Environmental determinants of behaviour in the rat fetus

Neuroimaging perspectives on fetal motor behavior

We are entering a new era of understanding human development with the ability to perform studies at the earliest time points possible. There is a substantial body of evidence to support the concept that early motor behaviour originates from supraspinal motor centres, reflects neurological integrity, and that altered patterns of behaviour precede clinical manifestation of disease. Cine Magnetic Resonance Imaging (cineMRI) has established its value as a novel method to visualise motor behaviour in the human fetus, building on the wealth of knowledge gleaned from ultrasound based studies. This paper presents a state of the art review incorporating findings from human and preclinical models, the insights from which, we propose, can proceed a reconceptualisation of fetal motor behaviour using advanced imaging techniques. Foremost is the need to better understand the role of the intrauterine environment, and its inherent unique set of stimuli that activate sensorimotor pathways and shape early brain development. Finally, an improved model of early motor development, combined with multimodal imaging, will provide a novel source of in utero biomarkers predictive of neurodevelopmental disorders.

Posture effects on spontaneous limb movements, alternated stepping, and the leg extension response in neonatal rats

The development of postural control is considered an important factor for the expression of coordinated behavior such as locomotion. In the natural setting of the nest, newborn rat pups adapt their posture to perform behaviors of ecological relevance such as those related to suckling. The current study explores the role of posture in the expression of three behaviors in the newborn rat: spontaneous limb activity, locomotor-like stepping behavior, and the leg extension response (LER). One-day-old rat pups were tested in one of two postures--prone or supine--on each of these behavioral measures. Results showed that pups expressed more spontaneous activity while supine, more stepping while prone, and no differences in LER expression between the two postures. Together these findings show that posture affects the expression of newborn behavior patterns in different ways, and suggest that posture may act as a facilitator or a limiting factor in the expression of different behaviors during early development.

Studies on the teratogenicity of anabasine in a rat model

A number of plant toxins have been shown to be teratogenic to livestock. The teratogenic action of some of these alkaloids is mediated by nicotinic acetylcholine receptors (nAChR). However, for many of these alkaloids it is difficult to obtain sufficient quantities of individual alkaloids to perform teratology studies in livestock species. Therefore the objective of this study was to determine if a rat model can be utilized to characterize the teratogenic nature of individual plant toxins that are nAChR agonists. In this study, we evaluated the teratogenicity of anabasine by feeding pregnant rats anabasine-containing rodent chow from gestational day (GD) 6-21. On GD21, the dams were euthanized and the gravid uteri were removed. The gravid uteri and individual pups were weighed. The pups were evaluated for bone malformations including cleft palate and scoliosis. Overall, the results of this study suggest that the rat is not a good model to study the teratogenicity of plant toxins that are nAChR agonists. It is possible that in the rat model, anabasine administered orally via the chow may not result in sufficient reduction in fetal movement to cause the significant malformations observed in livestock species.

Sensory feedback alters spontaneous limb movements in newborn rats: effects of unilateral forelimb weighting

Perinatal mammals show spontaneous movements that often appear random and uncoordinated. Here, we examined if spontaneous limb movements are responsive to a proprioceptive manipulation by applying a weight unilaterally to a forelimb of postnatal day 0 (P0; day of birth) and P1 rats. Weights were calibrated to approximate 0%, 25%, 50%, or 100% of the average mass of a forelimb, and were attached at the wrist. P0 and P1 pups showed different levels of activity during the period of limb weighting, in response to weight removal, and during the period after weighting. Pups exposed to 50% and 100% weights showed proportionately more activity in the nonweighted forelimb during the period of weighting, suggesting a threshold for evoking proprioceptive changes. Findings suggest that newborn rats use movement-related feedback to modulate spontaneous motor activity, and corroborate studies of human infants that have suggested a role for proprioception during early motor development.

