Harry N. Shair

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

Emissions of ultrasonic vocalizations (USVs) by rat pups (Rattus norvegicus) during hypothermia have consequences for recovery and warming. We investigated the effects on dam behavior of USVs emitted by 3- to 11-day-old pups during hypothermia at rectal temperatures between 18 and 22 degrees C. 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.

Acquisition and expression of a socially mediated separation response.

Separation and reunion responses have been used to investigate social relationships in many species, including humans. When isolated from their mothers and siblings, infant rats vocalize in the ultrasonic range. An isolated pup reduces its rate of vocalization when placed in contact with familiar stimuli, particularly social ones such as its dam or littermates. The isolated pups vocalization is greatly increased if the pup has been in contact with its mother immediately before isolation, a phenomenon called maternal potentiation. Early experience can play a role in the acquisition of potentiation. If rat pups are reared by both dam and sire, or even reared by the dam in the presence of the sires odor, the pups show potentiation to the sire instead of the fear-related behavioral inhibition. Littermates, home cage shavings, and other familiar stimuli from the rearing environment do not elicit increased vocalizations during a subsequent isolation. The neurobiological mechanisms by which the sire becomes capable of potentiating vocalization are unknown, but are hypothesized to depend on the processes underlying development of an odor preference. Expression of potentiation is hypothesized to be related to reward processes in part because dopamine activity plays a regulatory role. Activation of dopamine type 2 receptors in the nucleus accumbens blocks maternal potentiation without altering vocalization rate in an initial isolation. The modulation of isolation-induced vocalization by social interactions provides a paradigm for investigating the neurobehavioral mechanisms underlying acquisition and expression of early life social bonds.

POTENTIATION AND INHIBITION OF ULTRASONIC VOCALIZATION OF RAT PUPS : REGULATION BY SOCIAL CUES

Eight- and 11- to 12-day-old rat pups were tested in isolation and in the presence of an anesthetized adult under cold conditions. Pups of both ages reduced rates of ultrasonic vocalization (USV) when an adult was placed into the test cage, independent of whether the adult was their dam or an unrelated male. However, after removal of the dam, pups greatly increased their rates of USV over their first isolation period and in comparison with control pups. USV rates remained low after removal of the male. The temperature challenges faced by the pups in the two experimental conditions were the same. These phenomena are better explained by a hypothesis that postulates USV rate as being multiply determined, including by social cues, rather than a theory that considers thermal challenge only.

The ontogeny of maternal potentiation of the infant rats' isolation call.

Previous studies have shown that preweanling rat pups double or triple their rates of ultrasonic vocalization (USV) when isolated immediately after brief periods of maternal interaction (potentiation). We studied the ontogenetic pattern of USV and other behavioral responses of pups to 3-min periods of isolation in a novel test chamber, from 5 to 25 days postnatal age, before, during, and after 1 min or 5 min of interaction with an anesthetized or an active dam. USV potentiation did not develop until 7-9 days postnatal, a week after the initial isolation and maternal contact quieting responses were well established. Potentiation reached a peak at 13 days, and then declined until all USV responses ceased after 21 days. Other behavioral responses to isolation were not enhanced by maternal interaction at any age. The distinct ontogenetic pattern of this unusual response to maternal separation has implications for understanding its mode of development and possible adaptive value.

Ultrasonic vocalization, laryngeal braking, and thermogenesis in rat pups : a reappraisal

In these experiments we tested the hypothesis that the respiratory events underlying rat pup ultrasonic vocalization (USV) facilitate brown adipose tissue (BAT) thermogenesis, as proposed by Blumberg and Alberts (1990). Laryngeal denervation or tracheostomy were used to reduce or eliminate laryngeal braking and prevent USV in 9- to 10-day-old pups during recovery from deep hypothermia and during cooling induced by isolation for 1 hr at room temperature. Both forms of devocalization slowed rewarming of hypothermic pups, but neither had any effects on cooling rate or BAT thermogenesis in normothermic pups that were allowed to cool from 35 degrees C to 29 degrees C. Physiological effects of laryngeal braking on thermogenesis appear to be limited to conditions, such as severe hypothermia, in which ventilatory and oxygen transport functions are compromised. The results have implications for understanding the regulation and evolution of USV.

