Ultrasonic call characteristics of rat pups are altered following prenatal malnutrition

Thermoregulatory, metabolic and stress responses to spring shearing of aged ewes born to undernourished mothers

Maternal undernutrition during gestation affects the behaviour, metabolism, and sensitivity to stressors of the offspring. Shearing is a stressor that triggers physiological and behavioural changes and augments the thermoregulatory demands in sheep. The aim of this study was to compare the thermoregulatory, metabolic, and behavioural responses to spring shearing of aged ewes born to mothers who grazed different pasture allowances during gestation. Nineteen non-gestating six-year-old Corriedale ewes born to mothers who grazed two pasture allowances from 23 days before conception until 122 days of gestation were used. The pasture allowance offered to the mothers was high [HPA group; n = 11; 10-12 kg of dry matter (DM)/100 kg of body weight (BW)/day] or low [LPA group: n = 8; 5-8 kg of DM/100 kg of BW/day]. The adult offspring of both experimental groups were sheared during spring (Day 0), and remained outdoors, grazing natural grassland, and the behaviour, the surface temperature and the rectal temperature were recorded. Blood concentrations of albumin, total protein, glucose, and insulin were also determined. Data were compared with a mixed model. The LPA ewes had lower ear and nose maximum and minimum surface temperatures before shearing (P < 0.05). On Day 15, the average surface temperature of the vulva was lower in LPA than in HPA ewes (P < 0.05). After shearing, rumination frequency was greater in HPA than in LPA ewes (P = 0.01), and LPA ewes were observed more time standing up than HPA ewes (P < 0.0001). Insulin concentration tended to be greater in LPA than HPA ewes (P = 0.06). Maternal undernutrition during gestation modified the thermoregulatory responses and the acute behavioural changes after shearing in aged female offspring, whilst the metabolism was affected to a lesser degree. The long-term effects noticed in this study highlight the importance of providing proper nutrition to pregnant ewes.

Ultrasonic Vocalizations Emission across Development in Rats: Coordination with Respiration and Impact on Brain Neural Dynamics

Rats communicate using ultrasonic vocalizations (USV) throughout their life when confronted with emotionally stimulating situations, either negative or positive. The context of USV emission and the psychoacoustic characteristics of the vocalizations change greatly between infancy and adulthood. Importantly, the production of USV is tightly coordinated with respiration, and respiratory rhythm is known to influence brain activity and cognitive functions. This review goes through the acoustic characteristics and mechanisms of production of USV both in infant and adult rats and emphasizes the tight relationships that exist between USV emission and respiration throughout the rat's development. It further describes how USV emission and respiration collectively affect brain oscillatory activities. We discuss the possible association of USV emission with emotional memory processes and point out several avenues of research on USV that are currently overlooked and could fill gaps in our knowledge.

Biological Functions of Rat Ultrasonic Vocalizations, Arousal Mechanisms, and Call Initiation

This review summarizes all reported and suspected functions of ultrasonic vocalizations in infant and adult rats. The review leads to the conclusion that all types of ultrasonic vocalizations subserving all functions are vocal expressions of emotional arousal initiated by the activity of the reticular core of the brainstem. The emotional arousal is dichotomic in nature and is initiated by two opposite-in-function ascending reticular systems that are separate from the cognitive reticular activating system. The mesolimbic cholinergic system initiates the aversive state of anxiety with concomitant emission of 22 kHz calls, while the mesolimbic dopaminergic system initiates the appetitive state of hedonia with concomitant emission of 50 kHz vocalizations. These two mutually exclusive arousal systems prepare the animal for two different behavioral outcomes. The transition from broadband infant isolation calls to the well-structured adult types of vocalizations is explained, and the social importance of adult rat vocal communication is emphasized. The association of 22 kHz and 50 kHz vocalizations with aversive and appetitive states, respectively, was utilized in numerous quantitatively measured preclinical models of physiological, psychological, neurological, neuropsychiatric, and neurodevelopmental investigations. The present review should help in understanding and the interpretation of these models in biomedical research.

