Adolescent Male Rats Research Articles

Abstract # 3111 Chronic adolescent stress differentially sensitizes neuro-immune reactivity in male and female rats

Adversity early in life is a reliable predictor of mood disorders which involve excessive innate immune signaling. However, the mechanisms by which early life adversity promotes inflammation are not yet fully understood. Using a chronic adolescent stress (CAS) model in rats, we hypothesized that a history of CAS exaggerates induction of the pro-inflammatory NF-kappa-B pathway in adult rat hippocampus without impacting the peripheral immune response. We assessed potential sex differences to determine whether females, who suffer from mood disorders twice as often as males, are disproportionally affected by stress-primed inflammation. Male and female adolescent rats underwent the CAS paradigm or received no stress. Six weeks following the last stressor, all rats received a single systemic injection of either lipopolysaccharide (LPS) or vehicle to unmask possible immune-priming effects of CAS. RNA-Seq revealed that upon LPS stimulation, both male and female CAS rats displayed enhanced enrichment of the NF-kappa-B pathway in the hippocampus compared to non-stressed, same-sex controls. Peripheral inflammatory indices including splenic NF-kappa-B activity, serum cytokine and corticosterone concentrations were not altered by CAS in females, suggesting brain-specific CAS impact. Conversely, CAS males displayed lower serum corticosterone and exaggerated serum IL-1beta responses following LPS, suggesting glucocorticoid resistance. We conclude that while CAS enhances neuro-immune reactivity in both males and females months removed from the stressor exposure, the mechanism and manifestation of such alterations are sex-specific.

Sex differences in the intensity of cross-sensitization between methylphenidate and amphetamine in adolescent rats

Chronic use of psychostimulants such as methylphenidate (MPD) and amphetamine (Amph) leads to abuse and dependence. Cross-sensitization occurs when exposure to a drug causes a significant intensified response to a different drug as compared to the effect of the drug in subjects with no previous exposure. Cross-sensitization is used as an experimental correlate for a drug's potential to elicit dependence. The present study uses male and female adolescent rats to examine whether cross-sensitization occurs with MPD, a drug not traditionally considered to elicit dependence, and Amph, a drug considered to elicit dependence. The results showed that there is cross-sensitization with MPD to Amph in adolescent rats and that there is a significant difference in male and female responses. Cross-sensitization between MPD and Amph was observed in a linear dose dependent manner in males and in an inverted U-shape pattern in females. Males treated with the highest dose of 10.0 mg/kg MPD and females treated with the mid-dose of 2.5 mg/kg MPD showed the most robust cross-sensitization. Overall, adolescent female rodents had a greater intensity of response to MPD, Amph, and cross-sensitization between MPD and Amph. This study shows that there are significant sex differences in psychostimulant cross-sensitization in adolescence, indicating the maturity of the gonadal system is not the predominant reason for differences between male and female responses to psychostimulant drugs.

P.1.15 Impaired diacylglycerol kinase eta function in bipolar patient-derived human induced pluripotent stem cells

Although ketamine has long been known to increase locomotor activity, only recently was it realized that this behavioral effect varies according to both sex and age. The purpose of the present study was threefold: first, to measure the locomotor activating effects of ketamine in male and female rats across early ontogeny and into adulthood; second, to assess ketamine and norketamine pharmacokinetics in the dorsal striatum and hippocampus of the same age groups; and, third, to use curvilinear regression to determine the relationship between locomotor activity and dorsal striatal concentrations of ketamine and norketamine. A high dose of ketamine (80 mg/kg, i.p.) was administered in order to examine the complete cycle of locomotor responsiveness across a 280-min testing session. In separate groups of rats, the dorsal striata and hippocampi were removed at 10 time points (0–360 min) after ketamine administration and samples were assayed for ketamine, norketamine, and dopamine using HPLC. In female rats, ketamine produced high levels of locomotor activity that varied only slightly among age groups. Male preweanling rats responded like females, but adolescent and adult male rats exhibited lesser amounts of ketamine-induced locomotor activity. Ketamine and norketamine pharmacokinetics, especially peak values and area under the curve, generally mirrored age- and sex-dependent differences in locomotor activity. Among male rats and younger female rats, dorsal striatal ketamine and norketamine levels accounted for a large proportion of the variance in locomotor activity. In adult female rats, however, an additional factor, perhaps involving other ketamine and norketamine metabolites, was influencing locomotor activity.

