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 (J. T. Allin and E. M. Banks, 1971). By the 2nd wk of life, ultrasonic vocalizations are reduced when pups are tested in the company of a single anesthetized littermate (S. E. Carden and M. A. Hofer, 1990; Hofer and H. 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°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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interleukin-1 beta stimulates adrenocorticotropin and corticosterone release in 10-day-old rat pups

Clinical, radiological and biological features of 19 cases of serologically proven Mycoplasma pneumoniae pneumonia were compared with those of 21 cases of other types of pneumonia. Some clinical features were more frequent in M pneumoniae: patients older than 5 years, association with upper respiratory tract infection, skin rashes, acute course, unsuccessful treatment with penicillin. There were no specific radiological features. When compared with the complement fixation method, the serological diagnosis using agglutination technique appears to be more sensitive.     

Repeated isolation stress in the neonatal rat: Relation to brain dopamine systems in the 10-day-old rat.

Isolation of the rat pup from the nest and dam for one hour per day from PN 2–9 is a useful paradigm for producing stress in the neonate. These previously isolated rats respond to an amphetamine challenge with alterations in activity at the juvenile stage or as adults. Furthermore, when dopamine release is measured in the nucleus accumbens, juveniles release 3 times more dopamine after amphetamine than do controls. This study describes changes in behavior and brain dopamine systems at PN 10. Experiment 1 determined an appropriate amphetamine dose that could be used for behavioral activation at PN 10. Experiment 2 produced significant evidence of enhanced behavioral activation after the isolation paradigm and indicated that brain regions innervated by the mesolimbic dopamine system, septum, and hypothalamus display increased dopamine turnover and that the nigrostriatal pathway is less active. Likewise, in Experiment 3, in vivo microdialysis of the nucleus accumbens indicated that previously isolated pups respond to an amphetamine challenge with a several-fold increase in dopamine release over a 4-hour session. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Appetitive learning and extinction in 11-day-old rat pups: Effects of various reinforcement conditions.

Studied the acquisition and extinction of approach behavior in 96 11-day-old albino Sprague-Dawley rat pups in 3 experiments. The reinforcement in Exps I & II was 15 sec of nonnutritive suckling on an anesthetized lactating female. In Exp I, detention duration, 0- or 15-sec in the goal box on nonreward (N) trials, was studied in 2 groups whose acquisition training consisted of alternating blocks of rewarded and nonrewarded trials with a short (5-sec) intertrial interval. Exp II combined an examination of the effect of detention length with whether or not the mother was physically present, though inaccessible, on N trials with partially or continuously rewarded groups. Detaining Ss on N trials slowed the rate of extinction when the mother was present but increased the rate of extinction when she was absent. There was no evidence of a partial reinforcement extinction effect in any of the groups. The effectiveness of 6 types of reinforcement on promoting acquisition of approach behavior was assessed in Exp III. Equally good acquisition, but differences in extinction was obtained with an adult conspecific as the reinforcer, independent of sex and suckling, but there was no acquisition of approach responding when a sibling or no conspecific was in the goal box. These data extend earlier findings of appetitive learning and extinction in infant rats. They do not support the view that inhibitory mechanisms are absent in the rat until the 3rd or 4th wk of life. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of noradrenergic effects on ultrasonic vocalizations in rat pups.

The ontogeny of noradrenergic effects and the interaction of opioid and noradrenergic systems on vocalizations in rat pups from Day 10 to Day 18 were evaluated. Day 10 pups given clonidine (0.05 or 0.5 mg/kg) ip showed a sustained high level of calling throughout a 25-min isolation period that was reversed with yohimbine (0.1 mg/kg). Day 15 pups showed identical profiles with a lower baseline rate. Day 17 pups' calls were differentially affected according to dose; Day 18 pups reduced vocalizing with clonidine. In addition, it was found that at all ages when clonidine increased calling during isolation, the pups vocalized in the nest as well. Naltrexone, an opioid antagonist, lost its effectiveness to increase vocalizations after Day 15 unless it was given subsequent to clonidine. These results suggest that pups' vocalizations are differentially affected by noradrenergic and opioid stimulation or inhibition with developmental changes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unilateral conditioning of an odor aversion in 6-day-old rat pups.

