Cocaine treatment in neonatal rats affects the adult behavioral response to amphetamine

The effect of developmental exposure to the fungicide triadimefon on behavioral sensitization to triadimefon during adulthood

Triadimefon (TDF) is a triazole fungicide that acts as an indirect dopamine (DA) agonist by binding to the dopamine transporter (DAT) and increasing levels of synaptic DA. Studies in this laboratory have found that repeated dosing with TDF in adult mice leads to the development and robust expression of behavioral sensitization, a response mediated by dopaminergic and glutamatergic neurotransmitter systems, and causing long-term changes in dopaminergic function. Few studies have focused on the potential for TDF to be a developmental neurotoxicant. As such, the objective of the present study was to determine whether postnatal exposure to TDF would permanently alter DA systems and thereby influence TDF-induced expression of behavioral sensitization during adulthood. Male C57BL/6 mice were dosed intraperitoneally (i.p.) with 25 mg/kg TDF (TDF25), or oil (veh) from postnatal day (PND) 8 to 21. At 8-9 weeks of age, mice were split into four groups and treated with 75 mg/kg TDF (TDF75) or vehicle twice a week for a total of seven injections, with locomotor activity measured immediately after each injection. After a 2-week withdrawal period, mice were further split into eight groups, and challenged with TDF75 or vehicle to test for the expression of behavioral sensitization. Postnatal TDF exposure attenuated both the induction and expression of TDF-induced vertical but not horizontal sensitization in adults. Postnatal TDF exposure also produced long-term decreases in basal striatal dihydroxyphenylacetic acid (DOPAC) levels and nucleus accumbens shell DAT binding. These results indicate for the first time that TDF may be considered an environmental risk factor for developmental dopaminergic neurotoxicity.

Effects of perinatal exposure to delta 9-tetrahydrocannabinol on operant morphine-reinforced behavior

The present study examined the effects of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) when administered during the perinatal period on morphine self-administration in adulthood. To this end, pregnant Wistar rats were daily exposed to Delta(9)-THC from the fifth day of gestation up to pup weaning, when they were separated by gender and left to mature to be used for analyses of operant food- and morphine-reinforced behavior in a progressive ratio (PR) schedule. We also analyzed dopaminergic activity (DOPAC/DA) in reward-related structures during specific phases of the behavioral study. In both reinforcement paradigms, food and morphine, females always reached higher patterns of self-administration than males, but this occurred for the two treatment groups, Delta(9)-THC or vehicle. These higher patterns measured in females corresponded with a higher DOPAC/DA in the nucleus accumbens prior to the onset of morphine self-administration in comparison to males. Interestingly, DOPAC/DA was lower in Delta(9)-THC-exposed females compared to oil-exposed females and similar to oil- and Delta(9)-THC-exposed males. In addition, Delta(9)-THC-exposed females also exhibited a reduction in DOPAC/DA in the ventral tegmental area, which did not exist in males. All these changes, however, disappeared after 15 days of morphine self-administration and they did not reappear after 15 additional days of extinction of this response. Our data suggest that females are more vulnerable than males in a PR schedule for operant food and morphine self-administration; perinatal Delta(9)-THC exposure is not a factor influencing this vulnerability. The neurochemical analysis revealed that the activity of limbic dopaminergic neurons prior to morphine self-administration was higher in females than males, as well as that the perinatal Delta(9)-THC treatment reduced the activity of these neurons only in females, although this had no influence on morphine vulnerability in these animals.

Differential behavioral responses to chronic amphetamine in adult male and female rats exposed to postnatal cocaine treatment

The impact of cocaine exposure during development on behavioral sensitization as measured by locomotor activity and stereotypy following repeated intermittent administration of amphetamine is examined. Male and female Sprague-Dawley rats were exposed to cocaine at 50 mg/kg/day during postnatal days (PND) 11-20 and, as adults (PND193-212), were administered seven daily injections of 2.0 mg/kg amphetamine. Both locomotor activity and stereotypic behavior were assessed following the first and seventh injections. Control males and females showed sensitized behavior following repeated amphetamine injections with females showing greater locomotion while males showed increased stereotypy. Male rats pretreated with cocaine failed to develop sensitized locomotor or stereotypic responses following repeated amphetamine injections consistent with dampened D(1) receptor activity. Females pretreated with cocaine did not show a sensitized locomotor response but did display sensitization of stereotypy following repeated amphetamine administration. Thus, it appears that postnatal cocaine treatment produces differential effects on the circuits mediating sensitization behavior in male and female rats.

