Behavior In Juvenile Rats Research Articles

The protective effect of S-adenosylmethionine on chronic adolescent stress-induced depression-like behaviors by regulating gut microbiota

The efficacy and tolerability of current antidepressants for adolescent depression are inadequate. S-adenosylmethionine (SAMe), known for its effectiveness and minimal side effects in adult depression, remains unstudied in adolescents. This study explored the potential of SAMe to address depression-like behaviors in juvenile rats induced by chronic unpredictable mild stress (CUMS), with a focus on gut microbiome interactions. Adolescent male Wistar rats were subjected to a 4-week CUMS regimen and received daily intraperitoneal injections of 300 mg/kg SAMe. Behavioral assessments included the sucrose preference test, elevated plus maze test, open field test, and Y-maze test. Histopathological changes of the hippocampus and colon were observed by Nissl staining and hematoxylin and eosin staining, respectively. Gut microbiome composition was analyzed using Accurate 16S absolute quantification sequencing. The results showed that SAMe significantly improved behavioral outcomes, reduced histopathological damages in hippocampal neurons and colon tissues, and modulated the gut microbiota of depressed rats. It favorably altered the ratio of Bacteroidetes to Firmicutes, decreased the absolute abundance of Deferribacteres, and adjusted levels of key microbial genera associated with depression-like behaviors. These results suggested that SAMe could effectively counter depression-like behaviors in CUMS-exposed adolescent rats by mitigating hippocampal neuronal and colon damage and modulating the gut microbiota. This supports SAMe as a viable and tolerable treatment option for adolescent depression, highlighting the importance of the gut-brain axis in therapeutic strategies.

Sex differences in the structure and function of the vasopressin system in the ventral pallidum are associated with the sex-specific regulation of social play behavior in juvenile rats

Vasopressin (AVP) regulates various social behaviors, often in sex-specific ways, including social play behavior, a rewarding behavior displayed primarily by juveniles. Here, we examined whether and how AVP acting in the brain's reward system regulates social play behavior in juvenile rats. Specifically, we focused on AVP signaling in the ventral pallidum (VP), a brain region that is a part of the reward system. First, we examined the organization of the VP-AVP system in juvenile rats and found sex differences, with higher density of both AVP-immunoreactive fibers and AVP V1a receptor (V1aR) binding in males compared to females while females show a greater number of V1aR-expressing cells compared to males. We further found that, in both sexes, V1aR-expressing cells co-express a GABA marker to a much greater extent (approx. 10 times) than a marker for glutamate. Next, we examined the functional involvement of V1aR-expressing VP cells in social play behavior. We found that exposure to social play enhanced the proportion of activated V1aR-expressing VP cells in males only. Finally, we showed that infusion of a specific V1aR antagonist into the VP increased social play behaviors in juvenile male rats while decreasing these behaviors in juvenile female rats. Overall, these findings reveal structural and functional sex differences in the AVP-V1aR system in the VP that are associated with the sex-specific regulation of social play behavior.

Puberty Blocker, Leuprolide, Reduces Sex Differences in Rough-and-Tumble Play and Anxiety-like Behavior in Juvenile Rats.

We examined the effect of the puberty blocker, leuprolide acetate, on sex differences in juvenile rough-and-tumble play behavior and anxiety-like behavior in adolescent male and female rats. We also evaluated leuprolide treatment on gonadal and pituitary hormone levels and activity-regulated cytoskeleton-protein messenger RNA levels within the adolescent amygdala, a region important both for rough-and-tumble play and anxiety-like behavior. Our findings suggest that leuprolide treatment lowered anxiety-like behavior during adolescent development, suggesting that the maturation of gonadotropin-releasing hormone systems may be linked to increased anxiety. These data provide a potential new model to understand the emergence of increased anxiety triggered around puberty. Leuprolide also reduced masculinized levels of rough-and-tumble play behavior, lowered follicle-stimulating hormone, and produced a consistent pattern of reducing or halting sex differences of hormone levels, including testosterone, growth hormone, thyrotropin, and corticosterone levels. Therefore, leuprolide treatment not only pauses sexual development of peripheral tissues, but also reduces sex differences in hormones, brain, and behavior, allowing for better harmonization of these systems following gender-affirming hormone treatment. These data contribute to the intended use of puberty blockers in stopping sex differences from developing further with the potential benefit of lowering anxiety-like behavior.