In young rats, several forms of olfactory memory can be functionally localized to one side of the brain by restricting training stimuli to one naris and corresponding olfactory bulb. In this experiment, the analysis of lateralized olfactory learning in 6-day-old rat pups was extended by an evaluation of the consequences of aversive reinforcers in a unilateral olfactory conditioning paradigm. An olfactory aversion was conditioned by delivering a mild footshock to animals in the presence of a novel odor. Olfactory stimulation was confined to one naris and corresponding olfactory bulb by inserting a soft rubber plug into the opposite naris. This lateralization in processing resulted in unilateral memory for the odor aversion that was only expressed when the trained naris was open during an odor preference test. The hypothesis that the hedonic value (or valence) component of conditioning is represented in structures that are unilaterally accessed during training and testing is discussed. (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)     

Electromyographic patterns associated with nonnutritive sucking in 11–13-day-old rat pups.

Three experiments used an EMG technique to measure the frequency, duration, and intensity of nonnutritive sucking (NNS) in 56 11–13 day old Wistar pups. Ss were separated from their mothers for 2–6 or 20–24 hrs and then allowed to suckle an anesthetized dam for up to 3 hrs without receiving any milk. Jaw-muscle EMG and nipple detachments were recorded. EMG patterns representing 2 discrete modes of sucking were reliably discerned, as were changes in overall intensity of EMG. 20–24 hr separated Ss engaged in more frequent NNS bouts and bouts of longer duration than 2–6 hr separated Ss. Ss separated by 20–24 hrs also engaged in a mode of NNS not seen in 2–6 hr separated Ss. Overall EMG intensity was higher and frequency of nipple detachments was lower in Ss separated for 20–24 hrs. In both groups, but particularly the 20–24 hr Ss, frequency of some NNS patterns decreased as the length of the "dry" suckling increased. EMG intensity also decreased over time in both groups, and frequency of nipple detachments increased in 2–6 hr separated Ss. Data indicate that some aspects of NNS are highly labile and respond to variations of both deprivation from the mother and nutritive deprivation. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The isolation and companion comfort responses of 7- and 3-day-old rat pups are modulated by drugs active at the opioid receptor.

Rat pups emit ultrasonic vocalizations (USVs) when isolated in a novel environment. In 10-day-olds, USV has been shown to be reduced by either the administration of 0.125 mg/kg morphine (MOR) or the presence of a littermate; these effects were both reversed by naltrexone (NLX), an opioid receptor blocker. The present study reports that the same dose of MOR produced NLX-antagonized quieting without sedation in 7- and 3-day-old pups; higher doses of MOR decreased USV but produced motor deficits as well. The 0.125 mg/kg dose of MOR is less effective in reducing USV in 3- and 7-day-olds; calling rates declined by no more than 42%, compared with 65% at 10 days of age. The presence of a companion also lowered the USV of 3- and 7-day-olds by a lesser amount (55–57%) than the 67% seen in 10-day-olds or the 90% decline when pups are 2 weeks old. This suggests that age-related changes in the opioid system may be relevant to the increased salience of a social companion that comes with maturity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prenatal !b-endorphin can modulate some aspects of sexual differentiation in rats.

Sexually dimorphic traits were studied in offspring of rats injected with 33 μg rat β-endorphin (β-END) 3 times daily from Day 14 to Day 21 of pregnancy. β-END males had shorter neonatal anogenital distances than did controls and were more likely to show the female lordosis pattern as adults, but they did not differ in male copulatory behavior. When given a choice between spending time with an estrous female or a male, β-END males showed a lower preference for the female than did control males. The number and somal size of neurons in the bulbocavernosus and dorsolateral nucleus of the lumbar spinal cord were unaffected by drug exposure. Elevated β-END during fetal ontogeny apparently alters the differentiation of some, but not all, sexually dimorphic traits. The data suggest that endogenous opioids may contribute to the etiology of the prenatal stress syndrome. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of dopamine-depleting brain lesions in rat pups: Role of striatal serotonergic neurons in behavior.

