Anxiolytic-like effects of oleamide in group-housed and socially isolated mice

Oleamide (cis-9,10-octadecenoamide) is an endogenous sleep-inducing lipid and prototypic member of a new class of biological signaling molecules identified in recent years. In the present study, the anxiolytic-like effect of oleamide was studied in several experimental models of anxiety in group-housed and socially isolated mice. As the results show, socially isolated mice exhibited an anxiogenic-like profile in the elevated plus-maze test, the light/dark test, and the hole-board test, which could be significantly reversed by oleamide (10 or 20 mg/kg, i.p.). Moreover, oleamide significantly reduced the anxiety levels in grouped-housed mice. In the isolation-induced aggressive test, oleamide markedly reduced the attacking duration and increased the attacking latency. It is concluded that oleamide has an anxiolytic-like effect in socially isolated or group-housed mice, which suggests that fatty acid amides might be involved in the regulation of anxiety-related behavior in mice.     

Cortical regulation of subcortical dopamine systems and its possible relevance to schizophrenia

Summary A unique model of DA system regulation is presented, in which tonic steady-state DA levels in the ECF act to down-regulate the response of the system to pulsatile DA released by DA cell action potential generation. This type of regulation is similar in many respects to the phenomenon proposed to mediate the action of norepinephrine on target neurons; i.e., an increase in the signal-to-noise ratio as measured by postsynaptic cell firing (Freedman et al., 1977; Woodward et al., 1979). However, in this model the signal and the noise are neurochemical rather than electrophysiological. Furthermore, the noise (tonic DA in the ECF) actually down-regulates the signal (phasic DA release) directly, and thereby provides a signal of its own that affects the system over a longer time-course. Therefore, the difference between signal and noise may also depend on the time frame under which such determinations are made.     

Fetal asphyxia leads to the loss of striatal presynaptic boutons in adult rats

Fetal asphyxic insults in the brain are known to be associated with developmental and neurological problems like neuromotor disorders and cognitive deficits. Little is known, however, about the long-term consequences of fetal asphyxia contributing to the development of different neurological diseases common in the adult or the aging brain. For that reason the present study aimed to investigate the long-term effects of fetal asphyxia on synaptic organization within the adult rat brain. Fetal asphyxia was induced at embryonic day 17 by 75-min clamping of the uterine and ovarian arteries. Presynaptic bouton densities and numbers were analyzed in the striatum and prefrontal cortex at the age of 19 months. A substantial decrease in presynaptic bouton density and number was observed in the striatum of fetal asphyxia rats compared to control rats, while an increase was found in the fifth layer of the prefrontal cortex. These results suggest that fetal asphyxia can have long-lasting effects on synaptic organization that might contribute to a developmental etiology of different neurological disorders and aging.     

Alteration of dopamine D1 receptor-mediated motor inhibition and stimulation during development in rats is associated with distinct patterns of c-fos mRNA expression in the frontal-striatal circuitry

Dopamine D1 receptors have been implicated in various neurodevelopmental disorders, including attention-deficit/hyperactivity disorder. However, little is known about potential late maturational changes of the motor inhibitory and stimulatory role of these receptors. Here, we investigated the effects of a full and selective D1 receptor agonist, SKF-81297, on motor activity and expression of the plasticity-associated gene, c-fos, in the prefrontal cortex and striatum of juvenile and adolescent male rats. In general, SKF-81297 produced a biphasic effect on motor activity (locomotor and rearing activity), which consisted of an initial short inhibition followed by a long-lasting stimulation. These effects were dose- and age- dependent. The inhibitory phase was more pronounced in adolescent than in juvenile rats whereas the opposite was true for the stimulatory phase. During the initial inhibitory phase of the drug, c-fos mRNA expression was increased in the prefrontal cortex of juvenile rats but reduced in adolescent rats. There was also an increase in c-fos mRNA expression in the medial-dorsal striatum and olfactory tubercle, which was more evident in juvenile rats. In contrast, during the stimulatory phase, c-fos mRNA expression was increased in both the dorsal and ventral striatum, especially in the nucleus accumbens, as well as in the prefrontal cortex, in both age groups. The increase of c-fos mRNA in the dorsal striatum, however, was more pronounced in juvenile rats. These results indicate the presence of two distinct D1 receptor populations within the frontal-striatal circuitry, which have opposite effects on motor activity, and which have different maturational profiles.     