The medial preoptic area and its projections to the ventral tegmental area and the periaqueductal gray are activated in response to social play behavior in juvenile rats.

The medial preoptic area (MPOA) is well known for its role in sexual and maternal behaviors. This region also plays an important role in affiliative social behaviors outside reproductive contexts. We recently demonstrated that the MPOA is a central nucleus in which opioids govern highly rewarding social play behavior in adolescent rats. However, the neural circuit mechanisms underlying MPOA-mediated social play remain largely unresolved. We hypothesized that the MPOA unites a complementary neural system through which social play induces reward via a projection to the ventral tegmental area (VTA) and reduces a negative affective state through a projection to the periaqueductal gray (PAG). To test whether the two projection pathways are activated in response to social play behavior, we combined retrograde tract tracing with immediate early gene (IEG) expression and immunofluorescent labeling to identify opioid-sensitive projection pathways from the MPOA to VTA and PAG that are activated after performance of social play. Retrograde tracer, fluoro-gold (FG), was microinjected into the VTA or PAG. IEG expression (i.e., Egr1) was assessed and triple immunofluorescent labeling for mu opioid receptor (MOR), Egr1, and FG in the MPOA was performed after social play. We revealed that play animals displayed an increase in neurons double labeled for Egr1 + FG and triple labeled for MOR + Egr1 + FG in the MPOA projecting to both the VTA and PAG when compared to no-play rats. The increased activation of projection neurons that express MORs from MPOA to VTA or PAG after social play suggests that opioids may act through these projection pathways to govern social play. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

In utero and post-natal opioid exposure followed by mild traumatic brain injury contributes to cortical neuroinflammation, mitochondrial dysfunction, and behavioral deficits in juvenile rats

Maternal opioid use poses a significant health concern not just to the expectant mother but also to the fetus. Notably, increasing numbers of children born suffering from neonatal opioid withdrawal syndrome (NOWS) further compounds the crisis. While epidemiological research has shown the heightened risk factors associated with NOWS, little research has investigated what molecular mechanisms underly the vulnerabilities these children carry throughout development and into later life. To understand the implications of in utero and post-natal opioid exposure on the developing brain, we sought to assess the response to one of the most common pediatric injuries: minor traumatic brain injury (mTBI). Using a rat model of in utero and post-natal oxycodone (IUO) exposure and a low force weight drop model of mTBI, we show that not only neonatal opioid exposure significantly affects neuroinflammation, brain metabolites, synaptic proteome, mitochondrial function, and altered behavior in juvenile rats, but also, in conjunction with mTBI these aberrations are further exacerbated. Specifically, we observed long term metabolic dysregulation, neuroinflammation, alterations in synaptic mitochondria, and impaired behavior were impacted severely by mTBI. Our research highlights the specific vulnerability caused by IUO exposure to a secondary stressor such as later life brain injury. In summary, we present a comprehensive study to highlight the damaging effects of prenatal opioid abuse in conjunction with mild brain injury on the developing brain.

Effects of the Recurrent and Different Doses of Ketamine Exposure on Anxiety-like Behaviors and Locomotor Activity in Juvenile Rats.

Ketamine is a widely used anesthetic agent. Although the potential adverse effects of ketamine use in juvenile age are uncertain, certain studies reported that children exposed to recurrent anesthesia could face an increased risk of neurodevelopmental deficits in motor function and behavioral risks. We aimed to investigate the long-term effects of repeated exposure to various ketamine doses on anxious behavior and locomotor activity in juvenile rats. We aimed to investigate the long-term effects of repeated exposure to various ketamine doses on anxious behavior and locomotor activity in juvenile rats. Thirty-two Wistar Albino juvenile male rats were randomized into 5 mg/kg, 20 mg/kg, and 50 mg/kg ketamine (KET) and saline (Group C) Groups and KET was administered for 3 consecutive days at 3-hour intervals in 3 doses. Ten days after the last KET dose, behavioral parameters were analyzed with an open field test (OFT), elevated plus maze (EPM), and light-dark box (LDB). Satistical analysis was conducted with Kruskall-Wallis test followed by Dunn's Multiple Comparison Test. Unsupported rearing behavior decreased in 50 mg/kg KET Groups when compared to Group C. Incorrect transition time, total grooming time, and transfer latency time increased significantly in the 50 mg/kg KET Group when compared to Group C. These results suggested that 50 mg/kg KET led to anxiety-like behavior and destroyed memory and spatial navigation. Ketamine doses were associated with late effects of ketamine on anxiety- like behavior in juvenile rats. Further studies are needed to determine the mechanisms that play a role in the different effects of ketamine doses on anxiety and memory.

