Behavioral effects of prenatal exposure to pulsed-wave ultrasound in unanesthetized rats.

The present experiment examined the developmental neurotoxicity of pulsed-wave (pw) ultrasound in rats, using an exposure system designed to eliminate restraint or anesthesia from the exposure conditions. Pregnant Sprague-Dawley CD rats trained to remain immobile in a water-filled ultrasound exposure tank were scanned with 3-MHz pw ultrasound at spatial peak temporal average intensities (ISPTA) of 0, 2, 20, or 30 W/cm2 on embryonic days 4-20 for approximately 10 min/day. The data showed that such insonation produced no adverse effects on maternal weight gain or reproductive outcome, nor on the postnatal growth or survival of the offspring. No exposure-related alterations in behavioral development were observed in the offspring of rats scanned with pw ultrasound during gestation. In addition, there was no consistent evidence of an ultrasound-associated change in the adult offspring behaviors tested; i.e., no treatment effects were found on measures of locomotor activity, water maze learning, and acoustic startle reactivity. An effect on tactile startle was observed on some trials in the low exposure group male offspring, but this effect was neither dose dependent nor consistent with any other finding. Overall, these results indicate that the neurobehavioral development of rats was not altered by prenatal exposure to pw ultrasound at ISPTA levels of up to 30 W/cm2.

Neonatal methamphetamine-induced long-term acoustic startle facilitation in rats as a function of prepulse stimulus intensity.

Neonatal exposure to methamphetamine (MA) has previously been shown to induce acoustic startle facilitation when the animals were tested as adults. The present experiment sought to replicate and extend this effect using a lower dose of MA and to determine if the effect varied as a function of prepulse stimulus intensity. Sprague-Dawley CD rat offspring were culled on the day after birth to eight (preferentially retaining females). On days 1-10, progeny were injected SC with either 20 mg/kg of d-MA twice per day (doses spaced at least 8 h apart) or distilled water. On postnatal day 50, offspring were administered 51 acoustic startle trials followed by 36 prepulse trials. Prepulse intensities were 0, 70, 75, 80, 85, or 90 dB. MA progeny showed augmented startle response amplitudes on both paradigms but the effect was most pronounced on the prepulse trials. Prepulse intensity interacted with MA treatment in that significant facilitation in the MA animals occurred on 0 and 70 dB prepulse trials but was only a trend (p < 0.10) on 75, 80, 85, and 90 dB trials. This implies that the effect of MA is most likely upon the basic startle reflex and not upon inhibitory pathways that modify startle reactivity.

Stage-specific effects of prenatal d-methamphetamine exposure on behavioral and eye development in rats.

Pregnant Sprague-Dawley rats were treated with 0, 5, 10, 15, or 20 mg/kg d-methamphetamine (MA), expressed as the free base, by SC injection (b.i.d., 8 h apart) on days 7-12 or 13-18 of gestation. Plasma concentration of MA and amphetamine were determined after the last dose. MA reduced gestation weight gain. The late exposure resulted in an increase in maternal and offspring mortality and reduced offspring growth. Offspring treated early in gestation with MA showed delayed development of early locomotion. In addition, memory impairment, evidenced by decreased target quadrant times and platform crossings on test trials and increased latency on reversal trials in the Morris spatial navigation maze, reduced spontaneous alternation, and lengthened passive avoidance retention latency was seen in the early treated high-dose groups. A reduction of serotonin was found in the nucleus accumbens following late exposure to MA at 20 mg/kg. Animals in both exposure groups had eye defects; however, the type of defect was dependent on the developmental stage at the time of dosing. Anophthalmia occurred only after early MA exposure, whereas folded retina was drug related only after late MA exposure. The behavioral effects did not show graded dose dependency; however, the effects were sensitive to exposure period. The early exposed animals had more alterations in behavior whereas the late exposed group showed higher mortality, reduced body weights, and neurochemical alterations.

Prenatal exposure to sodium phenytoin in rats induces complex maze learning deficits comparable to those induced by exposure to phenytoin acid at half the dose.

