Nutritional variables and their effect on the development of ultrasonic vocalizations in rat pups

Measures of ultrasonic vocalizations were made on alternate days during the first and second weeks postpartum in rat pups reared by mothers fed either control (23%) or low protein (8%) diets. Compared to those reared by control mothers, pups reared by low protein mothers emitted significantly fewer ultrasonic vocalizations. The hypothesis that malnutrition might shift the age at which peak rate of vocalizations were emitted was not confirmed.     

Ontogeny of sexually dimorphic ultrasonic vocalizations in Mongolian gerbils

Sexual differentiation of emission rates (Experiment 1) and physical structure of ultrasonic vocalizations (Experiment 2) were investigated in Mongolian gerbils between 17 and 85 days of age. Animals from different litters were allowed to interact in iso- and heterosexual pairs. Vocalization rates increased in all groups, reaching a plateau at approximately day 56. Female pups had significantly higher rates of all vocalizations than male pairs before the plateau stage. Five stereotypic categories of physical structure were easily distinguished and confirmed by sound spectrographic analysis. Only mid-range frequencies of vocalizations appeared to decline throughout the juveniles' lives: this change may communicate the animal's age. Two male and one female categories were sexually dimorphic and similar in structure to those made during courtship interactions. Rates of male-type vocalizations appear to increase as testicular androgens start rising.     

Gastric saline infusion reduces ultrasonic vocalizations and brown fat activity in suckling rat pups

Under standard conditions involving isolation and cooling, it has been documented that intraoral infusion of milk and injection of the intestinal peptide cholecystokinin (CCK) result in an attenuation in ultrasonic vocalizations (USV) emitted by infant rat pups. One of the most effective stimuli in inhibiting ingestion in suckling rat pups is gastric distension, but the effect of gastric distension on USV production has not been reported. In this experiment, we subjected infant rats to intragastric infusion of isotonic saline (2% body weight) to produce a natural level of gastric distension and hydration. We found that this stimulus resulted in a powerful reduction in USV emissions in isolated 10-day-old rats. In a subsequent experiment, we found that gastric saline infusion also diminished brown adipose tissue (BAT) thermogenesis. There were different time courses of the gastric saline infusion effects on BAT thermogenesis and on USV emissions, however, suggesting that these processes may be independently regulated. We hypothesize that this stimulus induces a transient activation of the parasympathetic nervous system, which overrides the sympathetic control of BAT and USV production.     

Social,thermal, and temporal influences on isolation-induced and maternally potentiated ultrasonic vocalizations of rat pups

Sensory and temporal factors have been demonstrated to be involved in the regulation of isolation-induced ultrasonic vocalizations (USV) of young rats. Sensory cues include thermal, olfactory, and tactile modalities. Temporal factors include the time spent in isolation. The goal of the present research was to examine the interaction of these factors in both isolation-induced and maternally potentiated USV. Maternal potentiation of USV occurs when a brief interaction with the dam, even a passive (anesthetized) dam, elicits an augmented vocal response to a subsequent isolation, with rates of USV in rat pups well above those emitted in standard isolation tests. We found that passive maternal potentiation of USV did occur under all conditions tested. Neither a 30-min prior isolation nor high ambient temperature prevented an increase in USV rate over the rate of the original isolation. After 30-min isolation at warm temperatures when the rate of USV had fallen to zero, the pups increased vocalization in the presence of the dam as well as in the subsequent isolation. Temporal and thermal factors also interacted significantly in regulating the level of the USV emitted by the pups during the first isolation, in the presence of the anesthetized dam, and during the second isolation.     

Decreased venous return is neither sufficient nor necessary to elicit ultrasonic vocalizations 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.     

Effect of a social companion on the ultrasonic vocalizations and contact responses of 3-day-old rat pups.

Rat pups that are isolated in a novel environment emit ultrasonic calls. Vocalization in 3-day-old pups has been thought to be predominantly under thermal control (Allin & Banks, 1971). By the 2nd week of life, ultrasonic vocalizations are reduced when pups are tested in the company of a single anesthetized littermate (Carden & Hofer, 1990a; Hofer & Shair, 1978). In the present study, it was demonstrated that the vocalization rate of 3-day-old pups is also decreased when an anesthetized littermate is present in the isolation chamber. To determine whether this quieting was a function of the body heat of the companion, in a 2nd experiment, the axillary temperature of the companion was lowered until it was the same as the ambient temperature of the test chamber, 22 degrees C. In the presence of a cool companion, ultrasonic vocalizations were also reduced. For the last experiment, a textured plastic surrogate was substituted for the littermate. Calls were not diminished in the presence of the surrogate.     

