Behavioral effects of centrally administered arginine vasopressin in the rat fetus.

Arginine–8 vasopressin (AVP) was administered to rat fetuses on Embryonic Day 20 via intracisternal (IC), intrahemispheric (IH), or intrathecal (IT) injection. The IC administration of AVP promoted a 4-fold increase in motor activity, including the uncommon patterns of mouthing, licking, and facial wiping. The IH injection of AVP had little effect on fetal behavior, but IT injection resulted in pronounced increases in fetal activity, including mouthing, licking, and wiping. The IT administration of a V? antagonist blocked AVP effects, whereas IH injection potentiated AVP-induced changes in fetal behavior. The IC blockade of V? receptors suppressed facial wiping to a chemosensory fluid (lemon) and reduced oral grasping of an artificial nipple, whereas IH injection of the V? antagonist promoted facial wiping responses and increased grasping of the nipple. These data suggest that AVP may play a role in the development of responsiveness to stimuli encountered in the context of suckling. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral effects of milk in the rat fetus.

Intraoral infusion of milk to the rat fetus promoted changes in behavior (mouth and rearlimb movements), reduced responsiveness to perioral cutaneous stimulation, and resulted in expression of a fetal stretch response. Milk also altered the temporal organization of fetal movements over periods up to 30 min. The orosensory characteristics of milk, in the absence of ingestion, was sufficient to evoke these behavioral effects. Reduced responsiveness to a perioral stimulus had a rapid onset (     

An intrinsic source of behavioral regulation that influences discrete responses to cues important for the initiation of suckling.

The present experiment investigated the relationship between motor activity and oral grasping of an artificial nipple in newborn rats. Pups orally grasped the artificial nipple, and they performed more and longer oral grasps in the latter portion of the nipple presentation. Motor activity was cyclical, and this cyclicity was evident before and during presentation of the artificial nipple. The onset of an oral grasp response was preceded by a period of relatively low motor activity, and the termination of a grasp was followed by relatively high motor activity. The newborn rat pup's intrinsic oscillations in motor activity may regulate the expression of discrete responses to cues important for the initiation of suckling. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cocaine alters behavior in the rat fetus.

Changes in motor behavior and sensory responsiveness were characterized in rat fetuses on Gestational Day 21 after acute administration of various doses of cocaine. An increase in fetal motor activity was evident in the 3 highest doses (5, 10, and 20 mg/kg). Cocaine-exposed Ss showed reduced facial wiping in behavioral bioassays of cutaneous sensitivity (10 and 20 mg/kg) and chemosensory responsiveness (20 mg/kg). Changes in other behavioral measures indicated that fetuses detected and responded to these stimuli, suggesting that reduced facial wiping was due to a disruption of sensorimotor integration or motor coordination. Study of the fetus in vivo can provide insights into the mechanisms of cocaine's deleterious effects on CNS and behavioral development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fetal experience with milk or an artificial nipple alters appetitive and aversive responses to perioral cutaneous stimuli

Fetal rats exhibit oral grasping of an artificial nipple. The authors examined interactive effects of sensory stimuli normally encountered in the suckling environment on subsequent responses to the nipple. Embryonic Day 20 rat fetuses received an infusion of milk, lemon, or saline through a hollow artificial nipple or an intraoral cannula (producing no nipple stimulation). One minute after sensory pretreatment, behavioral responses of fetuses to an artificial nipple were recorded on videotape for frame-by-frame analysis. Preexposure to the artificial nipple decreased the number of oral grasps and facial wipes directed toward the artificial nipple but increased the duration of grasp responses. Milk uniformly reduced fetal responsiveness to the nipple. Furthermore, the artificial nipple enhanced fetal responses to perioral cutaneous stimulation, whereas milk suppressed perioral responsiveness. These data suggest that the perinatal rat's 1st experience with milk or the nipple can alter subsequent responses to suckling stimuli.     

Stimulus contingencies that permit classical conditioning of opioid activity in the rat fetus.