Effects of acute and chronic lithium treatment on amphetamine-induced dopamine increase in the nucleus accumbens and prefrontal cortex in rats as studied by microdialysis

Summary The effects of acute and chronic administration of lithium (Li) on the basal levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxy-indoleacetic acid (5-HIAA), and the amphetamine-induced DA increase were assessed in the Nucleus Accumbens (NAC) and Prefrontal Cortex (PFC) by brain dialysis in freely-moving rats. Acute Li (2meq/L) was locally administered by reverse dialysis. Chronic Li (2 meq/kg) was intragastrically administered for 14 days. No effect was observed after acute Li administration. However, after chronic Li administration, the basal levels of DOPAC and the amphetamine-induced DA increase in the NAC were significantly higher in the Li-treated rats than in the saline-treated controls. In the PFC, while the amphetamine-induced DA increase was not affected by chronic Li, the basal levels of DA and DOPAC were significantly decreased after Li administration. The effects of chronic Li in the NAC could be due to increased synthesis and/or decreased release of DA, whereas in the PFC the effects could be due to a decreased synthesis of DA. The absence of effects of acute Li administration is in agreement with the therapeutic inefficacy of the acute use of the cation. The changes observed after chronic treatment in the NAC and the PFC could be related to the effects of Li on mood disorders and cognitive functions, respectively.     

Effects of corticotropin-releasing hormone receptor antagonists on cocaine-induced dopamine overflow in the medial prefrontal cortex and nucleus accumbens of rats

Recent evidence suggests an important role for corticotropin-releasing hormone (CRH) and CRH receptors in cocaine reinforcement. CRH receptor antagonists reduce cocaine self-administration and attenuate the reinstatement of extinguished cocaine-seeking behavior, but little is known about the mechanisms involved. One possible mechanism for these effects may involve the cocaine-induced activation of CRH located in brain regions outside of the hypothalamus. CRH has been shown to increase dopaminergic transmission in regions relevant for cocaine reinforcement, such as the medial prefrontal cortex and the nucleus accumbens. Here, we report that CP-154,526, a CRH1-receptor antagonist, actually enhances cocaine-induced increases in dopamine overflow in the medial prefrontal cortex, measured using in vivo microdialysis. In contrast, the receptor antagonist did not alter cocaine-induced increases in dopamine in most of the nucleus accumbens, except for the most rostral part. These data suggest a surprising role for prefrontal cortex dopamine in the ability of CRH-receptor antagonists to attenuate cocaine seeking in rats.     

Cerebellar modulation of frontal cortex dopamine efflux in mice: relevance to autism and schizophrenia

Cerebellar and frontal cortical pathologies have been commonly reported in schizophrenia, autism, and other developmental disorders. Whether there is a relationship between prefrontal and cerebellar pathologies is unknown. Using fixed potential amperometry, dopamine (DA) efflux evoked by cerebellar or, dentate nucleus electrical stimulation (50 Hz, 200 muA) was recorded in prefrontal cortex of urethane anesthetized lurcher (Lc/+) mice with 100% loss of cerebellar Purkinje cells and wildtype (+/+) control mice. Cerebellar stimulation with 25 and 100 pulses evoked prefrontal cortex DA efflux in +/+ mice that persisted for 12 and 25 s poststimulation, respectively. In contrast, 25 pulse cerebellar stimulation failed to evoke prefrontal cortex DA efflux in Lc/+ mice indicating a dependency on cerebellar Purkinje cell outputs. Dentate nucleus stimulation (25 pulses) evoked a comparable but briefer (baseline recovery within 7 s) increase in prefrontal cortex DA efflux compared to similar cerebellar stimulation in +/+ mice. However, in Lc/+ mice 25 pulse dentate nucleus evoked prefrontal cortex DA efflux was attenuated by 60% with baseline recovery within 4 s suggesting that dentate nucleus outputs to prefrontal cortex remain partially functional. DA reuptake blockade enhanced 100 pulse stimulation evoked prefrontal cortex responses, while serotonin or norepinephrine reuptake blockade were without effect indicating the specificity of the amperometric recordings to DA. Results provide neurochemical evidence that the cerebellum can modulate DA efflux in the prefrontal cortex. Together, these findings may explain why cerebellar and frontal cortical pathologies co-occur, and may provide a mechanism that accounts for the diversity of symptoms common to multiple developmental disorders.     

