Hypothermic vocalizations of rat pups (Rattus norvegicus) and direct maternal search behavior.

Emissions of ultrasonic vocalizations (USVs) by rat pups (Rattus norvegicus) during hypothermia have consequences for recovery and warming. The effects on dam behavior of USVs emitted by 3- to 11-day-old pups during hypothermia at rectal temperatures between 18 and 22°C was investigated Rat dams were tested in a Y maze with the home cage as a start box. Dams were given, in one condition, a choice between a hypothermic pup emitting USVs or a hypothermic, silent (anesthetized) pup and, in the other, a choice between 2 hypothermic, silent pups. Although differing in some acoustic properties from normal isolation calls, USVs emitted by hypothermic pups both elicited maternal search behavior and acted as directional cues for dams, in comparisons with control dams exposed only to silent pups. Thus USVs of pups recovering from extreme hypothermia have communicative as well as physiological significance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultrasonic vocalizations by rat pups after adrenergic manipulations of brown fat metabolism.

Rat pups emit ultrasonic vocalizations (USVs) during cold challenge. R. F. Kirby and M. S. Blumberg (1998) suggested that when brown adipose tissue (BAT) thermogenesis fails to compensate for body heat loss and heart rate declines, infant pups maintain venous return to the heart with a mechanical maneuver that is accompanied by ultrasonic emissions. Thus, manipulations that attenuate or enhance BAT thermogenesis should have inverse effects on cold-induced USVs. The authors found that hexamethonium (10 mg/kg) and propranolol (1 and 20 mg/kg) attenuated BAT metabolism while enhancing USV production, and norepinephrine (NE, 800 μg/kg) enhanced BAT metabolism while ultrasonic emissions decreased. The findings are consistent with the hypothesis that BAT metabolism influences USVs during cold challenge by affecting cardiac rate and inducing compensatory, homeostatic responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dopaminergic modulation of kappa opioid-mediated ultrasonic vocalization, antinociception, and locomotor activity in the preweanling rat.

The purpose of this study was to determine whether dopamine (DA) systems modulate kappa opioid-mediated ultrasonic vocalizations (USVs), antinociception, and locomotion in young rats. Seventeen-day-old rats were injected with the kappa agonist U-50,488 (0.0-7.5 mg/kg) and saline, the D?-like receptor agonist R(-)-propylnorapomorphine (NPA; 0. 1 or 1.0 mg/kg), the indirect DA agonist cocaine (10 or 20 mg/kg), or the DA antagonist flupenthixol (0.25 or 0.5 mg/kg). USVs and locomotion were measured for 6 min, with antinociception being assessed with a tail-flick test. Kappa receptor stimulation produced analgesia and increased USVs and locomotion. U-50,488-induced analgesia was potentiated by NPA, whereas U-50,488-induced USVs were attenuated by both DA agonists. NPA and flupenthixol depressed U-50,488's locomotor effects. These results show that DA systems interact with kappa opioid systems to modulate USVs, antinociception, and locomotion in preweanling rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus control of maternal responsiveness to Norway rat ( Rattus norvegicus) pup ultrasonic vocalizations.

Mother rats (Rattus norvegicus; 6 to 8 days postpartum) approach and maintain proximal orientation to a pup that is emitting ultrasonic vocalizations (USVs) far more than do virgin females (W. J. Farrell & J. R. Alberts, 2002). We used a playback regimen to examine the roles of acoustic and nonacoustic cues in regulating maternal proximal orientation toward vocalizing pups. When presented with recorded USVs, mothers of 6- to 8-day-old pups and nulliparous virgin females exhibited equivalent levels of proximal orientation toward the playback speaker. Mothers did show enhanced proximal orientation toward recorded USVs, however, if a silent pup was positioned below the speaker. Pup odors appear to be crucial for the maternal response to vocalizing pups, as peripherally induced anosmia attenuated maternal proximal orientation toward a vocalizing pup. Furthermore, spatial contiguity between olfactory and auditory stimuli was required for a maximal maternal response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brief Maternal Interaction Increases Number, Amplitude, and Bout Size of Isolation-Induced Ultrasonic Vocalizations in Infant Rats (Rattus norvegicus).