Neurobehavioral effects of cinnabar and the cinnabar-containing pediatric prescription, Yi-Nian-Jin, in juvenile rats

BackgroundCinnabar, a mercury-containing mineral medicine, has long been widely used in pediatric prescriptions. The safety of cinnabar-containing prescriptions, particularly for children, is drawing increasing attention worldwide. However, whether cinnabar and these pediatric prescriptions have adverse effects on neurobehavior is unknown. Yi-Nian-Jin (YNJ), a classic pediatric prescription, contains 5.66% (w/w) cinnabar, along with other four herbs. YNJ is widely prescribed to promote digestion, eliminate phlegm, and prevent constipation in children (aged 0–6 years). In this study, we used YNJ as an example of cinnabar-containing pediatric prescriptions to determine mercury absorption, distribution, and accumulation and further investigate its potential neurotoxicity in juvenile rats. Material and methodsLow (67.9 mg/kg), middle (169.8 mg/kg), and high dose (339.6 mg/kg) of cinnabar, and low (1.2 g/kg), middle (3.0 g/kg), and high dose (6.0 g/kg) of YNJ were used in this study, corresponding to 3, 7.5, and 15 times the clinically equivalent dose, respectively. Juvenile rats were orally administered different doses of cinnabar or YNJ for 14 consecutive days. The mercury content in rat blood and tissues (brain, liver, and kidney) and serum biochemical changes on day 14 of consecutive administration and on day 14 after cessation were measured. Moreover, a series of behavioral assays (open field, elevated plus-maze, and Morris water maze assays) were performed after 14 consecutive days of administration. ResultsThe mercury absorption, distribution, and accumulation of cinnabar and YNJ in juvenile rats were substantially different. Mercury in cinnabar was absorbed to a greater extent than that in YNJ, and the mercury content in cinnabar high-dose group (cinnabar-H) was approximately seven times higher than that in YNJ high-dose group (YNJ-H) on day 14 of administration. In contrast, compared with that of cinnabar, the mercury content in YNJ accumulated more in the tissues, especially in the brain and kidney. Repeated administration of cinnabar or YNJ did not affect liver function, renal function, learning, and memory in juvenile rats. However, repeated administration of YNJ at a high dose (6.0 g/kg) affected locomotor activity in juvenile rats. Repeated administration of cinnabar (339.6 mg/kg) or YNJ (>1.2 g/kg) induced anxiety-related behavior in juvenile rats. ConclusionsMercury in YNJ exhibited lower absorption but higher accumulation in tissues than those of the mercury in cinnabar. Consecutive oral administration of cinnabar or YNJ had no impact on liver function, renal function, learning, and memory, but could cause motor dysfunction and anxiety in juvenile rats.

Social Play Behavior Is Critical for the Development of Prefrontal Inhibitory Synapses and Cognitive Flexibility in Rats.