Dissociation of prefrontal cortex and nucleus accumbens dopaminergic systems in conditional learning in rats

There is converging evidence that the prefrontal and mesolimbic dopaminergic (DAergic) systems are involved in the performance of a variety of tasks that require the use of contextual, or task-setting, information to select an appropriate response from a number of candidate responses. Performance on tasks of this nature are impaired in schizophrenia and in rats exposed to psychotomimetics; impairments that are often attenuated by administration of dopamine (DA) antagonists. Rats were trained on either a complex instrumental discrimination task, that required the use of task-setting cues, or a simple discrimination task that did not. Following training, microdialysis probes were implanted unilaterally in either the medial prefrontal cortex (mPFC) or nucleus accumbens (NAc) and samples were collected in freely moving animals during a behavioural test session. In Experiment 1, we found no difference in levels of DA in the mPFC of rats while they were performing the two discrimination tasks. Rats that performed the complex task did, however, show significantly higher mPFC DA levels relative to rats in the simple discrimination condition following the end of the behavioural test session. In Experiment 2, rats performing the conditional discrimination showed lower levels of DA in the NAc compared to the simple discrimination group both during the test session and after it. These results provide direct evidence that conditional discrimination tasks engage frontal and mesolimbic DAergic systems and are consistent with the proposal that regulation of fronto-striatal DA is involved in aspects of cognitive control that are known to be impaired in individuals with schizophrenia.     

Chronic administration of resveratrol prevents morphological changes in prefrontal cortex and hippocampus of aged rats

Resveratrol may induce its neuroprotective effects by reducing oxidative damage and chronic inflammation apart from improving vascular function and activating longevity genes, it also has the ability to promote the activity of neurotrophic factors. Morphological changes in dendrites of the pyramidal neurons of the prefrontal cortex (PFC) and hippocampus have been reported in the brain of aging humans, or in humans with neurodegenerative diseases such as Alzheimer's disease. These changes are reflected particularly in the decrement of both the dendritic tree and spine density. Here we evaluated the effect of resveratrol on the dendrites of pyramidal neurons of the PFC (Layers 3 and 5), CA1‐ and CA3‐dorsal hippocampus (DH) as well as CA1‐ventral hippocampus, dentate gyrus (DG), and medium spiny neurons of the nucleus accumbens of aged rats. 18‐month‐old rats were administered resveratrol (20 mg/kg, orally) daily for 60 days. Dendritic morphology was studied by the Golgi‐Cox stain procedure, followed by Sholl analysis on 20‐month‐old rats. In all resveratrol‐treated rats, a significant increase in dendritic length and spine density in pyramidal neurons of the PFC, CA1, and CA3 of DH was observed. Interestingly, the enhancement in dendritic length was close to the soma in pyramidal neurons of the PFC, whereas in neurons of the DH and DG, the increase in dendritic length was further from the soma. Our results suggest that resveratrol induces modifications of dendritic morphology in the PFC, DH, and DG. These changes may explain the therapeutic effect of resveratrol in aging and in Alzheimer's disease. Synapse, 2016. © 2016 Wiley Periodicals, Inc. Synapse 70:206–217, 2016. © 2016 Wiley Periodicals, Inc.     

