana is one of the most widely abused drugs in adolescence. In fact, children begin to smoke marijuana as early as 12 years of age. Studies have shown that preadolescent exposure to THC can induce long-lasting behavioral alterations as well as induce locomotor depression. However, THC effects on locomotor activity have not been studied in adolescents. Therefore, we wanted to assess the effects of THC on locomotor activity in male and female pre-adolescents and determine whether tolerance to such effects might develop.
To date, we have examined primarily early adolescent effects of repeated THC exposure and found that THC given by the oral route has very little effect on active and passive avoidance, activity during dosing, and mild effects on attentional processing. Other rats were dosed during postnatal days 22-40 and tested for non-spatial memory using a novelty preference test showed some impairment in short-term memory especially when the rats were 160 days of age.
Since there are some reports that oral dosing results in very slow increases in brain drug concentration, we have now changed our dosing method to an ip injection. We have started dosing our postnatal animals ip using the Pluronic F68 vehicle and are collecting data on the non-spatial delayed working memory test as well as the active place avoidance test. To date, the data on locomotor activity show a clear decrease in activity across the entire dosing period suggesting that tolerance to the effects of THC does not develop (Fig. 2). Also, the preadolescent males actually show an increase in activity after the first dose of THC. These sex-specific effects are interesting and deserve further study.
Figure 2. Repeated measures ANOVA showed a significant 4 way interaction between treatment, sex, age and time block (p=0.026).
1). In Veh group, activity of both male and female rats was increased significantly with age. However, such age related increases were not observed in THC-2 (2mg/kg THC/ day) groups.
2). At day 22 THC-2 males showed increased activity compared to vehicle males. This was not seen in the females.
3). THC significantly decreased activity on days 29 and 40 in both sexes for most time blocks.
Effects of Methylphenidate (Ritalin®) administered to periadolescent rats improves performance on the Radial Arm Maze (RAM).
Presented at the Society for Neuroscience, 2006; poster # 462.8. We have tested 12 cohorts of 12 subjects each in this protocol. On postnatal day 22 following lights out, each rat was weighed and intubated with either 0, 1 or 3 mg/kg methylphenidate (MPD) in water intragastrically. 40 min following the intubation, each rat was placed on the radial-8 arm maze and behavior recorded. Rats were tested until they reached criterion (7/8 arms entered w/o a repeat for 4/5 test days). We found that MPD improves performance on the RAM (@ 3mg/kg) within the first week of testing and has minimal effects on activity after chronic administration (at 60 days). However, when the subjects are tested for sensitivity to cocaine 2 weeks following treatment, pretreatment with MPD at the high dose enhanced cocaine-stimulated activity. We also found that MPD apparently dampens conditioned place preference for cocaine at 60 days of age.
Figure 3. Learning curves for 5 cohorts of subjects across the test days. The curves are generated by first showing "entries-to-re" for the subjects on each test day and then assigning a value of 8 entries (the maximum) to those rats that achieved criterion to allow for comparison of the groups as testing continued. The males that received 3 mg/kg showed a superior performance compared to the other groups as evidenced by the trend line (red) and this was significant in both sexes for the food-restricted animals. *represents significant difference between MPD 3 performance and MPD 0 in preplanned Dunnett's tests.
Molecular Changes in Human Brain Following Prenatal Drug Exposure.
Another project which is currently underway in the lab is that of the molecular alterations in human brain following prenatal drug exposure. This project, conducted in collaboration with Dr. Yasmin Hurd at Mt. Sinai School of Medicine, examines human fetal material for molecular alterations (Fig. 4). Through these studies, it is hoped that we will better understand the impact of THC, cocaine, and other drugs on neurobehavioral development in humans.
Figure 4. Prodynorphin (A) and proenkephalin (B) mRNA expression levels in the striatum of the human fetus (week 20). CN, caudate nucleus; NAc, nucleus accumbens; P, putamen; Pc, piriform cortex.
Dow-Edwards, D. L., Benveniste, H., Behnke, M., Bandstra, E. S., Singer, L., Hurd, Y. L., and Stanford, L. R. (2006). Neuroimaging of prenatal drug exposure. Neurotoxicol. Teratol. 28, 386-402.
Torres-Reveron, A., and Dow-Edwards, D. L. (2006). Prenatal cocaine dampened behavioral responses to methylphenidate in male and female adolescent rats.Neurotoxicol. Teratol. 28, 165-172.
Torres-Reverón, A., Melnick, S. M., Stephenson, S. I., and Dow-Edwards, D. L. (2006). Standardization of a novel blood sampling method through the jugular vein for use in the quantified [14C] 2-deoxyglucose method. J. Neurosci. Methods 150, 143-149.
Wang, X., Dow-Edwards, D., Anderson, V., Minkoff, H., and Hurd, Y. L. (2006). Discrete opioid gene expression impairment in the human fetal brain associated with maternal marijuana use. Pharmacogenomics J. 6, 255-264.
Zhao N., Harte, K. L., and Dow-Edwards, D. L. (2006). Preadolescent THC administration: tolerance to the locomotor-depressing effects. Society for Neuroscience Abstract 766.
Torres-Reverón, A., Hurd, Y. L., and Dow-Edwards, D. L. (2007). Gender differences in prodynorphin but not proenkephalin mRNA expression in the striatum of adolescent rats exposed to prenatal cocaine. Neurosci. Lett. 421, 213-217.
Zhu, N., Weedon, J., and Dow-Edwards, D. L. (2007). Oral methylphenidate improves spatial learning and memory in pre- and periadolescent Rats. Behav. Neurosci. 121, 1272-1279.
Dow-Edwards, D. L., and Zhao, N. (2008). Oral THC produces minimal behavioral alterations in preadolescent rats. Neurotoxicol. Teratol. 30, 385-389.
Dow-Edwards, D. L., Weedon, J., and Hellmann, E. (2008). Methylphenidate improves performance on the radial arm maze in periadolescent rats. Neurotoxicol. Teratol. 30, 419-277.
Zhao, N., Wang, H. W., and Dow-Edwards, D. (2008). Cocaine exposure during the early postnatal period diminishes medial frontal cortex Gs coupling to dopamine D1-like receptors in adult rat. Neurosci. Lett. 438, 159-162.
Dothlyn Dunkley, M.S., R.H.I.A., Project Specialist
Lauren Harte, B.S., Graduate Student
Maiko Iijima, B.S., Research Support Specialist
April Jackson, B.S., Senior Research Support Specialist
Nora Siegal, B.S., Graduate Student
Stacy Stephenson, A.A., Research Support Specialist
Ning Zhao, M.D., Research Associate Professor
Ning Zhu, B.S., Graduate Student
Ad hoc service on the NIDA study section.