Neonatal withdrawal following pre- and postnatal exposure to methadone in the rat.

Recent evidence has shown that infant rats undergo precipitated withdrawal following chronic postnatal injection of morphine. In this study we examined whether or not infants exposed to methadone prenatally via the placental blood supply and postnatally via the dam's milk would also experience precipitated withdrawal. Dam's were implanted on gestational day 14 with osmotic minipumps containing one of two concentrations of methadone to supply the opiate throughout gestation and the first postnatal week. Nontreated and pair-fed controls were used. On postnatal day 7, pups were injected with naltrexone and their locomotor activity and ultrasonic vocalizations measured. Methadone exposed pups were more active and vocalized more when injected with naltrexone than with saline. The controls did not show these behavioral changes. The milk of methadone-exposed dams apparently contains sufficient quantities of the opiate for dependence to develop. The results are consistent with other data that demonstrate that very young rat pups can experience an opiate abstinence syndrome that includes increased behavioral activation.

Prenatal administration of buprenorphine in the rat: effects on the rest-activity cycle at 22 and 30 days of age.

Three doses of buprenorphine (BUP) were administered by osmotic minipump from day 8 of gestation through parturition. In addition to 0.3, 1.0, and 3.0 mg/kg/day of BUP, a vehicle control group received sterile water via minipump and a nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. BUP produced a dose response reduction in maternal water intake and reduced maternal weight gain among the two high dose groups; resorptions and birthweight were unaffected. BUP increased perinatal mortality in the two high dose groups compared with the vehicle controls and produced inconsistent effects on postnatal growth. To examine the effects of BUP on the rest-activity cycle of the offspring, groups of 3 littermates from each of the treated and control groups were tested for an 8 h observation period on electronic activity monitors at 22 and 30 days of age. Unlike previous effects described for prenatally administered methadone, a disruption in the rest-activity cycle was not observed for any of the BUP treated groups.

Prenatal administration of buprenorphine using the osmotic minipump: a preliminary study of maternal and offspring toxicity and growth in the rat.

Buprenorphine, an opioid with mixed agonist-antagonist properties, is gaining new attention as an effective pharmacotherapy for opioid and possibly cocaine abuse. With a view to its consideration for use with pregnant clients and because so little is know of its potential developmental toxicity, we have carried out this preliminary study. Three doses of buprenorphine (BUP) were administered by osmotic minipump from day 8 of gestation through parturition. In addition to 0.3, 1.0, and 3.0 mg/kg/day of BUP, a vehicle control group received sterile water via minipump and a nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. BUP produced a dose response reduction in maternal water intake but had no effect on maternal weight gain, the frequency of resorptions, or birthweight. BUP had no effect on perinatal mortality and produced inconsistent effects on postnatal growth. The unique chemical and pharmacological properties of this compound, especially its bell-shaped or asymptotic dose response effects, are discussed with respect to the development of an adequate animal model to evaluate neurobehavioral effects and assess its safety for use during pregnancy.

The ontogeny of cannabinoid receptors in the brain of postnatal and aging rats.

It is recognized that a number of the biological effects of delta 9-tetrahydrocannabinol (THC) can be attributed to a cannabinoid receptor found in abundance in the brain. Due to observations that cannabinoid drugs exert some developmental toxicity, it was of interest to examine the developmental pattern of cannabinoid receptors in the brain of neonatal rats through young adulthood, and then to further examine the cannabinoid receptor during the aging process in the brain of rats 3 to 32 months of age. Using radioligand binding assays, this study demonstrated that cannabinoid receptor binding capacity increases progressively from birth to postnatal day (PND) 60. Within the striatum, a significant increase in binding occurred between PNDs 14 and 21. In the cerebellum, cannabinoid receptor binding capacity doubled at 7-day postnatal intervals until adulthood. Cannabinoid receptor binding in the cortex doubled between PNDs 7 and 14. Within the hippocampus, there were small incremental increases until the final adult level was reached at PND 21. There was no significant alteration in the affinity for CP-55940 during development. These findings might reflect an increased differentiation of neurons into cells possessing cannabinoid receptors, or an increase in the number of cannabinoid receptors on cell bodies or projections in regions undergoing developmental changes. Once the adult cannabinoid receptor levels have been reached, binding activity in the whole brain preparation neither increased nor declined during the normal aging process.

