IGF-I and IGF-I24-41 but not IGF-I57-70 affect somatic and neurobehavioral development of newborn male mice

Spontaneous running wheel exercise during pregnancy prevents later neonatal-anoxia-induced somatic and neurodevelopmental alterations

Introduction

About 15-20 % of babies that suffer perinatal asphyxia die and around 25 % of the survivors exhibit permanent neural outcomes. Minimization of this global health problem has been warranted. This study investigated if the offspring of pregnant female rats allowed to spontaneously exercise on running wheels along a 11-day pregnancy period were protected for somatic and neurodevelopmental disturbs that usually follow neonatal anoxia.

Methods

spontaneous exercise was applied to female rats which were housed in cages allowing free access to running wheels along a 11-day pregnancy period. Their offspring were submitted to anoxia 24-36 h after birth. Somatic and sensory-motor development of the pups were recorded until postnatal day 21 (P21). Myelin basic protein (MBP)-stained areas of sensory and motor cortices were measured at P21. Neuronal nuclei (NeuN)-immunopositive cells and synapsin-I levels in hippocampal formation were estimated at P21 and P75.

Results

gestational exercise and / or neonatal anoxia increased the weight and the size of the pups. In addition, gestational exercise accelerated somatic and sensory-motor development of the pups and protected them against neonatal-anoxia-induced delay in development. Further, neonatal anoxia reduced MBP stained area in the secondary motor cortex and decreased hippocampal neuronal estimates and synapsin-I levels at P21; gestational exercise prevented these effects. Therefore, spontaneous exercise along pregnancy is a valuable strategy to prevent neonatal-anoxia-induced disturbs in the offspring.

Conclusion

spontaneous gestational running wheel exercise protects against neonatal anoxia-induced disturbs in the offspring, including (1) physical and neurobehavioral developmental impairments, and (2) hippocampal and cortical changes. Thus, spontaneous exercise during pregnancy may represent a valuable strategy to prevent disturbs which usually follow neonatal anoxia.

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.

Gene-environment interaction during early development in the heterozygous reeler mouse: clues for modelling of major neurobehavioral syndromes

Autism and schizophrenia are multifactorial disorders with increasing prevalence in the young population. Among candidate molecules, reelin (RELN) is a protein of the extracellular matrix playing a key role in brain development and synaptic plasticity. The heterozygous (HZ) reeler mouse provides a model for studying the role of reelin deficiency for the onset of these syndromes. We investigated whether early indices of neurobehavioral disorders can be identified in the infant reeler, and whether the consequences of ontogenetic adverse experiences may question or support the suitability of this model. A first study focused on the link between early exposure to Chlorpyryfos and its enduring neurobehavioral consequences. Our data are interesting in view of recently discovered cholinergic abnormalities in autism and schizophrenia, and may suggest new avenues for early pharmacological intervention. In a second study, we analyzed the consequences of repeated maternal separation early in ontogeny. The results provide evidence of how unusual stress early in development are converted into altered behavior in some, but not all, individuals depending on gender and genetic background. A third study aimed to verify the reliability of the model at critical age windows. Data suggest reduced anxiety, increased impulsivity and disinhibition, and altered pain threshold in response to morphine for HZ, supporting a differential organization of brain dopaminergic, serotonergic and opioid systems in this genotype. In conclusion, HZ exhibited a complex behavioral and psycho-pharmacological phenotype, and differential responsivity to ontogenetic adverse conditions. HZ may be used to disentangle interactions between genetic vulnerability and environmental factors. Such an approach could help to model the pathogenesis of neurodevelopmental psychiatric diseases.

