Ultrasonic cries from infant rats stimulate prolactin release in lactating mothers

Behavioural actions of tuberoinfundibular peptide 39 (parathyroid hormone 2)

Tuberoinfundibular peptide of 39 residues (TIP39) acts via its endogenous class B G-protein coupled receptorthe parathyroid hormone 2 receptor (PTH2R). Hence, it is also known as parathyroid hormone 2. The peptide is expressed in the brain by a small number of neurons with a highly restricted distribution, which in turn project to a large number of brain regions that contain PTH2R. This peptide neuromodulator system has been extensively investigated over the past 20 years including its behavioural actions, such as its role in the control of nociception, fear and fear incubation, anxiety and depression-like behaviours, and maternal and social behaviours. It also influences thermoregulation and potentially auditory responses. TIP39 probably exerts direct effect on the neuronal networks controlling these behaviours based on the localization of PTH2R and local TIP39 actions. In addition, TIP39 also affects the secretion of several hypothalamic hormones providing the basis for indirect behavioural actions. Recently developed experimental tools have stimulated further behavioural investigations, and novel results obtained are discussed in this review.

Exposure to quinestrol and levonorgestrel affects maternal behavior and offspring development in midday gerbil (Meriones meridianus)

Quinestrol and levonorgestrel (EP-1, at a ratio of 1:2) are often used as anti-fertility compounds (sterilants) in rodents. As most of the research has focused on the sterility and damage caused in parental reproductive organs, there is little research on the effect of these contraceptive hormones on maternal behavior and offspring's early development. In this study, we examined maternal behavior after treatment with different doses of EP-1 (10 ml/kg) at postnatal days 3 and 10, separately. Various parameters were measured after treatment, including oxytocin expression, serum levels of estradiol and luteinizing hormone (LH), ovary damage after weaning of offspring, as well as the development and ultrasonic vocalizations (USVs) of midday gerbil (Meriones meridianus) offspring. At postnatal days 5 and 12, the EP-1 increased maternal licking, grooming, and retrieving behavior, while reducing contacting behavior. Oxytocin expression in the hypothalamic paraventricular and supraoptic nuclei increased, while the levels of estradiol and LH decreased. The ovaries and the development of follicles were clearly affected by the treatment. The EP-1 significantly reduced the pups' body weight, the amount and pulse duration of USVs, whereas the frequency range variation of USVs was increased. Overall, treatment with EP-1 during lactation significantly affected maternal behavior and impaired offspring early development in the midday gerbil.

Development of ultrasonic calls in rat pups follows similar patterns regardless of isolation distress

Ultrasonic vocalizations (USVs) emitted by rat pups have been extensively studied in the context of isolation from their mother and littermates. The heightened call rate of isolation-induced USVs indicates increased anxiety, whereas other acoustic parameters, such as frequency and call duration, are thought to be useful in reflecting developmental changes, which by weaning have developed into their adult form. However, it is possible that stress can affect the quality as well as the quantity of calls, and that as the pups become more mobile, the effects of the stress may change. Therefore, in the present study rats were tested in a test arena either in isolation or with littermates, so as to assess the effects of isolation stress on the developmental changes reported in the literature. Rat pups of both sexes were tested on multiple days from postnatal day (PND) 7 to weaning. Overall, the main changes in the frequency, duration, and types of calls were accounted for by age. The effects of isolation were minor, as were sex differences. This study indicates that the development of USVs in infant rats is a robust process and seemingly resistant to the effects of isolation-induced stress.

Thalamic integration of social stimuli regulating parental behavior and the oxytocin system

Critically important components of the maternal neural circuit in the preoptic area robustly activated by suckling were recently identified. In turn, suckling also contributes to hormonal adaptations to motherhood, which includes oxytocin release and consequent milk ejection. Other reproductive or social stimuli can also trigger the release of oxytocin centrally, influencing parental or social behaviors. However, the neuronal pathways that transfer suckling and other somatosensory stimuli to the preoptic area and oxytocin neurons have been poorly characterized. Recently, a relay center of suckling was determined and characterized in the posterior intralaminar complex of the thalamus (PIL). Its neurons containing tuberoinfundibular peptide 39 project to both the preoptic area and oxytocin neurons in the hypothalamus. The present review argues that the PIL is a major relay nucleus conveying somatosensory information supporting maternal behavior and oxytocin release in mothers, and may be involved more generally in social cue evoked oxytocin release, too.

Emotionally induced galactorrhoea in a non-lactating female--"Pseudo- Lactation"?

BACKGROUND

Galactorrhoea is a common clinical problem in endocrinology. Visual and auditory cues from the newborn are known to stimulate prolactin secretion in lactating women. However, hyperprolactinaemia and galactorrhoea in a non-lactating female due to visual and auditory stimuli from an unrelated newborn has not been reported in the past. We report the first such case of 'pseudo-lactation'.

