Juvenile Male Rats Research Articles

Effect of Silver Nanoparticles on Testes of Prepubertal Male Albino Rats and the Possible Protective Role of Vitamin E Supplement (Histological and Immunohistochemical Study)

Background: Silver nanoparticles (AgNPs) are one of the most eminent and commonly used nanoparticles in customer everyday products for both adults and children.Objective: This study objects to study the effect of prepubertal exposure of AgNPs on the histological structure of testis and the possible protective role of vitamin E.Materials and Methods: Twenty three days old juvenile male albino rats were used and divided into 3 groups. Group I control: subdivided into two subgroups: subgroup Ia (negative control), Rats received no treatment and sacrified at postnatal day (PND) 23 and 58. Subgroup Ib (vehicle control group), further subdivided into two subgroup Ib1, Ib2. Group II: subdivided into 2 subgroups: Subgroup IIa; rats treated with AgNPs intraperitoneally daily at dose of (50 μg /kg/day) for 35 days from 23 PND to 58 PND and Subgroup IIb; treated with AgNPs and vitamin E (vit. E) orally by gavage at a dose (150 mg /kg /day) dissolved in corn oil from age 23-58 PND, Group III; follow up group, rats received AgNPs left without treatment till 90 PND.Results: Testicular damage was also detected in AgNPs treated group as compared to the control group. Vit. E-treated subgroup and the follow up groups showed significant testicular improvement. A drastic decrease of testicular germinal epithelial height in AgNPs treated compared to control and vit. E treated rats. The expression of Bcl2 immunoreaction was also decreased in AgNPs-treated rats compared to the control and AgNPs and vit. E-treated groups.Conclusion: AgNPs induced structural changes on male reproductive system that can be ameliorated by Vit. E supplementation and limiting the exposure to the products rich in these particles.

Detrimental effects of the 'bath salt' methylenedioxypyrovalerone on social play behavior in male rats.

Methylenedioxypyrovalerone (MDPV) is the most popular synthetic cathinone found in products marketed as 'bath salts', widely abused among teenagers and young adults. Synthetic cathinones have pharmacological effects resembling those of psychostimulants, which are known to disrupt a variety of social behaviors. However, despite the popular use of MDPV by young people in social contexts, information about its effects on social behavior is scarce. To investigate the impact of MDPV on social behavior at young age, and the underlying neurobehavioral mechanisms, we focused on social play behavior. Social play behavior is the most characteristic social behavior displayed by young mammals and it is crucial for neurobehavioral development. Treatment with MDPV reduced social play behavior in both juvenile and young adult male rats, and its play-suppressant effect was subject to tolerance but not sensitization. As the behavioral effects of MDPV have been ascribed to dopaminergic and noradrenergic neurotransmission, and given the role of these neurotransmitters in social play, we investigated the involvement of dopamine and noradrenaline in the play-suppressant effects of MDPV. The effects of MDPV on social play were blocked by either the α2 adrenoceptor antagonist RX821002 or the dopamine receptor antagonist flupenthixol, given alone or together at sub-effective doses. In sum, MDPV selectively suppresses the most vigorous social behavior of developing rats through both noradrenergic and dopaminergic mechanisms. This study provides important preclinical evidence of the deleterious effects of MDPV on social behavior, and as such increases our understanding of the neurobehavioral effects of this popular cathinone.

Influence of in utero di-n-hexyl phthalate and di-cyclohexyl phthalate exposure on the endocrine glands and T3, T4, and TSH hormone levels of male and female rats: Postnatal outcomes.

The present study was designed to evaluate the effects of di-n-hexyl phthalate (DHP) and di-cyclohexyl phthalate (DCHP) on endocrine organs in rats. Oil control, 20-, 100-, and 500 mg/kg dose groups were selected and administered to pregnant rats on gestational days 6-19 by oral gavage. The neonatal stages of rats continued until postnatal day 20 and the- juvenile stages of rats continued until postnatal day of 32. The rats were allowed to mature until the neonatal and juvenile stages and there after, they were divided into four groups corresponding to the treatment levels. Body and organ weights were recorded, serum was collected, and thyroid, pancreas, pituitary gland, and adrenal gland were removed. There was a decrease in body weights in the 20- and 500mg/kg DHP and in the 20-mg/kg DCHP dose groups in neonatal male rats. In contrast, for female rats, there was an increase in body weights in the 100-mg/kg DCHP dose group and there was a decrease in body weights in the 500-mg/kg DHP dose group. Body weights were increased at 20 and 500 mg/kg in the DHP-exposed juvenile male rats. Serum thyroid-stimulating hormone (TSH) levels were increased in neonatal male rats, while they were increased in the 100-mg/kg DHP group of neonatal and juvenile female rats. Serum triiodothyronine (T3) levels were increased at the high dose of DHP for neonatal male rats and at the low and high dose levels of DCHP for female rats. Serum thyroxine (T4) levels were increased in neonatal rats for DHP. Also, some histopathological changes were observed in the thyroid, pancreas, adrenal, and pituitary gland. In conclusion, it was shown that DHP and DCHP caused negative effects on T3, T4, and TSH hormone levels.