Withdrawal from Brief Repeated Alcohol Treatment in Adolescent and Adult Male and Female Rats.

Early initiation of alcohol drinking has been associated with increased risk of alcohol dependence in adulthood. Although negative affect mediated in part by corticotropin-releasing factor (CRF) is a strong motivator for alcohol consumption in adults, comparisons of alcohol withdrawal in adolescents and adults generally have not included CRF-related measures such as anxiety. The purpose of the present study was to compare withdrawal signs including anxiety-like behavior after a brief multiday alcohol treatment in adolescent and adult male and female rats. Animals were treated with a 5-day regimen of alcohol injections (3 daily intraperitoneal injections of 1.5g/kg at 3-hour intervals, total of 15) starting on postnatal day (PN) 28 or PN 70. Spontaneous withdrawal signs and anxiety-like behavior (light/dark box) were assessed 18hours after the last injection as described. One cohort of rats was treated with alcohol, killed 18hours after the last injection, and blood was collected to assess corticosterone. Another cohort of rats was treated with alcohol or vehicle, given 1, 2, or 3 alcohol injections (1.5g/kg), and killed 1hour after final injection to determine blood alcohol concentration (BAC). Finally, adult and adolescent males and females received 5days of alcohol or vehicle treatment followed by a final challenge with alcohol (3g/kg), and blood was collected for corticosterone. BAC was comparable in adolescents and adults. Spontaneous withdrawal signs were comparable in adolescents and adults, and no sex differences were observed. Anxiety-like behaviors (time and distance in light, latency to emerge, and light entries) differed in alcohol- and vehicle-treated adults but not adolescents. Corticosterone was not elevated at withdrawal. Alcohol increased corticosterone significantly in vehicle-treated animals, but both adolescents and adults were tolerant to alcohol-induced elevation of corticosterone after 5days of alcohol treatment. These findings suggest that adolescents experience milder negative affect during withdrawal from brief alcohol exposures relative to adults but comparable suppression of hypothalamic-pituitary-adrenal axis function.

Effects of chronic caffeine exposure during adolescence and subsequent acute caffeine challenge during adulthood on rat brain serotonergic systems

Caffeine is the most commonly used drug in the world. However, animal studies suggest that chronic consumption of caffeine during adolescence can result in enhanced anxiety-like behavioral responses during adulthood. One mechanism through which chronic caffeine administration may influence subsequent anxiety-like responses is through actions on brainstem serotonergic systems. In order to explore potential effects of chronic caffeine consumption on brainstem serotonergic systems, we evaluated the effects of a 28-day exposure to chronic caffeine (0.3 g/L; postnatal day 28–56) or vehicle administration in the drinking water, followed by 24 h caffeine withdrawal, and subsequent challenge with caffeine (30 mg/kg; s.c.) or vehicle in adolescent male rats. In Experiment 1, acute caffeine challenge induced a widespread activation of serotonergic neurons throughout the dorsal raphe nucleus (DR); this effect was attenuated in rats that had been exposed to chronic caffeine consumption. In Experiment 2, acute caffeine administration profoundly decreased tph2 and slc22a3 mRNA expression throughout the DR, with no effects on htr1a or slc6a4 mRNA expression. Chronic caffeine exposure for four weeks during adolescence was sufficient to decrease tph2 mRNA expression in the DR measured 28 h after caffeine withdrawal. Chronic caffeine administration during adolescence did not impact the ability of acute caffeine to decrease tph2 or slc22a3 mRNA expression. Together, these data suggest that both chronic caffeine administration during adolescence and acute caffeine challenge during adulthood are important determinants of serotonergic function and serotonergic gene expression, effects that may contribute to chronic effects of caffeine on anxiety-like responses.