Regulation of EphB1 expression by dopamine signaling

The Eph family tyrosine kinase receptors and their ligands have been implicated in axon guidance and neuronal migration during development of the nervous system. In the current study, we aim to characterize the nature of changes in EphB1 receptor expression following increases or decreases in dopamine activity. Neonatal mice (P3) were injected with 6-hydroxydopamine and allowed 13 days to recover. These animals show a profound depletion of dopamine in all areas assayed, with a corresponding dose-dependent decrease in EphB1 expression. Day 3 pups were also injected either chronically (P3-P16) or acutely (P3 only) with cocaine to determine how enhancing dopamine signaling would affect EphB1 signal density. It was found that both treatments significantly increased expression of EphB1 in the cortex, striatum and substantia nigra. Finally, animals were treated prenatally (E15-E17) with cocaine and sacrificed on P7. These animals also showed an increase in EphB1 signal density, but only in the dopaminergic terminal areas in the cortex and striatum. These studies indicate that dopamine activity regulates developmental expression of the tyrosine kinase receptor EphB1.

Effects of neonatal cocaine treatment and gender on opioid agonist-stimulated [(35)S]GTP gamma S binding in the striatum and nucleus accumbens

Prenatal cocaine exposure increases mu-opioid receptor binding in dopaminergic terminal areas and enhances behavioral responsiveness to mu-opioid agonists. We investigated the influence of early postnatal cocaine treatment on in vitro mu- and delta-opioid receptor activation in male and female weanling rats. Pups received subcutaneous injections of either 20 mg/kg cocaine HCl or saline once daily on postnatal days 1 through 5. On postnatal day 25, animals were decapitated and their brains were removed and frozen for later sectioning. Opioid receptor activation was assessed in the striatum and the shell of the nucleus accumbens by autoradiographic analysis of agonist-stimulated [(35)S]GTP gamma S binding. Brain sections were incubated in the presence of [(35)S]GTP gamma S, GDP, and either the mu-opioid agonist [D-Ala(2)-N-MePhe(4)-Gly(5)-ol]enkephalin (DAMGO) or the delta-opioid agonist D-Pen(2)-D-Pen(5)-enkephalin (DPDPE). Baseline binding was assessed in the absence of agonist, and nonspecific binding was determined by the addition of unlabeled GTP gamma S. Film images were quantified using brain mash-calibrated [(14)C] standards. Neonatal cocaine treatment had no effect on either baseline or agonist-stimulated [(35)S]GTP gamma S binding. However, males exhibited significantly greater activation than females of delta-opioid receptors in both striatum and accumbens shell, regardless of neonatal treatment. These findings indicate a gender difference in delta-opioid receptor function that could mediate behavioral differences in response to opioid agonists.

Evaluation of neonatal exposure to cocaine on learning, activity, startle, scent marking, immobility, and plasma cocaine concentrations

Prenatal cocaine treatment produces equivocal effects on spatial learning and memory; however, no data are available on neonatal treatment as a model of human third-trimester exposure. Sprague-Dawley rats were treated on postnatal days (P) 1-10 or 11-20 with cocaine (15 mg/kg x 4 per day at 2-h intervals) or saline (P1-P20) and evaluated as adults in the Morris water maze and on tests of activity, startle, scent marking, swimming immobility, and sequential learning. Neonatal cocaine had no effect on mortality; however, early treatment reduced body weight, whereas later treatment did not. Neonatal cocaine had no effects on exploratory activity, swimming ability, sequential learning, multiday activity rhythms, scent marking, or swimming immobility, but augmented acoustic startle amplitude in the early-treated group. Neonatal cocaine also produced an interaction on spatial learning in which the cocaine early-treated males performed slightly more efficiently than controls. Plasma cocaine concentrations were significantly higher in the early-treated group than the later-treated group despite receiving the same weight-adjusted doses. It was concluded that neonatal cocaine, when administered during a stage of brain development analogous to human third trimester, induces few behavioral effects based on the assessments used in this study.

Prenatal cocaine exposure alters behavioral and neurochemical sensitization to amphetamine in adult rats

This study examined the neurochemical correlates of amphetamine (AMPH)-induced behavioral effects in prenatally saline (PSAL)-exposed or cocaine (PCOC)-exposed male rats. Pregnant Long-Evans rats received saline or saline containing cocaine hydrochloride (20 mg/kg s.c., b.i.d.) from gestational days 15-21. Animals were left with their biological mothers. Adult offspring were exposed to daily saline or AMPH (0.5, 1.5, or 5 mg/kg, i.p.) injections for 7 days. Behaviors were recorded in an open field during the first hour post-injection. PCOC rats did not exhibit behavioral anomalies during habituation to injection-stress or placement in the open field. PCOC rats displayed significant alterations in stereotyped responses to acute or intermittent exposure to various doses of AMPH. Within 48 h of the final testing day, striatal tissue was obtained from these animals and electrically-evoked [3H]acetylcholine (ACh) release was measured from striatal slices. Superfusion of tissue slices with various concentrations of AMPH (1-1000 nM) produced dose-dependent inhibition of ACh release in both PSAL and PCOC rats repeatedly injected with saline as adults. However, AMPH-induced inhibition of ACh release was decreased in PCOC rats repeatedly injected with AMPH as adults. At 5 mg/kg AMPH, PCOC rats exhibited increased mortality compared to PSAL rats. These data suggest that PCOC exposure produces long-lasting alterations in nigrostriatal transmission and behaviors mediated by this system.