PECULIARITIES OF UNITIOL INFLUENCE ON THE KIDNEY FUNCTIONING IN RATS OF THE JUVENILE AGE

This investigation shows an influence of different dosages of unitiol (sodium2,3-dimercaptopropanesulfonate) on the kidney functioning in juvenile rats.Purpose of the work is to study unitiol influence upon the kidney excretion function insexually mature rats at single and repeated injections.Material and methods. This investigation was performed on the juvenile male rats withthe body weight 95.0±8.5 g. The kidney functioning was determined for the single andrepeated (10, 20 and 30 days) injections of 5 % unitiol solution (50 mg/kg, subcutaneously)against a background of the additional water load realized through introduction of warmwater into the stomach in the volume of 5 % of the animal’s body weight. The concentrationOriginal research53Клінічна та експериментальна патологія. 2020. Т.19, №1(71) ISSN 1727-4338 https://www.bsmu.edu.uaof sodium, potassium ions, creatinine, proteins, ammonium, titratable acids and pH weredetermined in the rat’s urine and then compared with the corresponding values obtainedfrom the control and previous groups under study.Results. No significant changes were determined in the excretion and acid-regulationfunctions of the rat’s kidney in 2.5 hours after unitiol single injection against a backgroundof the water load. However, the concentration of sodium increased 1.7 times as large andthe concentration of potassium decreased correspondingly. No changes were registeredin diuresis while excretion of sodium increased 1.9 times as large, kaliuresis decreased1.6 times, sodium/potassium urine coefficient increased 2.6 times.After daily untiol injection during 10 days, concentration of sodium in the urine became3.2 times less in comparison with animal’s reaction to the single injection of the drugand 1.9 times less than that in the control group. Against a background of the 20 and30 days of the drug injection, the concentration of sodium has decreased almost thricecomparing to the control group value. Natriuresis decreased by 4 times comparing tothe value achieved after a single drug injection, decreased twice in comparison withthe control group and then it remained unchanged throughout the following 20- or 30-days long injections. No significant deviations from the control value were found in thepotassium concentration after the repeated injections of the drug. Kaliuresis decreasedafter the single injection but then it increased to its control value following the injection ofthe drug during 20 days. The urine sodium/potassium coefficient decreased 1.7-2.5 timescomparing to the control value after the repeated injections. No significant changes wereregistered throughout the entire experiment in the endogenous creatinine excretion andconcentration. The protein concentration decreased by 2.2 times comparing to its controllevel after unitiol application during 10 days and then it remained unchanged after 20-or 30-days long courses of injections. The indices of titratable acids and ammoniumexcretion became in 1.8 times less than those in the control group, then they increasedafter the 20th day and on the 30th day of injection they didn’t significantly differ fromthe control indices. The hydrogen excretion increased 2.4 and 2.8 times as large after20 and 30 days of the drug injection respectively at urine pH decrease. Unlike the singleinjection, the repeated unitiol injections significantly decrease natriuresis and the proteinexcretion with urine. Some age-related features of unitiol influence on the kidneys can beaccounted at different types of its administration as a chemical antidote.Conclusions. 1. Unitiol influence on the kidney functioning combined with the water loadin juvenile rats depends on the duration of application.2. The natriuretic effect increases and the kaliuretic effect decreases after a singleinjection of the drug when there is no significant influence on diuresis, excretion andacid-regulating parameters of the kidney. 3. A prolonged (10, 20, 30 days) application ofunitiol causes some intensification of sodium-retaining and hypoproteinuretic activitiescombined with some increase in the urine pH.