The number, amplitude, duration, and bout structure of isolation-induced ultrasonic vocalization (USV) of infant rats (Rattus norvegicus) were measured on postnatal Day 10. Measurements were made before and after a brief, 1-min, active interaction with their mother or before and after a "pick-up" control procedure. Consistent with prior studies, the number of USVs emitted was significantly increased in the period following the maternal reunion but not after the control procedure. The average amplitude of USVs was also greater following maternal reunion. Finally, analyses characterizing the bout structure of USV production indicated that the average bout size (i.e.. number of USVs/bout) was increased severalfold following the reunion with the mother, accounting for the greater rate of USV production during the second isolation period. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultrasonic vocalization behavior differs between lines of ethanol-preferring and nonpreferring rats

To further understand the relationship between emotional state and alcohol intake in rats, the tendency to emit ultrasonic vocalizations in response to an aversive, but nonpainful, air puff stimulus was tested in several rat lines. Included in this group were Maudsley Reactive (MR) and Non-Reactive (MNR) rats, and several lines of rats with either high ethanol preference or a low ethanol preference: Preferring, (P), Alko-Alcohol (AA), and Fawn-Hooded (FH) animals; and Non-Preferring (NP), Alko-Non-Alcohol (ANA), and Flinders Resistant Line (FRL). MR rats emitted fewer ultrasonic vocalizations (USVs) and showed less preference for ethanol than did MNR animals. An overall analysis that included the P, NP, FH, FRL, AA, and ANA groups demonstrated a significant negative correlation between the total number of USVs emitted and ethanol consumption. NP, FRL, and especially ANA rats (low ethanol-preferring) emitted the most USVs--to an extent similar to that typically found for normal rats. The duration of vocalizing was higher only in the NP and the FRL rats the relative to their P and FH comparison groups, respectively. In the ethanol-preferring and nonpreferring lines, the numbers of USVs emitted correlated positively with the duration of vocalizing, but not with the latency to vocalize, which in turn did not correlate strongly with ethanol intake. The latency to vocalize did not correlate significantly with ethanol intake across all drinking lines or MR or MNR rats, but was found to be higher in FH and AA rats relative to their nondrinking comparison groups. These associations suggest that the relationship between emotional state and ethanol drinking is complex and cannot be attributed to a simple elevated state of anxiety or emotionality. Further examination of the central nervous system mechanisms mediating the difference in USVs between paired lines of ethanol-preferring and nonpreferring rats may identify neurochemical factors that predict ethanol preference.     

Identification of types II, IX and X collagens at the insertion site of the bovine achilles tendon

The authors provide initial documentation that juvenile rats emit short, high-frequency ultrasonic vocalizations (high USVs, approximately 55 kHz) during rough-and-tumble play. In an observational study, they further observe that these vocalizations both correlate with and predict appetitive components of the play behavioral repertoire. Additional experiments characterized eliciting conditions for high USVs. Without prior play exposure, rats separated by a screen vocalized less than playing rats, but after only 1 play session, separated rats vocalized more than playing rats. This findings suggested that high USVs were linked to a motivational state rather than specific play behaviors or general activity. Furthermore, individual rats vocalized more in a chamber associated with play than in a habituated control chamber. Finally, congruent and incongruent motivational manipulations modulated vocalization expression. Although play deprivation enhanced high USVs, an arousing but aversive stimulus (bright light) reduced them. Taken together, these findings suggest that high USVs may index an appetitive motivation to play in juvenile rats.     

Anticipation of play elicits high-frequency ultrasonic vocalizations in young rats.

The authors provide initial documentation that juvenile rats emit short, high-frequency ultrasonic vocalizations (high USVs, ～55 kHz) during rough-and-tumble play. In an observational study, they further observe that these vocalizations both correlate with and predict appetitive components of the play behavioral repertoire. Additional experiments characterized eliciting conditions for high USVs. Without prior play exposure, rats separated by a screen vocalized less than playing rats, but after only 1 play session, separated rats vocalized more than playing rats. This finding suggested that high USVs were linked to a motivational state rather than specific play behaviors or general activity. Furthermore, individual rats vocalized more in a chamber associated with play than in a habituated control chamber. Finally, congruent and incongruent motivational manipulations modulated vocalization expression. Although play deprivation enhanced high USVs, an arousing but aversive stimulus (bright light) reduced them. Taken together, these findings suggest that high USVs may index an appetitive motivation to play in juvenile rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of transforming growth factor-beta1 and basic fibroblast growth factor on proliferation of cell cultures derived from human vestibular nerve schwannoma