Neurobehavioural disorders in the infant reeler mouse model: Interaction of genetic vulnerability and consequences of maternal separation

Studies on heterozygous (HZ) reeler mice suggest a relationship between reelin (a protein of extra cellular matrix) haploinsufficiency and the presence of altered neural networks and behaviour. Neonatal adverse and/or stimulating experiences might interfere with the emergence of this genetic-dependent phenotype. Repeated episodes of maternal separation early in ontogeny result in enduring neuroendocrine, neurochemical and behavioural alterations in the offspring. Therefore, in order to investigate whether developmental indexes of neurobehavioural disorders can be studied in the infant reeler mouse model, and whether ontogenetic adverse experiences may question or improve its suitability, homozygous reeler (RL), heterozygous (HZ) and wild-type (WT) mouse pups underwent maternal separation (SEP, 5h/day) or handling (H, 3min/day) on PND 2-6. As expected, a sex difference appeared, for measure of emotional and communicative behaviour in infant mice. On PND 7, compared to other genotypes, RL mouse pups from the H control group, showed reduced levels of ultrasound (USV) production and of locomotion. Surprisingly, this deficit in RL mice was fully reverted by maternal separation. Maternal separation per se reduced social motivation in the homing test at PND 9 in WT mice, with no effects on HZ and RL ones. Additionally, female pups emitted much lower levels of ultrasound production than males within the H control group. Such a baseline sex difference, however, disappeared in the SEP group. The present results provide evidence that unusual stress and related hormonal stimulation early in development may (i) independently shape individual phenotype and (ii) interact with a genetic make-up to substantially modify its "natural" developmental trajectories.

Transgenic mice expressing F3/contactin from the transient axonal glycoprotein promoter undergo developmentally regulated deficits of the cerebellar function

We have shown that transgenic transient axonal glycoprotein (TAG)/F3 mice, in which the mouse axonal glycoprotein F3/contactin was misexpressed from a regulatory region of the gene encoding the transient axonal glycoprotein TAG-1, exhibit a transient disruption of cerebellar granule and Purkinje cell development [Development 130 (2003) 29]. In the present study we explore the neurobehavioural consequences of this mutation. We report on assays of reproductive parameters (gestation length, litter size and offspring viability) and on somatic and neurobehavioural end-points (sensorimotor development, homing performance, motor activity, motor coordination and motor learning). Compared with wild-type littermates, TAG/F3 mice display delayed sensorimotor development, reduced exploratory activity and impaired motor activity, motor coordination and motor learning. The latter parameters, in particular, were affected also in adult mice, despite the apparent recovery of cerebellar morphology, suggesting that subtle changes of neuronal circuitry persist in these animals after development is complete. These behavioural deficits indicate that the finely coordinated expression of immunoglobulin-like cell adhesion molecules such as TAG-1 and F3/contactin is of key relevance to the functional, as well as morphological maturation of the cerebellum.

Increased brain levels of F2-isoprostane are an early marker of behavioral sequels in a rat model of global perinatal asphyxia

Perinatal asphyxia is a major cause of immediate and postponed brain damage in the newborn. It may be responsible for several delayed neurologic disorders and, in this respect, early markers of brain injury would be relevant for therapeutic intervention as well as for identification of infants at high risk for developmental disabilities. Biochemical measurements (brain F2-isoprostane levels) and behavioral tests (ultrasonic vocalization pattern on postnatal days (pnd) 5, 8, and 11, spontaneous motor behaviors on pnd 7 and 12, and homing response on pnd 10) were performed in a rat model of global perinatal asphyxia in the immature neonate. Caesarean section was performed in rats and the pups, still in uterus horns, were placed into a water bath at 37 degrees C for either 10 or 20 min. Caesarean delivered pups were used as controls. Pups experiencing severe (20 min), in contrast to those undergoing the 10 min, asphyctic insult presented with detectable abnormalities including early (two hours after the insult) increase in brain F2-isoprostane (a direct marker of oxidative injury) without detectable changes in PGE2, COX-2 and iNOS levels, and delayed physical (reduced weight gain on pnd 5 and thereafter) and behavioral disturbances (alterations in ultrasound emission on pnd 11 and spontaneous motricity levels mainly). These findings suggest that increased brain F2-isoprostane levels shortly after the asphyctic insult are predictive of delayed behavioral disturbances in the newborn rat. The present 20-min asphyxia model might serve for the assessment of preventive and curative strategies to treat neurologic/behavioral disturbances associated with perinatal asphyxia.