Sensory driven activity during early life is critical for setting up the proper connectivity of the sensory cortices. We ask here whether social play behavior, a particular form of social interaction that is highly abundant during postweaning development, is equally important for setting up connections in the developing prefrontal cortex (PFC). Young male rats were deprived from social play with peers during the period in life when social play behavior normally peaks [postnatal day 21-42] (SPD rats), followed by resocialization until adulthood. We recorded synaptic currents in layer 5 cells in slices from medial PFC of adult SPD and control rats and observed that inhibitory synaptic currents were reduced in SPD slices, while excitatory synaptic currents were unaffected. This was associated with a decrease in perisomatic inhibitory synapses from parvalbumin-positive GABAergic cells. In parallel experiments, adult SPD rats achieved more reversals in a probabilistic reversal learning (PRL) task, which depends on the integrity of the PFC, by using a more simplified cognitive strategy than controls. Interestingly, we observed that one daily hour of play during SPD partially rescued the behavioral performance in the PRL, but did not prevent the decrease in PFC inhibitory synaptic inputs. Our data demonstrate the importance of unrestricted social play for the development of inhibitory synapses in the PFC and cognitive skills in adulthood and show that specific synaptic alterations in the PFC can result in a complex behavioral outcome.SIGNIFICANCE STATEMENT This study addressed the question whether social play behavior in juvenile rats contributes to functional development of the prefrontal cortex (PFC). We found that rats that had been deprived from juvenile social play (social play deprivation - SPD) showed a reduction in inhibitory synapses in the PFC and a simplified strategy to solve a complex behavioral task in adulthood. Providing one daily hour of play during SPD partially rescued the cognitive skills in these rats, but did not prevent the reduction in PFC inhibitory synapses. Our results demonstrate a key role for unrestricted juvenile social play in PFC development and emphasize the complex relation between PFC circuit connectivity and cognitive function.

Binge drinking‐like behavior in juvenile rats causes long‐lasting cardiorespiratory dysfunction that persists until adulthood

Harmful alcohol abuse is associated with serious psychosocial and health damage, including cardiac and neurological morbidities. Americans drink 40% more than the global average and adolescents are the heaviest drinkers, displaying a pathological consumption pattern termed “binge drinking”, consisting in short episodes of heavy alcohol intake followed by long withdrawal periods. Despite adolescent binge drinking (ABD) drives severe impairments in neurological and cardiorespiratory function, there are no current health policies to prevent ABD or its physiological consequences. Indeed, little is known about the long‐term consequences of ABD in adulthood physiology. Therefore, we aimed to investigate the potential harmful effects of ABD on cardiac and respiratory (patho)physiology in the adult life. Sixteen male juvenile Sprague‐Dawley rats underwent ABD‐like alcohol administration protocol or control treatment, consisting of 2‐days “ON” and 2‐days “OFF” doses of ethanol (3.0 g/kg, 25% w/v in saline administered i. p.) beginning on post‐natal day (PND) 25 until PND 38. Once rats reached adulthood (PND80), respiratory and cardiac function were respectively assessed by whole‐body plethysmography and intraventricular pressure‐volume loops. Compared to controls, adult rats exposed to ABD displayed no differences in resting blood pressure, heart rate and pulmonary ventilation, but they showed a significant (p<0.05) increase in the breath‐to‐breath interval variability (40.8 ± 2.8 vs. 25.6 ± 2.3 ms; ABD vs. Control, respectively) and in the incidence of apneas/hypoapneas (AHI: 5.83 ± 0.40 vs. 2.50 ± 0.37 events/h; ABD vs. Control, respectively). Intraventricular cardiac function analysis using PV‐loops revealed a reduction in left ventricular compliance in ABD animals, evidenced by the augmented slope of the end diastolic pressure‐volume relationship (EDPVR: 0.0303 ± 0.006 vs. 0.009 ± 0.001 mmHg/µL; ABD vs. Control). Also, we found that ABD induced cardiac autonomic imbalance estimated by low/high frequency ratio of heart rate variability (LFHRV/HFHRV: 1.59 ± 0.23 vs. 1.01 ± 0.08) and increased arrhythmia incidence (53.6 ± 12.7 vs. 21.7 ± 5.7 events/h; ABD vs. Control). Our results shows that binge drinking in adolescence causes long‐lasting cardiorespiratory dysfunction that includes at least cardiac diastolic dysfunction, autonomic imbalance, and generation of irregular breathing all of them persisting until the adulthood.1Laboratory of Cardiorespiratory Control, Department of Physiology, Pontificia Universidad Católica de Chile, Santiago, Chile. 2Biomedical Department, Facultad of Health Science, Universidad de Antofagasta. 3Centro de Excelencia de Biomedicina en Magallanes (CEBIMA), Universidad de Magallanes, Punta Arenas, Chile. 4Centro de Envejecimiento y Regeneración CARE‐UC, Pontificia Universidad Católica de Chile, Santiago, Chile.

