Behavioral teratogenesis: a critical evaluation

Neuroleptics under high risk conditions

A critical review of various high risk situations in which neuroleptics could be used and have been used in clinical practice is presented. These high risk situations include: women of child bearing age (pregnant women, lactating and/or nursing mothers), the two extremes of life (children and the elderly), patients with sexual dysfunction, patients with tardive dyskinesia, non-psychotic psychiatric patients, physically ill and suicidal patients. The extraordinary applications of these drugs, such as for rapid tranquilization and megadose regimens are examined. The author provides guidelines for the use of neuroleptics in these clinical situations.

Behavioural effects of phenobarbitone. 1. Effects in the offspring of laboratory mice

Phenobarbitone at a concentration of 187.5 mg/l in drinking fluid of breeding mice and their offspring after weaning did not affect gestation period, litter size, litter weight or pup development before weaning, although a slight retardation of weight gain after weaning occurred. This level of phenobarbitone given to mice after weaning did not affect weight gain. The average daily intake of phenobarbitone ranged from 30 to 52 mg/kg body weight depending on age and sex. Behaviour of offspring and mice treated after weaning was examined by ethological analysis of encounters between unfamiliar mice of the same sex and treatment group in a neutral enclosure. After lifelong exposure to phenobarbitone mice at 5 and 15 weeks of age showed an increased amount of scanning and exploration of the unfamiliar cage coupled with a decrease of time spent in immobility. Difference from control levels was more pronounced at 15 than at 5 weeks of age, in part because controls showed more immobility and explored less as they matured. No behavioural changes were detected in mice treated with this level of phenobarbitone after weaning. Lifelong exposure to phenobarbitone did not affect agonistic behaviour in pair-housed males at 30 weeks of age, and under these circumstances no longer stimulated exploration to a significant extent.

Effects of haloperidol on cell proliferation in the early postnatal rat brain

Haloperidol, a widely used neuroleptic, produced a significant depression of the rate of [3H]thymidine incorporation into the DNA of 11-day-old rat brain. The reduction of in-vivo DNA synthesis rate was detectable by 4 h after subcutaneous injection of a single dose of haloperidol (20 mg/kg) and through the period 10-24 h after drug treatment the rate was less than 50% of that of controls in the forebrain. [3H]Thymidine incorporation returned to control values by 32 h. The effect on the cerebellum was similar but less pronounced. The depression was dose-dependent and a half-maximal effect was produced with haloperidol doses of 5-10 mg/kg. Parallel histological studies on treated rats suggested prolongation of the DNA synthesis phase of the cell cycle in the forebrain subependymal layer, associated with an increase in turnover time of about 15%.

Behavioural teratology: post-natal consequences of drug exposure in utero

The effects of pre-natal exposure to drugs that subsequently affect the post-natal behaviour without apparently causing noticeable brain damage forms the subject of behavioural teratology. This review summarizes the experimental studies of several investigators who showed that pre-natal administration of such psychotropic drugs as meprobamate, isocarboxazid and reserpine reduced the maze-learning ability of the mature offspring. A more detailed survey of the effects of D-amphetamine and diazepam is then given. Both drugs were not foetotoxic and only caused appreciable changes in locomotor activity of the offspring at least 14 days after birth. With the amphetamine treated rats, these changes were biphasic (elevated at 15 days and reduced at 21 days) whereas the diazepam treated animals showed a reduction in locomotor activity for at least 21 days after birth. The results of our own studies, and those of others, do not enable a correlation to be made between the effects of the various drugs on the development of specific central neurotransmitters and the behavioural deficits noticed. The review concludes with an outline proposal for screening drugs for their potential as behavioural teratogens. The possible mechanisms whereby behavioural teratogens may cause subtle changes in the maturation of the brain are also outlined.

Effect of prenatal phenytoin administration on postnatal development of the rat: a behavioral teratology study

Adult pregnant Wistar rats were treated with phenytoin (100 Mg/kg) orally from day 7 to 19 of pregnancy, and a control group was pair-fed during the whole treatment period. Within 24 hours after parturition , the offspring were culled to six to eight per litter and reared by fostering or cross-fostering. The physical and behavioral development of the offspring was observe up to 90 days of age. There was a reduced survival of the offspring and a reduction in body weight which persisted to the end of the experiment, though both of these effects could be reduced by cross-fostering. Certain neurological defects were also seen in the prenatal phenytoin group. For example, there was a delay of up to 15 days in the development of the dynamic righting reflex, a decrease in ability of offspring to stay on a rotating rod, and a decrease in ability to walk along elevated parallel rods. There seemed also to be some loss of cliff avoidance. However, there was no change in the development of crawling and walking activities at 9-21 days of age, and no important changes were observed in a head dipping test or in a conditioned avoidance test at 26-34 days. There was a significant decrease in brain weight of the treated group at age 3 days which remained significantly lower than the controls even at 90 days, but no change in the brain/body weight ratio. There was no difference in cerebellar DNA content.