Developmental exposure to chlorpyrifos alters reactivity to environmental and social cues in adolescent mice

Neonatal mice were treated daily on postnatal days (pnds) 1 through 4 or 11 through 14 with the organophosphate pesticide chlorpyrifos (CPF), at doses (1 or 3 mg/kg) that do not evoke systemic toxicity. Brain acetylcholinesterase (AChE) activity was evaluated within 24 h from termination of treatments. Pups treated on pnds 1-4 underwent ultrasonic vocalization tests (pnds 5, 8, and 11) and a homing test (orientation to home nest material, pnd 10). Pups in both treatment schedules were then assessed for locomotor activity (pnd 25), novelty-seeking response (pnd 35), social interactions with an unfamiliar conspecific (pnd 45), and passive avoidance learning (pnd 60). AChE activity was reduced by 25% after CPF 1-4 but not after CPF 11-14 treatment. CPF selectively affected only the G(4) (tetramer) molecular isoform of AChE. Behavioral analysis showed that early CPF treatment failed to affect neonatal behaviors. Locomotor activity on pnd 25 was increased in 11-14 CPF-treated mice at both doses, and CPF-treated animals in both treatment schedules were more active when exposed to environmental novelty in the novelty-seeking test. All CPF-treated mice displayed more agonistic responses, and such effect was more marked in male mice exposed to the low CPF dose on pnds 11-14. Passive avoidance learning was not affected by CPF. These data indicate that developmental exposure to CPF induces long-term behavioral alterations in the mouse species and support the involvement of neural systems in addition to the cholinergic system in the delayed behavioral toxicity of CPF.

Effects of perinatal exposure to a polybrominated diphenyl ether (PBDE 99) on mouse neurobehavioural development

Polybrominated diphenyl ethers (PBDEs), a class of widely used flame retardants, are extensively diffused in the environment as shown by several studies on sentinel animal species, as well as humans. Of particular concern are the reported high levels of PBDEs in human milk, as almost no information is available on their potential effects on developing organisms. We investigated the effects of perinatal PBDE exposure on mouse neurobehavioural development. 2,2',4,4,5-pentabromodiphenylether (PBDE 99; 0.6, 6 and 30 mg/kg per day) was administered daily to CD-1 Swiss females by gavage from gestational day (GD) 6 to postnatal day (PND) 21. Aroclor 1254 (A1254; 6 mg/ kg per day), a PCB mixture, was administered following the same schedule and served as a positive controL The PBDE 99 medium dose had an effect on litter viability. Sensori-motor development analysis (PNDs 2-20) revealed a delayed appearance of climbing response in the PBDE 99 high-dose group. On PND 11, the homing test revealed a trend for treated animals, particularly the A1254 group, to be more active than controls. This activity level alteration was strongly increased on PNDs 34 and 60 in an open-field arena. On PND 60, treated mice showed also an altered thigmotaxis, spending more time in the centre of the arena than controls. At adulthood, A1254 treated mice were still hyperactive, whereas the PBDE 99 groups tended to be hypoactive. These findings showed that perinatal exposure to PBDE 99 produces several behavioural alterations and that its effects are not always similar to those of A1254. The possibility of exposure of neonates to PBDEs warrants further studies to characterise their developmental neurotoxicity.

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.