Stress during pregnancy, or prenatal stress, is known to alter offspring behavior, morphology and physiology. We found that a heat, light and restraint stressor applied during the third trimester of pregnancy: 1) decreased the weight gain of adult female rats during pregnancy; 2) reduced the weight of pups, as well as the anogenital distance of male offspring, at birth; and 3) increased the number of ultrasonic vocalizations emitted by pups during isolation in a novel environment on Postnatal Day 14. These results closely approximate those we previously observed after peripheral administration of corticotropin-releasing factor to pregnant females during the third trimester. Together, the studies strongly suggest a role for corticotropin-releasing factor and/or other hormones of the hypothalamic-pituitary-adrenal system in mediating some of the effects of gestational stress.     

Anticipation of rewarding electrical brain stimulation evokes ultrasonic vocalization in rats.

Adult rats emit increased rates of 50-kHz ultrasonic vocalizations (USVs) before receiving social and pharmacological rewards. This study sought to determine whether anticipation of rewarding electrical stimulation of the brain (ESB) would also elicit these vocalizations. In Experiments 1 and 2, rats showed increased 50-kHz USVs before receiving experimenter-delivered ventral tegmental area (VTA) and lateral hypothalamic (LHy) ESB on a fixed time 20-s schedule. In Experiments 3 and 4, rats increased their rate of 50-kHz USVs in response to cues that predicted the opportunity to self-stimulate the VTA or LHy. Interestingly, unexpected termination of either type of ESB evoked 20-kHz, rather than 50-kHz, USVs. In Experiment 5, a cue that predicted daily 1-hr feeding sessions increased 50-kHz USVs, whereas a cue that predicted footshock decreased 50-kHz USVs. These effects could not be explained simply by changes in locomotor activity or general arousal. Together, these findings support the hypothesis that short 50-kHz USVs may selectively index a state of reward anticipation in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Decreased venous return is neither sufficient nor necessary to elicit ultrasonic vocalisations of infant rat pups.

It has been proposed that all ultrasonic vocalizations (USVs) in young rats are by-products of a cardiovascular response to decreased venous return, the abdominal compression reaction. To test the hypothesis, venous return was decreased in infant rats while USV and cardiovascular measures were monitored. Neither injection of the vasodilator sodium nitroprusside nor blood withdrawal from the superior vena cava or carotid artery elicited USV from pups in their home cage. Thus, decreased venous return by itself is not sufficient to elicit USV. To test whether venous return is a necessary mechanism for USV production, 5% dextrose in water or blood was infused intravenously into isolated pups that were producing USV. This artificial increase of venous return did not affect the rate of USV. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mild traumatic brain injury does not modify the cerebral blood flow profile of secondary forebrain ischemia in Wistar rats

The rat hippocampus is hypersensitive to secondary cerebral ischemia after mild traumatic brain injury (TBI). An unconfirmed assumption in previous studies of mild TBI followed by forebrain ischemia has been that antecedent TBI did not alter cerebral blood flow (CBF) dynamics in response to secondary ischemia. Using laser Doppler flowmetry (LDF), relative changes in regional hippocampal CA1 blood flow (hCBF) were recorded continuously to quantitatively characterize hCBF before, during, and after 6 min of forebrain ischemia in either normal or mildly traumatized rats. Two experimental groups of fasted male Wistar rats were compared. Group 1 (n = 6) rats were given 6 minutes of transient forebrain ischemia using bilateral carotid clamping and hemorrhagic hypotension. Group 2 (n = 6) rats were subjected to mild (0.8 atm) fluid percussion TBI followed 1 h after trauma by 6 min of transient forebrain ischemia. The laser Doppler flow probe was inserted stereotactically to measure CA1 blood flow. The electroencephalogram (EEG) was continuously recorded. During the forebrain ischemic insult there were no intergroup differences in the magnitude or duration of the decrease in CBF in CA1. In both groups, CBF returned to preischemic values within one minute of reperfusion but traumatized rats had no initial hyperemia. There were no intergroup differences in the CBF threshold when the EEG became isoelectric. These data suggest that the ischemic insult was comparable either with or without antecedent TBI in this model. This confirms that this model of TBI followed by forebrain ischemia is well suited for evaluating changes in the sensitivity of CA1 neurons to cerebral ischemia rather than assessing differences in relative ischemia.     