Ultrasonic Vocalizations in Rat and Mouse Pups

The ultrasonic vocalization (USV), or isolation calling response, of infant rats and mice has been studied as a measure of the intensity of an aversive affective state and as an early communicative behavior between pup and mother. The four protocols described in this unit are for the basic isolation testing procedure, and for elicitation of the contact quieting response to littermates and/or dam, the potentiation of isolation calling response by a prior brief maternal interaction and the predator‐induced suppression of USV by the scent of an unfamiliar male. These procedures for the elicitation of USV, and for its regulation by different kinds of social interaction, provides the basis for experimental research on the early development of emotion and communication in an animal model system.

Maternal interactions prior to separation potentiate isolation-induced calling in rat pups.

The vocal response rates of 12-13-day-old infant rats to isolation in a bare test box are markedly increased by brief (1-min) periods of contact with an anesthetized dam prior to isolation, without affecting other isolation-induced behaviors. No such potentiation followed brief contact with littermates, novel test conditions, or experimenter handling. Brief contact with the dam was equally effective in the test chamber or home cage and was not further enhanced by repeated contact-separation sequences. Passive contact became ineffective when prolonged to 30 min, and potentiation could not be restored by providing the additional reinforcing events of continuous suckling, periodic oxytocin-induced milk letdown, or bouts of simulated maternal licking. However, when pups engaged in active interaction with an awake dam, potentiation was significantly enhanced following 1-, 10-, and 30-min periods. A working hypothesis is outlined for the adaptive role of potentiation in the development of the rat pup.

Behavioral mechanisms for active maternal potentiation of isolation calling in rat pups.

The ultrasonic vocalization (USV) response of the isolated infant rat is a promising model for studying the neurobiology of an early anxiety state, and potentiation of the USV response after brief maternal encounters is a newly discovered behavioral regulator of this state. Using experimental variations in the contexts and patterns of maternal behavior during pup encounters and manual simulations of maternal behavior, we have identified several specific mother-pup interactions that cause potentiation. When one of these, pup carrying, was manually simulated, potentiation followed only if a characteristic postural transport response had been fully expressed by the pup. These behavioral mechanisms and other data suggest hypotheses for the development and adaptive role of maternal potentiation.

Independence of ultrasonic vocalization and thermogenic responses in infant rats.

: Ultrasonic vocalizations (USV) normally accompany brown adipose tissue (BAT) thermogenesis in infant rats exposed to cold. BAT activation (measured by implanted thermistors) was pharmacologically blocked with hexamethonium (20 mg/kg ip) in 12-13-day-old pups, but they nevertheless showed normal USV responses to cold. Activation of BAT in warm pups by norepinephrine (800 micrograms/kg sc) failed to elicit USV. It is concluded that BAT activation is neither necessary nor sufficient for USV production. To evaluate how tightly the two responses may be coupled centrally, rat pups deprived of nutrients for 24 hr, in which sympathetic activation is known to be inhibited centrally (Bignall, Heggeness, & Palmer, 1975), were studied. These pups vocalized with the same latency in response to cold as normals but failed to show evidence of concurrent BAT activation. It is concluded that USV and BAT thermogenesis are normally elicited together by cold but are not tightly linked physiologically.

The Influence of Olfaction on Potentiation and Inhibition of Ultrasonic Vocalization of Rat Pups

Twelve-day-old isolated rat pups reduce their rates of ultrasonic vocalization (USV) when an anesthetized adult is placed into the test cage, whether the adult is their dam or an unfamiliar male. USV rates remain very low even after removal of the male (inhibition). However, after removal of the dam, pups greatly increase their rates of USV over their first isolation period (potentiation). USV potentiation can be induced by either an awake, normally behaving dam or by one that is anesthetized. To test the role of olfaction in inhibition and potentiation, PND12 pups were rendered anosmic via intranasal infusion of 5% zinc sulphate (ZnSO4). Control pups were infused with normal saline. After overnight separation from the dam, the USV and other behaviors of pups were recorded during a 6-min test. Each pup was tested during an initial isolation period and a final isolation period. In the first experiment, an anesthetized adult (dam or unfamiliar male) or no companion was placed in contact with the pup during the middle minute. Anosmia prevented both potentiation and inhibition of USV by passive adult contact. Thus, it seems likely that pups use olfactory discrimination as the basis for these two highly differentiated vocal responses to social stimuli. Results from two additional experiments demonstrate that anosmia does not prevent potentiation when the adult dam is active and interacting with the pup on either postnatal day 12 or 8.