The neurobiology of cannabinoid dependence: sex differences and potential interactions between cannabinoid and opioid systems

Cannabis is the most widely used illicit drug in many western countries. Its psychoactive ingredient, delta9-tetrahydrocannabinol (THC), produces a variety of effects in animals and humans that are probably mediated by specific cannabinoid receptors in the brain and interactions with several neurotransmitter and neuromodulator systems. For instance, recent research has revealed an important mutual functional relationship between cannabinoids and endogenous opioid systems in mediating the pharmacological and behavioral actions produced by these agents, including their reinforcing effects. Perinatal exposure to and interactions between cannabinoids and opioids might also have long-term behavioral consequences lasting into adulthood. In this work, we present preliminary evidence examining the potential effects of maternal exposure to THC on the motivational properties of morphine in male and female adult rats, as measured by an intravenous opiate self-administration paradigm.

Behavioral responses to a D1 dopamine agonist in weanling rats treated neonatally with cocaine and delta9-tetrahydrocannabinol

We determined whether neonatal exposure to cocaine with or without delta9-tetrahydrocannabinol (THC) altered the behavioral responses of weanling rats to the full D1 dopamine (DA) agonist SKF 81297. Rats were injected SC once daily from postnatal day (PD) 1 through 5 with cocaine (20 mg/kg), the same dose of cocaine plus THC (10 mg/kg), or drug vehicle. On PDs 24, 25, or 26, male and female littermates were administered 3 or 10 mg/kg of SKF 81297 or saline vehicle, and then tested 15 min later in an open-field apparatus. Neither neonatal drug treatment nor gender influenced the behavioral responses to SKF 81297. The drug challenge did, however, produce several dose-dependent behavioral effects, including increases in locomotor activity, line crossing, sniffing, and headshakes, and a decreased incidence of rearing, grooming, and stationary behavior. Furthermore, even though earlier administration of cocaine and THC failed to alter D1 receptor sensitivity, animals in both neonatal treatment groups exhibited an overall increase in grooming behavior and a decrease in sniffing compared to controls when the results were combined across doses of SKF 81297. These findings indicate that early postnatal exposure to cocaine can alter certain behaviors independently of functional changes in the D1 receptor system.

Behavioral sensitization to apomorphine in adult rats exposed to cocaine during the preweaning period: a preliminary study

Sixty-day-old rats treated with cocaine (50 mg/kg SC) during postnatal days (PND) 11-20 received daily injections of apomorphine (2.0 mg/kg SC) for 10 consecutive days to examine the development of sensitization to a direct dopamine agonist. Behavior was monitored on days 1, 5, and 10, using a photobeam system, and on day 10 using the videotape assessments as well. Locomotor sensitization to apomorphine developed in the preweaning vehicle-treated males only. Neither the cocaine-treated males nor any females exhibited locomotor sensitization to repeated apomorphine injections at 2 mg/kg. There were no other treatment-related effects except for grooming, which showed an interaction between treatment and gender. Overall, every behavior analyzed showed significant apomorphine effects, except rearing. Margin time (wall hugging), grooming, and quiet were significantly decreased by apomorphine, while locomotion and the duration of sniffing were increased. In summary, these data indicate that with respect to locomotor activity, the development of sensitization to apomorphine at 2.0 mg/kg is prevented by preweaning cocaine administration in males. These data further suggest that developmental cocaine exposure produces long-term alterations in DA D1 receptor-mediated responses in male rats.

Stimulant-mediated c-fos induction in striatum as a function of age, sex, and prenatal cocaine exposure

Induction of the immediate-early gene c-fos by the stimulants cocaine and amphetamine (AMPH) was analyzed by Fos immunocytochemistry at different ages in the brains of prenatally cocaine-treated and control rats. Cocaine and AMPH induced c-fos in patches of striatal neurons during the first postnatal week, and thereafter produced a progressively more homogeneous pattern that was more dense medially. Quantification of Fos-immunoreactive cells in older rats revealed differences related to sex and prenatal cocaine treatment. Both cocaine and AMPH produced dose-dependent increases in the number of Fos-immunoreactive cells in striatum. Prenatal cocaine exposure resulted in increased Fos in males in response to AMPH (2 mg/kg) at P18 and cocaine (10 mg/kg) at 1-2 months. In females, prenatal cocaine treatment resulted in a reduced response to cocaine at 1-2 months. Increased c-fos induction was observed in control females compared to control males in response to low doses of stimulants; no such sex difference was observed in prenatally cocaine-treated rats. The dopamine D1 antagonist SCH23390 blocked cocaine-mediated c-fos induction in all groups. The NMDA antagonist MK-801 blocked cocaine-mediated c-fos induction in the medial striatum. In females only, MK-801 pretreatment resulted in a dramatic increase in the number of Fos-immunoreactive cells in lateral striatum. These findings indicate differences in the neural basis of c-fos induction in males and females, and changes in stimulant-mediated c-fos induction resulting from prenatal cocaine exposure.