Nandrolone administration abolishes hippocampal fEPSP-PS potentiation and passive avoidance learning of adolescent male rats

Despite the chronic effects of nandrolone decanoate (ND), the acute effects of ND on passive avoidance learning (PAL) and memory and its mechanism have not been investigated. This research examines the acute effect of ND on PAL, CA1 synaptic plasticity, testosterone and corticosterone serum levels, and the role of androgenic receptors (ARs). Adolescent male rats were treated with ND, 30 min before training and retention and after training test. AR antagonist was applied 15 min before ND. Hippocampal slices were perfused by ND. ND administration had an inverted U-shape effect on acquisition of PAL and on testosterone and corticosterone serum levels. The consolidation was only affected by high dose of ND. ND significantly decreased the retention of PAL across all doses. The magnitude of field excitatory postsynaptic potential long term potentiation was lower than that of control slices. In addition, an attenuation of field excitatory postsynaptic potential population spike coupling was also observed. Nilutamide could nullify the ND impairment effect. We concluded although a single dose of ND could affect all stages of PAL, its effects were more potent on retrieval, possibly arising from the acute effect of ND on the alterations of CA1 synaptic plasticity. In addition, ND may induce its effects directly through ARs and indirectly through plasma testosterone and corticosterone.

Chronic adolescent stress sex-specifically alters central and peripheral neuro-immune reactivity in rats

Adversity during development is a reliable predictor of psychiatric disorders such as depression and anxiety which are increasingly recognized to have an immune component. We have previously demonstrated that chronic adolescent stress (CAS) in rats leads to depressive-like behavior in adulthood along with long-lasting changes to the hypothalamic-pituitary-adrenal axis and pro-inflammatory cytokine induction in the hippocampus. However, the mechanisms by which CAS promotes hippocampal inflammation are not yet defined. Here we tested the hypothesis that a history of CAS exaggerates induction of the pro-inflammatory NFκB pathway in the adult rat hippocampus without compromising the peripheral immune response. We also assessed potential sex differences because it is unclear whether females, who are twice as likely to suffer from mood disorders as males, are disproportionally affected by stress-primed inflammation. Male and female adolescent rats underwent a CAS paradigm or received no stress. Six weeks following the last stressor, all rats received a single systemic injection of either lipopolysaccharide or vehicle to unmask possible immune-priming effects of CAS. An NFκB signaling PCR array demonstrated that CAS exaggerated the expression of NFκB-related genes in the hippocampus of both males and females. Interestingly, targeted qPCR demonstrated that CAS potentiated the induction of hippocampal IL1B and REL mRNA in female rats only, suggesting that some immune effects of CAS are indeed sex-specific. In contrast to the hippocampal findings, indices of peripheral inflammation such as NFκB activity in the spleen, plasma IL-1β, IL-6, TNF-α, and corticosterone were not impacted by CAS in female rats. Despite showing no pro-inflammatory changes to hippocampal mRNA, male CAS rats displayed lower plasma corticosterone response to LPS at 2 h after injection followed by an exaggerated plasma IL-1β response at 4 h. This potentially blunted corticosterone response coupled with excessive innate immune signaling in the periphery is consistent with possible glucocorticoid resistance in males. In contrast, the effects of CAS manifested as excessive hippocampal immune reactivity in females. We conclude that while a history of exposure to chronic adolescent stress enhances adult immune reactivity in both males and females, the mechanism and manifestation of such alterations are sex-specific.