Prenatal chronic stimulation of the endocannabinoid system affects the respiratory motor outputs of juvenile male and female rats

The use of drugs of abuse during pregnancy can severely affect the development of physiological systems including the central respiratory network, mainly because prenatal period is extremely susceptible to external and pharmacological interventions that may cause postnatal consequences to the offspring. The endocannabinoid system is already present in the central nervous system in early stages of embryonic development, including in areas responsible for respiratory control. Nevertheless, the effect of external cannabinoids on the central cardiorespiratory network development as well as in the chemosensitivity and the future consequences during juvenile period is still unclear. Here, we evaluate the effects of prenatal exposure to cannabinoid on the respiratory motor outputs of juvenile (P27–28) male and female rats by using a decerebrated, arterially perfused in situ preparation. To this end, osmotic pumps were implanted subcutaneously in pregnant rats at embryonic day 0 and delivered vehicle (VEH) or CB1 receptor agonist (WIN 55212‐2, 0.5 mg/Kg/day) for 21 days. In situ preparations of juvenile rats were used for recording the respiratory motor and sympathetic outputs during normocapnia (5% CO2), hypercapnia (8% CO2) and stimulation of peripheral chemoreceptors with potassium cyanide (KCN; 25 μg in 50 μL). Our data showed that prenatal WIN exposure resulted in a tonic increase in phrenic burst amplitude in male animals, which was sustained during the KCN and CO2 challenge, while WIN‐treated females exhibited elevated phrenic burst frequency. The activity of the vagus nerve was also higher in male WIN‐treated animals, either under basal condition, KCN or hypercapnic exposure, although no effects were observed in the female group. The frequency of late‐expiratory events in abdominal activity, which indicate active expiration, was significantly higher (37%) for male treated animals during KCN stimulus, with no significant effects in the female group. In both sexes, prenatal WIN treatment did not modify the levels of thoracic sympathetic activity. These results suggest that prenatal chronic stimulation of endocannabinoid system promotes alterations in the respiratory network development affecting the activity of nerves responsible for the ventilatory motor drive during juvenile period. These effects seem to be potentiated in males.Support or Funding InformationFAPESP and CNPq

Water Deprivation Enhances the Late Expiratory Activity of Abdominal Nerve During Hypercapnia and Hypoxia in Rats

It is known that osmolarity challenges produce reflex adjustments in cardiorespiratory function. Herein, we investigated whether 48 h of water deprivation (WD) modifies respiratory pattern under room air conditions and in response to either hypercapnia or hypoxia using male juvenile (60–90 g) and adults (280–320 g) Holtzman rats. Control rats (n=6–7/group) had continuous access to tap water and food, whereas water‐deprived (WD; n=6–8/group) rats had water, but not food removed for 48 h before the experiments. Adult unanesthetized rats were placed in whole‐body plethysmographic chamber (5 L) for recording oxygen consumption (VO2), carbon dioxide production (VCO2) and ventilatory parameters. VO2 and VCO2 were evaluated under baseline conditions (room air), whereas respiratory frequency (fR) and tidal volume (VT) were measured during baseline, hypercapnia (7% CO2 balanced in 93% O2, for 5 min) or hypoxia (7% O2 balanced in N2, for 5 min). Decorticated, arterially‐perfused in situ preparations of juvenile rats were also used for recording respiratory motor outputs during normocapnia (5% CO2), hypercapnia (8% CO2) and while potassium cyanide (KCN; 25 μg in 50 μL) was intra‐arterially infused. WD rats presented a reduction in VO2 (18 ± 0.5 mL.kg−1.min−1 STPD, vs. control: 23 ± 1.2 mL.kg−1.min−1 STPD; p<0.05) and VCO2 (17 ± 0.5 mL.kg−1.min−1 STPD, vs. control: 26 ± 1.5 mL.kg−1.min−1 STPD; p<0.05). At baseline, WD rats exhibited increased VT (9.7 ± 0.5 mL.kg−1, vs. control: 7.7 ± 0.3 mL.kg−1; p<0.05), but reduced fR (76 ± 2 breaths.min−1, vs. control: 103 ± 7 breaths.min−1; p<0.05), resulting in similar ventilation (VE) between groups (746 ± 54 mL.kg−1.min−1, vs. control: 799 ± 64 mL.kg−1.min−1). During hypercapnia, WD rats had a higher increase in VT (15.3 ± 1.1 mL.kg−1, vs. control: 10.2 ± 0.3 mL.kg−1; p<0.05) and VE (1745 ± 202 mL.kg−1.min−1, vs. control: 1239 ± 49 mL.kg−1.min−1; p<0.05) compared to control rats, with similar increase in fR (112 ± 5 breaths.min−1, vs. control: 122 ± 6 breaths.min−1). Under hypoxia, WD rats presented a greater increase in VT (12.2 ± 0.4 mL.kg−1, vs. control: 8.1 ± 0.8 mL.kg−1; p<0.05) and VE (1247 ± 71 mL.kg−1.min−1, vs. control: 991 ± 84 mL.kg−1.min−1; p<0.05) than control rats, with a lower increase in fR (102 ± 4 breaths.min−1, vs. control: 122 ± 3 breaths.min−1; p<0.05). In in situ preparations, the respiratory motor outputs at baseline were not modified by WD, however, WD produced a greater increase in late expiratory activity of abdominal (ABD) nerve during hypercapnia (22 ± 2 μV, vs. control: 15 ± 2 μV; p<0.05) and hypoxia (14 ± 2 μV, vs. control: 7 ± 1 μV; p<0.05). The results show that 48 h of WD produces a hypometabolic stated, modifies baseline VE and enhances the ventilatory response to hypercapnia and hypoxia in conscious rats. The increased ABD nerve activity might contribute to ventilatory response after WD.Support or Funding InformationCapes, CNPq, FAPESP (grant numbers: 2015/23467‐7; 2017/04649‐2)