Gravid Sprague-Dawley CD (VAF) rats were administered sodium phenytoin suspended in corn oil by gavage once per day on embryonic days 7-18 at a dose of 100 mg/kg. Controls were administered corn oil alone by gavage on E7-18. Litters were randomly culled to 10. Offspring were regularly weighted, mortality noted, and males checked for preputial separation. At approximately 50 days of age offspring were evaluated in a straight water-filled channel for swimming proficiency and motivation to escape. Following this, rats were tested in the Cincinnati multiple T-water maze and scored for errors, latency to find the goal, and presence of phenytoin-induced abnormal circling behavior while swimming. Sodium phenytoin-exposed dams gained weight normally and delivered normally. Offspring mortality in the sodium phenytoin group was not increased above controls. No treatment effects on preputial separation or offspring growth were observed. No differences between groups in swimming proficiency in straight channel performance were obtained. In the Cincinnati maze, phenytoin offspring committed significantly more errors and had longer latencies to find the goal than controls. Among the phenytoin offspring, those exhibiting abnormal circling committed more errors than noncircling animals. When compared to previous data using the same maze and test protocol, it was found that 100 mg/kg of sodium phenytoin induced performance deficits similar to those induced by a dose of 200 mg/kg of phenytoin acid. Accordingly, the present data help explain why other investigators have reported sodium phenytoin to be more developmentally neurotoxic than phenytoin acid. Because the prenatal neurotoxic effects seen with the salt of phenytoin occur at lower doses, it suggests that phenytoin is more developmentally neurotoxic than previously believed.

Long-term learning deficits and changes in unlearned behaviors following in utero exposure to multiple daily doses of cocaine during different exposure periods and maternal plasma cocaine concentrations.

Although the possible behavioral neurotoxic effects of in utero exposure to cocaine have been the subject of numerous experiments, only a limited number of different types of animal models of cocaine exposure, critical periods, or long-term effects of such exposures have been investigated. In the present experiment, the effects of multiple daily SC exposures to cocaine (20 mg/kg/dose x 5 doses per day) were investigated when administered to gravid Sprague-Dawley CD rats on embryonic days E7-12 or E13-18 compared to weight-matched, vehicle injected, pair-fed controls. Effects of exposure were assessed on general development, olfactory orientation behavior, early locomotion, startle reactivity, spontaneous motor activity, and learning on two different tasks (Morris and Cincinnati water mazes). The multiple cocaine dosing regimen produced maternal peak serum concentrations of cocaine 3 times higher than that of a single dose (approximately 1550 vs. approximately 550 ng/mL). Early-exposed cocaine offspring had lower olfactory orientation scores and reduced postweaning rearing and hole-poke motor activity, whereas late-exposed cocaine offspring had increased postweaning locomotor, rearing, and hole-poke activity. On the Morris hidden platform maze, the cocaine early-exposed females had longer latencies on acquisition than controls. On the Cincinnati multiple-T water maze, the early-exposed cocaine females and the late-exposed cocaine males had increased errors, whereas the early-exposed cocaine males had reduced errors. The effects on measures of learning, when taken together, and in light of their being in the early-exposed group, suggest that embryonic cocaine exposure may have subtle effects on cognition in the offspring as adults. Such effects represent a form of neurotoxicity not previously associated with prenatal cocaine exposure.

A new method for evaluating air-righting reflex ontogeny in rats using prenatal exposure to phenytoin to demonstrate delayed development.

The air-righting reflex has been used for many years to assess reflex integrity in rodent developmental neurotoxicity investigations. However, little refinement of the technique has occurred. We describe two methodological improvements: (a) an improvement in the method of positioning rats for air-righting, and (b) a stop-action photographic method to capture the rat's mid-air performance. We also compare results obtained using a visual scoring method to the newly developed photographically based scoring method. Prenatal phenytoin exposure has been shown to induce marked delays in air-righting development (14), therefore, phenytoin was used as a positive control treatment. Pregnant rats were administered 200 mg/kg phenytoin in propylene glycol or propylene glycol alone by gavage once/day on E7-18. Offspring were tested in the same apparatus twice and scored for air-righting success either by direct observation or photographed and the photographs scored subsequently. Rats were administered 6 trials per day (3 trials with each method) on days 16-24 of postnatal development. Detailed analyses of the two methods included subdividing phenytoin animals into those exhibiting the neurological abnormality of circling later in life and those that did not. Both methods revealed that phenytoin animals were delayed in air-righting development compared to controls and both methods revealed that phenytoin-circlers were more impaired than phenytoin-noncirclers. Advantages of the photographic method were that it provided a more precise method of scoring and a permanent record of the animal's response. One disadvantage was that it did not distinguish groups quite as well as the visual method.