Previous results from our laboratory have demonstrated that 3-day-old rats given dopamine (DA) -depleting brain lesions are spared the severe behavioral dysfunctions seen after comparable brain damage in adults. This behavioral sparing is accompanied by a sprouting of serotonin (5-HT) -containing neurons in the striatum. The present results extend these observations by demonstrating that rats given the brain lesions as 15- or 27-day-olds continue to suckle, wean, and grow into adulthood without exhibiting any obvious behavioral dysfunctions, yet striatal 5-HT levels do not increase. Moreover, combined destruction of DA- and 5-HT-containing neurons in 3-day-old rat pups also produced no obvious behavioral dysfunctions. These and other results indicate that increases in striatal 5-HT are not necessary for the behavioral sparing observed after DA-depleting brain lesions in neonatal rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Independence of benzodiazepine and opiate action in the suppression of isolation distress in rat pups.

To determine whether benzodiazepines (BDZs) quiet isolation distress in 10-day-old rat pups by causing a release of endogenous opioids, a blockade of the effects of chlordiazepoxide (CDP) by the opiate antagonist naltrexone (NLX) was sought. Nonsedating doses of morphine (MOR) (0.125 mg/kg) and CDP (2.0 mg/kg) were equally effective in reducing ultrasonic vocalizations and other indices of isolation distress. Appropriate blocking agents NLX (0.5 mg/kg) against MOR and Ro 15-1788 (4.0 mg/kg) against CDP returned distress measures to levels of saline-treated rat pups. However, NLX failed to reverse the quieting effects of CDP. If CDP potentiates endogenous opioid release, then NLX should block the CDP effect. A higher dose of CDP did not reveal a release of endogenous opioids, and a higher dose of NLX did not antagonize CDP. The quieting effects of BDZs on isolation distress do not appear to be mediated by the opiate system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Self-stimulation in 7- and 10-day-old rats.

It has been shown that the infant rat exhibits learned behaviors characteristic of the adult. With a modified self-stimulation paradigm, the present study explored whether 7- and 10-day-old Long-Evans rat pups could learn a discriminated operant to obtain direct electrical stimulation in neural sites that support self-stimulation in adults. By nudging 1 of 2 response manipulanda, at 2 ages (7 and 10 days) and temperatures (22 and 35°C), Ss self-stimulated with electrodes implanted in a variety of forebrain sites, including the prefrontal cortex, bed nucleus of the stria terminalis, medial nucleus of the amygdala, and the medial forebrain bundle. The only temperature-sensitive site might be the nucleus accumbens, which was positive only at the higher temperature in 10-day-olds. Results indicate that several forebrain sites demonstrate rewarding properties of stimulation in the preweanling rat pup. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of choline-free plasma induced by choline oxidase on regional levels of choline and acetylcholine in rat brain

Choline-free plasma (CFP) was induced in rats by intravenous (IV) injection of 56.0 x 10(2) units kg-1 of choline oxidase (ChO) which completely metabolized the free Ch circulating in the plasma for at least 15.0 h and caused subsequent significant decrease in the concentration of free Ch in the three brain regions examined, the striatum, hippocampus, and cortex. However, the treatment did not affect concentrations of acetylcholine (ACh) in these regions. By contrast, intraperitoneal (IP) injection of 1.0 mmol kg-1 Ch chloride resulted in a maximum concentration of free Ch in plasma in 5 min, after which tissue Ch in all regions examined increased (p < 0.001). Concomitant increases were observed in cortical and hippocampal ACh (p < 0.05) 20 min after the injection. It is thus suggested that the brain may possess compensative mechanisms to prevent the supply of free Ch from circulating to the brain during synthesis of ACh in the brain. It is also suggested that the CFP rat would be a useful and readily available animal model for future study.     

Effect of kitten vocalizations on maternal behavior.

Observation of 8 mother cats and their litters revealed that the previous occurrence of a kitten vocalization was associated with an increased probability that mothers would approach kittens, change to a different body position, shift their lactation position, or vocalize. Experimental study, in which the effects of kitten vocalizations were separated from other kitten-emitted cues, demonstrated that vocalizations reliably elicited approach and investigation of the sound source from mothers. Further, mothers exposed to kitten vocalizations removed kittens from a box and carried them to the home site. Repeated testing of mothers demonstrated that these effects of kitten vocalizations on maternal behavior remained strong across at least the 1st 30 days of life. It is concluded that vocalizations are a stimulus by which kittens influence their mother's behavior. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)