Influence of pH and plasticizers on drug release from ethylcellulose pseudolatex coated pellets.

Six potential plasticizers for an ethylcellulose (EC) pseudolatex coating system (Aquacoat) were evaluated at three levels (25, 30, and 35%) to study the influence of these additives on the release of a model compound, propranolol hydrochloride, from pellets in two different media, dilute HCl and phosphate buffer, pH 7.4. For the majority of the plasticizers, the release rate decreased when larger amounts of plasticizer were incorporated into the coating. However, for the plasticizers dibutyl sebacate and dibutyl adipate, no further reduction in the release rate was observed following dissolution testing in dilute HCl when the level of plasticizer was increased from 30 to 35%. This suggests that the saturation capacity of these plasticizers in the film coating had been exceeded. The media pH was found to influence the dissolution characteristics of the coatings. Faster release rates as well as earlier curve inflection points and T50% values were observed for plasticizers evaluated in phosphate buffer. All plasticizers used were independent of pH. Correlation of the dissolution results with properties of free films indicated that slower release (more complete film formation) is associated with softer and weaker films with greater elongation.

Prenatal administration of methadone in the rat: acoustic startle amplitude and the rest-activity cycle at 30 days of age.

Two doses of methadone were administered by osmotic minipump from Day 8 of gestation through parturition, a dosing technique previously shown to produce physical dependence in the dams. A pair-fed control group received sterile water via minipump and was allowed to eat and drink only the amount consumed by the high-dose group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. The effects of methadone on maternal and offspring toxicity replicated our previous findings. At 29-31 days of age each treated and control animal was tested either for changes in acoustic startle amplitude or the rest-activity cycle. Methadone treated offspring were no different from the controls on either measure. These findings support the hypothesis derived from our earlier research that prenatal exposure to methadone produces a prolonged but transitory opioid abstinence. This is evidenced by increased startle amplitude and a disturbed rest-activity cycle that peaks at approximately 3 weeks of age. We demonstrate that these effects are no longer evident at 4 weeks of age. Together, these findings define a state of hyperexcitability in the young rat that resolves by 1 month of age. This transitory state parallels clinical descriptions of human infants undergoing opiate abstinence.

The puzzle of cocaine's effects following maternal use during pregnancy: are there reconcilable differences?

This is a selective review of the clinical and epidemiological literature. It attempts to reconcile disparate and contradictory findings dealing with the morphologic, growth, and neurobehavioral effects reported to occur in neonates and young children exposed prenatally to cocaine. A history of cocaine use in the United States is briefly presented followed by impressionistic observations of some of the events that transpired during the cocaine epidemic of the 1980s. Based on the collective research findings, it is tentatively suggested that the teratogenic effects of prenatal cocaine may be produced only in those infants exposed to the highest doses reported in the literature. It remains unknown, however, whether or not these effects may be dependent on the concurrent abuse of alcohol and/or cigarettes. As to growth and neurobehavioral outcomes, effects attributable primarily to cocaine alone and not other substances of abuse appear to be only marginal and transitory. The data to support these conclusions are particularly tenuous and are thus offered only as working hypotheses. Because of the intractable methodological and interpretive problems inherent in human developmental research on substance abuse, any attempt to draw definitive conclusion is admittedly premature. Because these methodological problems also complicate the efforts of ongoing studies, answers to these persistent questions may not be readily forthcoming.

Prenatal administration of methadone in the rat increases offspring acoustic startle amplitude at age 3 weeks.