Behavioral teratologic effects of prenatal exposure to continuous-wave ultrasound in unanesthetized rats.

While there are no known risks associated with diagnostic ultrasound, uncertainty about the safety of prenatal ultrasound exposure remains. The purpose of the present experiment was to evaluate the behavioral teratogenic potential of continuous-wave (cw) ultrasound in rats, in the absence of maternal anesthesia or restraint. Pregnant CD rats, trained to remain immobile in a water-filled ultrasound exposure tank, were scanned with 3 MHz cw ultrasound at levels of 0, 2, 10, 20, or 30 W/cm2 ISPTA (spatial peak, temporal average intensity) on gestational days 4-20 for approximately 10 min/day. Offspring were examined postnatally for survival, growth, physical landmarks of development, behavioral development, and the adult functions of locomotor activity, learning and memory, and startle reactivity. No effects of prenatal ultrasound were found on maternal characteristics, offspring survival or growth, physical or behavioral landmarks of development, or adult tests of passive avoidance or startle. Effects at the highest intensity were obtained on corner and side locomotor activity and in a multiple-T water maze on measures of errors of commission and time spent finding the goal. The results showed that prenatal cw ultrasound in rats can induce effects on some postnatal neurobehavioral functions at high exposure intensities (30 W/cm2), but at lower intensities (2-20 W/cm2) no consistent evidence of neurobehavioral effects was observed.

A developmental neurotoxicity evaluation of the effects of prenatal exposure to fluoxetine in rats.

Fluoxetine is a widely used serotonin reuptake inhibitor effective in the treatment of depression. This experiment assessed the potential developmental neurotoxicity of fluoxetine. Sprague-Dawley CD rats were treated once per day on Days 7-20 of gestation with 0, 1, 5, or 12 mg/kg of fluoxetine (free base) dissolved in distilled water. One control group received water by gavage; animals in this group were provided food and water ad libitum. The second control group (PF) also received water by gavage; animals in this group had their food and water restricted by pair-feeding and watering them to the 12 mg/kg fluoxetine group. Litters were culled to 12 after birth and offspring (male/female pairs) were tested neurobehaviorally at three developmental stages (preweaning, juvenile, and adult). At each stage, two pairs per litter received tests of locomotor activity, acoustic startle, and startle after administration of one of two pharmacological challenges (one pair each receiving fluoxetine or apomorphine). Two pairs were also tested for spontaneous alternation, passive avoidance, and complex learning in a water maze. At the highest dose, fluoxetine caused maternal weight loss during pregnancy, reduced litter sizes at birth, and increased neonatal mortality. No effects on long-term growth or survival were seen. Prenatal fluoxetine exposure produced no significant effects on locomotor activity, spontaneous alternation, passive avoidance, or water maze performance. A few scattered interactions involving treatment group were obtained on startle, but no pattern of treatment-related changes was evident. Regional wet and dry brain weights taken at each stage were not affected by prenatal fluoxetine exposure. The data suggest that fluoxetine is not developmentally neurotoxic in the rat.

Trans-2-ene-valproic acid is less behaviorally teratogenic than an equivalent dose of valproic acid in rats.

Although animal experiments have shown the trans-2-ene metabolite (t-2-ene-VPA) of valproic acid (VPA) to be pharmacologically equivalent to the parent compound in terms of anticonvulsant activity, it is considerably less teratogenic in studies which have examined prenatally exposed fetuses for morphological defects. This has made t-2-ene-VPA an attractive potential antiepileptic agent. However, while neurobehavioral alterations have also been observed in rats prenatally exposed to VPA, even at doses below those which produce malformations, the developmental neurotoxicity of t-2-ene-VPA had not previously been examined. The current study evaluated the long-term behavioral effects of prenatal exposure to t-2-ene-VPA. Pregnant CD rats were treated with 300 or 400 mg/kg t-2-ene-VPA by gavage on days 7-18 of gestation, doses previously shown to produce no teratogenicity. A VPA group was administered 300 mg/kg for comparison. The pharmacokinetic profiles of the two compounds were similar. Behavioral findings in offspring prenatally exposed to VPA were consistent with previous findings, i.e., VPA offspring exhibited decreased locomotor activity, increased swimming maze errors, and reduced tactile startle responding compared to controls. In the 400 mg/kg t-2-ene-VPA group, Cincinnati maze errors and auditory startle reactivity were increased, while no significant behavioral effects were detected in the 300 mg/kg t-2-ene group. These results indicate that the developmental neurotoxicity of t-2-ene-VPA is lower than that of VPA but is still significant.