CASE PRESENTATION

An 18-year-old girl with type 1 diabetes mellitus presented with galactorrhoea. Apparently galactorrhoea was preceded by seeing the baby, hearing her cries or when remembering her memories. Her menstrual cycles were normal and did not complain of any headache or visual disturbances. She was only on metformin and insulin. Symptoms have rapidly resolved after the newborn was shifted to another location. Examination revealed scanty nipple discharge with gentle pressure. Investigations revealed an elevated serum prolactin of 62.5 ng/mL (2717.4 pmol/L) and fasting plasma glucose of 142 mg/dL (7.9 mmol/L) and HbA1c of 7.6%. Her thyroid function was normal and MRI at the time of galactorrhoea was not available. At 3 months prolactin was normal and MRI revealed only a slight asymmetry of the pituitary without evidence of microadenoma.

CONCLUSION

The strong temporal relationship between her symptoms and emotional attachment to the newborn with exclusion of other causes on clinical, biochemical and radiological evidence, raise the possibility that transient hyperprolactinaemia was due to a transient lactotroph hyperplasia and hyper function which had been triggered by the stimulatory cues from the newborn.Emotionally induced "pseudo lactation" may be a rare but important cause for transient hyperprolactinaemia in a non-lactating female.

Preoptic inputs and mechanisms that regulate maternal responsiveness

The preoptic area is a well-established centre for the control of maternal behaviour. An intact medial preoptic area (mPOA) is required for maternal responsiveness because lesion of the area abolishes maternal behaviours. Although hormonal changes in the peripartum period contribute to the initiation of maternal responsiveness, inputs from pups are required for its maintenance. Neurones are activated in different parts of the mPOA in response to pup exposure. In the present review, we summarise the potential inputs to the mPOA of rodent dams from the litter that can activate mPOA neurones. The roles of potential indirect effects through increased prolactin levels, as well as neuronal inputs to the preoptic area, are described. Recent results on the pathway mediating the effects of suckling to the mPOA suggest that neurones containing the neuropeptide tuberoinfundibular peptide of 39 residues in the posterior thalamus are candidates for conveying the suckling information to the mPOA. Although the molecular mechanism through which these inputs alter mPOA neurones to support the maintenance of maternal responding is not yet known, altered gene expression is a likely candidate. Here, we summarise gene expression changes in the mPOA that have been linked to maternal behaviour and explore the idea that chromatin remodelling during mother-infant interactions mediates the long-term alterations in gene expression that sustain maternal responding.

Analysis of ultrasonic vocalizations emitted by infant rodents

Altricial rodent pups emit ultrasonic vocalizations (USVs), which are whistle-like sounds with frequencies between 30 and 90 kHz. These signals play an important communicative role in mother-offspring interaction because they elicit in the dam a prompt response as concerning care-giving behaviors. To investigate neurobehavioral development, the analysis of the number of USVs presents several advantages: (1) USVs are one of the few responses produced by very young rodents that can be quantitatively analyzed and elicited by quantifiable stimuli; (2) USV emission follows a clear ontogenetic profile from birth to the second to third week of life, thus allowing longitudinal analysis during very early post-natal ontogeny. The reported role played by several receptor agonists and antagonists in modulating the USV rate makes this measure highly informative in investigating the effects of toxicants and, more generally, psychoactive compounds on the development of selected brain systems.

Paralemniscal TIP39 is induced in rat dams and may participate in maternal functions

The paralemniscal area, situated between the pontine reticular formation and the lateral lemniscus in the pontomesencephalic tegmentum contains some tuberoinfundibular peptide of 39 residues (TIP39)-expressing neurons. In the present study, we measured a 4 times increase in the level of TIP39 mRNA in the paralemniscal area of lactating mothers as opposed to nulliparous females and mothers deprived of pups using real-time RT-PCR. In situ hybridization histochemistry and immunolabeling demonstrated that the induction of TIP39 in mothers takes place within the medial paralemniscal nucleus, a cytoarchitectonically distinct part of the paralemniscal area, and that the increase in TIP39 mRNA levels translates into elevated peptide levels in dams. The paralemniscal area has been implicated in maternal control as well as in pain perception. To establish the function of induced TIP39, we investigated the activation of TIP39 neurons in response to pup exposure as maternal, and formalin injection as noxious stimulus. Both stimuli elicited c-fos expression in the paralemniscal area. Subsequent double labeling demonstrated that 95% of neurons expressing Fos in response to pup exposure also contained TIP39 immunoreactivity and 91% of TIP39 neurons showed c-fos activation by pup exposure. In contrast, formalin-induced Fos does not co-localize with TIP39. Instead, most formalin-activated neurons are situated medial to the TIP39 cell group. Our data indicate that paralemniscal neurons may be involved in the processing of maternal and nociceptive information. However, two different groups of paralemniscal neurons participate in the two functions. In particular, TIP39 neurons may participate in the control of maternal functions.