Prenatal ontogeny of the dopamine-dependent neurobehavioral phenotype in Pitx3-deficient mice

Mouse models with prenatal alterations in dopaminergic functioning can provide new opportunities to identify fetal behavioral abnormalities and the underlying neural substrates dependent on dopamine. In this study, we tested the hypothesis that prenatal loss of nigrostriatal function is associated with fetal akinesia, or difficulty initiating movement. Specific behaviors were analysed in fetal offspring derived from pregnant Pitx3(ak) /2J and C57BL/6J dams on the last 4 days before birth (E15-18 of a 19-day gestation). Using digital videography, we analysed: (i) behavioral state, by quantification of high- and low-amplitude movements, (ii) interlimb movement synchrony, a measure of the temporal relationship between spontaneous movements of limb pairs, (iii) facial wiping, a characteristic response to perioral tactile stimulation similar to the defensive response in human infants, and (iv) oral grasp of a non-nutritive nipple, a component of suckling in the human infant. Pitx3 mutants showed a selective decrease in interlimb movement synchrony rates at the shortest (0.1 s) temporal interval coupled with significantly increased latencies to exhibit facial wiping and oral grasp. Collectively, our findings provide evidence that the primary fetal neurobehavioral deficit of the Pitx3 mutation is akinesia related to nigrostriatal damage. Other findings of particular interest were the differences in neurobehavioral functioning between C57BL/6J and Pitx3 heterozygous subjects, suggesting the two groups are not equivalent controls. These results further suggest that fetal neurobehavioral assessments are sensitive indicators of emerging neural dysfunction, and may have utility for prenatal diagnosis.

The integrated development of sensory organization

The natural environment provides a flux of concurrent stimulation to all our senses, and the integration of information from different sensory systems is a fundamental feature of perception and cognition. How information from the different senses is integrated has long been of concern to several scientific disciplines, including psychology, cognitive science, and the neurosciences, each with different questions and methodologies. In this article, I briefly explore some of these recent advances in the understanding of the development of sensory integration and organization and discuss implications of these advances for the care and management of the preterm infant.

Voluntary exercise in pregnant rats positively influences fetal growth without initiating a maternal physiological stress response

The effects of increased physical activity during pregnancy on the health of the offspring in later life are unknown. Research in this field requires an animal model of exercise during pregnancy that is sufficiently strenuous to cause an effect but does not elicit a stress response. Previously, we demonstrated that two models of voluntary exercise in the nonpregnant rat, tower climbing and rising to an erect bipedal stance (squat), cause bone modeling without elevating the stress hormone corticosterone. In this study, these same models were applied to pregnant rats. Gravid Wistar rats were randomly divided into three groups: control, tower climbing, and squat exercise. The rats exercised throughout pregnancy and were killed at day 19. Maternal stress was assessed by fecal corticosterone measurement. Maternal bone and soft tissue responses to exercise were assessed by peripheral quantitative computed tomography and dual-energy X-ray absorptiometry. Maternal weight gain during the first 19 days of pregnancy was less in exercised than in nonexercised pregnant control rats. Fecal corticosterone levels did not differ between the three maternal groups. The fetuses responded to maternal exercise in a uterine position-dependent manner. Mid-uterine horn fetuses from the squat exercise group were heavier ( P < 0.0001) and longer ( P < 0.0001) and had a greater placental weight ( P = 0.001) than those from control rats. Fetuses from tower-climbing dams were longer ( P < 0.0001) and had heavier placentas ( P = 0.01) than those from control rats, but fetal weight did not differ from controls. These models of voluntary exercise in the rat may be useful for future studies of the effects of exercise during pregnancy on the developmental origins of health and disease.

Opioid mediation of amniotic fluid effects on chemosensory responsiveness in the neonatal rat

The present study investigated if oral exposure to milk or amniotic fluid (AF) alters responsiveness to sensory stimulation in the neonatal rat, and whether these effects are mediated by the opioid system. Facial wiping evoked by intraoral lemon infusion was used as a measure of sensory responsiveness. Pups were tested in a supine posture, because they showed more paw-face strokes during facial wiping than pups tested prone (Experiment 1). Moreover, pups orally exposed to milk (Experiment 2) or AF (Experiment 3) showed a diminished wiping response to lemon compared to controls exposed to water. Blockade of opioid receptors with the nonselective antagonist naltrexone (Experiment 4) or the kappa antagonist nor-binaltorphimine (Experiment 5) reinstated higher levels of facial wiping after AF exposure. These findings confirm developmental continuity between fetal and neonatal behavioral responses to AF and the ability of AF to induce activity at kappa receptors of the endogenous opioid system.