The possible ameliorative effect of carnosine in protein deficient diet induced testicular damage.

Background: Malnutrition due to protein deficiency is an emerging problem worldwide particularly in the developing countries. Reproductive system development and growth depends on maintaining healthy nutrition especially in childhood and adolescence. The present study aims at studying the possible protective efficacy of carnosine in testicular atrophy, defective spermatogenesis and reduced reproductive performance induced by supplementation of protein deficient diet (PDD) to male rats. Methods: Forty juvenile male albino rats were allocated into four equal groups; each group is 10 rats (i) normal control rats, (ii) protein deficient diet (PDD) group (received PDD for 75 days and saline intraperitoneal (IP) 5 days/week), (iii) carnosine (CAR) group (received carnosine 250 mg/kg body weight (bw), IP 5 days/week for 75 days); (iv) CAR-PDD group (received PDD for 75 days and carnosine 250 mg/kg body weight (bw), IP 5 days/week). Results: PDD supplementation lead to decreased body and testicular weights, reduced sex hormones and sperm count, motility and vitality (Live: Death ratio). In addition, the PDD-treated group had decreased levels of the antioxidant enzymes as reduced catalase (CAT) and glutathione (GSH) levels in testicular tissue. These toxic effects were accompanied by elevation of the pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-α). Increased proapoptotic marker; caspase-9 and decreased Bcl-2 was also found. On the other hand, CAR co-administration with PDD significantly evaded these effects which were confirmed histologically. Conclusion: CAR could be used as complementary supplements in malnutrition for protection against PDD induced testicular atrophy in male albino rats.

Hippocampal cognitive impairment in juvenile rats after repeated mild traumatic brain injury

There is growing awareness that repeated mild traumatic brain injury (r-mTBI) can cause deficits in learning and memory performance, however there is still a paucity of preclinical data identifying the extent of these deficits. Epidemiological data shows that juveniles are at high risk to sustain r-mTBI, and these injuries may cause significant changes in cognitive abilities, as they occur during a period where the brain is still maturing. This is particularly true for the hippocampus, a brain region important for learning and memory processes. R-mTBI during the juvenile period may disrupt functional capacity of the hippocampus, and thus the normal development of cognitive processes associated with this structure. To examine this issue we used a model of awake closed head injury (ACHI) and administered 8 impacts over a 4 day period to juvenile male and female rats (P25-28). A neurological assessment was preformed after each impact, and anxiety and learning related behaviours were examined 1 and 7 days after the last impact. Our results indicate that r-mTBI was associated with sensorimotor deficits in the acute phase immediately after each procedure. R-mTBI also reduced the capacity for hippocampal-dependent learning for at least 7 days post-injury, but did not result in any long-lasting changes in anxiety-related behaviours.

Histone deacetylase inhibition reduces ventral tegmental area dopamine neuronal hyperexcitability involving AKAP150 signaling following maternal deprivation in juvenile male rats.