Models of anxiety: ultrasonic vocalizations of isolated rat pups

Described in this unit is the ultrasonic distress vocalization test in rat pups. This test is a reliable method for detecting anxiolytic properties of test compounds. In this test, ultrasonic vocalizations (30 to 50 kHz) are elicited by separating rat pups of 9 to 11 days of age from their mother and littermates for a brief period of time. The test can be performed under two different stress conditions. Pups are placed in isolation in either a warm (37°C) or cold (18°C) environment for 5 min. The total number and duration of ultrasonic calls emitted by the pups during this period is used as an index of anxiety. Established anxiolytic compounds, including benzodiazepines, serotonin(1A) receptor agonists, and selective serotonin reuptake inhibitors (SSRIs), consistently reduce the number and cumulative duration of these ultrasonic distress vocalizations.

Development of translational methods in spectral analysis of human infant crying and rat pup ultrasonic vocalizations for early neurobehavioral assessment

The purpose of this article is to describe the development of translational methods by which spectrum analysis of human infant crying and rat pup ultrasonic vocalizations (USVs) can be used to assess potentially adverse effects of various prenatal conditions on early neurobehavioral development. The study of human infant crying has resulted in a rich set of measures that has long been used to assess early neurobehavioral insult due to non-optimal prenatal environments, even among seemingly healthy newborn and young infants. In another domain of study, the analysis of rat put USVs has been conducted via paradigms that allow for better experimental control over correlated prenatal conditions that may confound findings and conclusions regarding the effects of specific prenatal experiences. The development of translational methods by which cry vocalizations of both species can be analyzed may provide the opportunity for findings from the two approaches of inquiry to inform one another through their respective strengths. To this end, we present an enhanced taxonomy of a novel set of common measures of cry vocalizations of both human infants and rat pups based on a conceptual framework that emphasizes infant crying as a graded and dynamic acoustic signal. This set includes latency to vocalization onset, duration and repetition rate of expiratory components, duration of inter-vocalization-intervals and spectral features of the sound, including the frequency and amplitude of the fundamental and dominant frequencies. We also present a new set of classifications of rat pup USV waveforms that include qualitative shifts in fundamental frequency, similar to the presence of qualitative shifts in fundamental frequency that have previously been related to insults to neurobehavioral integrity in human infants. Challenges to the development of translational analyses, including the use of different terminologies, methods of recording, and spectral analyses are discussed, as well as descriptions of automated processes, software solutions, and pitfalls.

Tuberoinfundibular peptide of 39 residues is activated during lactation and participates in the suckling-induced prolactin release in rat

Tuberoinfundibular peptide of 39 residues (TIP39) and the PTH-2 receptor (PTH2R) constitute a peptide-receptor neuromodulator system. Based on the abundance of TIP39 fibers and axonal terminals as well as PTH2R-containing neurons and their processes in the hypothalamic para- and periventricular and arcuate nuclei TIP39 has been suggested to play a role in neuroendocrine regulation. We showed previously that TIP39 expression decreased dramatically by adulthood. In the present study, using in situ hybridization histochemistry, real-time RT-PCR, and immunohistochemistry, we found that TIP39 mRNA and peptide expression levels are markedly elevated in the posterior intralaminar complex of the thalamus (PIL) of lactating dams, one of the three locations of TIP39-containing cell bodies in the brain. In addition, in mother rats, these TIP39 neurons showed Fos expression in response to pup exposure. Transection of TIP39 fibers originating in the PIL resulted in an ipsilateral disappearance of TIP39 immunoreactivity throughout the mediobasal hypothalamus of mother rats, suggesting that TIP39 fibers there arise from the PIL. To elucidate the function of TIP39 activation in dams, mothers separated from their pups for 4 h on postpartum d 9 received injection of a PTH2R antagonist into the lateral ventricle 5 min before returning the pups. Blood samples were taken seven times during the experimental period through jugular cannulae. The PTH2R antagonist administered in two different concentrations markedly inhibited suckling-induced elevation of plasma prolactin levels in a dose-dependent manner. These results suggest that TIP39 neurons in the PIL may regulate suckling-induced prolactin release in rat dams.