Fluoride Stimulates Anxiety- and Depression-like Behaviors Associated with SIK2-CRTC1 Signaling Dysfunction.

Using Sprague-Dawley rats and rat PC12 cells treated with sodium fluoride (NaF), we investigated the effects of SIK2-CRTC1 signaling on the neurobehavioral toxicity induced by fluoride. The in vivo results demonstrated that NaF treatment induced anxiety- and depression-like behaviors in juvenile rats, resulting in histological and ultrastructural abnormalities in the rat hippocampus and medial prefrontal cortex. Moreover, NaF exposure induced neuronal loss and excessive apoptosis. We also found that NaF elevated the expression of SIK2 and reduced the expression of CRTC1, brain-derived neurotrophic factor (BDNF), and VGF. The in vitro results showed that NaF suppressed cell viability, induced SIK2-CRTC1 signaling dysfunction, and caused excessive apoptosis in PC12 cells. Notably, targeted knockout of SIK2 with SIK2-siRNA or blocking of SIK2-CRTC1 signaling with 7,8-dihydroxyflavone (7,8-DHF) (as well as venlafaxine) can reduce apoptosis and increase cell viability in vitro. These findings suggest that neuronal death resulting from abnormal SIK2-CRTC1 signaling contributes to neurobehavioral toxicity induced by fluoride.

Corticosterone Induces Depressive-Like Behavior in Female Peri-Pubescent Rats, but Not in Pre-Pubescent Rats

Background There are no data on the effect of exogenous corticosterone on depressive-like behavior in juvenile rats. Furthermore, it has not been tested whether the effects of corticosterone in female rats is different before or after puberty. Objective We tested the effect of corticosterone treatment on female pre- and peri-pubescent juvenile rats on depressive-like behavior. Methods Female juvenile rats were divided into pre-pubescent (post-natal day 7–27) or peri-pubescent (post-natal day 28–48) groups and administered daily corticosterone (40 mg kg−1 day−1) for 21 days. Depressive-like behavior was assessed using a modified forced swim test and the sucrose preference test. After behavioral assessment, brains were analyzed to determine if there were changes in cell proliferation and newborn neuron survival in the dentate gyrus of the dorsal hippocampus. Results Chronic corticosterone treatment did not affect behavior or neurogenesis in female pre-pubescent juvenile rats. However, female peri-pubescent rats injected with corticosterone showed increased depressive-like behavior as well as a decrease in cell proliferation in the subgranular zone. Furthermore, there was an inverse correlation between time spent immobile in the forced swim test and cell proliferation in the granule cell layer in peri-pubescent rats. Conclusions Corticosterone induces depressive-like behavior in peri-pubescent, but not in pre-pubescent female rats. Finally, our results suggest that depressive-like behavior may be associated with a decrease in hippocampal cell proliferation in female peri-pubescent rats.

Involvement of the ventral tegmental area in socially rewarding behavior in juvenile rats

Involvement of the ventral tegmental area in socially rewarding behavior in juvenile rats

Systemic treatment with the enteric bacterial metabolic product propionic acid results in reduction of social behavior in juvenile rats: Contribution to a rodent model of autism spectrum disorder.

The role of the gut microbiome and its enteric metabolites, such as short-chain fatty acids (SCFAs), in the etiology of autism spectrum disorders (ASDs) has recently received increased attention. Of particular interest has been the SCFA, propionic acid (PPA). Several different rodent models have been developed using PPA treatment to examine behaviors of relevance to ASD. The effects of systemic (intraperitoneal, i.p.) administration of PPA on social behavior, anxiety-related behavior, and locomotor activity in juvenile male rats (age 35days) were examined in this study. Rats received seven i.p. injections of buffered PPA (500mg/kg) or phosphate-buffered saline. Behavior was video-recorded during social interaction in a large open field (first four injections) or assessed in an automated activity system (individual animals, last three injections). PPA treatment significantly reduced social interaction, increased anxiety-related behavior, and produced hypoactivity and increased abnormal motor movements. These findings suggest that PPA alters behaviors of relevance to ASD in juvenile rats. These results contribute to the behavioral validity of the rodent model of ASD with systemic PPA treatment.