The effect of cholinergic stimulation on rat pup ultrasonic vocalizations

As cholinergic stimulation increases vocalizations in adult rats, the present study investigated the effects of systemic oxotremorine, a cholinergic agonist, on the production of separation calls in rat pups of different ages and whether these effects are in response to central versus peripheral stimulation. The first experiment examined the dose-response effects of oxotremorine on the number of vocalizations and acoustic parameters of 10-, 15-, and 17-day-old rat pups. In contrast to other studies on adult rats, pup vocalizations were decreased while marginally changing acoustic parameters. The second experiment, using muscarinic antagonists, showed that pretreatment with atropine sulfate, which can cross the blood-brain barrier (BBB), reversed the call-reducing effect of oxotremorine whereas pretreatment with atropine methyl nitrate, which does not cross BBB, did not. Suppression of vocalizations by oxotremorine may be explained by central activation and not the peripheral effects of the drug. Dissimilar effects of cholinergic stimulation of infant and adult rat brains may be attributed to a differential role of the cholinergic system during development and maturity.     

Ontogeny of the noradrenergic innervation of the rat hippocampal formation

Summary The noradrenergic (NA) innervation of the rat hippocampal formation arrives embryonically into a structure in which cytogenesis and cell migration are still active processes. At embryonic day 18 (E18) the first fluorescent axons appear in the septal end of CA3 at the boundary of the marginal zone and cortical plate, the future stratum lucidum. By birth axons invade the subiculum and also course along the septo-temporal axis in a longitudinal associational system in stratum moleculare of CA3. The innervation of the area dentata increases significantly by postnatal day four (P4). The innervation pattern throughout the dentate and Ammon's horn is fairly complete by P10. High affinity uptake of ³H-NA also matures embryonically and correlates postnatally with the extent of innervation estimated by fluorescence histochemistry. The levels of endogenous NA develop more slowly, showing only 60–80% of older adult values by P48.Compared to the maturation of other hippocampal afferents, the NA innervation is extremely precocious. It is localized in areas which could allow it to have significant trophic functions during early stages of histogenesis. In addition, its presence in the rapidly developing structure may contribute to its eventual distribution in a relatively less organized terminal pattern than that of the later-arriving entorhinal, commissural and septal afferents.     

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 microg/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.     

Social stress effects on territorial marking and ultrasonic vocalizations in mice

Acute social defeat (SD) leads to transient and persistent physiological and behavioral changes. We examined the effects of acute SD on territorial urine marking and ultrasonic courtship vocalizations in DBA/2 male mice. Both behaviors are considered androgen dependent and are influenced by social status, with dominant mice displaying more of both behaviors. In Experiment 1, male mice that received SD displayed prolonged inhibition of territorial urine marking, relative to nondefeated control mice (NOSD). In addition, territorial marking increased with repeated tests. In Experiment 2, male mice that received 3 successive days of SD displayed fewer ultrasonic courtship vocalizations at 30 min. post-SD1 and 30 min. post-SD2, relative to NOSD mice. In Experiment 2, we also observed decreased territorial marking 4 weeks post-SD. In sum, SD induced prolonged inhibition of territorial marking, but had only transient effects on ultrasonic courtship vocalizations, suggesting that different mechanisms may mediate the maintenance of these behaviors.     

Playback of female rat ultrasonic vocalizations during sexual behavior

Both male and female rats emit ultrasonic vocalizations during mating. In an earlier study, female vocalizations were shown to be associated with female darting: when the female was devocalized, she increased her rate of darting. In a preliminary playback study, tape-recorded female ultrasounds were presented to devocalized females paired with intact males. Darting was reduced towards presurgical control levels. In this study, the playback experiment was replicated using a refined procedure to present female ultrasounds to the mating rats. Taped vocalizations were obtained from females, and were presented in a manner which more closely approximated the patterning of ultrasound production seen in the intact female. Each rat pair was tested three times: once prior to the devocalization of the female, and twice afterwards. In one postsurgical test, taped ultrasounds were presented during mating; in the other, tape hiss was presented. Several patterns of behavior increased in frequency when the female was devocalized relative to the control condition, but decreased when tape recorded ultrasounds were presented. These patterns included female darting and approaches towards the partner by both males and females. The darting results confirm and extend the findings of our earlier paper. Changes in approach behavior were not observed previously because the male was confined in the earlier study. This study contains the first direct evidence that female vocalizations affect the socio-sexual behavior of the male.     

Sonographic structure of isolation-induced ultrasonic calls of rat pups

Sonographic analysis of isolation-induced calls of 10- to 17-day-old Sprague-Dawley rat pups showed that average acoustic parameters of calls changed with pups' age. Average call duration increased with age from 80 ms to over 140 ms in 15-day-old pups. The peak frequency increased from approximately 50 kHz to an average of 64 kHz in 17-day-old pups, and the average bandwidth increased from 34 to 45 kHz in 17-day-old pups. Analysis of the sonographic structure of pup calls additionally revealed a tendency to produce two or more alternating sweeps of sound frequency in each call. Development of sweeps is the most typical feature of pup calls with a dominant call type resembling "U" or inverted "U" shape in the sonogram. Number of "U" or inverted "U" call types significantly increased with pups' age. It is concluded that pups developed and strengthened those acoustic features of distress calls which play a role in intraspecific communication and maximize pup survival.     