Mesotelencephalic dopamine neurochemical responses to glucocorticoid administration and adrenalectomy in Fischer 344 and Lewis rats

The effects of alterations in peripheral corticosterone levels on multiple dopamine neurochemical estimates were examined in inbred Fischer and Lewis inbred rat strains. 2x2 ANOVA's (treatment x strain) showed a main effect for treatment (1 week CORT versus placebo) on the concentrations of the dopamine metabolites homovanillic acid and dihydroxyphenylacetic acid in the medial prefrontal cortex, with lower levels after treatment, but no significant treatment versus strain interaction. There was no effect of CORT treatment on DA metabolites in the nucleus accumbens shell or dorsal striatum. DOPA accumulation in any terminal region examined and tyrosine hydroxylase protein content in the ventral tegmental area were also not affected by 1 week of corticosterone in either strain. One week after adrenalectomy, homovanillic acid but not dihydroxyphenylacetic acid concentrations were significantly increased in the medial prefrontal cortex, dorsal striatum, and nucleus accumbens shell in the Lewis but not the Fischer strain, with a significant treatment x strain interaction only in the dorsal striatum. Based on these findings, the effect of adrenalectomy on DOPA accumulation and extracellular DA concentrations was examined in the Lewis strain only. Adrenalectomy produced a decrease in DOPA accumulation in the dorsal striatum with no significant change in the other regions. Adrenalectomy did not alter estimates of extracellular dopamine concentrations determined by in vivo no net flux microdialysis but did significantly increase in vivo dopamine recovery in the dorsal striatum. The findings indicate a pattern of changes in neurochemical measurements consistent with a small magnitude inhibition of basal dopamine metabolism, but not with a change neuronal activity, release or reuptake.     

Evaluation of the relationship between anxiety during withdrawal and stress-induced reinstatement of cocaine seeking

The initial termination of cocaine consumption in human addicts is associated with heightened anxiety states and low levels of craving. Craving, however, tends to increase progressively over time, remains high for extended periods of time, and can be exacerbated by stressors, leading to relapse. Laboratory rats, likewise, exhibit heightened states of anxiety after withdrawal from drug, and follow a time course of cocaine seeking that parallels the time course of craving reported in humans. In addition, laboratory rats show heightened susceptibility to relapse when exposed to stressors after extended periods of withdrawal, and exhibit persistent and heightened expressions of stress-induced anxiety. The general objective of this paper is to consider the relationship between anxiety states after withdrawal from cocaine and stress-induced reinstatement of cocaine seeking in laboratory rats, and to identify the neural substrates involved. The focus of the review is on studies addressing the roles of corticotropin-releasing factor (CRF) and noradrenaline pathways of the extended amygdala circuitry, and their direct or indirect interactions with the mesocorticolimbic dopamine system, in anxiety after withdrawal from cocaine and stress-induced reinstatement of cocaine seeking. Furthermore, the effects of time after withdrawal from cocaine and amount of cocaine exposure during self-administration on the activity of CRF, noradrenaline, and dopamine pathways of the extended amygdala and mesocorticolimbic systems will be considered. The review will highlight how changing levels of activity within these systems may serve to alter the nature of the relationship between anxiety and stress-induced reinstatement of cocaine seeking at different times after withdrawal from cocaine.     

Early environment contributes to developmental disruption of MPFC after neonatal ventral hippocampal lesions in rats

Using a putative animal model of schizophrenia, neonatal rat ventral hippocampal (VH) lesions, combined with cross-fostering Lewis and Fisher rats, we previously demonstrated that the postpubertal expression of amphetamine-induced hyperlocomotion after lesioning depends on the early environment of the pups. However, an important question that emerged from our studies was whether the early environment leads to sparing of function within the VH or to the disruption of another structure, such as the medial prefrontal cortex (MPFC). To answer this question, we took advantage of the natural variation in maternal care of Sprague-Dawley rat dams and separated them into high and low arched back nursing (ABN) groups. Then, on postnatal day 7 (PD7) the pups from the two groups of dams were lesioned in the VH. As a measure of VH function, the rats were tested in a reference memory paradigm, which demonstrated that nVH-lesioned rats raised by high or low ABN dams had pronounced deficits, suggesting that VH functions are not fully spared. Next, the integrity of the MPFC was tested in a number of paradigms in which MPFC function has been implicated. In all three paradigms a similar result was found, that only lesioned rats raised by high ABN dams displayed deficits, such as a lack of MPFC control of amphetamine-induced locomotion, decreased working memory, and decreased anxiety. These results suggest that the early environment does not affect the recovery of the VH to nVH lesion. Rather, the early environment interacts with nVH lesions in such a way that disrupts the development and function of MPFC.     