Lipopolysaccharide (LPS) induced sickness in early adolescence alters the behavioral effects of the short-chain fatty acid, propionic acid, in late adolescence and adulthood: Examining anxiety and startle reactivity

Early life immune challenges are risk factors for neurodevelopmental disorders. In adolescence, they elicit behavioral symptoms that resemble clinical disorders. Stressors during this time may alter signaling from the gut microbiome, which increases the risk for psychiatric disorders. It was hypothesized that adolescent immune challenges may interact with a gut bacterial product, the short-chain fatty acid, propionic acid (PPA), to potentiate symptoms of anxiety and sensory abnormality. The present study investigated the effects of repeated lipopolysaccharide (LPS) exposure during early adolescence, on the behavioral effects of PPA in late adolescence and adulthood. Male adolescent rats were injected with LPS (0.2 mg/kg i.p.) or the vehicle on postnatal days (P) 28, P30, P32, and P34. They were later administered either PPA (500 mg/kg i.p.) or the vehicle during late adolescence on P40 and P43, and were subsequently tested on the light-dark anxiety test and acoustic startle response, respectively. In adulthood, the rats were again injected with PPA or the vehicle and tested on the light-dark and acoustic startle tasks on P74 and P77. The results of this study showed that LPS and PPA both decreased locomotor activity. PPA reduced vertical activity, percent prepulse inhibition, and acoustic startle response magnitude. LPS increased anxiogenic behaviors and induced a delayed increase in acoustic startle response magnitude in adulthood. Although no LPS and PPA interactions were found, the results of this study suggest that early adolescent immune activation can induce long-term behavioral changes that resemble the complex phenotypes of clinical disorders.

Differential effects of adolescent and adult-initiated exercise on cognition and hippocampal neurogenesis.

Adolescence is a critical period for postnatal brain maturation and thus a time when environmental influences may affect cognitive processes in later life. Exercise during adulthood has been shown to increase hippocampal neurogenesis and enhance cognition. However, the impact of exercise initiated in adolescence on the brain and behavior in adulthood is not fully understood. The aim of this study was to compare the impact of voluntary exercise that is initiated during adolescence or early adulthood on cognitive performance in hippocampal-dependent and -independent processes using both object-based and touchscreen operant paradigms. Adult (8 week) and adolescent (4 week) male Sprague-Dawley rats had access to a running wheel (exercise) or were left undisturbed (sedentary control) for 4 weeks prior to behavioral testing and for the duration of the experiment. Results from touchscreen-based tasks showed that reversal learning was enhanced by both adult and adolescent-initiated exercise, while only exercise that began in adolescence induced a subtle but transient increase in performance on a location discrimination task. Spontaneous alternation in the Y-maze was impaired following adolescent onset exercise, while object memory was unaffected by either adult or adolescent-initiated exercise. Adolescent-initiated exercise increased the number of hippocampal DCX cells, an indicator of neurogenesis. It also promoted the complexity of neurites on DCX cells, a key process for synaptic integration, to a greater degree than adult-initiated exercise. Together the data here show that exercise during the adolescent period compared to adulthood differentially affects cognitive processes and the development of new hippocampal neurons in later life.

Development of working memory in the male adolescent rat

Working memory develops over the course of adolescence, and neuroimaging studies find development-associated changes in the activity of prefrontal cortical brain regions. Establishment of a rodent model of working memory development would permit more comprehensive studies of the molecular and circuit basis for working memory development in health and disease. Thus, in this study, working memory performance was compared between adolescent and adult male Sprague-Dawley rats using an operant-based, delay-match-to-sample working memory task. Adolescent and adult rats showed similar rates of learning the task and similar performance at a low cognitive load (delays ≤ 6 s). However, when the cognitive load increased, adolescents exhibited impaired working memory performance relative to adults, until postnatal day 50 when performance was not significantly different. Despite evidence that cannabinoids disrupt working memory, we found no effect of acute treatment with the cannabinoid receptor agonist, WIN55212,2, at either age. Moreover, expression of glutamate and GABA receptor subunits was examined in the prelimbic and infralimbic prefrontal cortex across development. NMDA receptor subunit GluN2B expression significantly decreased with age in parallel with improvements in working memory. Thus, we show evidence that rats can be used as a model to study the molecular underpinnings of working memory development.