Anxiety-like behavior and neuroendocrine changes in offspring resulting from gestational post-traumatic stress disorder

Exposure to stressful environmental events during the perinatal period can increase vulnerability to psychopathologies that cause neuroendocrine changes associated with deficits in emotional behavior that can appear early in life. Post-traumatic stress disorder (PTSD) is a frequent, chronic, and disabling disorder that negatively impacts the emotional, social, and cognitive behaviors of affected individuals. Thus, we induced PTSD in pregnant rats by applying inescapable footshocks and then investigated the behavioral parameters similar to anxiety in offspring at prepubertal age, in addition to the plasma levels of maternal and offspring corticosterone and expression of glucocorticoid receptors (GR) in the offspring's hippocampus. With the dams, maternal behavior, open field, and object recognition tests were performed. With the male and female offspring, we performed the following: quantification of ultrasonic vocalizations, elevated plus-maze test, evaluation of exploratory activity in the open field, and hole board test, as well as plasma corticosterone measurements and Western blotting for GR. Our results showed that gestational PTSD affected maternal behavior, led to anxiety-like symptoms, increased corticosterone levels, and increased GR expression in the offspring's hippocampus. Therefore, our data can contribute to the understanding of the onset of early (childhood and juvenile/pre-pubertal phases) anxiety owing to exposure to a traumatic event during the gestation period.

Perinatal high-fat diet impairs pup retrieval and induces sex-specific changes in ultrasonic vocalization characteristics of rat pups

Rodent pups emit ultrasonic vocalizations (USVs) to solicit maternal behavior, promoting their survival. Conversely, maternal behaviors affect the expression of pup USVs. We previously demonstrated that a maternal diet high in saturated fat (HFD) alters maternal behavior and is associated with early maturation of pups and their stress physiology. Here, we assessed the developmental profiles of pup USVs using quantitative and qualitative measures on postnatal days (PND)7 and 13. Quantitative measures included call counts, duration, and frequency, while qualitative measures examined calls' sonographic structures. HFD offspring lacked the typical decrease in USV numbers with age observed among control offspring. They also had shorter calls at PND7 compared to control and HFD offspring at PND13. HFD female offspring showed a greater number of one-frequency-sweep calls, while male pups showed a greater number of two-frequency-sweep calls compared to control offspring. Concomitantly, HFD dams showed impaired pup retrieval on PND7. The data suggest that fewer USVs of shorter duration in HFD offspring may alter dam solicitation and thus impair maternal pup retrieval. This study highlights the impacts of perinatal HFD exposure on the dyadic reciprocal interaction between dam and pups, which may set the stage for long-lasting effects on offspring physiology and behavior.

Prenatal vitamin D deficiency does not exacerbate behavioural impairments associated with prenatal ethanol exposure in juvenile male mice

There is a high prevalence of vitamin D deficiency and exposure to low levels of ethanol in pregnant women. However, there are a paucity of studies that have addressed the impact of both vitamin D deficiency and ethanol exposure on the offspring's vulnerability to neurodevelopmental disorders later in life. The aim of this study was to examine whether the absence of vitamin D during gestation in mice would alter the effects of prenatal exposure to low dose ethanol on the behaviour and dopaminergic gene expression patterns of juvenile mice. Four-week old female C57BL/6J mice were placed on a prenatal vitamin D deficient (PVD) or standard diet for 6 weeks and mated at 10 weeks of age. Females were exposed to either 10%(v/v) ethanol or water between gestational days 0-8 and all were offered water thereafter. We found that blood ethanol concentration in the dams was not affected by maternal diet. Behavioural analyses of the offspring included ultrasonic vocalizations (USV) at postnatal day (P) 7, locomotion and social interaction at P21. The main findings were increased USV calling rate and impaired social interaction in males with prenatal ethanol exposure (PrEE). Gene expression analysis of transcripts involved in dopamine regulation revealed a main effect of ethanol exposure on dopamine- and cyclic adenosine monophosphate- regulated neuronal phosphoprotein (Darpp-32), a main effect of vitamin D diet on Dopamine 2 Receptors (D2R) and a main effect of Sex on Tyrosine Hydroxylase (TH) expression. The combination of PVD-PrEE did not exacerbate the alterations resulting from PVD or PrEE. Despite the limited evidence to support the interaction of PVD and PrEE during the postnatal period, males were more vulnerable than female offspring to the detrimental effects of PrEE. Therefore, based on these studies in mice we suggest that maintenance of optimal vitamin D levels and abstinence from ethanol during pregnancy would reduce risk of later disruption to brain function and behaviour in the offspring.