Ghrelin, a Potential Antidepressant in Adult Rats, does not Reduce Depressive‐like Symptoms in Juvenile Rats

BackgroundDepression is a chronic psychiatric disorder that affects children and adolescents across the globe. There is an unmet need for better treatment options for juvenile patients. The brain‐gut peptide hormone ghrelin has been shown to reduce depressive‐like behavior and increase hippocampal neurogenesis in adult rodent models. However, there have been no studies to support this same role for ghrelin in behavior or neurogenesis in juvenile rats.MethodsGhrelin was dissolved in artificial cerebrospinal fluid (aCSF, vehicle) and injected via intracerebroventricular (icv) injection, using stereotaxic coordinates, in juvenile Sprague‐Dawley rats (PND 22, 51±1.3 g). To evaluate a dose‐response relationship and determine the most effective concentration of ghrelin (0.2, 0.5, or 1 nM), a Feeding Behavior Assay was used. Behavioral tests to measure peptide effects on depression included the Forced Swim Test (FST) and the Tail Suspension Test (TST). Hippocampal mitogenesis [mitotic cell division] and neurogenesis were quantified using immunohistochemistry: mitogenesis was visualized using the exogenous cell tracer BrdU, and neurogenesis was visualized using both BrdU and the endogenous neuronal marker NeuN.ResultsRats treated with 0.5 nM ghrelin, compared to the other concentrations tested, consumed the greatest amount of food; therefore, the 0.5 nM concentration of ghrelin was used in all subsequent experiments. The TST showed that the ghrelin treated rats spent more time immobile than the control rats (p=0.043, n=8/group), indicating a greater degree of depressive‐like behavior. On the other hand, the FST showed no difference in behavior between the groups. Furthermore, there was a larger inter‐individual variability in the FST than in the TST (p=0.007, n=8/group). Preliminary mitogenesis and neurogenesis experiments did not yield a difference between ghrelin and vehicle groups.ConclusionsFeeding behavior results indicated that 0.5 nM ghrelin produced the most potent peptide effect. The FST did not yield a difference between treatment and control groups. The TST was shown to work for juvenile rats, and it showed that ghrelin increases immobility time, compared to the vehicle group. Tests to measure depressive‐like behavior showed a significant increase in immobility time in the ghrelin treated group. These results suggest that ghrelin induces depressive‐like behavior in juvenile rats, which is in contrast with results obtained from adult rat studies, where ghrelin reduced depressive‐like behavior. This study further highlights the urgent need to better understand depression in juveniles, so that more effective treatment options are explored and developed. We are currently testing whether ghrelin treatment increases the rates of mitogenesis and neurogenesis to identify changes in brain regions implicated in the etiology of depression.Support or Funding InformationFunded by the A.T. Still University of Health Sciences ‐ Kirksville College of Osteopathic Medicine Graduate Program CommitteeThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Perinatal hypothyroidism increases play behaviors in juvenile rats

Thyroid hormones play an instrumental role in the development of the central nervous system. During early development, the fetus is dependent on maternal thyroid hormone production due to the dysfunction of its own thyroid gland. Thus, maternal thyroid dysfunction has been shown to elicit significant abnormalities in neural development, neurochemistry, and behavior in offspring. Previous reports have suggested that human maternal hypothyroidism may increase the chances of having children with autism spectrum disorder and attention-deficit/hyperactivity disorder. However, very few studies have evaluated social behaviors in animal models of perinatal hypothyroidism. To evaluate the possibility that hypothyroidism during development influences the expression one of the most commonly observed non-reproductive social behaviors, juvenile play, we used the validated rat model of perinatal hypothyroidism by methimazole administration (MMI; 0.025% in drinking water) from GD12-PD23. Control animals had regular drinking water. During adolescence (PD33-35), we tested subjects for juvenile play behavior by introducing them to a same-sex, unfamiliar (since weaning) littermate for 30min. Play behaviors and other behaviors (sleep, social contact, locomotion) were then scored. MMI-treated subjects played more than twice as much as control animals, and the increase in some behaviors was particularly dramatic in males. Locomotor and other affiliative social behaviors were unaffected. These data suggest that perinatal hypothyroidism may alter the organization of the neural networks regulating play behaviors, but not other social behaviors. Moreover, this implicates perinatal hypothyroidism as a potential etiological factor in the development of neurobehavioral disorders, particularly those characterized by heightened social interactions and impulsivity.