Optimization and initial experience of a multisection balanced steady-state free precession cine sequence for the assessment of fetal behavior in utero

BACKGROUND AND PURPOSE

The assessment of motor function is an essential component of neurologic examinations, which imaging studies have extended to the fetus. US assessment is hampered by a limited FOV, whereas MR imaging has the potential to be an alternative. Our objectives were to optimize a cine MR imaging sequence for capturing fetal movements and to perform a pilot analysis of the relationship between the frequency of movements and uterine spatial constrictions in healthy fetuses.

MATERIALS AND METHODS

Initially, a bSSFP cine sequence was selected for optimization, and various compromises were explored in all acquisition parameters to achieve an effective balance between anatomic coverage of the fetus and the temporal resolution of cine data, with the aim of maximizing both. Subsequently, cross-sectional qualitative and quantitative analyses of fetal movements were performed prospectively by using a cohort of 37 healthy fetuses (median GA, 29 weeks; range, 20-37 weeks) with the optimized cine protocol. Two smaller subgroups were selected for representative sampling of overall behavior patterns by using cine data of longer duration and for volumetric quantification of free intrauterine space.

RESULTS

The optimized cine sequence, with TR/TE of 3.21/1.59 ms, coupled with parallel imaging and partial-Fourier imaging, resulted in a section-acquisition time of 0.303 seconds. Anatomic coverage was enhanced by using a combination of thick sagittal sections (30-40 mm) and multisection acquisitions to display movements in all fetal limbs, head, and trunk simultaneously. All expected motor patterns were observed throughout this gestational period, and a significant decreasing trend in overall movement frequency with age was demonstrated (r = -0.514, P = .0011). Also a significant negative correlation was found between overall movement frequency and the total intrauterine free space (r = -0.703, P = .0001). Furthermore, a significant decrease in the frequency of leg movements was shown in fetuses older then 30 weeks' GA compared with those younger than that (P = .015).

CONCLUSIONS

Cine MR imaging is effective for observing fetal movements from midgestation with near full-body coverage. Also, reductions in free space with increasing GA appear to be a factor in the gradual reductions in overall levels of fetal activity as well as in restrictions in movement within specific regions of the fetal anatomy.

Foetal pain?

The majority of commentary on foetal pain has looked at the maturation of neural pathways to decide a lower age limit for foetal pain. This approach is sensible because there must be a minimal necessary neural development that makes pain possible. Very broadly, it is generally agreed that the minimal necessary neural pathways for pain are in place by 24 weeks gestation. Arguments remain, however, as to the possibility of foetal pain before or after 24 weeks. Some argue that the foetus can feel pain earlier than 24 weeks because pain can be supported by subcortical structures. Others argue that the foetus cannot feel pain at any stage because it is maintained in a state of sedation in the womb and lacks further neural and conceptual development necessary for pain. Much of this argument rests on the definition of terms such as 'wakefulness' and 'pain'. If a behavioural and neural reaction to a noxious stimulus is considered sufficient for pain, then pain is possible from 24 weeks and probably much earlier. If a conceptual subjectivity is considered necessary for pain, however, then pain is not possible at any gestational age. Regardless of how pain is defined, it is clear that pain for conceptual beings is qualitatively different than pain for non-conceptual beings. It is therefore a mistake to draw an equivalence between foetal pain and pain in the older infant or adult.

Developmental explanation and the ontogeny of birdsong: Nature/nurture redux

Despite several decades of criticism, dichotomous thinking about behavioral development (the view that the behavioral phenotype can be partitioned into inherited and acquired components) remains widespread and influential. This is particularly true in study of birdsong development, where it has become increasingly common to diagnose songs, elements of songs, or precursors of songs (song templates) as either innate or learned on the basis of isolation-rearing experiments. The theory of sensory templates has encouraged both the dichotomous approach (by providing a role for genetic blueprints to guide song learning) and an emphasis on structural rather than functional aspects of song development. As a result, potentially important lines of investigation have been overlooked and the interpretation of existing data is often flawed. Evidence for a genetic origin of behavioraldifferencesis frequently interpreted as evidence for the genetic determination of behavioralcharacters. The technique of isolation rearing remains the methodology of choice for many investigators, despite the fact that it offers only a rather crude analysis of the contribution of experience to song development and provides no information at all about genetic contributions to development. The latter could in principle be elucidated by the application of developmental-genetic techniques, but it is unlikely that these can easily be applied to the study of birdsong. Because developmental questions are so often posed in terms of the learned–innate dichotomy, “experience” is taken to be synonymous with “learning” and the possible role of nonobvious contributions to song development has largely been ignored. An alternative approach, based on Daniel Lehrman's interactionist theory of development, permits a more thorough appreciation of the problems that have yet to be addressed, and provides a more secure conceptual foundation for theories of song development.