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.

Teratologic evaluation of rats prenatally exposed to pulsed-wave ultrasound.

While there are no known risks associated with diagnostic ultrasound, uncertainty about the safety of prenatal ultrasound exposure remains. The purpose of the present experiment was to evaluate the teratogenic potential of pulsed-wave (pw) ultrasound in rats, in the absence of maternal anesthesia or restraint. Pregnant CD rats, trained to remain immobile in a water-filled ultrasound exposure tank, were scanned with 3-MHz pw ultrasound at levels of 0, 2, 20 or 30 W/cm2 ISPTA (spatial peak, temporal average intensity) on gestational days 4-19 for approximately 10 min/day. Examination of fetuses on E20 revealed no increase in skeletal or visceral malformations in groups exposed to pw ultrasound in utero. The number of implantations/dam was significantly increased in all pw ultrasound exposure groups compared to sham-exposed animals and, in a possibly related finding, resorptions were increased in the two highest exposure groups. Although significantly increased compared to controls, resorption frequencies in these groups were low (< 10%). No exposure-related changes in fetal weights were observed in offspring of rats scanned with pw ultrasound during gestation. The results indicate that, under the conditions described, no overt embryotoxicity is associated with gestational exposure to pw ultrasound intensities of up to 30 W/cm2.

Preliminary evidence for methamphetamine-induced behavioral and ocular effects in rat offspring following exposure during early organogenesis.

Gravid Sprague-Dawley CD (VAF) rats received 50 mg/kg (d,l)-methamphetamine (MA) HCl (expressed as free base, N = 15) or distilled water (N = 6) by SC injection x 2/day in a 3 ml/kg volume on embryonic (E) days 7-12. Control rats were pair-fed to MA-exposed dams on days E7-18. No control dams failed to deliver; however, of 15 MA-exposed dams 4 did not deliver (2 died and 2 had completely resorbed litters). One additional MA litter had all the offspring die shortly after birth. There was no difference between groups on offspring postnatal (P) body weight. The offspring exposed prenatally to MA had significantly lower olfactory orientation scores (P9, 11, 13) to their home cage scent. In a test of early activity (P10, 12, 14) the MA-exposed progeny were marginally less active than controls. MA-exposed offspring exhibited hyperreactivity and marginally shortened response latency on a test of acoustic startle (P27). Motor activity showed no differential response in MA treated or control offspring to MA (P63) or fluoxetine challenge (P70). However, the MA offspring were more active than controls with respect to central and side activity during the second week of testing. No group differences were found for performance in a straight swimming channel or on the number of errors committed or latency to escape in a complex (Cincinnati) water maze (P84). Prenatal exposure to MA also induced eye defects (i.e., anophthalmia, microphthalmia and folded retina) in 16.7% of the progeny. However, MA did not effect hippocampal or neostriatal monoamine levels when measured on P28.(ABSTRACT TRUNCATED AT 250 WORDS)

Branched chain amino acids improve radial-arm maze acquisition and water maze forced-choice learning in rat offspring exposed in utero to hyperphenylalaninemia.

Maternal phenylketonuria results in a high incidence of children born mentally retarded. We showed that the large neutral amino acids valine, isoleucine, and leucine (VIL) ameliorate the effects of intrauterine hyperphenylalaninemia in rats on a test of complex maze learning. To further test the ameliorative effects of VIL on intrauterine CNS development during hyperphenylalaninemia, gravid rats were administered a phenylalanine/p-chlorophenylalanine (index group) supplemented diet with or without VIL added. Controls were given standard diet with or without VIL. All groups were pair-fed to the index group. As adults, the progeny exposed in utero to hyperphenylalaninemia showed characteristic learning impairments in a complex water (Cincinnati) maze on forced and elective-choice phases of the task and deficits in radial-arm maze and Morris maze acquisition, whereas those exposed to hyperphenylalaninemia combined with VIL showed no deficits in the forced-choice phase of Cincinnati maze learning and no evidence of radial-arm maze deficits. However, the improvement was not complete, with no ameliorative effects obtained on the elective-choice phase of the Cincinnati maze or on the Morris hidden platform test. No deficits were seen on phases containing test trials for memory function (Olton and Morris mazes). The acquisition differences occurred in the absence of any effects of VIL on maternal weight gain during gestation, maternal serum amino acid concentrations of phenylalanine or tyrosine, or effects on offspring growth. VIL alone produced no adverse or enhancing effects on learning or memory. Based on these data it was concluded that the VIL supplement continues to show promise as a potential treatment for intrauterinely acquired mental deficiency associated with maternal phenylketonuria.