Two doses of methadone were administered by osmotic minipump from Day 8 of gestation through parturition, a dosing technique previously shown to produce physical dependence in the dams. A pair-fed control group received saline via minipump and was allowed to eat and drink only the amount consumed by the high dose group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. The effects of methadone on maternal and offspring toxicity replicated our previous findings. At 21-23 days of age, acoustic startle amplitude was measured for each treated and control animal. Because prenatal methadone exposure resulted in reduced body weight at the time of testing, it was necessary to analyze startle amplitude using weight as a covariate. This analysis showed that the methadone treated offspring had a significantly enhanced mean startle amplitude compared with the controls. These findings support the hypothesis derived from our earlier research that prenatal exposure to methadone produces a prolonged state of CNS hyperexcitability similar to clinical descriptions of human infants undergoing opiate abstinence.

Methadone during pregnancy: the search for a valid animal model.

It has long been known that maternal addiction to opiates during pregnancy produces passive addiction in the newborn. When the synthetic opiate, methadone, became widely used for the treatment of heroin addiction, attention was focused on its possible reproductive and developmental toxicity. The clinical data clearly indicate that prenatal exposure to methadone produces a neonatal abstinence syndrome and that the symptoms, characterized by generalized CNS arousal, persist for as long as 4-6 month after birth. Long-term neurobehavioral follow-up studies to pre-school age have not found any obvious cognitive impairments or deficits in IQ. Some of the children, however, may be at risk for developing problems of fine motor coordination and attention deficit disorder that are likely to lead to poor school performance. These effects probably have complex origins and include primary drugs effects, postnatal/environmental interactions and genetic susceptibilities. Regardless of their interpretation, however, it is important to emphasize that from a risk/benefit point of view, most workers would agree that methadone maintenance poses far fewer hazards, both to the mother and her offspring, than continued abuse of heroin with its associated medical complications, psychosocial turmoil, but most importantly, risk of HIV infection. Because of their pharmacological relevance to the issue of human kinetics, it is hoped that the more recent animal studies of prenatal methadone exposure using the osmotic mini-pump will shed more light on the problem of developmental toxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prenatal exposure to cocaine on the rest-activity cycle of the preweanling rat.

Either 45 or 60 mg/kg cocaine HCl was administered from days 8-22 of gestation. Pair-fed and nontreated groups served as controls and all treated and control litters were fostered at birth to untreated dams. To examine whether cocaine produces effects on the rest-activity cycle of the offspring, groups of three littermates from each of the treated and control groups were tested for an 8-h observation period on electronic activity monitors at 22 days of age. Neither activity level nor the rest-activity pattern were affected by cocaine. These findings are discussed in relation to previous studies of cannabis and methadone effects on the rest-activity measure.

Prenatal administration of methadone using the osmotic minipump: effects on maternal and offspring toxicity, growth, and behavior in the rat.

Two doses of methadone were administered by osmotic minipump from day 8 of gestation through parturition. A pair-fed control group received saline via minipump and was allowed to eat and drink only the amount consumed by the high dose group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. Naloxone challenge of the dams after parturition showed that drug treatment produced physical dependence. Methadone treatment reduced maternal weight gain but had no effect on either the frequency of resorptions or birthweight. Both doses of methadone increased perinatal mortality but only the high dose produced a decrement in postnatal growth. To examine the effects of methadone on the rest-activity cycle of the offspring, groups of three littermates from each of the treated and control groups were tested for an 8 h observation period on electronic activity monitors at 22 days of age. No behavioral effects were observed for either control group or the low dose methadone group. The high dose methadone offspring, however, spent less time resting, showed disrupted rhythmicity, and poor state regulation. These findings are discussed in relation to earlier studies using once per day methadone administration as well as clinical descriptions of infants undergoing opiate abstinence.

Prenatal delta-9-tetrahydrocannabinol in the rat: effects on auditory startle in adulthood.

Either 15 or 30 mg/kg of delta-9-tetrahydrocannabinol (delta-9-THC) was administered to pregnant rats by gastric intubation from Day 2 through Day 22 of gestation. Pair-fed and nontreated groups served as controls and all treated and control litters were surrogate fostered at birth to untreated dams. When treated and control male and female offspring were tested for differences in auditory startle at 57-60 days of age, no effects were observed among any of the groups. These findings are compared with other neurobehavioral studies of adult offspring prenatally exposed to cannabis.