The stimulus properties of two common over-the-counter drug mixtures: dextromethorphan + ephedrine and dextromethorphan + diphenhydramine

Two groups of rats were trained in a two-choice drug discrimination procedure under a fixed-ratio 10 schedule of food reinforcement. One group of rats (n=12) was trained to discriminate the presence and absence of a drug mixture containing 10 mg/kg dextromethorphan + 10 mg/kg diphenhydramine. The other group of rats (n=12) was trained to discriminate the presence and absence of another drug mixture containing 10 mg/kg dextromethorphan + 10 mg/kg ephedrine. Cross-generalization tests conducted with each of the stimulus elements demonstrated that (1) the drug mixtures were not perceived as new entities distinct from their component elements and (2) the stimulus element saliency may be a factor determining the nature of discriminative control by drug mixtures. Cross-generalization tests conducted with the psychomotor stimulants, cocaine and amphetamine, engendered complete generalization to the training cues in both groups, whereas, pentobarbital engendered predominantly saline- or default-lever responding. These data suggest a potential abuse liability for both of these common over-the-counter drug mixtures and cautions against the use of such combinations in pediatric patients.

Preweaning cocaine administration alters the adult response to quipazine: comparison with fluoxetine

This study investigated whether exposure to cocaine during the preweaning period affects the behavioral response to administration of a challenge dose of quipazine, a relatively nonselective serotonin (5-HT) mixed agonist/antagonist, in adulthood. To determine whether selective inhibition of the 5-HT transporter during the preweaning period would produce a cocaine-like pattern of effects, another group of rats was given fluoxetine, a highly selective and potent inhibitor of the 5-HT transporter, and was tested along with the cocaine-treated rats. Male and female rats received 25 mg/kg cocaine HCl (82.5 mumol/kg), 25 mg/kg fluoxetine HCl (72.3 mumol/kg), or vehicle subcutaneous (s.c.) during postnatal days 11-20. Both treatments reduced weight gain during the injection period only. At 60 days of age, subjects were administered a single dose of quipazine (0, 0.4, or 1.0 mg/kg, s.c.) and placed in the Accuscan activity monitor for 1 h of behavioral recording. Overall, distance traveled, vertical activity, and time in the center of the chamber decreased during the initial time blocks of the session and vertical activity decreased with increasing doses of quipazine. Females in general showed greater overall activity levels than males as well as greater responsivity to quipazine. Preweaning cocaine exposure produced different effects in males and females. In males, cocaine enhanced the response to quipazine for vertical activity whereas it had no effect on quipazine-induced alterations on the other two behaviors. On the other hand, cocaine-treated females showed dampened dose-related quipazine responses across all behavioral measures. Fluoxetine administration produced a dampening of the quipazine effect for vertical activity and distance traveled in males and females. Therefore, these data indicate that cocaine administration during the preweaning period of development produced an increase in the effect of a serotonergic drug to alter vertical activity in males and a global dampening of the behavioral responses to that same drug in females. Preweaning fluoxetine treatment produced effects that resembled those produced by cocaine in females, a dampening of serotonergic responsivity, along with an overall decrease in locomotor activity. Because the majority of effects are seen during the initial portion of the behavioral session, a time of heightened activity in response to a novel environment, the data suggest that inhibition of the 5-HT transporter during the preweaning period alters serotonergic influences over novelty-induced activity but that brief periods of inhibition or other actions of cocaine, such as those at the catecholamine transporters, prevent this from happening, particularly in males.

Prenatal cocaine exposure produces gender-specific motor effects in aged rats

This investigation employed a longitudinal analysis of a complex motor skill in rats that were exposed prenatally to cocaine. Offspring were derived from four maternal treatment groups: 50 mg/kg cocaine, their pair-fed controls, 25 mg/kg cocaine, and freely fed controls. Cocaine was administered via gavage from gestation day 6-20. A maternal fostering procedure was used. Pairs of male and female littermates began training when 9, 13, or 19 months old. The behavioral procedure involved fixed-ratio (FR) lever pressing to obtain brief periods of wheel running. The oldest males from the 50 mg/kg, 25 mg/kg, and pair-fed groups performed significantly fewer wheel revolutions per opportunity than females or freely fed males. In general, animals earned fewer opportunities to run as the FR requirement was increased over sessions. However, within each age-by-gender group, subjects from the four treatment groups performed equivalent amounts of lever pressing. The specific effect on the motor aspect of the procedure may have resulted from a reduction of motor coordination, balance, or strength, or a diminished capacity of wheel running to serve as a reinforcing stimulus in a cocaine-sensitive subgroup.