Physical interpretation of information entropy: Numerical evidence of the Collins conjecture

The effect of altering the dietary Ca:P ratio during critical points of growth (based on reproductive and skeletal age) on kidney calcification in female rats was investigated. Groups of weanling animals were fed one of three nutritionally complete but calcium-altered diets (0.25, 0.5 or 1.0 g Ca/100 g diet) from 4 to 12 wk of age (Phase 1). Phosphorus concentration remained constant at 0.4 g/100 g diet resulting in Ca:P molar ratios of 0.48, 0.96 and 1.92, respectively. During Phase 2, the same animals within each diet group were then rerandomized into one of the above diets and fed for an additional 25 wk. Each group contained five rats. The data from the nine treatment groups were analyzed statistically using a two-way ANOVA (Phase 1 dietary Ca level by Phase 2 dietary Ca level). The level of dietary Ca during Phase 1 only exerted a significant influence on kidney Ca accumulation. Rats fed the two lower dietary Ca levels, and hence lower dietary Ca:P molar ratios, during Phase 1 had two- to threefold greater kidney Ca concentration and kidney ash Ca concentration than rats fed the diet with the highest dietary Ca level (1.92 Ca:P molar ratio) during Phase 1, regardless of the Ca intake during Phase 2. In contrast, the dietary Ca:P molar ratio during Phase 2 had little effect either positively or negatively on the kidney Ca concentration that had been established during Phase 1. The results indicate that dietary-induced nephrocalcinosis in female rats is irreversible and is induced primarily before the completion of adolescence (approximately 12 wk of age) in Sprague-Dawley female rats.     

Ultrasonic vocalizations are elicited from rat pups in the home cage by pentylenetetrazol and U50,488, but not naltrexone.

Although isolated rat pups emit ultrasonic vocalizations (USVs), those kept warm and undisturbed in the home cage with their littermates seldom do. Drugs were administered to 10-day-old Wistar rat pups in the home cage to determine whether pharmacological agents can elicit USVs in this familiar environment. Ss were injected with U50,488, a highly selective kappa opioid agonist; pentylenetetrazol (PTZ), an anxiogenic drug that binds at the GABA-benzodiazepine receptor complex; or naltrexone (NLX), an opiate receptor blocker, and then were returned to their littermates in the home cage. U50,488 increased USV and activity levels, lowered body temperature, and disrupted contact with littermates. PTZ raised activity levels but had a smaller effect on vocalization rates and did not alter temperature or contact with littermates. Behavioral measures and body temperature were unchanged by NLX. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mother's milk and adult presence: Two factors determining initial dietary selection by weanling rats.

Reports 3 experiments with (a) 10 female hooded rats and their litters (reduced to 6 pups/litter); (b) 1 male and 4 female wild rats (Rattus norvegicus) and 2 litters (6 pups/litter) born to colony members; and (c) 6 litters of wild and 4 litters of hooded rat pups. Results indicate that adult Ss were capable of influencing their pups' choice of diet during weaning in 2 ways: (a) cues transmitted from a mother to her pups during the nursing period were sufficient to determine the dietary preference of the young at weaning, and (b) the presence of adult Ss at a feeding site was sufficient to determine the choice of feeding site by the pups independent of cues transmitted during the nursing period. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sleep: a prerequisite for reflex milk ejection in the rat