Ultrasonic calls of bank vole pups isolated and exposed to cold or to nest odor

Bank vole pups produce ultrasounds when isolated from the nest, as other rodents do. The present study was intended to elucidate the possible interaction between the social stress of isolation from the mother and the physical stress of low ambient temperature during the nesting period. Although bank vole pups removed from nests and monitored at nest temperature vocalized at high frequency, the number and duration of signals increased at lower ambient temperature. In the tested voles it appears that exposure to cold was the most important stimulus of vocalization during the preweaning period. This effect can be enhanced by prolonged isolation from the mother, manifested as longer duration of calls. Moreover, vocalization was reduced not only by the odor from the home nest, but also by exposure to bedding of an alien lactating bank vole or even a lactating mouse fed the same diet. This suggests that the olfactory signals affecting the ultrasonic vocalization of bank vole pups probably are a mixture of volatile metabolites related to the physiological status and diet of rodent females. The reported experiments provide convincing evidence that the vocalization of bank vole pups is affected by isolation from the mother, by ambient temperature, and by olfactory signals released by lactating rodent females.

Prolactin responses to infant cues in men and women: effects of parental experience and recent infant contact

We used a longitudinal design to test whether parental experience differentially affects the development of prolactin responses to infant cues in men and women. Couples provided two blood samples at three tests, one test just before their babies were born, and two tests during the early postnatal period (n=21). Nine couples repeated the tests near the birth of their second babies. In the 30 min between the two samples, couples listened to recorded infant cries at the prenatal test and held their baby (fathers) or a doll (mothers) at the postnatal tests. Blood samples were analyzed for prolactin concentrations. Prolactin values were then related to sex and parity differences as well as to questionnaire data concerning emotional responses to infant cries and previous infant contact. We found that (1) prior to the birth of both the first and second babies, women's prolactin concentrations increased after exposure to infant stimuli, whereas men's prolactin concentrations decreased; postnatal sex differences varied with parity; (2) women's prolactin reactivity did not change significantly with parental experience; (3) the same men's prolactin concentrations decreased after holding their first newborns but increased after holding their second newborns; this change was not gradual or permanent; (4) men reporting concern after hearing recorded infant cries showed a different postnatal pattern of prolactin change after holding their babies than men not reporting concern; and (5) men who had little contact with their babies just prior to testing had a more positive prolactin response than men who had recently held their babies for longer periods. Although parental experience appears to affect men's prolactin responses, differences in reactivity were also related to patterns of recent infant contact and individual differences in responses to infant cues.

Ontogeny in the family

When ontogeny takes place in a family, and parents provide essential resources for development, the parents become an environmental component to the development of a wide range of offspring traits. Because differences among parents may partly reflect genetic variation, this environmental component contains genes and may itself evolve. Also, when offspring play an active role in family interactions, offspring become a social environmental component to parents, affecting their behavior in turn, which potentially results in reciprocal social selection. Thus, an evolutionary process of coadaptation to family life, additionally driven by conflicts of interests, may have shaped the expression and development patterns underlying infant behaviors. The complex genetics arising from family interactions can be formalized by extending standard quantitative genetic models. These models demonstrate how the explicit consideration of the family environment can profoundly alter both the expression and evolutionary response to selection of behaviors involved in family interactions. Behavioral genetic studies have begun to unravel the complex genetics underlying infant solicitation behaviors and parental provisioning, although many focus on one side of the interaction. A genetic analysis incorporating interactions among family members explicitly may be critical because the genes underlying the expression of parental provisioning indirectly affect offspring behaviors, and vice versa.

Reduced anxiety in postpartum rats requires recent physical interactions with pups, but is independent of suckling and peripheral sources of hormones

Changes in emotional behavior occur across the reproductive cycle in female rodents, with reduced anxiety found during the postpartum period, but relatively little is known about factors contributing to this decreased anxiety. Using increased duration of time spent in the open arms of an elevated plus-maze as an indicator of reduced anxiety, it was found in a series of experiments that (1) anxiety is significantly reduced in Long-Evans females during the first week of lactation, but not thereafter, (2) relatively recent contact with pups before testing (within 4 h) is necessary for their reduced anxiety, (3) dams that receive only distal sensory cues from pups for the 4 h prior to testing do not show reduced anxiety, (4) the absence of nipples, and therefore a lack of suckling by pups, has no effect on dams' anxiety, (5) cesarean delivery of pups 2 days prior to expected parturition did not alter later anxiety in dams, (6) hypophysectomy during mid-pregnancy or ovariectomy within 24 h after parturition also did not prevent reduced anxiety in dams, and (7) differences in anxiety between lactating and virgin females are greatest 4-8 min after being placed in the plus-maze. Therefore, exposure to their own peripheral hormones through mid-pregnancy is sufficient to prime female rats to show reduced anxiety, but only if they later have recent physical interaction with pups. Furthermore, because suckling and the peripheral hormones released during suckling appear to be unnecessary, decreased anxiety in maternal rats may instead be regulated by the transient intracerebral release of neuropeptides or neurotransmitters while dams receive other types of tactile inputs from their infants.