Dissociation between mesocortical dopamine release and fear-related behaviours in two psychogenetically selected lines of rats that differ in coping strategies to aversive conditions

The mesocortical and mesolimbic dopaminergic (DAergic) pathways are activated by either aversive or rewarding stimuli. The functional tone of these DAergic neurons also increases during the execution of cognitive tasks. The present study was designed to examine the relationship between mesocortical and mesolimbic DAergic function and the expression of fear-related behaviours as compared with attention- and cognition-related mechanisms (e.g. coping strategies), in response to aversive conditions. To this aim, we used two psychogenetically selected rat lines, Roman high-avoidance (RHA/Verh) and Roman low-avoidance (RLA/Verh), which display drastically different emotion- and coping-related behaviours in response to stressors: RLA/Verh rats are 'reactive copers' and more fearful than RHA/Verh rats, which are 'proactive copers'. Brain dialysis experiments demonstrated that tail-pinch (TP) and the anxiogenic compounds pentylenetetrazol (PTZ) and ZK 93426 increased DA output in the medial prefrontal cortex (PFCX) of RHA/Verh but not RLA/Verh, rats. In contrast, in the shell compartment of the nucleus accumbens (NAC shell), TP caused a small increase in DA output only in RLA/Verh rats, whereas PTZ and ZK 93426 had no significant effect on either line. RHA/Verh rats displayed more robust and longer lasting coping activity and less frequent freezing and self-grooming episodes than did RLA/Verh rats after TP, PTZ or ZK 93426. This dissociation between fear-related behaviour and cortical DAergic activation argues against the view that the latter may be involved in the control of fear-like responses. We therefore propose that the activation of mesocortical DAergic projections by aversive stimuli underlies the cognitive mechanisms that are triggered in an attempt to gain control over the stressor.     

Chronic administration of the neurotrophic agent cerebrolysin ameliorates the behavioral and morphological changes induced by neonatal ventral hippocampus lesion in a rat model of schizophrenia

Neonatal ventral hippocampal lesion (nVHL) in rats has been widely used as a neurodevelopmental model to mimic schizophrenia-like behaviors. Recently, we reported that nVHLs result in dendritic retraction and spine loss in prefrontal cortex (PFC) pyramidal neurons and medium spiny neurons of the nucleus accumbens (NAcc). Cerebrolysin (Cbl), a neurotrophic peptide mixture, has been reported to ameliorate the synaptic and dendritic pathology in models of aging and neurodevelopmental disorder such as Rett syndrome. This study sought to determine whether Cbl was capable of reducing behavioral and neuronal alterations in nVHL rats. The behavioral analysis included locomotor activity induced by novel environment and amphetamine, social interaction, and sensoriomotor gating. The morphological evaluation included dendritic analysis by using the Golgi-Cox procedure and stereology to quantify the total cell number in PFC and NAcc. Behavioral data show a reduction in the hyperresponsiveness to novel environment- and amphetamine-induced locomotion, with an increase in the total time spent in social interactions and in prepulse inhibition in Cbl-treated nVHL rats. In addition, neuropathological analysis of the limbic regions also showed amelioration of dendritic retraction and spine loss in Cbl-treated nVHL rats. Cbl treatment also ameliorated dendritic pathology and neuronal loss in the PFC and NAcc in nVHL rats. This study demonstrates that Cbl promotes behavioral improvements and recovery of dendritic neuronal damage in postpubertal nVHL rats and suggests that Cbl may have neurotrophic effects in this neurodevelopmental model of schizophrenia. These findings support the possibility that Cbl has beneficial effects in the management of schizophrenia symptoms.     