Prenatal behavior of the C57BL/6J mouse: a promising model for human fetal movement during early to mid-gestation

The study of fetal neurobehavioral development in genetically altered mice promises a significant advance in our understanding of the prenatal origins of developmental disabilities in humans. Despite their importance, little is known about fetal neurobehavioral development in mice. In this study, we observed prenatal behavioral patterns of the C57BL/6J mouse, a common background strain for genetically altered mice, and report their similarity to those observed in the early to mid-gestation human fetus. Fetal offspring from pregnant C57BL/6J dams were observed on the day before birth (E18 of a 19-day gestation). Scoring and analysis of fetal movement included Prechtl's Method for Qualitative Assessment, Interlimb Movement Synchrony, a measure of the temporal relationship between movements of limb pairs, and Behavioral State, quantified through detailed analysis of high and low amplitude limb movements. With the exception of fetal breathing movements, all categories and patterns of behavior typically reported in the early to mid-gestation human fetus were observed in the C57BL/6J mouse fetus. Our results suggest that behavioral analysis of fetal C57BL/6J mice may yield important new insights into early to mid-gestation human behavioral development.

Prenatal Development of Interlimb Motor Learning in the Rat Fetus

The role of sensory feedback in the early ontogeny of motor coordination remains a topic of speculation and debate. On E20 of gestation (the 20th day after conception, 2 days before birth), rat fetuses can alter interlimb coordination after a period of training with an interlimb yoke, which constrains limb movement and promotes synchronized, conjugate movement of the yoked limbs. The aim of this study was to determine how the ability to express this form of motor learning may change during prenatal development. Fetal rats were prepared for in vivo study at 4 ages (E18-21) and tested in a 65-min training-and-testing session examining hind limb motor learning. A significant increase in conjugate hind limb activity was expressed by E19, but not E18 fetuses, with further increases in conjugate hind limb activity on E20 and E21. These findings suggest substantial development of the ability of fetal rats to modify patterns of interlimb coordination in response to kinesthetic feedback during motor training before birth.

Conjugate limb coordination after experience with an interlimb yoke: evidence for motor learning in the rat fetus

This study investigated the capacity of the E20 rat fetus to adaptively alter patterns of interlimb coordination in a prenatal model of motor learning. Fetal limb movement was manipulated with an interlimb yoke, consisting of a fine thread attached at the ankles, which created a physical linkage between two limbs. Exposure to the yoke resulted in a gradual increase in conjugate movements of the yoked limbs during a 30-min training period, which persisted after removal of the yoke. Training effects were evident when the yoke was applied to two hindlimbs, two forelimbs, or a homolateral forelimb-hindlimb pair. A savings in the rate of acquisition also was observed when fetuses experienced yoke training in a second session. These data argue that the rat fetus can respond to kinesthetic feedback resulting from variation in motor performance, which suggests that experience contributes to the development of coordinated motor behavior before birth.

Prenatal methylazoxymethanol exposure alters evoked responses in fetal rats

Although there is considerable interest in identifying methods to detect central nervous system impairment early in development, few behavioral assessment tools are available for detecting CNS deficits in the fetus. In the present study, methylazoxymethanol [MAM; Midwest Research Institute, (MRI)] was used to induce deficits in CNS development in fetal rats to assess effects on coordinated fetal behavior. Fetuses were exposed by administering MAM to pregnant rats on E17 of gestation via intraperitoneal injection and then were prepared for behavioral testing 3 days later on E20. After externalization from the uterus into a warm saline bath, fetal subjects received either an intraoral infusion of lemon extract to evoke a facial wiping response or were presented with an artificial nipple to evoke an oral grasping response. Interlimb coordination and paw-face contact during facial wiping were disrupted in MAM-exposed fetuses. Similarly, MAM exposure diminished the ability of fetuses to grasp or maintain oral contact with the artificial nipple. Although clear disruptions of movement coordination were seen in the MAM-treated subjects, there were no significant differences from saline controls in weight or anatomical measures. Together, these findings suggest that behavioral assessments of fetal motor coordination may be useful in identifying neural insult during prenatal development.