Neuroprotective Effects of Intranasal IGF-1 against Neonatal Lipopolysaccharide-Induced Neurobehavioral Deficits and Neuronal Inflammation in the Substantia Nigra and Locus Coeruleus of Juvenile Rats

Neonatal lipopolysaccharide (LPS) exposure-induced brain inflammation resulted in motor dysfunction and brain dopaminergic neuronal injury, and increased the risks of neurodegenerative disorders in adult rats. Our previous studies showed that intranasal administration of insulin-like growth factor-1 (IGF-1) protects against LPS-induced white matter injury in the developing rat brain. To further examine whether IGF-1 protects against LPS-induced brain neuronal injury and neurobehavioral dysfunction, recombinant human IGF-1 (rhIGF-1) at a dose of 50 µg/pup was administered intranasally 1 h following intracerebral injection of LPS (1 mg/kg) in postnatal day 5 (P5) Sprague-Dawley rat pups. Neurobehavioral tests were carried out from P7 to P21, and brain neuronal injury was examined at P21. Our results showed that LPS exposure resulted in disturbances of motor behaviors in juvenile rats. Moreover, LPS exposure caused injury to central catecholaminergic neurons, as indicated by a reduction of tyrosine hydroxylase (TH) immunoreactivity in the substantia nigra (SN), ventral tegmental area (VTA) and olfactory bulb (OB), and brain noradrenergic neurons, as indicated by a reduction of TH immunoreactivity in the locus coeruleus (LC) of the P21 rat brain. The LPS-induced reduction of TH+ cells was observed at a greater degree in the SN and LC of the P21 rat brain. Intranasal rhIGF-1 treatment attenuated LPS-induced central catecholaminergic neuronal injury and motor behavioral disturbances, including locomotion, beam walking test and gait analysis. Intranasal rhIGF-1 administration also attenuated LPS-induced elevation of IL-1β levels and numbers of activated microglia, and cyclooxygenase-2+ cells, which were double labeled with TH+ cells in the SN, VTA, OB and LC of the P21 rat brain. These results suggest that IGF-1 may provide protection against neonatal LPS exposure-induced central catecholaminergic neuronal injury and motor behavioral disturbances, and that the protective effects are associated with the inhibition of microglia activation and the reduction of neuronal oxidative stress by the suppression of the neuronal cyclooxygenase-2 expression.

Specific 50-kHz vocalizations are tightly linked to particular types of behavior in juvenile rats anticipating play.

Rat ultrasonic vocalizations have been suggested to be either a byproduct of physical movement or, in the case of 50-kHz calls, a means to communicate positive affect. Yet there are up to 14 distinct types of 50-kHz calls, raising issues for both explanations. To discriminate between these theories and address the purpose for the numerous 50-kHz call types, we studied single juvenile rats that were waiting to play with a partner, a situation associated with a high number of 50-kHz calls. We used a Monte-Carlo shuffling procedure to identify vocalization-behavior correlations that were statistically different from chance. We found that certain call types (“split”, “composite” and “multi-step”) were strongly associated with running and jumping while other call types (those involving “trills”) were more common during slower movements. Further, non-locomotor states such as resting and rearing were strongly predictive of a lack of vocalizations. We also found that the various sub-types of USVs can be clustered into 3–4 categories based on similarities in the way they are used. We did not find a one-to-one relationship between any movements and specific vocalizations, casting doubt on the motion byproduct theory. On the other hand, the use of specific calls during specific behaviors is problematic for the affect communication hypothesis. Based on our results, we suggest that ultrasonic calls may serve to coordinate moment-to-moment social interactions.

The Effect of Congenital and Postnatal Hypothyroidism on Depression-Like Behaviors in Juvenile Rats.