Differential effects of prenatal cocaine and retinoic acid on activity level throughout day and night

Prenatal cocaine exposure is associated with disrupted state control and lowered activity levels. Prenatal retinoic acid excess also influences activity levels in laboratory rats. Activity level is usually monitored during a brief period in young offspring. The effects of these drugs on pup activity levels throughout the day is unknown. There is also little information on the long-lasting effects of these teratogens in adult animals. We compared the daily activity of rats which were prenatally exposed to cocaine or retinoic acid (RA). Appropriate control groups were also used. The offspring were evaluated for activity levels in a neophobic situation and for a 22-h period in same-sex groups of 3 littermates. As both pups and adults, the cocaine groups were hypoactive while the RA group was hyperactive when first placed into the testing cage (neophobic situation). Similarly, during the remainder of the 22-h testing period, the pup and adult cocaine animals exhibited reduced activity levels while the RA animals exhibited elevated activity levels. Thus, prenatal cocaine and retinoic acid exposures affected offspring activity levels differently, both drugs have long-lasting neurobehavioral effects that persist into adulthood, and effects are influenced by time-of-day. Strain-dependent differences and mechanisms of action are discussed.

Effects of cocaine on the rat cerebral commissure

We investigated the effects of cocaine on the corpus callosum, the nerve fibre bundle that connects the bilateral cerebral hemispheres. Our experiments in rats confirmed that, in the control group, the mid-sagittal area of the corpus callosum in the adult male was significantly larger than this area in the female. Early postnatal exposure to cocaine abolished this sexual dimorphism, that is, cocaine-treated males had a significantly smaller callosal area than the control males. Cocaine induced no significant changes in the weight of the body or brain. There were no significant sex differences in the midline sagittal area of the anterior commissure, and no apparent effects of cocaine exposure were determined in this structure. These findings suggest that early postnatal exposure to cocaine abolishes the sexual differentiation of the corpus callosum in male rats.

Modification of acoustic startle reactivity by cocaine administration during the postnatal period: comparison with a specific serotonin reuptake inhibitor

This study investigated whether exposure to cocaine during postnatal period affects the acoustic startle response (ASR) following administration of the serotonin (5-HT) agonists, 8-OH-DPAT and mCPP, in adulthood. To test the hypothesis that alterations in reactivity may be due to cocaine's effects at the 5-HT carrier, another group of rats was given fluoxetine, a specific 5-HT uptake inhibitor, during the same postnatal period and tested along with the cocaine-treated rats. Male and female rats received 25 mg/kg/day cocaine HCl, fluoxetine HCl, or vehicle SC during postnatal days 11-20. At 75 days of age, subjects were ASR tested for 30 min on 2 consecutive days. On the first test day, there was a significant effect of treatment and gender with post hoc analysis indicating that, overall, the males were more reactive than the females and that the fluoxetine-treated males showed a pattern of reactivity resembling sensitization. On the second test day, subjects received a dose of the 5-HT1A agonist 8-OH-DPAT, the 5-HT1B/2C agonist, mCPP, or saline prior to being placed in the startle chamber. Cocaine-exposed males showed an enhanced response to 8-OH-DPAT and a reduction in the depression produced by mCPP administration compared to their response to saline. Fluoxetine exposed males showed a significant increase in startle response following saline administration compared to the rats receiving vehicle during the postnatal period and 8-OH-DPAT produced an insignificant enhancement of that startle response. mCPP reduced startle in fluoxetine-treated males as it did in the postnatal vehicle-treated controls. In females, the postnatal cocaine and fluoxetine treatments did not alter the response to 8-OH-DPAT or mCPP compared to females receiving vehicle during the postnatal period. Together these data indicate that, in males, whereas postnatal cocaine alters the development of the 5-HT system as evidenced by an altered startle response to 5-HT agonists, cocaine does not produce the same alteration as that produced by the administration of a specific 5-HT uptake inhibitor during the same period of development.

Neonatal cocaine exposure and activity rhythms in rats

This study looked at the effects of neonatal cocaine exposure on activity rhythms over a 48-h period in rats. Subjects were artificially-reared from postnatal days (PN) 4-10 via intragastric cannulas. The four treatment groups included two cocaine doses (20 and 40 mg/kg per day), an artificially-reared control and a normally reared suckled control. Subjects were tested at PN 38-40 in an automated running wheel. Neonatal cocaine exposure did not alter activity rhythms over the 48-h test period. However, there was a gender-specific effect of neonatal cocaine exposure on response to the novel test chamber and to the experimenter. The 20 mg/kg cocaine-exposed females showed increased running wheel activity relative to all other groups after placement in the running wheel. During the second 24-h period, cocaine-exposed females from both cocaine groups showed increased activity relative to controls following the entry of an experimenter to the test room. These findings suggest that female rats exposed to cocaine neonatally show an increased response to novel environments and stimuli.