In a prenatal model of classical conditioning, rat fetuses received presentations of an artificial nipple (conditioned stimulus; CS) paired with milk (unconditioned stimulus). Infusion of milk promotes activity in the kappa opioid system of the fetus, but after 2, 3, or 6 pairings with the artificial nipple, milk evoked both kappa and mu opioid activity. The nipple CS has no effect on opioid activity, but after pairing with milk evoked a mu opioid response. Conditioned mu opioid activity was evident in 60% of subjects tested after I paired conditioning trial. Significantly more fetal subjects (90%) exhibited conditioned opioid activity if preexposed to the nipple twice before conditioning. CS preexposure altered behavior during the conditioning trial, with preexposed fetuses showing more pronounced responses to milk infusion. Exposure to familiar stimuli facilitates classical conditioning of physiological responses, including opioid activity, during the first suckling episode. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Central administration of cocaine produces age-dependent effects on behavior in the fetal rat.

Rat fetuses were exposed to cocaine, lidocaine, or saline on Gestational Day 20 or 21 to provide information about cocaine effects on behavior during prenatal development. Cocaine was administered into the cisterna magna of individual fetal subjects to restrict effects to the CNS. Behavioral effects of cocaine were compared with lidocaine to help distinguish the effects of cocaine on monoamine systems in the brain from its properties as a local anesthetic. Cocaine promoted 3–5 fold increases in fetal motor activity in the absence of explicit sensory stimulation, in contrast to the slight suppressive effects of lidocaine. Cocaine and lidocaine also reduced coordinated behavioral responses to an artificial nipple. The behavioral effects of cocaine administered into the CNS of fetal subjects suggest specific mechanisms of action on developing neural and behavioral systems in the late prenatal period. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The development of behavior before birth.

Study of the fetus in vivo provides a simple system for experimental study of early neurobehavioral development. This review summarizes research on the development of behavior before birth including studies where fetuses are exposed to stimuli that mimic features of the neonatal environment, such as milk and an artificial nipple. These stimuli reliably evoke responses from fetal subjects, including species-typical behavior such as the stretch response and oral grasping of the artificial nipple. Contingent presentations of the nipple and milk can result in classical conditioning, including activation of the endogenous opioid system. Quantitative analysis of fetal motor behavior coupled with the use of ecologically relevant sensory manipulations provide a means for assessing integrated output of the developing nervous system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of the stretch response in the rat fetus: Kappa opioid involvement.

Previous studies have demonstrated that the kappa opioid system is functional and plays a role in mediating the stretch response of the rat fetus on Day 21 of gestation. In this study, a kappa opioid agonist (U50,488) was administered on Days 19, 20, or 21, and fetal behavior was recorded after infusion of either milk or saline. Activation of the kappa opioid system promoted stretching in response to saline on Days 20 and 21. Although fetuses on Day 19 did not stretch, videotape analysis indicated that kappa opioid manipulation promoted modest increases in rearlimb activity and changes in fetal body posture that typically occur antecedent to the stretch. These findings suggest that functional maturity of the kappa opioid system may be a limiting factor in the expression of the fetal stretch response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation to chemosensory stimuli in the rat fetus: Effects of endogenous kappa opioid activity.

On Day 21 of gestation, rat fetuses respond to chemosensory stimuli by expressing stereotypic facial wiping behavior. A series of 4 experiments was conducted to investigate (1) the influence of morphine on fetal responsiveness to a single chemosensory infusion, (2) the effect of naloxone blockade of endogenous opioid activity on diminished fetal responsiveness over a series of chemosensory infusions, (3) the effect of endogenous opioids on the recovery of fetal responsiveness to infusion after various dishabituation procedures, and (4) the influence of selective mu and kappa opioid receptor antagonists on fetal habituation. These experiments confirm that fetuses habituate after a brief series of chemosensory infusions and that dishabituation promoted by presentation of a novel stimulus is facilitated by pharmacological blockade of kappa opioid receptors. Endogenous activity in the kappa opioid system may be functional in modulating the sensory environment around the time of birth. (PsycINFO Database Record (c) 2010 APA, all rights reserved)