Traumatic early life stress (ELS) is linked to dopamine (DA) dysregulation which increases the probability of developing psychiatric disorders in adolescence and adulthood. Our prior studies demonstrated that a severe early life stressor, a 24-hr maternal deprivation (MD) in juvenile male rats, could lead to altered DA signaling from the ventral tegmental area (VTA) due to impairment of GABAergic synaptic plasticity (promoting GABAergic long-term depression, LTD) with concomitant changes in the abundance of synaptic regulators including A-kinase anchoring protein (AKAP150). Importantly, these MD-induced synaptic changes in the VTA were accompanied by upregulation of histone deacetylase 2, histone hypoacetylation, and were reversible by HDAC inhibition. Using cell-attached and whole-cell patch clamp recordings, we found that MD stress also increased spontaneous VTA DA neuronal activity and excitability in juvenile male rats without affecting intrinsic excitability. Postsynaptic chemical disruption of AKAP150 and protein kinase A interaction increased VTA DA neuronal excitability in control non-MD rats mimicking the effects of MD on DA cell excitability with similar changes in membrane properties. Interestingly, this disruption decreased MD-induced VTA DA hyperexcitability. This MD-induced DA neuronal hyperexcitability could also be normalized at 24hr after injection of the class 1 HDAC inhibitor, CI-994. Altogether, our data suggest that AKAP150 plays a critical role in the regulation of VTA DA neuronal excitability and that HDAC-mediated targeting of AKAP150 signaling could normalize VTA DA dysfunction following ELS thereby providing novel therapeutic targets for prevention of later life psychopathology.

Early weaning modulates eating behavior and promotes hypofunction of the serotonergic (5HT) system in juvenile male rats.

Early life stress (ELS) has been associated with developmental impairments. Early weaning (EW)is a postnatal stress model consisting of interruption of lactation and maternal care. The 5HT-system has been associated with neurobehavioral modulations promoted by ELS. Thus, the present work aims to investigate the effects of early weaning on feeding behavior and serotonergic system of juvenile male rats. For this, rats were submitted to early (PND15) or natural (PND30) weaning and had the body weight, food intake in circadian phases, and food intake in response to fenfluramine assessed. mRNA expression of serotoninergic receptors (5HT1A and 5HT2C) and transporter (SERT) was assessed in the hypothalamus and brainstem, as well as NPY and POMC mRNA expression in hypothalamus. The results show that early weaning promoted changes in the percentage of weight gain during lactation period and increase in body weight at PND40. It was also observed that EW promoted increase and decrease in food intake in light and dark phase, respectively, and leads to a decreased action of fenfluramine on inhibition of food intake. In addition, early weaning promoted increased NPY and SERT mRNA expression in the hypothalamus and 5HT2C in the brainstem. Together, the data indicate that the stress caused by early weaning impairs the eating behavior of juvenile male rats through hypofunction of the 5HT-system.

Reproductive disorders in male rats induced by high-fructose consumption from juvenile age to puberty.

There is compelling evidence that a hypercaloric, high-fructose diet can cause metabolic syndrome (MetS) and a whole range of other metabolic changes. In the context of androgen deficiency, MetS in boys merits special attention, but the effects of fructose-rich diet in youth on future male reproductive function are still poorly evidenced. The aim of this study was to address this issue and analyse the effects of high-fructose intake starting from weaning to puberty (postnatal day 23 up to 83) on the reproductive function of male rats. For this purpose juvenile male Wistar rats were divided in two groups: control and the group receiving 10 % fructose solution instead of drinking water. Reproductive function was evaluated in terms of fertility, sperm count, testes/epididymis morphology, and serum sex hormones. The fructose-treated group showed a decrease in testosterone and twofold increase in luteinising and follicle-stimulating hormone levels in the serum. This was accompanied with lower testis/epididymis weights, sperm count, and changed testis/epididymis morphology. Their fertility remained unchanged, but the fertility of females mating with these males diminished. In addition, pre-implantation and post-implantation embryonic death rate rose in these females. Our results have confirmed that high fructose consumption from early age until puberty can impair the reproductive function of male rats, and call for further animal and epidemiological investigation.

Acute and Persistent Alterations of Cerebellar Inflammatory Networks and Glial Activation in a Rat Model of Pediatric Mild Traumatic Brain Injury.