Objective:The aim of this study was to investigate depression-like behaviors of juvenile rats with congenital and postnatal hypothyroidism.Methods:Twenty-seven newborn rat pups were used. First, 6-month-old Wistar Albino female rats were impregnated. Methimazole (0.025% wt/vol) was given to dam rats from the first day of pregnancy until postnatal 21 days (P21) to generate pups with congenital hypothyroidism (n=8), whereas in the postnatal hypothyroidism group (n=10), methimazole was given from P0 to P21. In the control group (n=9), dam rats were fed ad libitum and normal tap water. Offspring were fed with breast milk from their mothers. The behavioral parameters were measured with the juvenile forced swimming test (JFST). The procedure of JFST consisted of two sessions in two consecutive days: the 15-minute pre-test on day 1 and the 5-minute test on day 2.Results:Increased immobility and decreased climbing duration were observed in both congenital and postnatal hypothyroidism groups. Decreased swimming duration was detected in the postnatal hypothyroidism group. Both hypothyroidism groups had a lower body weight gain compared with the control group, while the congenital hypothyroidism group had the lowest body weight.Conclusion:Our results showed that hypothyroidism had negative effects on depression-like behavior as well as on growth and development. Both congenital and postnatal hypothyroidism caused an increase in immobility time in JFST. New studies are required to understand the differing results on depression-like behavior between congenital and postnatal hypothyroidism.

Characterization of juvenile play in rats: importance of sex of self and sex of partner.

BackgroundJuvenile social play is observed in many mammalian species, and its disruption in several neuropsychiatric disorders has greatly increased interest in understanding the origins and sources of variability in this behavior.MethodsWe quantified social play behavior in juvenile rats and investigated the impact of sex and familiarity of the play partner. Sex differences in play behavior were investigated by comparing males and females from either same- or mixed-sex pairs with data pooled over 12 days of analysis. Whether play was altered based on the sex of the play partner was assessed using a paired analysis to compare play with a same- or opposite-sex play partner for both males and females. Additionally, a repeated measures design was utilized to determine whether play changed with increasing age. On postnatal day 33, a novel play partner was introduced. We used a repeated measures analysis to compare postnatal day 33 with the previous day. These approaches were used to assess the effects of age, sex, sex of partner, and familiarity of partner on total social play behavior as well as how play was broken down into components, such as pouncing, pinning, chasing, and boxing.ResultsThere were sex differences in total frequency of play, and specific parameters of play behavior, such as chasing, pouncing, pinning, and boxing. Additionally, males significantly altered their play behavior in response to the sex of their play partner, whereas females were more sensitive to the familiarity of the play partner.ConclusionsThis study provides critical groundwork for uncovering factors that regulate social play behavior and can be used to guide future mechanistic based work.

Dynamic changes in extracellular release of GABA and glutamate in the lateral septum during social play behavior in juvenile rats: Implications for sex-specific regulation of social play behavior

Social play is a motivated and rewarding behavior that is displayed by nearly all mammals and peaks in the juvenile period. Moreover, social play is essential for the development of social skills and is impaired in social disorders like autism. We recently showed that the lateral septum (LS) is involved in the regulation of social play behavior in juvenile male and female rats. The LS is largely modulated by GABA and glutamate neurotransmission, but their role in social play behavior is unknown. Here, we determined whether social play behavior is associated with changes in the extracellular release of GABA and glutamate in the LS and to what extent such changes modulate social play behavior in male and female juvenile rats. Using intracerebral microdialysis in freely behaving rats, we found no sex difference in extracellular GABA concentrations, but extracellular glutamate concentrations are higher in males than in females under baseline conditions and during social play. This resulted in a higher glutamate/GABA concentration ratio in males vs. females and thus, an excitatory predominance in the LS of males. Furthermore, social play behavior in both sexes is associated with significant increases in extracellular release of GABA and glutamate in the LS. Pharmacological blockade of GABA-A receptors in the LS with bicuculline (100ng/0.5μl, 250ng/0.5μl) dose-dependently decreased the duration of social play behavior in both sexes. In contrast, pharmacological blockade of ionotropic glutamate receptors (NMDA and AMPA/kainate receptors) in the LS with AP-5+CNQX (2mM+0.4mM/0.5μl, 30mM+3mM/0.5μl) dose-dependently decreased the duration of social play behavior in females, but did not alter social play behavior in males. Together, these data suggest a role for GABA neurotransmission in the LS in the regulation of juvenile social play behavior in both sexes, while glutamate neurotransmission in the LS is involved in the sex-specific regulation of juvenile social play behavior.