Classical conditioning of responses to an artificial nipple in the rat fetus: mu and kappa opioid systems

The rat fetus exhibits oral grasp responses when presented with an artificial nipple in utero. Preexposure to milk produces a transient decrease in oral grasp responses. The effect of milk on oral grasping is mediated by endogenous activity in brain opioid systems. Specifically, milk triggers mu activity in rostral brain regions and kappa opioid activity in caudal brain regions to decrease oral grasping of the artificial nipple. Reexposure to the artificial nipple after it has been paired with milk during a classical conditioning trial results in a conditioned reduction in oral grasping that is evident when fetuses are reexposed to the nipple. The classically conditioned decrease in oral grasping is mediated by mu opioid activity in rostral brain regions and kappa opioid activity in caudal brain regions. Endogenous opioid systems, activated by exposure to milk and the nipple, may regulate the processing of sensory information during suckling in the rat.

Maternally directed orienting behaviors of newborn rats

We observed an organized repertoire of behaviors performed by newborns of the laboratory rat when placed under suspended artificial surfaces simulating various properties of the awake dam's ventrum. Pups traveled and wriggled, turned on their sides and upside down, ventroflexed and probed into the surface while on side or upside down, and audibly barked, all in a state of heightened behavioral arousal. Within 48 to 72 hr after birth, these behaviors generally increased with the addition to the simulation of more maternal features, including the texture of the dam's ventral fur and odor, separately and in combination. In addition, the behaviors were intensified by 18 hours of maternal deprivation. The possible functional relations among the components of this repertoire, which we refer to as "maternally directed orienting and proximity-seeking behaviors," and between these behaviors and nipple attachment and suckling, are discussed.

Neonatal responsiveness to alcohol odor and infant alcohol intake as a function of alcohol experience during late gestation

It has been previously suggested that maternal alcohol intoxication during the last days of pregnancy promotes fetal experiences that include chemosensory processing of the drug. In this study pregnant Wistar-derived rats were administered saline or one of two alcohol doses (1 or 2 g/kg) during gestational days 17-20. Immediately after birth, pups were tested in regard to motor-eliciting properties of the odor of amniotic fluid or alcohol, or of these stimuli presented as a configuration. Saline controls showed significantly shorter duration of overall motor activity and head movements when stimulated with the biological cue (amniotic fluid) than when exposed to a novel stimulus (ethanol alone or configured with the amniotic fluid). The opposite pattern was found in pups with prenatal experience with the higher alcohol dose. In a second experiment, the impact of similar alcohol treatments on infant consumption of different tastants, including alcohol and a configuration of sucrose and quinine, was tested. This configuration appears to mimic psychophysical properties of ethanol. Consumption of water, sucrose, or quinine was unaffected by the prenatal status of the subjects. Antenatal alcohol experience with the lower alcohol dose (1 g/kg) increased both alcohol and sucrose-quinine consumption. The 2 g/kg alcohol animals also ingested more sucrose-quinine relative to saline controls. As a whole, the results confirm the hypothesis that an intrauterine alcohol sensory memory selectively affects neonatal recognition of the alcohol's olfactory attributes and infant intake of either alcohol or solutions that share certain sensory equivalence with this psychopharmacological agent.

Classical conditioning in the fetal rat with a long delay between presentation of CS and US

A single paired presentation of the artificial nipple and milk results in classical conditioning of changes in perioral responsiveness in the E20 rat fetus. This classical conditioning is evidenced by a reduction in responding to perioral tactile stimulation. The results of Experiment 1 confirmed the specificity of milk as an unconditioned stimulus to support classical conditioning. Experiment 2 demonstrated that single-trial classical conditioning with the artificial nipple CS and milk US was possible with a delay of 30 s between nipple and milk presentations. Further, measurements of fetal motor behavior during the delay between CS and US presentations indicated that a single 15-s presentation of the artificial nipple increased movements of the mouth for 30 s after removal of the artificial nipple. Experiment 3 demonstrated that three exposures to the artificial nipple prolonged the expression of mouthing for up to 120 s and made possible single trial classical conditioning with a delay of 120 s between CS and US presentations. The capacity of the fetal CNS to maintain a "behavioral trace" for an ecologically important stimulus, such as the nipple, could have adaptive significance in the early development of motivated behavior.