Prenatal exposure to cocaine selectively disrupts motor responding to D-amphetamine in young and mature rabbits

Acute administration of D-amphetamine probed the functional effects of prenatal exposure to cocaine on the integrity of monoaminergic systems in preweanling (48-56 days old) and adult (> or = 140 days old) Dutch belted rabbits. D-Amphetamine sulfate (0, 0.3, 1.0, 3.3 and 6.0 mg/kg, s.c.) produced equivalent dose-related reductions in food intake in 180 day-old rabbits that had been exposed in utero on gestational days 8-29 to cocaine or saline. Intrauterine exposure to cocaine also did not alter the incidence of exploratory behaviors stimulated by D-amphetamine during the anorexia test. In contrast, however, prenatal cocaine virtually eliminated stereotyped head bobbing elicited by the highest dose of D-amphetamine. When responses to 5.0 mg/kg D-amphetamine were measured during a 90-min open field test, prenatal cocaine prevented head bobbing in preweanling rabbits and reduced this behavior by 92% in 140 day-old adults. Prenatal cocaine also diminished the intensity of other motor responses in the open field in the adults but not in preweanlings. In normal rabbits, the D1 antagonist R(+)-SCH 23390 (0.01 mg/kg, s.c.) blocked D-amphetamine-induced head bobbing. Thus, prenatal exposure to cocaine produces an early and persistent deficit in behavioral responding to a high dose of D-amphetamine. The deficit is especially selective at the time of weaning, broadens to affect more motor behaviors with maturation and may reveal impaired D,-mediated dopaminergic neurotransmission in the brain.

The effects of cocaine on cerebral metabolic function in periweanling rats: the roles of serotonergic and dopaminergic uptake blockade

This report examines the short-term effects of cocaine exposure during postnatal (PoN) days 11-21 on the metabolic function of major central neuronal systems in the rat. It also examines the effects of inhibition of serotonin and dopamine uptake during this period of development. By comparing the effects of fluoxetine, a serotonin uptake inhibitor, and GBR12909, a dopamine uptake inhibitor, to the effects of cocaine, the contributions of these pharmacologic actions to the neurochemical effects of cocaine were determined. Four groups of rats were injected subcutaneously: cocaine 25 (mg/kg), fluoxetine (25/kg), GBR12909 (25 mg/kg) and vehicle-injected. On day 21 all received their final dose of drug or vehicle 20 minutes prior to the deoxyglucose procedure. Glucose utilization in 43 of 56 brain regions selected for analysis showed a main effect of treatment (P < or = 0.05, ANOVA) and 7 showed significant treatment X gender interactions. Females demonstrated a markedly greater sensitivity to the effects of cocaine than did the males. Both males and females showed a negligible response to fluoxetine treatment. In the female cocaine-treated group, 10 of 13 motor structures, 7 of 12 sensory structures, 10 of 24 limbic structures, 2 of 2 association areas, and 3 of 5 hypothalamic structures demonstrated significantly increased rates of glucose utilization compared to the vehicle-injected group (P < or = 1 =0.05, Dunnett test). In the cocaine-treated males, only 3 of 56 regions were affected. The gender differences in response to RBR12909 were less apparent. In the females, 11 regions showed increased rates of glucose utilization, while in the males 7 regions were stimulated. Fluoxetine produced the smallest overall effect with 2 structures showing increases in metabolism in the females and 2 structures showing decreases in metabolism in the males. The present study therefore suggests at 21 days of age, that inhibition of dopamine uptake makes a more significant contribution to the metabolic effects of cocaine than inhibition of serotonin uptake and that females are more sensitive to the effects of cocaine than males. Furthermore, the sexual dichotomy seen in the long-term effects of cocaine; females show the greater effect; is also seen at the time of drug administration.

Adult reactivity in rats exposed to cocaine during two early postnatal periods

This study investigated whether exposure to cocaine during two periods of postnatal development affects the acoustic startle response (ASR) in adulthood. Female rats received 50 mg/kg/day cocaine HCl or vehicle SC during either postnatal days 1-10 or 11-20. At 60-65 days of age, subjects were ASR tested for 30 min on 2 consecutive days. Overall, ASR was increased on day 1 compared to day 2. Also comparisons between groups within each session and injection schedule showed that subjects exposed to cocaine during postnatal days 1-10 exhibited increased ASR amplitude on the second day of testing compared to controls. No group differences in response latency were observed. Therefore, these data indicate that, for female rats, cocaine alters the development of the pathways involved in modification of the acoustic startle response in a way consistent with a disruption of long-term habituation, but that the critical period for this disruption in females is postnatal days 1-10 and not 11-20.

Prenatal cocaine alters later sensitivity to cocaine-induced seizures

Rats that had been prenatally exposed to cocaine were tested later in life for their sensitivity to cocaine-kindled seizures and acute cocaine-induced seizures. When treated daily with cocaine, beginning at one month of age, males prenatally exposed to 40 mg/kg cocaine developed seizures in a fewer number of days than those prenatally exposed to saline. Prenatally cocaine-treated females did not seize more rapidly than controls in the cocaine kindling paradigm; however, they were more susceptible to seizures in response to an acute high dose of cocaine. These results suggest that rats prenatally cocaine-treated are more sensitive to the seizure-producing effects of cocaine later in life, and this enhanced sensitivity is differentially expressed in males and females.