Electroencephalographic activity (EEG) was recorded from the frontal cortex of unanaesthetized and urethane-anaesthetized lactating rats and analysed in relation to the pattern of milk ejection evoked by the nursing pups. The EEG of the anaesthetized rat fluctuated without experimental intervention between three distinctive patterns defined as synchronized, desychronized, and stage III activity, whilst reflex milk ejection recurred at intervals of about 6 min (range 2- greater than 20 min) throughout the 1-4 h period the pups were left attached to the nipples. For greater than 10 s before and for up to 60 s after each milk ejection, as judged from recordings of intramammary pressure and pup behaviour, the EEG was invariably synchronized throughout. Conversely, milk ejection (n greater than 300) was never observed during long periods of desynchronized, or stage III EEG activity. The vigorous increase in the sucking of the pups at milk ejection failed to produce a desynchronization (arousal) of the EEG as observed with other forms of sensory stimulation. Indeed, the sucking of the pups appeared to produce a soporific change i, the maternal EEG for spontaneous periods of desynchronization were not observed in the 30-60 min following the initial attachment of the pups to the nipples. Similar EEG patterns were seen in the unanaesthetized rat, though arousal from the synchronized state was more easily produced, e.g., by weak auditory signals. Milk ejection, as judged from the behaviour of the pups, recurred at intervals of 2 min or more during each 20-80 min period of nursing. The rat appeared somnolent for most of the nursing period and the EEG was always synchronized for greater than 10 s before each milk ejection (n greater than 200), though her eyes usually remained open. Arousal and desynchronization of the EEG was invariably observed in association with the increased pup behaviour at milk ejection. From these observations and the knowledge that oxytocin release from the neurohypophysis occurs about 10 s before milk ejection, we conclude that a synchronized EEG pattite for the expression of the milk-ejection reflex in the rat.     

Postnatal maternal separation during the stress hyporesponsive period enhances the adrenocortical response to novelty in adult rats by affecting feedback regulation in the CA1 hippocampal field

The aim of the present experiment was to study the effects of early postnatal maternal separation on behavioural and adrenocortical responses to novelty in rats tested as adults. Sprague-Dawley rat pups were exposed to daily maternal separation (5 h/day) from postnatal day 2 to 6, during the stress hyporesponsive period. Since this procedure requires physical contact with the animals, a first control group of daily handled pups was introduced. A second control group, consisting of pups never handled or separated from the mother, was also considered. At postnatal day 45, the rats were tested in a two-compartment exploratory apparatus: the maternally separated and the non-handled rats, whose behavioural performance did not differ, showed higher emotional behaviour when compared with the handled rats (P < 0.05), suggesting that the handling procedure but not maternal separation improved the capacity to cope with novelty. Corticosterone plasma levels were found to be higher in the maternally separated rats than in the other two groups (P < 0.05), either at resting conditions or at 30 min after novelty exposure (P < 0.05). Levels of nuclear glucocorticoid receptor immunoreactivity in the CA1 hippocampal field were shown to be regulated by novelty exposure, as expected, in both the handled and the non-handled rats but not in the maternally separated rats. In conclusion, repeated maternal separation periods of 5 h/day during the first week of life produced long-lasting effects on the hippocampal regulation of the hypothalamic-pituitary-adrenocortical axis, which appear to be associated with increased responsiveness to stress stimuli in adulthood.     

Plasma concentrations and cardiovascular influence of lidocaine infusions during isoflurane anesthesia in healthy dogs and dogs with subaortic stenosis