A method for measuring locomotor behavior in rodents: contrast-sensitive computer-controlled video tracking activity assessment in rats.

A newer locomotor activity system for rodents is described. The system consists of a black, ventilated test chamber, internally lighted with a ceiling mounted video camera. The camera's image is transmitted to a contrast-sensitive tracker which maps the point of highest contrast and relays the digitalized coordinates to a PC. Dedicated software stores the information and simultaneously displays a map of the tracked subject. To illustrate the system's utility, results from an experiment are presented using an established behavioral teratogen, phenytoin. Pregnant Sprague-Dawley CD rats were exposed to 0 or 200 mg/kg of phenytoin by gavage on embryonic days 7-18 and the offspring tested in the videotracker activity monitoring device. Phenytoin is known to induce hyperactivity and circling behavior in the offspring. The system revealed that phenytoin-exposed offspring that exhibit neurological impairment were hyperactive compared to controls and the effect was predominantly seen in females. These animals exhibited more section transitions and more central and peripheral activity. When peripheral activity was subdivided into that occurring along corners versus sides, it was found that corner activity represented only a small component of the group differences whereas the side component represented most of the effect. Moreover, phenytoin offspring exhibiting the circling defect were found to display a qualitatively different pattern than noncirclers or controls. Videotracking represents a different approach to the analysis of locomotor activity patterns in experimental animals compared to older methods. Two advantages of this method are higher spatial resolution and not having to pre-specify data capture intervals. Other features are detailed regional movement information and qualitative mapping of ambulatory patterns.

A teratologic evaluation of continuous-wave, daily ultrasound exposure in unanesthetized pregnant rats.

Pregnant Sprague-Dawley rats were trained to remain immobile when placed in water in an ultrasound exposure tank and exposed to 0, 0.1, 2.0, or 30.0 W/cm2 ISPTA (spatial peak, temporal average), 3.0-MHz continuous wave (cw) ultrasound on embryonic (E) days 4-19 for approximately 15 min/day. On E20 fetuses were removed; weighed; examined for external, skeletal, and visceral malformations; and uteri were examined for resorptions. Analyses revealed no increase in pre-implantation loss and no effects on maternal body weight, food, or water consumption. No increase in skeletal or visceral malformations was found, in fact exposed groups had a lower incidence of defects than controls. A significant increase in resorptions in the lowest exposure group (0.1 W/cm2) was obtained, but the effect was isolated, non-dose dependent and not credible as a treatment-related effect. No reduction in fetal weight was obtained, in fact the lowest (0.1-W/cm2) and middle (2.0-W/cm2) exposure level groups weighed slightly more than controls. The immobility procedure succeeded in avoiding anesthetization or forced restraint of the dams, thereby eliminating these factors as potential confounders. The results demonstrated that in unanesthetized, unrestrained rats in utero exposure to incident intensities of ultrasound of up to 30.0 W/cm2 cw ultrasound (or estimated internal exposures of 4-21 W/cm2, depending on body orientation to the incident beam) produced no evidence of embryotoxicity based on fetal necropsy data.

Lack of teratogenicity of trans-2-ene-valproic acid compared to valproic acid in rats.

The teratogenicity of trans-2-ene-valproic acid (300 and 400 mg/kg) was compared with that of valproic acid (VPA; 300 mg/kg) and controls (corn oil) administered by gavage to Sprague-Dawley CD rats on embryonic (E) days 7-18. At the 300 mg/kg dose, trans-2-ene-VPA produced no change in maternal weight, number of implantations, proportion of resorptions, proportion of malformations, or fetal weight. By contrast, the same dose of VPA (300 mg/kg) reduced maternal weight during gestation, increased malformations (12.0% vs. 0.7% in controls), and reduced fetal body weight by 25.1%. An even higher dose of trans-2-ene-VPA (400 mg/kg) produced a reduction in maternal body weight during treatment and reduced fetal body weight (by 7.9%), but did not increase resorptions or malformations in the fetuses. On day E18, maternal serum drug concentrations of VPA were higher in the VPA-treated group compared with those of trans-2-ene-VPA in the trans-2-ene-VPA-treated groups at 1 hr posttreatment. At 6 hr posttreatment the reverse was seen. trans-2-ene-VPA may be absorbed more rapidly and distributed differently than VPA. Overall, the data support the view that trans-2-ene-VPA at equal or higher doses than VPA is not teratogenic in rats.