Manipulation of the dopamine system affects fetal and neonatal responses to an artificial nipple

Rat fetuses respond to stimuli that they will encounter later while suckling. When exposed to an artificial nipple (AN) E21 fetuses show overall behavioral activation, mouthing, facial wiping, and oral grasping of the AN. The present experiments examined fetal and neonatal responses to the AN after central nervous system injection of receptor-binding drugs for the dopamine system. The D2 agonist drug quinpirole increased appetitive responses to the AN in the fetus and neonate. Activity at the D2 dopamine receptor promotes expression of fetal behavioral responses that are similar to those shown by the neonatal rat at the nipple. Motor responses also were elicited in neonatal pups that normally do not attach to the artificial nipple. These findings suggest that the dopamine system may regulate oral capture of the nipple in the neonatal rat.

A developmental and component analysis of active sleep

A wide variety of hypotheses have been put forth that address the functional significance of active sleep. Despite the well-accepted fact that active sleep expresses itself predominantly in the perinatal period, the vast majority of these functional hypotheses are applicable largely, if not exclusively, to the adult. We build on the developmental approaches of previous researchers and propose that the individual components of active sleep (e.g., myoclonic twitches, rapid eye movements) exhibit unique developmental and phylogenetic histories and may serve independent functions in the developing organism. This dynamic perspective leads to specific experimental approaches aimed at the developmental roles of these components in the neonate, their maintenance roles in the adult, and the means by which these various components coalesce temporally in what is commonly referred to as a behavioral state.

Cocaine alters cyclic motor activity in the fetal rat

Individual rat fetuses were exposed to cocaine by injection into the cisterna magna on E20 or E21 of gestation. On E20, cocaine elevated motor activity throughout the 20-min session, with activity increasing to double SAL-injected levels by the end of the session. On E21, overall activity also was elevated after cocaine, increasing four- to fivefold in the first 5 min of the session, and decreasing to twice the levels of SAL controls thereafter. Movement time series were subjected to spectral analysis to characterize cyclic motor organization. Cyclicity was evident in 67% of control and 97% of cocaine-injected fetuses. Cocaine increased the number of peaks in the movement spectrum and resulted in greater spectral density at the primary frequency of cyclic movement. Prenatal exposure to cocaine may alter patterns of cyclicity in the fetus, with consequences for the normal development of attention and behavioral state in the neonate.

Intracisternal administration of SKF-38393 and SCH-23390: behavioral effects in the rat fetus

The dopamine D1 agonist SKF-38393 and the D1 antagonist SCH-23390 were administered into the central nervous system of the E21 rat fetus via intracisternal (IC) injection. IC injection of SKF-38393 promoted a dose-dependent increase in fetal motor activity, principally including movements of the forelimbs, head, and body trunk. IC injection of SCH-23390 did not affect overall activity, but selectively suppressed forelimb, rearlimb, and head movements and promoted an increase in mouthing, licking, and facial wiping. Administration of SCH-23390 after IC injection of SKF-38393 was effective in completely reversing the behavioral effects of the D1 agonist. These findings suggest that central manipulation of dopamine D1 receptors can have direct and potent behavioral effects in the term rat fetus.

Functional analysis of spontaneous movements in preterm infants

Spontaneous movements of premature infants between 25 and 34 weeks conceptional age were observed for 1 hr on two or three occasions. Subjects had low-risk prognoses and were clinically stable at the time of testing. Behavioral acts were scored using a 0/1 time sampling technique in 60 continuous, 1-min time blocks. Temporal associations between individual movements were found using chi-square analyses. Some associated behaviors contained combinations consistent with neonatal action patterns, for example, single and bilateral leg kicking, head turning, and mouthing. Features of state organization were also evident in that general motor activity (GM), which has been used as a marker of active sleep (AS) in neonates, was found to cluster temporally with startle, facial, and head movements but not eye movements. Behavioral quiescence (> or = 5 s) was dissociated from AS-related behaviors (GM, facial, head, and eye movements). Combinations of state-segregated behaviors were more likely to exhibit co-occurrence within 1-min intervals in infants 30 weeks conceptional age and older.