Following a traumatic brain injury (TBI), inflammation is a well-documented but poorly understood phenomenon, especially at later time-points (i.e., beyond 72 h) and in brain areas outside the cortex. The cerebellum, important for motor and cognitive functioning, represents an area of the brain equally affected by TBI that is seldom evaluated despite its potential involvement in persistent deficits after injury. In the context of TBI and inflammation, most studies focus on severe TBI in adult males, with fewer studies on pediatric mild TBI in both sexes. Our study addresses this gap by profiling neurological function and cerebellar inflammation over time in the juvenile male and female rat brain following a mild, closed-head weight-drop injury (mTBI). At 24 h, 72 h, 7 days, and 21 days post-mTBI, animals were subjected to behavioral testing to evaluate TBI effects over time. Alongside behavioral deficits up to 7 days post-injury, inflammatory profiling by multi-plex enzyme-linked immunosorbent assay (ELISA) revealed increased inflammatory markers, including CXCL1, interleukin (IL)-5, and vascular endothelial growth factor alpha (VEGFα), in plasma at 24-72 h and in the cerebellum at 72 h post-injury. Network analysis of cytokines also showed increased inter-relationships between multiple mediators at all time-points, emphasizing the persistent and dynamic changes to inflammatory patterns after mTBI. Transcript levels of microglia/macrophage activation markers, including Iba1 and CX3CR1, were significantly elevated at 7 days post-TBI in both sexes, and at 21 days in females, suggesting activation of immune cells in the cerebellum. When examining the protein expression of GFAP and CX3CR1, a significant increase in CX3CR1 was noted in males at 21 days but not in females. Characterizing the evolution of cerebellar inflammation in pediatric mTBI provides insight into potential mechanisms of persistent changes that could contribute to neurological dysfunction.

Traffic-related particulate matter affects behavior, inflammation, and neural integrity in a developmental rodent model

Recent studies indicate that exposure to airborne particulate matter (PM) is associated with cognitive delay, depression, anxiety, autism, and neurodegenerative diseases; however, the role of PM in the etiology of these outcomes is not well-understood. Therefore, there is a need for controlled animal studies to better elucidate the causes and mechanisms by which PM impacts these health outcomes. We assessed the effects of gestational and early life exposure to traffic-related PM on social- and anxiety-related behaviors, cognition, inflammatory markers, and neural integrity in juvenile male rats. Gestating and lactating rats were exposed to PM from a Boston (MA, USA) traffic tunnel for 5 h/day, 5 days/week for 6 weeks (3 weeks gestation, 3 weeks lactation). The target exposure concentration for the fine fraction of nebulized PM, measured as PM2.5, was 200 μg/m3. To assess anxiety and cognitive function, F1 male juveniles underwent elevated platform, cricket predation, nest building, social behavior and marble burying tests at 32–60 days of age. Upon completion of behavioral testing, multiple cytokines and growth factors were measured in these animals and their brains were analyzed with diffusion tensor MRI to assess neural integrity. PM exposure had no effect on litter size or weight, or offspring growth; however, F1 litters developmentally exposed to PM exhibited significantly increased anxiety (p = 0.04), decreased cognition reflected in poorer nest-organization (p = 0.04), and decreased social play and allogrooming (p = 0.003). MRI analysis of ex vivo brains revealed decreased structural integrity of neural tissues in the anterior cingulate and hippocampus in F1 juveniles exposed to PM (p < 0.01, p = 0.03, respectively). F1 juvenile males exposed to PM also exhibited significantly decreased plasma levels of both IL-18 (p = 0.03) and VEGF (p = 0.04), and these changes were inversely correlated with anxiety-related behavior. Chronic exposure of rat dams and their offspring to traffic-related PM during gestation and lactation decreases social behavior, increases anxiety, impairs cognition, decreases levels of inflammatory and growth factors (which are correlated with behavioral changes), and disrupts neural integrity in the juvenile male offspring. Our findings add evidence that exposure to traffic-related air pollution during gestation and lactation is involved in the etiology of autism spectrum disorder and other disorders which include social and cognitive deficits and/or increased anxiety.

Developmental exposure to low levels of ethinylestradiol affects social play in juvenile male rats.

Juvenile social play contributes to the development of adult social and emotional skills in humans and non-human animals and is therefore a useful endpoint to study the effects of endocrine disrupters on behavior in animal models. Ethinylestradiol (EE2), a widely produced, powerful synthetic estrogen is widespread in the environment mainly because it is a component of the contraceptive pill. To understand whether clinical or environmental exposure to EE2 during critical perinatal periods can affect male social play, we exposed 72 male Sprague-Dawley rats to EE2 or vehicle either during gestation (from gestation day (GD) 5 through 20) or during lactation (from postnatal day (PND) 1 through 21). Two doses of EE2 were used to treat the dams: a lower dose in the range of possible environmental exposure (4ng/kg/day) and a higher dose similar to that received during contraceptive treatment (400ng/kg/day). Social play was observed between PND 40 and 45. A principal component analysis (PCA) of frequencies of behavioral items observed during play sessions allowed to allocate behaviors to the two main components that we named aggressive-like play and defensive-like play. Aggressive-like play was increased by gestational and decreased by lactational exposure. Defensive-like play was decreased by treatment. For both types of play the lower dose (4ng/kg/day) was as effective as the higher one. Total social activity was increased by gestational and decreased by lactational exposure. These findings provide further evidence that exposure to low and to very low doses of EE2 during critical periods of development can affect essential aspects of social behavior, and that the timing of exposure is critical to understand its developmental action.