Neurobehavioral effects of prenatal lamivudine (3TC) exposure in preweaning mice

The present study provides a characterization of the behavioral changes induced in preweaning mice by prenatal exposure to lamivudine (3TC), an antiviral drug recently entered in the clinical practice to treat HIV patients. Pregnant CD1 mice were given per os bidaily either 3TC at different doses (125, 250, or 500 mg/kg) or vehicle solution (saline 0.9%) from pregnancy day 10 to delivery. Data on reproductive performance, such as gestation length, litter size, and offspring viability, were collected. Offspring were then examined for a series of different somatic and behavioral end points, including sensorimotor development, ontogenetic pattern of ultrasonic vocalization, passive avoidance learning, and locomotor activity. In the absence of gross changes in somatic and sensorimotor development, a slight change in ultrasound emission was found on postnatal day (PND) 3, with 125 and 500 mg/kg 3TC-treated offspring emitting a lower number of ultrasounds. Learning and retention performances of a passive-avoidance task on PND 20-21 were unaffected by 3TC treatment, while decreased habituation in an automated locomotor activity test was evident in male offspring exposed to 250 and 500 mg/kg 3TC.

Insulin-like growth factor-1 ameliorates age-related behavioral deficits

Insulin-like growth factor-1 has been found to be involved in the regulation of several aspects of brain metabolism, neural transmission, neural growth and differentiation. Because decreased insulin-like growth factor-1 and/or its receptors are likely to contribute to age-related abnormalities in behavior, the strategy of replacing this protein is one potential therapeutic alternative. The present study was designed to assess whether cognitive deficits with ageing may be partially overcome by increasing the availability of insulin-like growth factor-1 in the brain. Fischer-344 x Brown Norway hybrid (F1) male rats of two ages (four-months-old and 32-months-old) were preoperatively trained in behavioral tasks and subsequently implanted with osmotic minipumps to infuse the insulin-like growth factor-1 (23.5 microg/pump) or a vehicle, i.c.v. Animals were retested at two weeks and four weeks after surgery. Insulin-like growth factor-1 improved working memory in the repeated acquisition task and in the object recognition task. An improvement was also observed in the place discrimination task, which assesses reference memory. Insulin-like growth factor-1 had no effect on sensorimotor skills nor exploration, but mildly reversed some age-related deficits in emotionality. These data indicate a potentially important role for insulin-like growth factor-1 in the reversal of age-related behavioral impairments in rodents.

Ultrasonic vocalizations by infant laboratory mice: a preliminary spectrographic characterization under different conditions

During the first 2 to 3 weeks of life, isolated neonatal mice emit ultrasonic vocalizations, with various conditions such as hypothermia or olfactory or tactile stimulation eliciting this behavior. Although it is known that pup vocalizations stimulate prompt expression of maternal behavior, the communicative role of infant ultrasonic calls is still a matter of investigation. A fine-grained spectrographic analysis of ultrasonic calls emitted by pups exposed to different conditions was performed. Forty 8-day-old outbred CD-1 mice (Mus musculus) were isolated from their mothers and littermates and randomly exposed to one of the following conditions: (a) odor from the nest, (b) social isolation, (c) low temperature-isolation, (d) tactile stimulation, or (e) odor from a conspecific adult male. Upon consideration of the spectrogram typology and emission frequency interval, it appears that the conditions under which vocalizations are emitted influence the sound characteristics of call production.

Neurobehavioral development, adult openfield exploration and swimming navigation learning in mice with a modified beta-amyloid precursor protein gene