Interactions between whole-body heating and citalopram on body temperature, antidepressant-like behaviour, and neurochemistry in adolescent male rats

Evidence suggests that affective disorders are associated with altered thermoregulation, and it has been hypothesized that therapeutic strategies targeting body-to-brain thermosensory systems may be effective for treating depression. Consistent with this hypothesis, a recent randomized, double blind, placebo-controlled clinical trial has suggested that infrared whole-body hyperthermia has therapeutic potential for the treatment of depression. Preclinical models may help uncover the mechanism(s) underlying the antidepressant-like effects of whole-body heating. We have previously shown that exposure to whole-body heating potentiates antidepressant-like behavioural responses following administration of a behaviourally subthreshold dose of the selective serotonin reuptake inhibitor citalopram, but the neurochemical and behavioural interactions between whole body heating and behaviourally effective doses of citalopram are not known. In these experiments, we examined the effects of whole-body heating, either with or without treatment of a suprathreshold dose of citalopram (20 mg/kg, s.c.), on body temperature, antidepressant-like behavioural responses in the forced swim test, and tissue concentrations of serotonin and its metabolite, 5-hydoxyindoleacetic acid (5-HIAA), in the prefrontal cortex of adolescent male Wistar rats. Although whole-body heating did not potentiate the behavioural effects of suprathreshold citalopram, citalopram was observed to increase body temperature and potentiate the effects of whole-body heating on body temperature. Whole-body heating, by itself, decreased serotonin concentrations in the infralimbic cortex to a level similar to that observed following treatment with citalopram, suggesting that these treatments have convergent effects on a mesolimbocortical system innervating the medial prefrontal cortex, an effect that was correlated with effects of treatment on body temperature.

Rewarding Effects of Nicotine in Adolescent and Adult Male and Female Rats as Measured Using Intracranial Self-stimulation.

Tobacco is highly addictive, and after the development of dependence, it is difficult to quit smoking. Therefore, it is important to understand the factors that play a role in the initiation of smoking. The rewarding effects of nicotine play a role in the initiation of smoking and the goal of the present study was to determine the rewarding effects of nicotine in adolescent and adult male and female rats. Male and female Wistar rats were prepared with intracranial self-stimulation (ICSS) electrodes between postnatal day (P) 23 and 33. They were then trained on the ICSS procedure and the effect of nicotine (0, 0.03, 0.1, 0.3 mg/kg) on the reward thresholds and response latencies was investigated during adolescence (P40-59) or adulthood (>P75). Nicotine lowered the brain reward thresholds of the adult and adolescent male and female rats. The nicotine-induced decrease in the reward thresholds was the same in the adult male and adult female rats. However, nicotine induced a greater decrease in the reward thresholds of the adolescent female rats than the adolescent male rats. Nicotine decreased the response latencies of all groups and there was no effect of age or sex. Nicotine enhances reward function and psychomotor performance in adolescent and adult male and female rats. Adolescent female rats are more sensitive to the acute rewarding effects of nicotine than adolescent male rats. Therefore, the rewarding effects of nicotine might play a greater role in the initiation of smoking in adolescent females than in adolescent males. The great majority of people start smoking during adolescence. The present studies suggest that during this period female rats are more sensitive to the acute rewarding effects of low and intermediate doses of nicotine than male rats. The rewarding properties of nicotine play a role in the initiation of smoking and establishing habitual smoking. Therefore, the present findings might explain why adolescent females are at a higher risk for becoming nicotine dependent than adolescent males.

Combined ∆9-tetrahydrocannabinol and moderate alcohol administration: effects on ingestive behaviors in adolescent male rats.