Comparison of the behavioral teratogenic potential of phenytoin, mephenytoin, ethotoin, and hydantoin in rats.

Pregnant Sprague-Dawley CD rats were orally administered either phenytoin (PHT, 200 mg/kg), mephenytoin (MPH, 100 mg/kg), ethotoin (ETH, 600 mg/kg), hydantoin (HYD, 1,200 mg/kg) or vehicle (propylene glycol) on days 7-18 of gestation. Mean (+/- S.E.) maternal serum concentrations of PHT, MPH, and ETH 1 hour after dosing on gestational day 18 were 16.0 +/- 3.3, 10.7 +/- 3.0, and 65.2 +/- 10.45, respectively, and free fractions were 16%, 18%, and 11% respectively. The free fraction for PHT is similar, but was lower for both MPH and ETH than that seen in humans. Preweaning mortality for PHT, MPH, ETH, HYD, and controls was 25%, 6.3%, 12.5%, 2.0% and 0.8%, respectively. The MPH and ETH-exposed animals weighed approximately 6.6% less than controls throughout the study; the other groups did not differ significantly. PHT offspring showed increased early locomotor activity. Only PHT-exposed animals (27%) exhibited abnormal circling behavior after weaning. PHT-circlers accounted for higher levels of activity in an open-field test and for longer straight channel swimming times. PHT-circlers and noncirclers differed from one another and controls on performance of a complex (Cincinnati) maze and on the development of the air-righting reflex. Offspring prenatally exposed to MPH showed an early delay in air-righting. ETH and HYD offspring were not consistently different from controls in behavior. The data suggest the following ordinal relationship among the drugs for behavioral teratogenesis: PHT much greater than MPH greater than ETH congruent to HYD congruent to CON. The effects of PHT are consistent with previous findings. Data on the other drugs suggest that other hydantoins do not possess the behavioral teratogenic efficacy of PHT and that PHT may be unique in its effects on CNS development.

An analysis of factors influencing complex water maze learning in rats: effects of task complexity, path order and escape assistance on performance following prenatal exposure to phenytoin.

Three hypotheses on factors determining performance in a complex water maze were tested in rats prenatally exposed to phenytoin. The hypotheses were: 1) that increasing maze complexity would better differentiate experimental effects; in particular, that an expanded version of a maze originally described by Biel would better differentiate groups than Biel's original design; 2) that path order is an important factor determining performance; specifically, that path sequence AB would better differentiate experiments from controls than the opposite order (sequence BA); and 3) that repeated trial failures interfere with learning, a problem putatively prevented by employing assisted (i.e., guided) escape. The specific prediction was that rats tested with assisted escape would learn faster and produce better group differentiation than rats tested with unassisted escape. Pregnant female Sprague-Dawley CD rats were gavaged on days 7-18 of gestation with propylene glycol alone (Control) or containing 100 or 200 mg/kg of phenytoin. Straight channel swimming trials followed by maze trials were begun on separate male/female offspring pairs from each litter on postnatal days 50, 70, or 90. The results confirmed hypothesis 1, i.e., the more complex maze better differentiated phenytoin-related group differences. This was true regardless of whether the phenytoin rats exhibiting circling were included in the analyses or not. The results disconfirmed hypothesis 2, i.e., that path order AB would better differentiate the groups than path order BA. Rather, the data supported the alternate hypothesis, that path order was not a significant determinant of prenatal drug-related maze deficits. This was unchanged regardless of whether phenytoin offspring exhibiting circling were or were not included in the analyses. The implication is that path B alone was sufficient to detect phenytoin's effects on maze performance. Finally, the overall results disconfirmed hypothesis 3, i.e., assisted escape failed to differentiate groups any better than unassisted escape regardless of whether circlers were or were not included in the analyses. However, when more detailed analyses were performed only on rats that failed to find the goal on the first or second trials of path B, an assistance effect was noted. The effect (fewer errors) only occurred in the controls and only on the first two trials of path B. It was concluded that assisted escape was, at best, a minor contribution to improved maze performance.