Sex and experience influence behavioral responses of adult rats to potentiated and nonpotentiated ultrasonic vocalizations of pups

Responsiveness of adult rodent caretakers to infant rodents is necessary for their survival and proper development. Both olfactory and auditory cues are known to influence adult behavior toward the young. In the present study, we found that adults respond differentially to a recording of potentiated vs. non-potentiated ultrasound vocalizations of a 12-day-old rat pup, either in the presence or absence of olfactory cues. The combination of olfactory and potentiated ultrasonic vocalization produced the greatest effect. Adult behavior was also affected by the adults' sex and parental experience in an interaction. Parental experience of females made them more responsive to the type of ultrasonic vocalization; males were little affected. Female experience, of course, includes the hormonal changes due to pregnancy and lactational state. The results are consistent with a communicatory function for isolation-induced ultrasonic vocalization.     

Ontogeny of behavioral and hormonal responses to stress in prenatally stressed male rat pups

Effects of prenatal stress on stress-induced behavioral and hormonal responses were investigated in preweanling rats at two ages. Prenatal stress treatments involved the application of uncontrollable electric shocks to pregnant rats every other day throughout gestation. Offspring of undisturbed rats in home cages served as controls. When male pups were 14 and 21 days old, ultrasonic vocalizations and freezing were recorded in 10-min tests involving isolation, and isolation with the application of electric foot shocks at either 0.5- or 2.0-mA intensity. Immediately before and after each test, tail-flick latencies were measured in order to assess alterations in stress-induced analgesia. Stress-induced secretion of ACTH was measured in plasma obtained after the second tail-flick test. Results indicated that 14-day-old prenatally stressed pups emitted significantly fewer ultrasonic vocalizations and exhibited significantly lower percent increases in tail-flick latencies than control pups. Plasma ACTH, however, was significantly elevated in prenatally stressed rats, suggesting that exposure to different tests was a stress-inducing event. At 21 days of age, prenatally stressed rats no longer differed significantly from control males in the exhibition of ultrasonic vocalizations, defensive freezing, and tail-flick latencies. Plasma ACTH content, however, was significantly lower in prenatally stressed than control males after exposure to the isolation with 2.0-mA shock test. The involvement of motivational, maturational, and mediational factors is examined in order to account for these age-dependent and stressor-dependent differences in behavioral and hormonal responses occurring between prenatally stressed and control pups.     

U50, 488 increases ultrasonic vocalizations in 3-, 10-, and 18-day-old rat pups in isolation and the home cage

Separation-induced calling in the young of many species can be modulated by the opioid system. Morphine reduces ultrasonic vocalizations (USVs) produced by isolated rat pups, an effect blocked by naltrexone. Central administration of the mu and delta opiate receptor agonists DAMGO and DPDPE reduce USV; kappa receptor agonist U50,488 increases them. We now find that peripheral U50,488 not only boosted calling rates in isolated 3-, 10-, and 18-day-old rat pups, but also induced calling in pups of these ages tested in the home cage with their littermates, where USVs are seldom heard in nature. U50,488 lowered rectal temperature, although temperature loss and USV were not correlated within drug treatment groups.© 1994 John Wiley & Sons, Inc.     

Ultrasonic vocalizations by rat pups in the cold: an acoustic by-product of laryngeal braking?

Isolated rat pups respond to cold exposure physiologically by increasing metabolic heat production and behaviorally by emitting ultrasound. The relationship between these 2 responses was investigated by monitoring oxygen consumption, heat production by brown adipose tissue, respiratory rate, and ultrasound production during cold exposure in pups 10-12 days of age. All 3 physiological measures increased contemporaneously with the initiation of ultrasound. Pups also exhibited a respiratory pattern characterized by the prolongation of expiratory duration in relation to inspiratory duration. Ultrasound was often detected during these prolonged expirations, suggesting that pups were using laryngeal braking. Laryngeal braking is thought to enhance oxygen uptake in the lungs. Thus, ultrasound may be an acoustic by-product of a respiratory maneuver that increases oxygen delivery to metabolically active tissues during cold exposure.     

Genetic influences on ultrasonic vocalizations in young mice

Ultrasonic calls produced by young mice elicit maternal investigation and retrieval, and their characteristics have been shown to vary with age and genotype. In this study, we completed a full Mendelian cross of two inbred strains BALB/cJ and DBA/2J. The major result was the detection of directional dominance for a high rate of calling. Other characteristics were influenced by additive and maternal effects in the absence of directional dominance. We estimate the number of loci involved in the rate of calling to be about 1—facilitating studies of a gene-to-behavior pathway.