Whereas co-use of alcohol and marijuana is prevalent in adolescents, the effects of such drug co-exposure on ingestive and cognitive behaviors remain largely unexplored. We hypothesized that co-exposure to alcohol and ∆9-tetrahydrocannabinol (THC), the main psychoactive constitute of marijuana, alters feeding behavior and cognition differently from either drug alone. Male rats received daily THC (3-20mg/kg/day) or oil vehicle through subcutaneous injection or consumption of a cookie with access to saccharin or saccharin-sweetened alcohol during adolescence (P30-45). Barnes maze and sucrose preference tests were applied to assess spatial memory and behavioral flexibility and abstinence-related anhedonia, respectively. Subcutaneous THC did not affect alcohol intake but dose-dependently increased acute (3h) chow intake and reduced weight gain. Moderate alcohol consumption reduced the acute hyperphagic effect of subcutaneous THC. By contrast, oral THC at a dose > 5mg/kg robustly reduced alcohol intake without affecting 3-h chow intake. At this dose, some rats stopped consuming the THC-laced cookies. Furthermore, oral THC reduced weight gain, and co-exposure to alcohol alleviated this effect. Chronic subcutaneous, but not oral, THC reduced sucrose intake during abstinence. Neither treatment impaired cognitive behaviors in the Barnes maze. Moderate alcohol and THC consumption can interact to elicit unique outcomes on ingestive behaviors and energy balance. Importantly, this study established a novel model of voluntary alcohol and THC consumption for studying mechanisms underlying the consequences of adolescent onset co-use of the two drugs.

Predator odor exposure in early adolescence influences the effects of the bacterial product, propionic acid, on anxiety, sensorimotor gating, and acoustic startle response in male rats in later adolescence and adulthood

It is becoming evident than the adolescent period is a sensitive period in stress response programming. Stressors during this time may alter signaling from the gut microbiome, which has been shown to increase the risk for psychiatric disorders. It was hypothesized that adolescent stressors may potentiate the symptoms of anxiety and sensory abnormalities induced by a gut bacterial product, the short-chain fatty acid, propionic acid (PPA). The present study investigated the effects of repeated predator odor exposure during early adolescence on male rats administered PPA in late adolescence and adulthood on a behavioral test battery. Male adolescent Long-Evans rats were repeatedly exposed to a worn or unworn cat collar stimulus in early adolescence on postnatal days (P) 28, P30, P32, and P34. They were administered either PPA (500 mg/kg i.p.), or its vehicle in late adolescence on P40 and P43, and were subsequently tested on the light-dark anxiety task and acoustic startle task, respectively. In adulthood, the rats were again injected with PPA or its vehicle on P74 and P77, and subsequently tested on the light-dark apparatus and acoustic startle task, respectively. The repeated predator odor exposure was aversive and produced long-term anxiogenic effects as measured by the light-dark apparatus. PPA decreased activity and percent prepulse inhibition of the acoustic startle response, with its effects on vertical activity, a putative measure of escape behavior, being potentiated by prior predator stress. PPA's effects in adulthood were diminished in comparison to adolescence. These results suggest the importance of evaluating the effects of early adolescent stress on subsequent environmental insults on the development of behavioral abnormalities.

ARC and BDNF expression after cocaine self-administration or cue-induced reinstatement of cocaine seeking in adolescent and adult male rats.

Recreational drug use peaks during adolescence. Our research with adolescent vs adult male rats, however, shows that rats taking cocaine as adolescents have lower levels of cue-induced reinstatement of drug-seeking than adults, despite similar levels of intravenous (i.v.) cocaine self-administration. Lower rates of reinstatement in younger rats could be explained by higher levels of brain plasticity. Two neuroplasticity-related genes, activity-regulated cytoskeletal-associated gene (Arc) and brain-derived neurotrophic factor (Bdnf), influence cocaine self-administration and cue-induced reinstatement. We tested whether reinstatement of cocaine seeking correlates with expression of these genes in reinforcement-related brain regions. Adolescent and adult male rats (postnatal day 35 or 83-95 at start) were allowed to acquire lever-pressing maintained by i.v. infusions of cocaine in daily 2-h sessions over 13days. At one of three experimental time points, rats were sacrificed and tissue collected to analyze Arc and Bdnf mRNA by in situ hybridization in the entire medial prefrontal cortex and entire nucleus accumbens, as well as relevant subregions: prelimbic cortex, infralimbic cortex, and nucleus accumbens core and shell. Despite taking similar amounts of cocaine, adolescents reinstated less than adults. Gene expression was most notable in the prelimbic cortex, was generally higher in adolescent-onset groups, and was higher with longer abstinence. These data partially support the hypothesis that higher levels of Arc and/or Bdnf gene expression in reinforcement-related brain regions of younger animals contribute to lower rates of extinction responding and/or reinstatement. Future studies should include mechanistic analysis of Arc, Bdnf, and their signaling pathways in age-dependent effects of cocaine.