Proximal control of fetal rat behavior

We examined the influence of the amniotic sac on spontaneous movement in late gestation fetal rats. Using techniques for in vivo observation of fetal behavior, Day 21 rat fetuses were exteriorized from the uterus, with umbilical connections to the dam intact, and videotaped for 15 min either: (a) through the intact amniotic membranes, or (b) following removal of the membranes. Analysis of fetal behavior categories replicated the findings of previous investigators: Movements of the head, forelimbs, and rearlimbs were significantly increased by sac removal, as was the total frequency of behavior categories and the simultaneous occurrence of different behavior categories. Frame-by-frame analysis of videotaped behavior revealed that amniotic sac removal increased the frequency of movement bouts without altering the overall amount of time that fetuses spent moving. Movement bout durations ranged from 50 msec to 70 s. The average duration of movement bouts was significantly reduced for fetuses lacking the amniotic sac as compared to fetuses within the sac, as was the overall distribution of movement bout durations. Frequency distributions of movement bout durations and interbout interval (IBIs) revealed that sac removal significantly increased the occurrence of short (1-2 s) movement bouts and reduced the frequency of protracted movement bouts and interbout intervals (> 10-s duration). Taken together, these findings indicate that the quantitative dimensions of fetal rat movements are influenced by proximal features of the uterine environment. During prenatal life, the amniotic sac appears to sustain movement, possibly by providing proprioceptive feedback or physical support to the fetus, or by regulating the chemical milieu.

Alcohol in the amniotic fluid prior to cesarean delivery: effects of subsequent exposure to the drug's odor upon alcohol responsiveness

Rat fetuses during the last day of gestation have the capacity to process ethanol and non-ethanol-related chemosensory cues present in the amniotic fluid. Recent studies suggest that the consequences related to cesarean delivery act as an unconditioned stimulus that is associated with these cues. In the first experiment, ethanol neonatal responsiveness assessed through a motor activity test was analyzed in pups that received ethanol or saline in utero proximal to cesarean delivery. Different factors and the interaction among them, were analyzed in this experiment: (i) ethanol concentration administered into the amniotic sac (0, 6, or 18% v/v), (ii) delay between administration and cesarean section (3, 10, or 30 min), and (iii) postnatal exposure to ethanol odor prior to test (0, 7.5, or 15 min). Only animals exposed to ethanol 10 min prior to delivery differed from vehicle-exposed subjects. Subsequent postnatal exposure to ethanol odor attenuated the magnitude of prenatally established effects. In the second experiment it was observed that prenatal ethanol exposure was sufficient to increase ethanol intake during Postnatal Day 11. Again, this effect was strongly attenuated when pups were exposed to the odor of the drug prior to assessment procedures. These results suggest that (i) associations between chemosensory cues in the amniotic fluid and consequences related with perinatal manipulations are likely to occur and (ii) postnatal reexposure to similar cues exerts an effect comparable to an extinction phenomenon.

Fetal behavior and the dopamine system: activity effects of D1 and D2 receptor manipulations

Binding studies have indicated that D1 and D2 dopamine receptor subtypes are present in rats before birth, but it is not known whether these receptors are functional during the prenatal period. In the present study, day-21 rat fetuses were prepared for direct observation after pharmacological manipulation of D1 and/or D2 receptors. The D1 agonist SK&F38393 induced a marked increase in fetal activity (i.e., forelimb, rearlimb, and head movements) while the D2 agonist quinpirole produced a slight suppression in activity. Coadministration of both agonists resulted in low levels of fetal activity, suggesting an interaction between D1 and D2 receptors. Administration of the D2 antagonist sulpiride resulted in little change in fetal behavior but was effective in blocking the behavioral activation induced by the D1 agonist. The D1 antagonist SCH23390, administered alone or in combination with the D2 antagonist, produced a modest increase in fetal activity that included mouthing and facial wiping behavior. These data provide evidence that the dopamine system is functional and capable of mediating behavioral effects in the near-term rat fetus. Further, manipulation of dopamine receptors results in a different pattern of behavioral effects than has been reported in older animals. The observation that fetal behavior is influenced by these pharmacological challenges suggests that drugs of abuse known to affect the dopamine system, such as cocaine, may cause profound changes in fetal behavior in utero that could consequently lead to alterations in behavioral and CNS development.