Maternal alterations induced by exposure to an unfamiliar home cage in early underfed dams

The expression of different behavioral components in the adult rat depends on a number of early influences, including age, hormones, manipulations of sensory cues, and perinatal undernutrition, all of which impact the development of brain areas underlying adaptive processes, maternal behavior, and the response to novelty. The current study investigates the effects of pre- and neonatal undernutrition on various components of maternal behavior of dams exposed to the challenge of an unfamiliar home cage on days 4, 8, and 12 of lactation. Food restriction was initiated from gestational day (G) G6 to G19 when dams received 50-70% of the normal balanced diet, followed by 100% from G20 to G21. After birth, pups were underfed by alternating every 12h between two lactating dams, one of which, had ligated nipples. Weaning was at 25days of age followed by an ad libitum diet until postpartum day 90, when females were mated, and subsequently tested for maternal behavior in an unfamiliar cage. The results indicated that in early underfed mothers the frequency of handling wood shavings and of, approaching, licking, crouching, and grasping pups for retrieval was significantly reduced. Moreover, self-grooming increased substantially in the underfed dams, but the frequency of rearing was reduced. Additionally, the body weight of pups nursed by early underfed dams was significantly lower than that of control pups. These findings suggest a relation between early food restriction and the deficient maternal care observed when these dams were challenged by exposure to an unfamiliar home cage.

Reduction in ultrasonic vocalizations in pups born to rapid eye movement sleep restricted mothers in rat model

The effects of rapid eye movement sleep restriction (REMSR) in rats during late pregnancy were studied on the ultrasonic vocalizations (USVs) made by the pups. USVs are distress calls inaudible to human ears. Rapid eye movement (REM) sleep was restricted in one group of pregnant rats for 22 hours, starting from gestational day 14 to 20, using standard single platform method. The USVs of male pups were recorded after a brief isolation from their mother for two minutes on alternate post-natal days, from day one till weaning. The USVs were recorded using microphones and were analysed qualitatively and quantitatively using SASPro software. Control pups produced maximum vocalization on post-natal days 9 to 11. In comparison, the pups born to REMSR mothers showed not only a reduction in vocalization but also a delay in peak call making days. The experimental group showed variations in the types and characteristics of call types, and alteration in temporal profile. The blunting of distress call making response in these pups indicates that maternal sleep plays a role in regulating the neural development involved in vocalizations and possibly in shaping the emotional behaviour in neonates. It is suggested that the reduced ultrasonic vocalizations can be utilized as a reliable early marker for affective state in rat pups. Such impaired vocalization responses could provide an important lead in understanding mother-child bonding for an optimal cognitive development during post-partum life. This is the first report showing a potential link between maternal REM sleep deprivation and the vocalization in neonates and infants.

Effect of prenatal cocaine on early postnatal thermoregulation and ultrasonic vocalization production

Prenatal cocaine exposure can alter the postnatal care received by rat pups. Such effects could be caused in part by alterations in pup-produced stimuli that elicit early postnatal maternal care. Pup ultrasonic vocalizations are thought to be a particularly salient stimulus, and when paired with other cues, may elicit maternal attention. Cocaine is known to acutely alter thermoregulatory and cardiac function, thus prenatal cocaine may affect vocalizations through altering these functions. The data presented here determine the impact of full term prenatal cocaine exposure, saline exposure, or no exposure on thermogenic capacity, cardiac function, and the resulting ultrasonic vocalizations across the early postnatal period (days 1–5). Results indicated that while sharing many similar characteristics with saline-exposed and untreated animals, prenatal cocaine exposure was associated with specific alterations in vocalization characteristics on postnatal day 1 (PND 1), including call amplitude. Furthermore, numerous spectral parameters of their vocalizations were found altered on PND 3, including rate, call duration, and frequency, while no alterations were found on PND 5. Additionally, cocaine-exposed pups also showed a reduced thermoregulatory capacity compared to saline animals and reduced cardiac mass compared to untreated animals on PND 5. Together, these findings indicate that prenatal cocaine may be altering the elicitation of maternal care through its impact on vocalizations and thermoregulation, and suggests a potential mechanism for these effects through cocaine's impact on developing stress systems.

Neonatal behavioral changes in rats with gestational exposure to lipopolysaccharide: a prenatal infection model for developmental neuropsychiatric disorders

Exposure to prenatal infections has been widely associated with the increased risk for neuropsychiatric disorders of developmental origin such as schizophrenia and autism. Although several behavioral and cognitive deficits have been detected during adulthood in rodent models of prenatal infections, early behavioral changes have not been well characterized. In a prenatal lipopolysaccharide (LPS) model, we have previously observed significant alterations in the neuronal cytoarchitecture during early postnatal life. In the present study, we aimed to investigate the potential effects of prenatal immune activation on early neurophenotypic presentations using a set of behavioral test battery. Female Sprague-Dawley rats were administered with 100 μg/kg LPS (intraperitoneally) at gestational days 15 and 16. During the first postnatal week, we found no significant effect on maternal behavior or mother-pup interaction by this treatment. Also, no major changes in physical developmental milestones of pups were noted from postnatal (P) days P6 to P16. Importantly, prenatal LPS-exposed pups had a significant decrease in the number and duration of ultrasonic vocalization calls at P3 and P5. Prenatal LPS treatment also led to impairments in nest-seeking behavior and odor-stroke associative learning in neonatal rats at P8 and P9. At the molecular level, we detected significant decrease in the expression of cortical 5HT1A and 5HT1B messenger RNA at P3. These data suggest that prenatal exposure to an immune activator can significantly impair the social/communicative behavior in the neonate offspring, which may be relevant to childhood and premorbid abnormalities reported in autism and schizophrenia subjects.