Diffusion MRI abnormalities in adolescent rats given repeated mild traumatic brain injury.

ObjectiveMild traumatic brain injury (mTBI) is a serious health concern in the adolescent population. Repeated mTBI may result in more pronounced deficits, and has been associated with long‐term neurological consequences including neurodegeneration. As such, there is a critical need for the development of objective mTBI biomarkers to help guide medical management. Diffusion‐weighted imaging (DWI) is an advanced magnetic resonance imaging (MRI) technique that may detect brain abnormalities after mTBI. Diffusion tensor imaging (DTI) is the most commonly applied DWI method, and initial studies have reported DTI changes in mTBI patients. Furthermore, new DWI methods (e.g., track‐weighted imaging; TWI) are being developed that may also be sensitive to mTBIs, but remain to be comprehensively studied.MethodsThis study utilized the Awake Closed Head Injury (ACHI) model of mTBI to investigate changes in DTI and TWI following repeated mTBI in adolescent male and female rats. A total of four ACHI impacts, two/day over two consecutive days, were delivered beginning on postnatal day 25. At 1 day and 7 days postinjury, rats were euthanized and brains were collected for DWI analyses.ResultsRats given repeated mTBI displayed changes in fractional anisotropy and radial diffusivity (i.e., DTI measures), as well as track density (i.e., TWI).InterpretationThese findings are consistent with initial DTI findings in mTBI patients, suggest that TWI may complement DTI, support the utility of DWI measures as biomarkers in mTBI, and further validate the ACHI rat model of mTBI.

P-Coumaric acid stimulates longitudinal bone growth through increasing the serum production and expression levels of insulin-like growth factor 1 in rats

The aim of the present study was to examine the effects of p-coumaric acid on the longitudinal growth of the long bone in adolescent male rats. Teatment with p-coumaric acid significantly increased the tibial length and the height of each growth plate zone and the ratio of 5-bromo-2′-deoxyuridine-positive cells relative to total proliferative cells. Expression of insulin-like growth factor 1 and its receptor in the proliferative and hypertrophic zones, and serum levels of growth hormone and insulin-like growth factor 1 were significantly increased as well in the p-coumaric acid-treated group. Via increasing both the serum level of insulin-like growth factor 1 and its expression, p-coumaric acid could promote cell proliferation in growth plate zones. These results suggest that p-coumaric acid has the potential to increase height and may be a feasible alternative to growth hormone therapy.

Inosine alleviates depression-like behavior and increases the activity of the ERK-CREB signaling in adolescent male rats.

Inosine, a major breakdown product of adenosine by the enzyme adenosine deaminase, binds to adenosine receptors and initiates intracellular signaling events. Adenosine and inosine have already been described as capable of modulating depression-like behavior in adult rodent model. In this study, we investigated the antidepressant-like effect of inosine, acutely administered (10 or 50 mg/kg, intraperitoneal), in postnatal day 28 male Sprague-Dawley rats. The effects of inosine were assessed using the forced swimming test and locomotor activity test. Changes in the extracellular signal-regulated kinases (ERK)-cyclic AMP response element binding protein (CREB) signaling pathway in the hippocampus and prefrontal cortex were examined by western blot analysis. The results showed that inosine had an antidepressant-like effect in the forced swimming test in adolescent rats without affecting locomotor activity. Furthermore, we found that inosine increased the activity of ERK and CREB in the hippocampus and prefrontal cortex. Inosine administered intraperitoneally may alleviate depression-like behaviors in adolescent rats, and the ERK-CREB signal system may be the target of the antidepressant action of inosine.