OBJECTIVE: To determine the plasma concentrations and cardiovascular changes that occur in healthy dogs and dogs with aortic stenosis that are given an infusion of lidocaine during isoflurane anesthesia. STUDY DESIGN: Phase 1, controlled randomized cross-over trial; Phase 2, before and after trial ANIMALS: Phase 1, 6 healthy dogs (4 female, 2 male) weighing 23.8 +/- 7.4 kg; Phase 2, 7 dogs (4 female, 3 male) with moderate to severe subaortic stenosis (confirmed by Doppler echocardiography) weighing 31.1 +/- 14.5 kg. METHODS: After mask induction, intubation, and institution of positive pressure ventilation, instrumentation was performed to measure hemodynamic variables. After baseline, measurement at an end-tidal isoflurane concentration of 1.9% (phase 1) or 1.85% (phase 2), a loading dose infusion of lidocaine at 400 microg/kg/min was given. Phase 1: Maintenance doses of lidocaine were administered consecutively (40, 120, and 200 microg/kg/min) after the loading dose (given for 10, 10, and 5 minutes, respectively) in advance of each maintenance concentrations. Measurements were taken at the end of each loading dose and at 25 and 35 minutes during each maintenance level. The same animals on a different day were given dextrose 5% and acted as the control. Phase 2: Dogs were studied on a single occasion during an infusion of lidocaine at 120 microg/kg/ min given after the loading dose (10 minutes). Measurements occurred after the loading dose and at 25 and 35 minutes. A blood sample for lidocaine concentration was taken at 70 minutes. Data were compared using a one-way ANOVA for phase 1, and between phase 1 and 2. Statistical analysis for phase 2 was performed using a paired t-test with a Bonferroni correction. A P value < or = .05 was considered significant. RESULTS: Phase 1: Plasma lidocaine concentrations achieved with 40, 120, and 200 microg of lidocaine/kg/min were 2.70, 5.27, and 7.17 microg/mL, respectively. A significant increase in heart rate (HR) (all concentrations), central venous pressure (CVP), mean pulmonary arterial pressure (PAP), and a decrease in stroke index (SI) (200 microg/kg/min) were observed. An increase in systemic vascular resistance (SVR) and mean PAP, and a decrease in SI also followed the loading dose given before the 200 microg/kg/min infusion. No other significant differences from the control measurements, during dextrose 5% infusion alone, were detected. Phase 2: Plasma lidocaine concentrations achieved were 5.35, 4.23, 4.23, and 5.60 microg/mL at 10, 25, 35, and 70 minutes, respectively. They were not significantly different from concentrations found in our healthy dogs at the same infusions. A significant but small increase in CVP compared with baseline was noted after the loading dose. There were no significant differences from baseline shown in all other cardiovascular data. There were no statistically significant differences in any measurements taken during the lidocaine infusion between the dogs in phase 1 and phase 2. Dogs with aortic stenosis tended to have a lower cardiac index than healthy dogs at baseline (88 v 121 mL/kg/min) and during lidocaine infusion (81 v 111 mL/kg/min). A small, statistically significant difference in systolic PAP was present at baseline. CONCLUSIONS: There does not appear to be any detrimental cardiovascular effects related to an infusion of lidocaine at 120 microg/kg/min during isoflurane anesthesia in healthy dogs or dogs with aortic stenosis. The technique used in this study resulted in therapeutic plasma concentrations of lidocaine.CLINICAL RELEVANCE: Methods shown in the study can be used in clinical cases to achieve therapeutic lidocaine levels without significant cardiovascular depression during isoflurane anesthesia.     

Factors influencing cortisol and behavioral responses to maternal separation in guinea pigs.

Infant guinea pigs recently were found to respond to brief maternal separation with an increase in plasma cortisol (COR) levels. The present experiments were conducted to further characterize this response and compare it with the COR separation response previously observed in primates. In Exp 1, separation of guinea pig pups from their mothers did not elevate the plasma COR levels of the pups at either 30 or 180 min when they remained alone in their home cages during the separation. Exp 2 showed that COR levels of pups placed alone in a novel cage were greater at 30, 90, and 180 min than were those of pups placed in the cages together with their mothers. In contrast, the separated pups vocalized more than did pups tested with their mothers during the initial 30 min only. In Exp 3, pups raised on inanimate surrogates responded less intensely to rearing-figure separation in terms of COR and vocalizations than did mother-reared controls. Results indicate differences (response to home cage separation) and similarities (dissociation of COR and vocalization responses, effect of surrogate separation) in the separation responses of guinea pig and primate infants. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Maternal presence and rearing condition affect responses to live predator in kangaroo rats (Dipodomys heermanni arenae).

Experiment 1 compared the responses of wild-caught adult and captive-born adult and juvenile kangaroo rats (Dipodomys heermanni arenae) to a live snake. Wild-caught adult rats were less active and monitored the snake more than during a control condition; captive-born juvenile rats did not behave differently during snake and control tests. Snake-naive adult rats behaved more like the wild-caught adult rats, but not on all measures. In Experiment 2, pups were tested at 25 and 50 days of age in 4 conditions: no-snake control, alone with the snake, with a sibling and the snake, and with the mother and the snake. Pups did not behave differently during control and snake tests, but during tests with the mother, pups faced the snake less and followed the mother. Younger pups were more often near the mother than a sibling and followed the mother more when the snake was present. Development of defensive behavior may depend on both predator experience and maternal influence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)