Prenatal delta-9-tetrahydrocannabinol in the rat: effects on postweaning growth.

Either 15 or 30 mg/kg of delta-9-tetrahydrocannabinol (delta-9-THC) was administered from Day 2 through Day 22 of gestation. Pair-fed and nontreated groups served as controls and all treated and control litters were fostered at birth to untreated dams. When weighed at 57-60 days of age, pair-fed controls were significantly heavier than the nontreated, whereas the treated animals were intermediate between the controls. These findings are discussed with respect to nutritional studies that have reported postnatal growth enhancement following prenatal maternal undernutrition and the possibility that prenatal delta-9-THC inhibits this effect.

Animal models of opiate, cocaine, and cannabis use.

A traditional concern with drugs administered during pregnancy has been teratogenicity or the production of gross structural malformations. Beginning in the 1970s, it became increasingly evident that the issue of drug safety and risk assessment went far beyond structural defects. During the 1980s, the newly emerged research specialty of "developmental toxicology" came to encompass a wide range of adverse toxic outcomes that include not only birth defects but also neurobehavioral and other functional effects as well. Substances of use and abuse--the opiates, cocaine, and cannabis--have come to exemplify a diverse group of compounds that produce a broad spectrum of developmental outcomes. Unlike alcohol, neither the use of heroin nor methadone during pregnancy is associated with an increased risk of birth defects but both produce a neonatal abstinence syndrome that can persist for as long as 6 months; follow-up to preschool years suggests possible risk of attention deficit and problems of fine motor coordination. Methodologic weaknesses of opiate animal models, especially with respect of appropriate dosing schedules, have hampered meaningful extrapolation of these studies to human risk assessment. Given the renewed interest in methadone maintenance as an important therapeutic intervention to reduce exposure to the human immunodeficiency virus, better designed animal studies are needed urgently to assess developmental risk, but these must incorporate techniques that better model human pharmacokinetics. Animal models of early cocaine exposure, driven by human reports of serious risk to the fetus and newborn, have found reproductive hazard, risk of neurobehavioral effects as well as altered CNS function. Whereas animal studies need to explore routes of administration other than sc and ig, particularly the volatilized form of cocaine, to date it appears that the processes of somatic growth and morphogenesis in rodents are not as sensitive to cocaine as is the functional development of the CNS. Finally, animal studies of cannabis have taught us some major methodologic and interpretive lessons for the continuing development and refinement of animal models of drugs of abuse. Of particular importance is that poorly controlled experiments that do not adequately consider the confounding influences of maternal toxicity, both prenatally and postnatally, are likely to yield a high rate of false-positive results. This is well illustrated by those studies of cannabis that antedated the current concern for pair-feeding and surrogate fostering. Nearly all of the studies that failed to include nutritional and fostering controls found neurobehavioral effects that included changes in activity as well as impairments in learning and memory.(ABSTRACT TRUNCATED AT 400 WORDS)

Issues of risk assessment: lessons from the use and abuse of drugs during pregnancy.

Therapeutic uses and risks associated with the opioids, cannabis, cocaine, and phencyclidine are discussed as well as limitations of the developmental animal and clinical pediatric literature, especially with respect to problems of quantitative risk assessment. Human and animal developmental findings for methadone and cannabis are compared with respect to long-term behavioral effects with special emphasis on pharmacological and interpretive issues. It is suggested that neonatal withdrawal is the most serious neurobehavioral sequela associated with maternal use of opioid and other sedative-hypnotic compounds. Withdrawal phenomena are described and attempts to develop animal models are discussed. Methodological considerations including surrogate fostering, pair-feeding, and problems associated with the administration of compounds to lactating dams are discussed in the context of the adequacy of the EPA developmental neurotoxicity battery to characterize risk for abuse substances as well as the new NIDA medication compounds.

Prenatal phencyclidine in rats: effects on apomorphine-induced climbing.