Assessment of adult skeletons to detect prenatal exposure to 2,4,5-T or Trifluralin in mice

A group of 88 spontaneously occurring variations of the skeleton were studies in adult CD-1 mice which had been exposed in utero to the herbicides 2,4,5-T or Trifluralin, administered to their dams by gavage, in an attempt to detect subtle biological effects of these compounds even in the absence of gross malformations. Sixty-seven characters showed variation in this population. Of these, 19 were significantly different in frequency from untreated controls in mice having receiving a teratogenic dose of 2,4,5-T, with an average difference of 23.7%. Seventeen of them were increased in frequency. By contrast, only three traits differed from untreated among mice receiving a no-effect dose of 2,4,5-T. Twelve traits differed significantly from untreated in the Trifluralin-treated group; the average difference was 18.8%, with 10 of the traits being increased in frequency. Two clusters of affected variants specific to the 2,4,5-T high dose group included frontal bone variants in the skull (presence of an interfrontal bone and fusion of the frontals) and variants in the cervical vertebrae (imperfect foramina in the first and second cervicals, dyssymphysis of the second cervical, and a shift of the arch foramen from the fourth to the fifth cervical). Two other effects peculiar to the 2,4,5-T-treated specimens were a loss of the prominent dorsal spine of the second thoracic vertebra and a reduction in the number of caudal vertebrae. The most obvious effects specific to the Trifluralin treatment were an increase in occurrence of 14 ribs, an undoubled foramen ovale, and the occurrence of accessory foramina in the cervical vertebrae. A striking increase in frequency of parted frontals was seen in both 2,4,5-T high dose and Trifluralin-treated groups. The skeletal variant assay system may be used as a postnatal screen for detecting prenatal exposure to potentially noxious substances.

Enduring behavioural and biochemical effects in the adult rat after prolonged postnatal administration of haloperidol

Rats were administered 0.5 mg/kg SC of haloperidol (H) or saline (S) daily from day 1 after birth until 20 days of age. At 60 days of age (40 days after the postnatal treatment with H or S was interrupted) the stereotyped behaviour and the effects on locomotor activity elicited by apomorphine in S- and H-pretreated rats were investigated. The intensity of apomorphine (0.5--1 mg/kg, SC)-induced stereotyped behaviour was significantly greater in the H-pretreated group than in S-pretreated animals and this was accompanied by a much more marked reduction of locomotor activity in H-pretreated than in S-pretreated rats. Finally, at 80 days of age (60 days after the postnatal treatment with H or S was interrupted) rats were subjected to a Differential Reinforcement of Low Rates schedule (DRL 15-s). The results indicate that the acquisition of the DRL task performance criterion (Rs/Rf less than or equal to 2.5) was significantly more rapid on S-pretreated rats than in H-pretreated ones. In parallel biochemical experiments, acute H produced smaller increases in dopamine turnover in chronic H-treated rats compared with S-treated controls. These data indicate that H treatment in neonatal rats induces behavioural and biochemical changes which can be observed up to 60 days after H withdrawal.

Gestational caffeine modifies offspring behaviour in mice

Dams from two strains of mice, BALB/c C57BR were tested during gestation with caffeine, at doses of about 60, 80 and 100 mg/kg/day, in their drinking water. The resulting offspring were behaviourally tested over a 6-month period commencing at age 9 months. When compared with controls, mice from dams that had received caffeine demonstrated longer latencies in a passive avoidance test, and differences were also noted for female C57BR offspring in activity and habituation measures. Having controlled as far as possible for post-natal maternal and environmental effects, the most likely conclusion is that caffeine has a direct pharmacological action on the foetus, and should therefore be classed as a behavioural teratogen in mice.