Behavioral effects of neonatal cocaine exposure using a rodent model

This study examined the effects of neonatal cocaine exposure on behavior using a rodent model. Rat pups were implanted with intragastric cannulas on postnatal day (PND) 4 and artificially reared (AR) from PND 4-10. The AR groups included two cocaine doses (20 mg/kg per day and 60 mg/kg per day) and an AR control. A sham surgery control group was also included that was reared naturally by its dam. Offspring from these neonatal treatment groups were examined for suckling performance (PND 13), passive avoidance learning (PND 23-24), activity (PND 18-21), or spontaneous alternation (PND 21). Neonatal cocaine exposure had no effect on suckling measures or passive avoidance learning. Activity was increased in the 60 mg/kg per day cocaine group relative to controls. In addition, spontaneous alternation was delayed in the 20 mg/kg per day cocaine-exposed females relative to all other groups. These data suggest that neonatal cocaine exposure may alter performance on some relatively simple tasks. More work is clearly warranted to look at the effects of neonatal cocaine exposure on more complex behaviors.

Physiological and behavioral effects of early embryonic exposure to ethanol and cocaine in the young chick

The physiological and behavioral effects of embryonic exposure to ethanol and cocaine, given during active neurogenesis (embryonic days E3 and E4), were studied in 1- and 2-day-old chicks. Broiler chicks (n = 131) from five embryonic treatment conditions were tested: incubative controls (n = 28), vehicle (saline plus 50 micrograms/ml bacitracin; n = 27), 10 mg ethanol (n = 20), 150 micrograms cocaine (n = 25), or co-drug (10 mg ethanol and 150 micrograms cocaine; n = 31). Compared with controls, embryo mortality for the cocaine alone embryos was significantly increased. No significant embryonic treatment effects among chicks were found for hatching times, body weights at hatch and testing, and temperature regulation when cold stressed. Behaviorally, chicks were first trained to key-peck for heat/light reward (autoshaping). Chicks in all groups increased responding from autoshape session 1 to session 2 (24 trials/session). In an acquisition-extinction session (12 trials/phase), chicks in all groups except those in the co-drug group decreased responding from acquisition to extinction. In a second acquisition-extinction session following a drug challenge of 0.5 mg/kg apomorphine, chicks in all embryonic treatment groups showed enhanced responding. Hence, in those chicks that survived, the selected doses of ethanol and cocaine produced minimal physiological and behavioral effects individually, but when given together did produce a significant deficit in extinction responding.

Methamphetamine exposure during early postnatal development in rats: I. Acoustic startle augmentation and spatial learning deficits

Methamphetamine (MA) induces neurotransmitter reductions and neurotoxicity at high doses in adult animals, but its effects on early brain development and behavior have received less attention. In this experiment the effects of MA exposure during a period equivalent to the human third trimester were examined. Rats (Sprague-Dawley CD) were injected subcutaneously with d-MA (30 mg/kg b.i.d.) early in postnatal development (days 1-10), later (postnatal days 11-20), or with water during both of these periods. Both early and later MA-exposed offspring exhibited augmented acoustic startle and impaired performance in a complex multiple-T water maze. Only the early MA exposure group showed a persistent deficit in weight while only the later MA exposure group showed impaired learning in the Morris hidden platform maze. Effects on locomoter activity are reported in the accompanying article. It was concluded that the effects of MA are both long lasting and stage dependent and involve cognitive as well as arousal functions.

Methamphetamine exposure during early postnatal development in rats: II. Hypoactivity and altered responses to pharmacological challenge

Methamphetamine induces neurotransmitter reductions and neurotoxicity at high doses in adult animals, but its effects on early brain development and behavior have received little attention. In this experiment the effects of methamphetamine exposure during a period equivalent to the human third trimester were examined. Rats (Sprague-Dawley CD) were injected subcutaneously with d-methamphetamine (d-MA) (30 mg/kg b.i.d.) early in postnatal development (days 1-10), later (postnatal days 11-20), or with water during both of these periods. Both early and later MA-exposed offspring exhibited reduced locomotor activity. The effect was most evident at 30 days of age and was smaller at 45 and 60 days and only present at these latter ages in males. Only the early MA exposure group showed prolonged suppression of activity in response to a challenge dose of fluoxetine and a persistent deficit in weight while only the later MA exposure group showed attenuated suppression of activity in response to a challenge dose of fluoxetine. Based both on the present data and those in the preceding article, it was concluded that the effects of MA are both long lasting and stage dependent and involve arousal as well as cognitive functions.