Ghrelin Induces Place Preference for Social Interaction in the Larger Peer of a Male Rat Pair

Social interaction is important for survival in most social species including humans. To ensure social activities, individuals experience reward from social interaction, generating a powerfully reinforcing process. Here we hypothesized that reward from social interaction in a juvenile male rat pair may be enhanced by ghrelin, a circulating hormone that has been shown to enhance reward from other natural (e.g. food, sex) as well as artificial reinforcers (e.g. alcohol and other drugs of abuse). To this end, we assessed the impact of ghrelin and a ghrelin antagonist on preference for a chamber previously paired to the presence of a social partner in a conditioned place preference paradigm. We found that ghrelin increased and a ghrelin antagonist decreased preference for social interaction, but only in the heavier partner in a social pair. In addition, we found that administered ghrelin induced a positive association between preference for social interaction and body weight difference within socially interacting pairs, where larger ghrelin treated rats preferred social interaction, whereas smaller ghrelin treated rats avoided it, which raises the question if ghrelin could have a role in implementing social hierarchies in rats. In summary, we conclude that ghrelin signaling increases the reward from social interaction in a manner that reflects the degree of divergence in body weight between the social pair.

Activation of oestrogen receptor α induces a novel form of LTP at hippocampal temporoammonic-CA1 synapses.

17β estradiol (E2) rapidly regulates excitatory synaptic transmission at the classical Schaffer collateral (SC) input to hippocampal CA1 neurons. However, the impact of E2 on excitatory synaptic transmission at the distinct temporoammonic (TA) input to CA1 neurons and the oestrogen receptors involved is less clear. Extracellular recordings were used to monitor excitatory synaptic transmission in hippocampal slices from juvenile male (P11-24) Sprague Dawley rats. Immunocytochemistry combined with confocal microscopy was used to monitor the surface expression of the AMPA receptor (AMPAR) subunit, GluA1 in hippocampal neurons cultured from neonatal (P0-3) rats. Here, we show that E2 induces a novel form of LTP at TA-CA1 synapses, an effect mirrored by the ERα agonist, PPT, and blocked by an ERα antagonist. ERα-induced LTP is NMDA receptor (NMDAR)-dependent and involves a postsynaptic expression mechanism that requires PI 3-kinase signalling and synaptic insertion of GluA2-lacking AMPARs. ERα-induced LTP has overlapping expression mechanisms with classical Hebbian LTP, as HFS-induced LTP occluded PPT-induced LTP and vice versa. In addition, activity-dependent LTP was blocked by the ERα antagonist, suggesting that ERα activation is involved in NMDA-LTP at TA-CA1 synapses. ERα induces a novel form of LTP at juvenile male hippocampal TA-CA1 synapses. As TA-CA1 synapses are implicated in episodic memory processes and are an early target for neurodegeneration, these findings have important implications for the role of oestrogens in CNS health and neurodegenerative disease.

The role of the estrogen receptor-α gene, Esr1, in maternal-like behavior in juvenile female and male rats

The estrogen receptor-alpha (ER-α) is an important ligand activated transcription factor that works to control gene transcription in many species. Previous studies have shown estrogen to be an important hormone in the regulation of maternal behavior. Like adult female rats, both male and female juvenile rats exhibit increased level of maternal-like behavior when exposed to pups. The aim of this study was to determine whether ER-α is critical for the expression of maternal-like behavior in juvenile male and female rats. ER-α knock-out and wildtype (WT) juvenile male and female rats were generated and tested for maternal behaviors. Latencies to display maternal-like behaviors that included retrieval, grouping and crouching responses, revealed no genotype differences between KO and WT subjects. Male juvenile rats exhibited slightly shorter latencies than WT juvenile female rats indicating a sex difference in the latency to display these responses. Additionally, ER-α KO females exhibited a delay in onset of vaginal opening compared to WT females, indicating a role for ER-α in sexual maturation. The behavioral findings indicate that ER-α is not obligatory for the expression of full maternal-like behavior in male and female juvenile rats. Understanding this neurobiological system will help to elucidate the developmental involvement of the endocrine and brain networks in the regulation of maternal behaviors in mammals.