Effects of prenatal amphetamine exposure on the development of behavior in rats

Female rats, maintained on 20 ml water per day, were treated with either 0, 2 or 5 mg/kg/day d-amphetamine sulfate mixed with their drinking water. Treatment was started 30 days prior to mating and continued to parturition of litters. Differences in weight gain during pregnancy were noted for the drug treated mothers, with the differences disappearing after drug treatment was stopped. Turnover latencies at 1 and 3 days of age, eye opening, and vaginal opening were delayed in the offspring of drug treated females. Drugged animals were slower than controls in a behavioral test of bridge crossing at 14 days postpartum. No differences in open field activity were noted.

Effect of maternally administered methadone on discrimination learning of rat offspring

Shape discrimination learning by four groups of 150-day-old Sprague-Dawley rats was studied. The groups were the offspring of mothers on the following schedules: (1) prenatal and postnatal methadone, (2) prenatal methadone and postnatal saline, (3) prenatal and postnatal methadone, and (4) prenatal and postnatal saline. The hypothesis investigated was that the methadone groups would show a deficit in learning when compared to the saline-control group. This hypothesis was upheld for the prenatal methadone group and the postnatal methadone group.

Prenatal exposure to diazepam alters behavioral development in rats

Characteristic potentiation of rat locomotion responses and acoustic startle reflexes that normally appear in the third postnatal week was absent in rats exposed to diazepam during the third week of gestation. Loss of these behaviors suggests a long-term effect that may result from changes in cellular development. Tissue undergoing neuronal differentation may be especially sensitive to drugs that act on the central nervous system, and the period in which differentiation occurs is perhaps critical for the induction of changes that are later expressed as altered behavior.

Chronic administration of haloperidol during development: behavioral and psychopharmacological effects

Chronic haloperidol treatment during prenatal and postnatal development was found to induce long-term behavioral and psychopharmacological effects. Rats tested shortly after termination of the chronic treatment at weaning or as young adults were hyperactive in the open field and exhibited an attenuated behavioral response to amphetamine and an accentuated cataleptic response to later doses of haloperidol, when compared with control offspring of the same age. Tests at an intermediate interval (adolescence period) showed no significant difference from control offspring on any of these behavioral measures. Adult rats administered haloperidol chronically for the same duration were also hyperactive after termination of treatment. In contrast to the effects of haloperidol during development, these adults exhibited an accentuated behavioral response to amphetamine and an attenuated cataleptic response to a later dose of haloperidol. Compensatory mechanisms in response to chronic haloperidol treatment during development thus appear to be different from those in adulthood.

Phencyclidine: effects of chronic administration in the female mouse on gestation, maternal behavior, and the neonates

Phencyclidine (PCP) (5 mg/kg) was administered daily throughout gestation and pups were crossfostered or fostered after birth. Prenatal weight gain, lenght of gestation, length of parturition, and the size and birth weight of the litters were not affected by PCP administration. No congenital malformations were evident and the mother's health during chronic exposure remained normal. Physical development of the pups (indicated by neonatal weight gain, pinna opening, and eye opening), and neurological development (indicated by the maturity of four reflex actions) were normal for the PCP pups. Behaviorally, PCP pups were slightly more active in the open field at 60 days. Maternal behavior was not influenced by drug treatment, but was affected by the fostering procedures.

The state and future requirements of teratogenic testing

The results obtained in various laboratories are compared with the authors experiences in the field of experimental teratology. From these findings some conclusions are derived to support teratological test programmes. Some basic requirements of embryotoxicity tests are also formulated.

Avoidance conditioning and Hebb-Williams maze performance in rats treated prenatally with alcohol

Throughout gestation pregnant Wistar rats consumed a nutritious liquid diet containing 35% ethanol-derived calories. Control mothers were fed lab chow. Subsequently, the offspring of the ethanol-fed mothers were found to be impaired on two-way avoidance conditioning when compared to control offspring, but did not differ from controls in their performance on the Hebb-Williams maze. Fostering and cross-fostering procedures indicated that the effect was due to prenatal influences arising from the drug treatment.

Prenatal alcohol consumption and open-field behaviour in rats: effects of age at time of testing

Throughout gestation pregnant Wistar rats consumed a nutritious liquid diet containing 35% ethanol-derived calories. Control mothers were fed lab-chow. Subsequently, the offspring of the ethanol-fed mothers displayed significantly greater activity (ambulation) in an open-field test at 28 and at 56 days of age, but not at 112 days of age. No differences in defecation were observed at any age.