Effects of prenatal cocaine exposure on the nigrostriatal dopamine system: an in vivo microdialysis study in the rat

Pregnant rats were given injections of saline (0.5 ml/kg) or cocaine (10 mg/kg, 20 mg/ml, s.c.) twice daily between gestational days 7-21. Offspring were examined by microdialysis between postnatal days 10-125 to study the effects of prenatal cocaine exposure on the nigrostriatal dopamine (DA) system. Twenty-min dialysis samples were collected and assayed for DA, DOPAC and HVA. After four baseline samples, the rat was exposed to 20 min of intermittent tail pinch and monitored for four samples; then each rat received an acute injection of cocaine (20 mg/kg, i.p.) and six additional samples were collected. Basal dialysate concentrations of all DA markers, estimated from pre-implantation calibration of the probes, were markedly reduced in young rats ('pups', 10-30 days old) as compared with adult rats (40-125 days old). Compared to control pups, basal DA, as well as DOPAC and HVA, were elevated in the prenatal-cocaine pups. Tail pinch (a mild stressor) produced a significant increase in DA only in the pups prenatally exposed to cocaine. The increase in basal DA induced by an acute cocaine injection (20 mg/kg) was also greater and more prolonged in the prenatal-cocaine pups. In older rats (40-125 days) there were no group differences in any of the DA parameters. Thus prenatal exposure to cocaine produces an activation of the DA system which persists after birth but returns to normal in older rats.

Lack of behavioral sensitization to repeated cocaine administration from postnatal days 1 to 10

This research determined whether sensitization (or tolerance) to the behavioral effects of cocaine in rat pups would occur following repeated cocaine administration. Rats were injected daily with 20 mg/kg of cocaine HCl s.c. from postnatal day 1 to day 10, injected with saline vehicle only, or left untreated during this period. On day 11, animals from each group were challenged with either 0, .625, 1.25, or 2.50 mg/kg of cocaine and their behavioral responses were recorded. Prior cocaine treatment did not influence the acute effects of cocaine on ultrasonic vocalizations or on any observed motor responses. In contrast, the cocaine- and saline-treated pups differed in a similar manner from the untreated control group on several behavioral measures. These results indicate that the sensitizing effects of repeated cocaine administration are not manifested during the neonatal period. However, the stimulation (stress) of handling and injection may alter the subsequent responsivity of infant rats to a cocaine challenge.

Prenatal cocaine and cell development in rat brain regions: effects on ornithine decarboxylase and macromolecules

Prenatal cocaine exposure has been shown to cause neurobehavioral abnormalities. To determine whether effects on basic patterns of cell development underlie these functional deficits, we examined the aftermath of acute and chronic cocaine exposure on ontogenetic patterns of ornithine decarboxylase (ODC), a key regulator of cell replication/differentiation, DNA synthesis as monitored by [3H]thymidine incorporation, and markers of cell number (DNA content) and cell size (protein/DNA ratio). Administration of 30 mg/kg SC of cocaine to pregnant rats on gestational day 20 resulted in acute increases of ODC throughout the brain. When the same dose of cocaine was given daily from gestational days 8 through 20, ODC elevations persisted into the neonatal period but disappeared by the middle of the first postnatal week. Although this treatment regimen retarded maternal weight gain, there was little or no effect on pup body or brain region weights. Similarly, minor changes in DNA synthesis were seen in two brain regions (forebrain, cerebellum), but DNA content was largely unaffected. Postnatal cell growth was significantly reduced in the forebrain, as evidenced by deficits in protein/DNA but, again, the magnitude of effect was quite small. Raising the daily dose of cocaine to 100 mg/kg resulted in significant maternal mortality and fetal resorptions in surviving dams. Shortening the treatment regimen to a 3-day period (gestational days 18 through 20) eliminated the effects on maternal weight gain and on postnatal pup brain region ODC.(ABSTRACT TRUNCATED AT 250 WORDS)

Cocaine in utero enhances the behavioral response to cocaine in adult rats

The effects of cocaine exposure in utero on cocaine-induced behaviors and dopamine (DA) transmission in the nigrostriatal and mesolimbic pathways were measured in adult rats. Pregnant rats received either saline or cocaine (1 or 3 mg/kg, IV) daily throughout gestation. When offspring were 3 months of age, locomotor and stereotypic behaviors were rated after an injection of either saline or cocaine (10 mg/kg, IP). Cocaine in utero increased the response to cocaine in adult offspring and increased basal locomotion in female offspring. Cocaine in utero increased amphetamine-stimulated release in female offspring but decreased release in males. On the other hand, male rats that had received cocaine in utero exhibited greater basal tritium release. One injection of cocaine increased amphetamine-stimulated [3H]DA release from striatal slices of male rats but not female rats. Neither cocaine in utero nor in vivo affected D2 DA receptor binding in striatum nor nucleus accumbens. Thus, cocaine in utero behaviorally sensitized animals to subsequent cocaine exposure and increased [3H]DA release from nigrostriatal endings, but the relationship of these two variables depended upon gender.

Cocaine effects on fetal development: a comparison of clinical and animal research findings

The clinical and animal literature describing the effects of cocaine use during pregnancy is reviewed. The difficulties associated with studying populations using illicit drugs during pregnancy and the multiple risk factors present in cocaine-using pregnant women limit the strength of the drug-associated effects. Nevertheless, cocaine use during pregnancy is associated with a significant number of obstetrical complications, small for gestational age infants and neurobehavioral abnormalities. In animal studies, only the neurobehavioral abnormalities could be demonstrated following the administration of non-toxic doses of cocaine. Furthermore, animal studies indicate that neurochemical changes, including those identified in the neuroendocrine axis, persist into adulthood.