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.

The effects of prenatal stress on motivation in the rat pup

Exposure to prenatal stress (PNS) has been shown to induce a set of psychological and behavioral changes in developing offspring. We used the rodent model to investigate whether PNS produces changes in the ability of the pup to express social motivation. We used a set of behavioral tasks including monitoring ultrasonic vocalizations after isolation, a conditioned place preference, and a novel and familiar odor approach test. Pregnant Long-Evans rats were exposed to an unpredictable, variable stressor twice daily during the third week of gestation. Isolation vocalizations were assessed on postnatal day (PND) 10. Pup affinity for the dam was evaluated on PND 15. Typically, pups display a selective preference for an odor-paired environment only after the odor has been associated with the dam. This previous association produces a positive conditioned stimulus (CS). Normally, pups exposed to a neutral CS (odor paired with cotton balls) do not form this place preference. Results indicate that PNS exposed pups had significantly increased distress vocalizations and an equal preference for the positive and neutral conditioned stimuli. This type of alteration in forming early preferences could be detrimental because of decreases in the specificity of social learning and an impaired responsiveness in social relationships.

Ultrasonic vocalizations: a tool for behavioural phenotyping of mouse models of neurodevelopmental disorders

In neonatal mice ultrasonic vocalizations have been studied both as an early communicative behaviour of the pup-mother dyad and as a sign of an aversive affective state. Adult mice of both sexes produce complex ultrasonic vocalization patterns in different experimental/social contexts. Vocalizations are becoming an increasingly valuable assay for behavioural phenotyping throughout the mouse life-span and alterations of the ultrasound patterns have been reported in several mouse models of neurodevelopmental disorders. Here we also show that the modulation of vocalizations by maternal cues (maternal potentiation paradigm) - originally identified and investigated in rats - can be measured in C57BL/6 mouse pups with appropriate modifications of the rat protocol and can likely be applied to mouse behavioural phenotyping. In addition we suggest that a detailed qualitative evaluation of neonatal calls together with analysis of adult mouse vocalization patterns in both sexes in social settings, may lead to a greater understanding of the communication value of vocalizations in mice. Importantly, both neonatal and adult USV altered patterns can be determined during the behavioural phenotyping of mouse models of human neurodevelopmental and neuropsychiatric disorders, starting from those in which deficits in communication are a primary symptom.

Prenatal malnutrition alters diazepam-mediated suppression of ultrasonic vocalizations in an age dependent manner

The sensitivity of prenatally malnourished rats to the ultrasonic vocalization (USV) suppressant effect of diazepam (a non-specific benzodiazepine (BZ) receptor agonist) was investigated. Male offspring of dams provided with a protein deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy were compared to the offspring of mothers provided with a diet of adequate protein content (25% casein). At postnatal day 7 or 11, pups were injected with vehicle or one of five doses of DZ (0.03, 0.1, 0.3, 1 or 3mg/kg) 30 min after removal from their dam. Thirty minutes later they were subjected to 2 min of cooling on a 20 degrees C surface and their USVs were quantified. DZ dose-dependently suppressed USV at both ages. At P7, the USV suppressant effect of DZ was the same for both groups. However, by P11 the prenatally malnourished rats showed significantly greater suppression of USV by 0.03 and 0.1mg/kg DZ than well-nourished controls. These differences were not related to degree of temperature loss or body weight. Thus, differential sensitivity to BZ receptor agonists develops in the second postnatal week in prenatally malnourished rats. This reflects either an altered program of development of the GABAergic system, or adaptive, compensatory changes in the GABAergic system in response to more extensive functional disturbances in the developing brain.