Maternal olfaction differentially modulates oxytocin and prolactin release during suckling in goats

In postparturient goats, olfactory recognition of the young allows the establishment of a selective bond between the mother and her kids. Once this bond is formed, the mother rejects alien young that attempt to suckle. We tested whether the development of the maternal selective bond in goats modulates prolactin (PRL) and oxytocin (OT) release in response to suckling. On day 37 of lactation, serial blood samples were taken during nursing of the mother's own or alien kid(s) in 10 intact/selective goats and in 10 goats rendered anosmic/nonselective through prepartum peripheral ZnSO(4) irrigation. Spontaneous nursing behavior was also studied weekly from day 7 to 30 of lactation, at which time milk production was measured. Maternal selectivity had no effect on PRL release, in contrast to OT release, which was significantly affected by this factor. Intact mothers released OT only when nursing their own kids, but not with aliens, while anosmic/nonselective dams showed an increase in OT levels regardless of the identity of the kids. In addition to these effects on maternal selectivity, the amplitude of the response of both hormones was lower in anosmic mothers than in intact mothers. Finally, nursing behavior and milk production were not significantly affected by anosmia. We conclude that maternal selective behavior in goats, which relies on the individual olfactory signature of the kid, modulates the OT, but not the PRL, response to suckling. In addition, perception of the smell of the young appears to have a general facilitatory effect, independent of the kid's identity, on the release of both hormones.

Ultrasonic vocalisation emitted by infant rodents: a tool for assessment of neurobehavioural development

Ultrasonic vocalisations (USVs) emitted by altricial rodent pups are whistle-like sounds with frequencies between 30 and 90 kHz. These signals play an important communicative role in mother-offspring interaction since they elicit in the dam a prompt response concerning caregiving behaviours. Both physical and social parameters modulate the USV emission in the infant rodent. Recently, a more detailed analysis of the ultrasonic vocalisation pattern, considering the spectrographic structure of sounds has allowed a deeper investigation of this behaviour. In order to investigate neurobehavioural development, the analysis of USVs presents several advantages, mainly: (i) USVs are one of the few responses produced by very young mice that can be quantitatively analysed and elicited by quantifiable stimuli; (ii) USV production follows a clear ontogenetic profile from birth to PND 14-15, thus allowing longitudinal neurobehavioural analysis during very early postnatal ontogeny. The study of this ethologically-ecologically relevant behaviour represent a valid model to evaluate possible alterations in the neurobehavioural development of perinatally treated or genetically modified infant rodents. Furthermore, the role played by several receptor agonists and antagonists in modulating USV rate makes this measure particularly important when investigating the effects of anxiogenic and anxiolytic compounds, and emotional behaviour in general.

Prolactin levels and maternal behavior induced by ultrasonic vocalizations of the rat pup

The relationship among ultrasonic vocalization (USV), prolactin and maternal behavior was investigated in lactating rat mothers and their pups. The lactating mother had a cannula inserted into the external jugular vein, and was exposed to USVs emitted from a pup immediately. Changes of prolactin and maternal behavior were determined. Prolactin increased dramatically during exposure to USVs, when maternal search, retrieving and nest building behavior appeared significantly. These results suggested that the relationship among USV, prolactin and maternal behavior was included in communication between lactating mother and pup.

Comparative study on isolation calls emitted from hamster pups

Waveforms of isolation calls emitted from hamster pups, which were Syrian hamsters, Djungarian hamsters, and Chinese hamsters, were compared in a basic study on improving reproduction by decrease of cannibalism, because it was reported that maternal behavior was induced by isolation calls in rodents. Isolation calls of hamster pups, isolated from their mother and receiving cold stress, were collected by Real-Time Spectrogram (RTS), and calculated to spectrograms and power spectra by SIGNAL. Isolation calls consisted of ultrasonic vocalizations (USVs) and audible vocalizations (ADVs) in each species. Waveforms of isolation calls emitted by the hamster pups, were shown to have several characteristic features. In this study, the species specificity of isolation calls was shown in hamster pups. It would seem that the species specificity originates in the differences of sensitivity to cold stress via the autonomic nerve in hamsters.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

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.