Chronic oral methylphenidate treatment increases microglial activation in rats.

Methylphenidate (MP) is a widely prescribed psychostimulant used to treat attention deficit hyperactivity disorder. Previously, we established a drinking paradigm to deliver MP to rats at doses that result in pharmacokinetic profiles similar to treated patients. In the present study, adolescent male rats were assigned to one of three groups: control (water), low-dose MP (LD; 4/10mg/kg), and high dose MP (HD; 30/60mg/kg). Following 3months of treatment, half of the rats in each group were euthanized, and the remaining rats received only water throughout a 1-month-long abstinence phase. In vitro autoradiography using [3H] PK 11195 was performed to measure microglial activation. HD MP rats showed increased [3H] PK 11195 binding compared to control rats in several cerebral cortical areas: primary somatosensory cortex including jaw (68.6%), upper lip (80.1%), barrel field (88.9%), and trunk (78%) regions, forelimb sensorimotor area (87.3%), secondary somatosensory cortex (72.5%), motor cortices 1 (73.2%) and 2 (69.3%), insular cortex (59.9%); as well as subcortical regions including the thalamus (62.9%), globus pallidus (79.4%) and substantia nigra (22.7%). Additionally, HD MP rats showed greater binding compared to LD MP rats in the hippocampus (60.6%), thalamus (59.6%), substantia nigra (38.5%), and motor 2 cortex (55.3%). Following abstinence, HD MP rats showed no significant differences compared to water controls; however, LD MP rats showed increased binding in pre-limbic cortex (78.1%) and ventromedial caudate putamen (113.8%). These findings indicate that chronic MP results in widespread microglial activation immediately after treatment and following the cessation of treatment in some brain regions.

Adolescent Inhalant Abuse Results in Adrenal Dysfunction and a Hypermetabolic Phenotype with Persistent Growth Impairments

Background/Aims: Abuse of toluene products (e.g., glue-sniffing) primarily occurs during adolescence and has been associated with appetite suppression and weight impairments. However, the metabolic phenotype arising from adolescent inhalant abuse has never been fully characterised, and its persistence during abstinence and underlying mechanisms remain unknown. Methods: Adolescent male Wistar rats (post-natal day 27) were exposed to inhaled toluene (10,000 ppm) (n = 32) or air (n = 48) for 1 h/day, 3 days/week for 4 weeks, followed by 4 weeks of abstinence. Twenty air rats were pair-fed to the toluene group, to differentiate the direct effects of toluene from under-nutrition. Food intake, weight, and growth were monitored. Metabolic hormones were measured after exposure and abstinence periods. Energy expenditure was measured using indirect calorimetry. Adrenal function was assessed using adrenal histology and hormone testing. Results: Inhalant abuse suppressed appetite and increased energy expenditure. Reduced weight gain and growth were observed in both the toluene and pair-fed groups. Compared to the pair-fed group, and despite normalisation of food intake, the suppression of weight and growth for toluene-exposed rats persisted during abstinence. After exposure, toluene-exposed rats had low fasting blood glucose and insulin compared to the air and pair-fed groups. Consistent with adrenal insufficiency, adrenal hypertrophy and increased basal adrenocorticotropic hormone were observed in the toluene-exposed rats, despite normal basal corticosterone levels. Conclusions: Inhalant abuse results in negative energy balance, persistent growth impairment, and endocrine changes suggestive of adrenal insufficiency. We conclude that adrenal insufficiency contributes to the negative energy balance phenotype, potentially presenting a significant additional health risk for inhalant users.