The processing of beta-amyloid precursor protein (betaAPP) and its metabolites plays an important role in the pathogenesis of Alzheimer's disease (AD) and Down's syndrome. The authors have reported elsewhere that a targeted mutation resulting in low expression of a shortened betaAPP protein (betaAPP(delta/delta)) entails reduced learning abilities. Here the authors investigate whether these effects were caused by postnatal developmental actions of the altered protein. The authors examined 35 mice carrying the betaAPP(delta/delta) mutation for somatic growth and sensorimotor development during the first 4 postnatal weeks (pw) and compared them with 31 wildtype litter-mates. Thereafter, the same mice were tested at about 10 weeks of age for openfield behavior and for swimming navigation learning. Mutant mice showed both transient and long-lasting deficits in development. Body weight deficit started to emerge at postnatal day (pd) 12, peaked with a 15.1% deficit at pd 27 and lasted until pw 33-37. Significant transient deficits in mutant mice during sensorimotor development were observed in three time windows (pd 3-10, pd 11-19 and pd 20-27), long-lasting effects, manifest at pw 8-12 and pw 33-37, emerged at any of the three periods. In the adult mice, exploratory activity of betaAPP mutants in the openfield arena was severely reduced. In the Morris water maze task, mutant mice showed moderate escape performance deficits during the acquisition period but no impairment in spatial memory. The authors conclude that a defective betaAPP gene impairs postnatal somatic development, associated with transient as well as long-lasting neurobehavioral retardation and muscular weakness. Comparison with earlier data suggests that early postnatal handling may attenuate some of the non-cognitive performance deficits in the water maze. Further, the manifestation and time course of behavioral yet not neuropathological symptoms in betaAPP mutant mice resemble in some aspects those of the human Down's syndrome.

Methodological analysis in behavioral toxicology: an ethotoxicological approach

A constraint in the development of laboratory animal models of human disease conditions is their applicability to the natural environment in which a given animal species evolved. The range of behavioral patterns that can be carefully assessed and quantified in the laboratory is sometimes limited. Although field studies reflect behavioral responses in natural settings, they may also have methodological limitations. Laboratory techniques are not applicable to wild species since natural conditions cannot be brought into a laboratory in an inexpensive or reliable way. However, it is possible to create near-natural settings which may not fulfill all the criteria of the actual context of evolution, but which can be controlled by the experimenter. We recommend an integrative style of approach considering laboratory constraints and, at the same time, the ecological niche in which a given behavioral pattern evolved. This type of ethological assessment may be useful when carrying out toxicological studies on both wild and laboratory mammals.

The role of the insulin-like growth factors in the central nervous system

Increasing evidence strongly supports a role for insulin-like growth factor-I (IGF-I) in central nervous system (CNS) development. IGF-I, IGF-II, the type IIGF receptor (the cell surface tyrosine kinase receptor that mediates IGF signals), and some IGF binding proteins (IGFBPs; secreted proteins that modulate IGF actions) are expressed in many regions of the CNS beginning in utero. The expression pattern of IGF system proteins during brain growth suggests highly regulated and developmentally timed IGF actions on specific neural cell populations. IGF-I expression is predominantly in neurons and, in many brain regions, peaks in a fashion temporally coincident with periods in development when neuron progenitor proliferation and/or neuritic outgrowth occurs. In contrast, IGF-II expression is confined mainly to cells of mesenchymal and neural crest origin. While expression of type I IGF receptors appears ubiquitous, that of IGFBPs is characterized by regional and developmental specificity, and often occurs coordinately with peaks of IGF expression. In vitro IGF-I has been shown to stimulate the proliferation of neuron progenitors and/or the survival of neurons and oligodendrocytes, and in some cultured neurons, to stimulate function. Transgenic (Tg) mice that overexpress IGF-I in the brain exhibit postnatal brain overgrowth without anatomic abnormality (20-85% increases in weight, depending on the magnitude of expression). In contrast, Tg mice that exhibit ectopic brain expression of IGFBP-1, an inhibitor of IGF action when present in molar excess, manifest postnatal brain growth retardation, and mice with ablated IGF-I gene expression, accomplished by homologous recombination, have brains that are 60% of normal size as adults. Taken together, these in vivo studies indicate that IGF-I can influence the development of most, if not all, brain regions, and suggest that the cerebral cortex and cerebellum are especially sensitive to IGF-I actions. IGF-I's growth-promoting in vivo actions result from its capacity to increase neuron number, at least in certain populations, and from its potent stimulation of myelination. These IGF-I actions, taken together with its neuroprotective effects following CNS and peripheral nerve injury, suggest that it may be of therapeutic benefit in a wide variety of disorders affecting the nervous system.