Rat pup ultrasonic vocalization: effects of benzodiazepine receptor ligands

The involvement of the GABA(A)-benzodiazepine receptor complex in rat pup ultrasonic vocalisations was studied by testing benzodiazepine receptor ligands with varying intrinsic activity and selectivity for benzodiazepine subtype receptors. Ultrasonic vocalisations were recorded under two temperature conditions (37 degrees C and 18 degrees C), presumably reflecting a low and high stress state. The latency to the negative geotaxis response, a measure of motor coordination and the rectal temperature were determined to assess putative side effects of drugs. The full, non-selective benzodiazepine receptor agonists diazepam, chlordiazepoxide, alprazolam and oxazepam suppressed ultrasonic vocalisations both at 37 degrees C and 18 degrees C conditions, although more efficaciously at 37 degrees C. The partial, non-selective benzodiazepine receptor agonist bretazenil and the partial benzodiazepine, selective receptor agonist alpidem significantly reduced ultrasonic vocalisations at 37 degrees C, but not at 18 degrees C. The full benzodiazepine, selective receptor agonist zolpidem behaved like other full, non-selective benzodiazepine receptor agonists by reducing ultrasonic vocalisations under both high and low temperature. The effects of zolpidem indicate that activation of benzodiazepine, receptors alone already suffices to suppress ultrasonic vocalisations. The non-selective, benzodiazepine receptor antagonist flumazenil and the partial, non-selective benzodiazepine receptor inverse agonist FG 7142 (N'-methyl-beta-carboline-3-carboxamide) and the full, non-selective benzodiazepine receptor inverse agonist DMCM (6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate) had no significant effect on ultrasonic vocalisations under both temperature conditions. The involvement of benzodiazepine receptors in rat pup ultrasonic vocalisations (37 degrees C-condition) was confirmed by antagonism of the ultrasonic vocalisations reducing effects of chlordiazepoxide by flumazenil (1 or 3 mg/kg). Using the rat pup ultrasonic vocalisations paradigm under 18 degrees C and 37 degrees C conditions combined with measurements of negative geotaxis-latencies and rectal temperatures it is possible to (1) distinguish benzodiazepine receptor agonists from other anxiolytics because of dissimilar dose response curves at 37 degrees C and 18 degrees C, (2) differentiate partial from full receptor agonists by absence of effects at the 18 degrees C condition, (3) suggest a key role for benzodiazepine, receptors in the modulation of ultrasonic vocalisations. These data contribute to the predictive validity of pup vocalizations as an animal model of anxiety.

Repeated exposure of rat pups to isolation attenuates isolation-induced ultrasonic vocalization rates: reversal with naltrexone

Young rat pups are dependent on the dam for their survival, thus isolation of the neonatal rat pup from the dam presents the young organism with a variety of stressors. The question examined in this study concerns the ability of the young rat pup to modify its response to isolation following repeated exposure to that isolation as well as the role played by endogenous opiates in this process. Following repeated isolations, pups were seen to decrease vocalization rates. Altering the context in an attempt to dishabituate animals failed to reverse the decreased vocalization rate. However, opiate receptor blockade attenuated this decrease when administered subsequent to the first isolation period but not prior to the last isolation period. These results suggest that the development of this attenuated response to isolation stress is opiate-mediated but that once established, its expression is not dependent on endogenous opiate release.

Neurobehavioral changes produced in rats by prenatal exposure to carbon monoxide

Wistar female rats were exposed to relatively mild concentrations of carbon monoxide (75 and 150 ppm) from day 0 to day 20 of pregnancy. The results show that prenatal exposure to CO (150 ppm) produced a significant reduction in the minimum frequency of ultrasonic calls emitted by rat pups removed from their nest. Moreover, a significant decrease in the responsiveness (rate of calling) to a challenge dose of diazepam (0.25 mg/kg) was found in male pups exposed to CO (150 ppm) during gestation. Prenatal CO (75 and 150 ppm) did not significantly affect locomotor activity or D-amphetamine-induced hyperactivity in both 14- and 21-day-old animals. Furthermore, adult male rats exposed to this chemical (150 ppm) during gestation exhibited significant alterations in the acquisition of an active avoidance task. CO-induced learning disruption does not seem to be linked to changes in the emotionality of animals. These findings suggest that gestational exposure to CO induces in rat offspring both short- and long-term behavioral changes characterized by altered ontogeny of emotional responsiveness to environmental challenges and by learning impairment.

Alterations to the pattern of ultrasonic calling after prenatal exposure to aluminium sulfate

Pregnant CBA mice were exposed to aluminium sulfate at a dose of 200 mg/kg body wt injected intraperitoneally during Days 10 to 13 of gestation. We used a variety of ethological measures, which have been shown to be sensitive indicators of toxicants, to assess effects on the mother and the behavioral development of pups. Prenatal aluminium resulted in a reduction in the rate of ultrasonic calling by pups accompanied by a shift in the timing of peak calling; treated pups exhibited decreased growth and delays in neurobehavioral development. The treatment received by a pup's foster mother was also found to influence development. We recommend ultrasonic calling as a sensitive measure in studies of behavioral teratogenicity.