Contributions of undernutrition and handling to huddling development of rats

When newborn rats are separated from the mother, they consistently exhibit the huddling response to maintain body temperature and physical contact. Therefore, we investigated if preweaning handling/sensory stimulation may overcome the huddling deficiencies associated to neonatal undernourishment/maternal deprivation of Wistar rats maintained at constant temperature (30 degrees C). The data indicated that initial and final temperatures in the pile of undernourished (U) and undernourished stimulated (Us) pups was reduced compared to their controls (C and Cs, respectively). Huddling latency was prolonged at 5 days of age in the Us group and at 20 days of age in the U pups. On postpartum day 5, U and Us subjects were similar in battery and pile-huddling performance compared to their controls; thereafter, the frequency of battery type was low and pile type was high (in frequency) in all experimental treatments. The frequency of recycling from the pile in the Us pups in most of the ages was significantly reduced compared to U and C subjects, suggesting that early sensory stimulation possibly accelerates the maturation of thermoregulatory brain structures underlying the huddling response and causing increased physical contacts. The data provide evidence that both neonatal undernutrition/maternal deprivation and early sensory stimulation may modify the huddling response by reducing or increasing, respectively, brain mechanisms underlying huddling. The amount of physical contact the newborns receive from their littermates and the mother may be a fundamental source of sensory cues for neuronal maturation and brain functioning.

Organization of olfactory glomeruli in neonatally undernourished rats

Newborn rats maintain mother-litter bonds by using olfactory signals. At birth, units in the olfactory glomeruli (OG) are immature and vulnerable to noxious epigenetic factors like undernutrition. Because little is known about the effects of neonatal undernutrition upon the OG morphological organization, different OG parameters were studied in undernourished Wistar rats at 7, 14 and 21 days of age. The issue was addressed by analyzing the olfactory bulb (OB) cross sectional area, the total number and area of OGs in the OB coronal sections, and the distribution of OG area in dorsal and ventral quadrants. Reductions in the OB and OG cross sectional areas were detected at 7 and 14 days posnatally. OG area comparisons by OB quadrants were reduced along the study in quadrants, with larger effects in medial than in lateral OB quadrants. Current OG cytoarchitectonic modifications may affect the newborn capabilities for odour discrimination by disrupting early mother-litter interactions.

Neonatal ethanol exposure but not neonatal cocaine selectively reduces specific isolation-induced vocalization waveforms in rats

This study was designed to examine the interaction of neonatal ethanol and cocaine exposure on isolation induced ultrasonic vocalizations using an oral gavage method of drug administration. There were 5 neonatal treatment groups including 3.0 g/kg ethanol, 20 mg/kg cocaine, both 3.0 g/kg ethanol and 20 mg/kg cocaine, an intubated control and a nonintubated control. Drug was administered twice daily from postnatal days (PND) 4 - 10. On PND 14, subjects were tested for a 6 min test to assess the rate and type of ultrasonic vocalizations displayed. As previously reported using an intragastric "artificial rearing" administration procedure, pups exposed to ethanol displayed reductions in the number of ultrasonic vocalizations across the test session. Pups exposed to both drugs showed similar deficits to those pups receiving ethanol alone. In contrast, cocaine had no effect on this outcome measure. Sonographic analysis of the vocalizations revealed that ethanol's effects appeared to be selective to certain waveforms rather than a general reduction across all wave types and again, cocaine had no impact on the proportion of the various wave types. These findings provide further support that neonatal ethanol exposure can have significant effects on maternal/infant communication and may play a role in many of the long-term effects associated with ethanol exposure during development.

Effects of prenatal protein malnutrition and acute postnatal stress on granule cell genesis in the fascia dentata of neonatal and juvenile rats

Although postnatal genesis of granule cells in the hippocampal fascia dentata is known to be influenced by prenatal protein deprivation or by stress, the combined effects of prenatal protein malnutrition and stress on these cells are unknown. This study was designed to examine this combined effect. Well-nourished and prenatally malnourished pups on postnatal day 7 (P7) were stressed by maternal separation and reduction of body temperature and on postnatal day 30 (P30) by immobilization with restraint. Bromodeoxyuridine (BrDU) was injected at the time of stress, and 2 h later, the numbers of immunolabeled cells were quantified by standard stereological techniques. In comparison to controls, prenatally malnourished rats showed a significantly lower number of cells tagged in the fascia dentata on P7 (p < or =0.05), and a significantly higher number of cells (p < or =0.05) on P30. In both age groups, control rats exposed to acute stress showed a significantly decreased number of cells tagged in the fascia dentata (p < or =0.05). In contrast, neurogenesis in malnourished rats was not significantly affected by acute stress at either age. Thus, the pattern of neurogenesis in the fascia dentata and its response to stress has been fundamentally altered by prenatal protein deprivation.