Either 5 or 10 mg/kg of phencyclidine (PCP) in saline was administered by subcutaneous injection to gravid dams during the last two weeks of gestation. A pair-fed control group was administered the vehicle alone and allowed to eat and drink only the amount consumed by the 10 mg/kg group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. Among the dams receiving 10 mg/kg of PCP, food and water intake was initially reduced to 33-43% of nontreated controls, but then returned to control levels. Surprisingly, after 3 days of drug administration, water intake of PCP-treated dams exceeded that of the nontreated dams by approximately 15%. Compared with the nontreated dams, both PCP groups and pair-fed control dams gained significantly less body weight from conception to term. PCP had no significant effect on number of implantation sites or number of live births, however, PCP produced an apparent selective embryolethal effect on males and body weight reduction in all groups at birth. Prenatal PCP did not alter the sensitivity to apomorphine-induced climbing behavior during the second postnatal week. These results are discussed with respect to published animal and clinical studies of PCP exposure during pregnancy.

The effects of prenatal exposure to delta-9-tetrahydrocannabinol on the rest-activity cycle of the preweanling rat.

Either 15 or 50 mg/kg of delta-9-tetrahydrocannabinol (delta-9-THC) was administered from Day 2 through Day 22 of gestation. Pair-fed (0 mg/kg) and nontreated groups served as controls and all treated and control litters were fostered at birth to untreated dams. To examine whether delta-9-THC produces effects on the rest-activity cycle of the offspring, groups of 3 littermates from each of the treated and control groups were tested for an 8 hr observation period on electronic activity monitors at 17, 22 and 30 days of age. Whereas all treated and control groups showed age-dependent changes in activity, neither activity level nor the rest-activity pattern were affected by delta-9-THC. These findings are discussed in relation to neurobehavioral studies of activity changes following prenatal exposure to cannabis.

Comparison of oral and subcutaneous routes of cocaine administration on behavior, plasma drug concentration and toxicity in female rats.

Oral and subcutaneous routes of administration of cocaine HCl were investigated in female Wistar rats for food and water consumption, locomotor activity, stereotypic behaviors, plasma drug concentrations and injection site pathology. Animals received either 40 or 80 mg/kg/day by gastric intubation (PO-40 and PO-80 respectively) or 20 or 40 mg/kg/day subcutaneously (SC-20 and SC-40). All groups received the drug or the vehicle for 16 consecutive days. Locomotor activity and stereotypy were evaluated on Days 1, 5, 10, and 15. Plasma drug concentrations and injection site pathology were determined on Day 16. Subcutaneous administration was associated with a sensitization to the effects of cocaine on locomotion and stereotypy, higher blood levels than oral administration at the same dose, and severe dermal lesions. However, there were no differences in any measure between the SC-20 and SC-40 groups. Oral cocaine was also associated with behavioral sensitization. However, unlike the SC route, oral cocaine was characterized by dose-related increases in locomotion and stereotypy in the absence of gastrointestinal pathology. Inasmuch as oral administration resulted in dose-response relationships and low toxicity while subcutaneous administration did not, these factors should be considered in future studies utilizing chronic cocaine administration.

Plasma concentrations of delta-9-tetrahydrocannabinol in dams and fetuses following acute or multiple prenatal dosing in rats.

Delta-9-tetrahydrocannabinol (THC) was administered by gastric intubation to pregnant rats to study the effects of dose-level and dosing regimen on plasma concentration in dams and fetuses. Two multiple-dose groups were administered either 15 or 50 mg/kg of delta-9-THC once daily during the last two weeks of gestation. Two acute groups were administered the same dose as above but only once on the last day of gestation. Sixty min after receiving the last dose all dams and their fetuses were sacrificed by decapitation, blood collected, centrifuged and plasma removed. Quantitative measurement of delta-9-THC in plasma was carried out using GS/MS. Among the dams, plasma concentrations covaried with dose and multiple dosing produced higher concentrations than acute, especially at the high dose. Among the fetuses, plasma concentrations were approximately 10% of those found in the dams. The fetuses from the high, multiple-dose dams similarly yielded significantly higher concentrations. These findings are discussed with respect to other studies of the placental transfer of delta-9-THC and effects of postnatal developmental.