Ultrasonic vocalization and body temperature maintenance in infant voles of three species (Rodentia: Arvicolidae)

Infant voles thermoregulate poorly and produce ultrasonic vocalizations when cooled. Vocalizing and the ability to maintain body temperature in isolated pups cold-challenged at 5 degrees C or 22 degrees C were studied in nestling Clethrionomys glareolus, Microtus agrestis, and Arvicola terrestris. The tendency to vocalize varied with age, since pups vocalized more in their 2nd week than in their 1st or 3rd weeks. Rate of vocalizing was correlated with sound pressure level of vocalizations. Their was no apparent relation between vocalizing rate and deep body temperature. M. agrestis pups vocalized most and A. terrestris pups least, and all three species vocalized more at the lower temperature. Maximal vocalizing occurred in mid aged M. agrestis (at 5 degrees C) with mean of 1291 vocalizations/20 min and mean SPL of 80 dB (decibels re: 20 microN/m2). It is suggested that the vocalizing response is an adaptation related to risk from hypothermia in infant voles.

Infant rat separation is a sensitive test for novel anxiolytics

1. Rat pups emit ultrasonic calls during brief episodes of social separation. These calls have been variously described as "distress" calls and may be related to the separation cries expressed by the young of many mammalian species. 2. Ultrasonic call of rat pups are modulated by environmental stimuli such as ambient temperature, olfactory and tactile stimuli associated with the nest. 3. Calls are also sensitive to a variety of purported anxiolytic and anxiogenic drugs, including the benzodiazepines, serotonin agonists, and ligands at the NMDA-glycine receptor complex. 4. In addition to providing a simple test for the anxiolytic properties of drugs, this model may also provide new insights about the development and neurobiology of anxiety.

Effects of prenatal alcohol exposure on rat pups' ability to elicit retrieval behavior from dams

Research on fetal alcohol syndrome (FAS) has historically held that postnatal deficits result directly from prenatal alcohol exposure. Such exposure may alter infant behavior, and this in turn may affect maternal responsiveness and consequently increase the infant's risk for postnatal deficits. This study examined the effect of prenatal alcohol exposure on postnatal blood ethanol concentrations, pup development, and the ability of pups to elicit retrieval behaviors from the dam. Dams given access to a 15% ethanol solution throughout gestation and lactation showed blood ethanol concentrations of 0.1%, whereas their pups had concentrations below the sensitivity of the test. Prenatal alcohol exposure was shown to have pharmacological effects on the pup's righting reflex and nutritional effects on its rate of weight gain. Control pups were better able to elicit retrieval behavior from control and alcoholic dams than were fetally alcoholic pups. These results indicate that the condition of the pup can influence maternal responsiveness which, in turn, can influence pup development.

Estradiol and parental experience, but not prolactin are necessary for ultrasound recognition and pup-retrieving in the mouse

The effects of estradiol, prolactin and experience with pups on pup-retrieving and on the recognition of ultrasonic distress calls of the young by adult ovariectomized female mice were studied. Treatment with estradiol benzoate or experience with pups (for 5 days) induced pup-retrieving in 40% and 60% of the animals, respectively, as compared to 0% in inexperienced ovariectomized females. However, if pup-experience was achieved in the presence of estradiol, retrieving was shown by 90.5% of the animals. In addition, in this case models of the ultrasonic distress calls of the pups were significantly preferred ("recognized") in a discrimination task by the females. These females also showed a sharp increase in serum prolactin concentrations. Depleting prolactin from the blood by cysteamine, however, neither reduced the retrieving score nor disturbed ultrasound recognition. Thus prolactin is dispensable for maintaining maternal pup-retrieving and ultrasound recognition. The process of achieving pup-experience is enhanced by the presence of estradiol. Possible actions of estradiol in the brain are discussed.

Subtle behavioural changes produced in rat pups by in utero exposure to haloperidol

Prenatal exposure to a dopamine receptor blocking agent such as haloperidol (given to the mother at a dose of 0.5 mg/kg s.c. from day 4 to day 15 of gestation) produced subtle behavioural changes in rat pups. Haloperidol decreased the rate of ultrasonic vocalization in 4-day-old male pups removed from the nest. The changes in ultrasonic emission elicited by in utero exposure to this neuroleptic were markedly different from those produced by its administration during the early postnatal period. Moreover, adult male rats treated prenatally with haloperidol exhibited a significant increase in the intensity of ultrasonic 22 kHz post-ejaculatory calls emitted during sexual behaviour. The duration of the period of the 22 kHz calls emission was also significantly increased by haloperidol treatment. These results confirm that ultrasonic vocalization in rats is a sensitive indicator of subtle changes in adverse treatments administered during development.

Ultrasonic vocalization in response to unavoidable aversive stimuli in rats: effects of benzodiazepines

The effects of two benzodiazepine derivatives (diazepam, 0.5-1 mg/kg; alprazolam, 1.25-2.5 mg/kg) on ultrasonic calling elicited in adult rats by unavoidable aversive stimuli (footshocks) were investigated. The results show that either diazepam or alprazolam affected the duration of ultrasonic calls. In particular, a significant decrease in the length of ultrasounds was found in the group of animals treated with these benzodiazepines. The effects of diazepam were counteracted by the benzodiazepine-antagonist Ro 15-1788. On the other hand, neither a neuroleptic agent, such as haloperidol (0.5-1 mg/kg), nor an antidepressant, such as desipramine (5-10 mg/kg) influenced the parameters of ultrasonic emission in this experimental situation. The present results suggest that ultrasonic vocalization in response to unavoidable aversive stimuli could be considered as a potential new tool for studying drugs with antianxiety properties.