Ultrastructure characterization of pancreatic β-cells is accompanied by modulatory effects of the HDAC inhibitor sodium butyrate on the PI3/AKT insulin signaling pathway in juvenile diabetic rats

Genetic and epigenetic factors contribute equally to the pathogenesis of type 1 diabetes mellitus. Sodium butyrate (NaB) has been reported to improve glucose homeostasis by modulation of the p38/ERK MAPK pathway. This work aims to evaluate the effect of NaB on the ultrastructure of pancreatic β-cells and the PI3/AKT pathway. Juvenile albino male rats were used to establish a type 1 diabetes model using streptozotocin injection and NaB in a pre- and post-treatment schedule. Plasma glucose, insulin levels, and glucose tolerance were evaluated. Light and electron microscopy and immunohistochemistry were performed using Ki-67, caspase-3, and insulin. NaB treatment resulted in a significant improvement in plasma glucose levels, plasma insulin levels/expression, and ameliorated diabetes-induced histological alternations. Additionally, it increased the expression of phosphorylated AKT. These findings provide evidence that NaB may be useful in the treatment of juvenile diabetes.

An age- and sex-dependent role of catecholaminergic neurons in the control of breathing and hypoxic chemoreflex during postnatal development

The respiratory system undergoes significant development during the postnatal phase. Maturation of brainstem catecholaminergic (CA) neurons is important for the control and modulation of respiratory rhythmogenesis, as well as for chemoreception in early life. We demonstrated an inhibitory role for CA neurons in CO2 chemosensitivity in neonatal and juvenile male and female rats, but information regarding their role in the hypoxic ventilatory response (HVR) is lacking. We evaluated the contribution of brainstem CA neurons in the HVR during postnatal (P) development (P7-8, P14-15 and P20-21) in male and female rats through chemical injury with conjugated saporin anti-dopamine beta-hydroxylase (DβH-SAP, 420 ng·μL−1) injected in the fourth ventricle. Ventilation (V̇E) and oxygen consumption were recorded one week after the lesion in unanesthetized rats during exposure to normoxia and hypoxia. Hypoxia reduced breathing variability in P7-8 control rats of both sexes. At P7-8, the HVR for lesioned males and females increased 27% and 24%, respectively. Additionally, the lesion reduced the normoxic breathing variability in both sexes at P7-8, but hypoxia partially reverted this effect. For P14-15, the increase in V̇E during hypoxia was 30% higher for male and 24% higher for female lesioned animals. A sex-specific difference was detected at P20-21, as lesioned males exhibited a 24% decrease in the HVR, while lesioned females experienced a 22% increase. Furthermore, the hypoxia-induced body temperature reduction was attenuated in P20-21 lesioned females. We conclude that brainstem CA neurons modulate the HRV during the postnatal phase, and possibly thermoregulation during hypoxia.

Relationships between play and responses to tickling in male juvenile rats

Play is a putatively positive experience and of key interest to the study of affective state in animals. Rats produce 50 kHz ultrasonic vocalisation (USVs) during positive experiences, including social play and tickling. The tickling paradigm is intended to mimic social play resulting in positively valanced ultrasonic vocalisation (USV) production. We tested two hypotheses on the relationship between tickling and play: that tickling would increase play behaviour or that play behaviour would increase in anticipation of tickling, and that tickling would share some specific properties of play (rebound and emotional contagion of unexposed cage mates). Male Wistar rats (N = 64, with 32 rats/cohort) of 28 days of age were housed in pairs with one rat assigned to be tickled and one as the non-tickled control. Production of 50 kHz USVs and hand-following behaviour was measured. Prior to handling, solitary and social play was recorded for 5 min in the home cage. A two-day break in tickling was used to assess a potential rebound increase in responses to tickling. Only one rat within each cage was handled to assess emotional contagion through changes in the behaviour of the cage-mate. Solitary but not social play increased prior to tickling relative to controls (p = 0.01). There were marked differences between cohorts; tickled rats in C2 produced less 50 kHz USVs than those in C1 (p = 0.04) and overall, C2 rats played less than rats in C1 (social p = 0.04 and solitary p < 0.001) and had a lighter start weight on arrival (p = 0.009) compared with cohort 1 (C1). In C1, there was evidence of rebound in USV production (p < 0.001) and a contagious effect of tickling reflected by increased hand-following in cage mates (p = 0.02). We found a positive relationship between start weight and USV responses to tickling (Rs = 0.43, p < 0.001), suggesting that the divergence in USV production may be due to developmental differences between cohorts. The results suggest that the relationship between tickling and play is complex in that tickling only affected solitary and not social play, and that tickling responses showed rebound and contagion effects on cage-mates which were specific to cohort responses to tickling.