Ultrasonic vocalization in rat pups: effects of early postnatal exposure to SCH 23390 (a DA1-receptor antagonist) and sulpiride (a DA2-receptor antagonist)

Early postnatal administration of SCH 23390 and sulpiride induced marked changes in the ultrasonic vocalization elicited by the removal of rat pups from their nest. In particular, SCH 23390 produced a significant increase in the length, as well as in the sound pressure level, of ultrasonic calls; moreover, a significant decrease in minimum and maximum frequency values was found in pups treated with this DA1-receptor antagonist. Sulpiride significantly reduced the rate of calling, as well as the pressure level of sounds, whereas it did not influence other parameters of the ultrasonic emission. These behavioural alterations seemed to be the consequence of an impaired functional maturation of the dopamine (DA) system; however, the different changes caused by SCH 23390 and sulpiride, respectively, suggest that DA1- and DA2-receptor populations could play a distinct role in the ultrasonic calling during early postnatal life.

Ultrasonic calling in rodents: a new experimental approach in behavioural toxicology

Ultrasonic calls are emitted by many species of rodents in a variety of situations. In particular, infants commonly emit such calls when removed from the nest; the rate and intensity of calling are related to the degree of development of homoiothermy. The relevant biological significance of these signals is documented by their capability to promote parental behaviour, such as maternal retrieval. There is recent evidence that ultrasonic vocalization in rodent pups could be valuable as a bioassay in Behavioural Toxicology. In particular, the results of our recent studies together with those of other authors suggest that ultrasonic calls emitted by infant rats could be considered a useful test in detecting subtle effects of adverse treatment during development.

Ultrasonic vocalization in rat pups: effects of early postnatal exposure to haloperidol

The effects of prolonged postnatal administration of haloperidol (H) on ultrasonic vocalization elicited by the removal of rat pups from their nest were investigated. The results show that the number of ultrasonic calls was significantly reduced by H exposure from the 8th until the 14th day after birth. Conversely, this neuroleptic significantly increased the duration of ultrasound from the 4th up to the 16th day of age. Moreover, changes in the frequency of calls were produced by early postnatal treatment with H. These alterations could be due to an impaired functional maturation of the dopaminergic system produced by neonatal exposure to H. Furthermore, the present data suggest that ultrasonic vocalization may be considered as an early sensitive indicator of subtle changes elicited by the postnatal treatment with a dopamine receptor blocking agent at dose levels below those associated with overt signs of neurotoxicity.

Parental fanning behavior and prolactin cell activity in the male three-spined stickleback Gasterosteus aculeatus L

During the period that sexually mature male three-spined sticklebacks display parental fanning behavior, the rate of synthesis and release of the prolactin cells in the hypophysis, as estimated with quantitative electron microscopy, is enhanced considerably. This finding points to involvement of endogenous prolactin in the regulation of parental fanning behavior in this species.

Do pup ultrasonic cries provoke prolactin secretion in lactating rats?

Marked prolactin (PRL) secretion in response to the ultrasonic distress vocalizations of rat pups in lactating dams deprived of their pups for 6 hr was reported by others. In two experiments, this phenomenon could not be confirmed under our testing conditions at either 1 or 2 weeks postpartum, although behavioral responses to the ultrasounds were noted. In addition, suckling-induced PRL secretion did not differ consistently as a function of the tape recording (pup ultrasounds, 45 kHz artificially produced ultrasounds, or blank tape) heard prior to the return of pups. The functional significance of rat pup ultrasounds is considered.

Decreased dopamine turnover in the median eminence in response to suckling in the lactating rat

The effects of suckling on the turnover of dopamine (DA) and norepinephrine (NE) were studied in terminal projection fields of the tuberoinfundibular (median eminence, ME), nigrostriatal (caudate nucleus, CN), incertohypothalamic (medial preoptic nucleus, MPN) and mesolimbic (nucleus accumbens, NA) dopaminergic neurons. Decreased dopamine turnover in the median eminence was found in suckled compared with nonsuckled rats at 10 days postpartum. This effect was specific as dopamine turnover in the CN, NA and MPN and norepinephrine turnover in the ME, NA and MPN were not affected by suckling. The suckling-induced prolactin response is markedly blunted in rats 20 days postpartum. In these rats, median eminence dopamine turnover did not decrease significantly in response to suckling. These results are consistent with the hypothesis that median eminence dopamine is a physiological prolactin inhibitory factor mediating suckling-induced prolactin release.