Dendritic morphology changes in neurons from the ventral hippocampus,amygdala and nucleus accumbens in rats with neonatal lesions into the prefrontal cortex

Neonatal prefrontal cortex (nPFC) lesions in rats could be a potential animal model to study the early neurodevelopmental abnormalities associated with the behavioral and morphological brain changes observed in schizophrenia. Morphological alterations in pyramidal neurons from the ventral hippocampus (VH) have been observed in post‐mortem schizophrenic brains, mainly because of decreased dendritic arbor and spine density. We assessed the effects of nPFC‐lesions on the dendritic morphology of neurons from the VH, basolateral‐amygdala (BLA) and the nucleus accumbens (NAcc) in rats. nPFC lesions were made on postnatal day 7 (PD7), after dendritic morphology was studied by the Golgi‐Cox stain procedure followed by Sholl analysis at PD35 (prepubertal) and PD60 (adult) ages. We also evaluated the effects of PFC‐lesions on locomotor activity caused by a novel environment. Adult animals with nPFC lesions showed a decreased spine density in pyramidal neurons from the VH and in medium spiny cells from the NAcc. An increased locomotion was observed in a novel environment for adult animals with a PFC‐lesion. Our results indicate that PFC‐lesions alter the neuronal dendrite morphology of the NAcc and the VH, suggesting a disconnection between these limbic structures. The locomotion paradigms suggest that dopaminergic transmission is altered in the PFC lesion model. This could help to understand the consequences of an earlier PFC dysfunction in schizophrenia. To evaluate possible dendritic changes in neonatal prefrontal cortex lesions in schizophrenia‐related regions including nucleus accumbens, ventral hippocampus and basolateral amygdala, we used the Golgi‐Cox stain samples at PD35 and PD70. Our results suggest that neonatal prefrontal cortex damage alters dendritic parameters in limbic regions, and this has potential implications for schizophrenia. Synapse 69:314–325, 2015 . © 2015 Wiley Periodicals, Inc.     

Opposing roles for dopamine D1- and D2-like receptors in discrete cue-induced reinstatement of food seeking

We used a rat reinstatement model to test the involvement of dopamine D₁- and D₂-like receptors in discrete cue-induced reinstatement of food seeking. At a dose that did not alter responding during food self-administration, the D₁-like antagonist SCH-23390 blocked reinstatement of food seeking, while the D₂-like antagonist eticlopride significantly increased reinstatement responding. Thus, these results establish opposing roles for D₁- and D₂-like receptors in discrete cue-induced relapse to food seeking.     

Repeated ethanol exposure during adolescence alters the developmental trajectory of dopaminergic output from the nucleus accumbens septi

Individuals who begin using alcohol prior to 14 years of age are 4 times more likely to progress to addiction than those who do not initiate use until 21 years of age. The nucleus accumbens septi undergoes dramatic developmental transitions during the adolescent period, and dopaminergic activity within this region has been identified as a central neurochemical mediator of drug reward, addiction and dependence. Thus, alcohol-induced neurochemical alterations in dopaminergic activity within this brain region likely mediate the heightened vulnerability to addiction observed in adolescent alcohol users. To investigate this idea, Sprague–Dawley rats were exposed to intraperitoneal injections of either saline or ethanol (0.5, 1.0 or 2.0 g/kg) twice daily over four days beginning on postnatal day 21, 31, 41 or 56. Cannulas were implanted toward the nucleus accumbens septi, subsequent in vivo microdialysis was used to collect samples, and both basal and ethanol-stimulated dopamine overflow was measured using high performance liquid chromatography with electrochemical detection. A developmental transition in basal levels of dopamine in the nucleus accumbens septi was apparent with peak levels at postnatal day 45. An ethanol challenge produced unique responses across ages, with greater peak effects relative to baseline in younger animals (postnatal day 25 and 35). Following repeated exposure to ethanol, a significant increase in basal dopamine was apparent for all ages, and when these animals were challenged with ethanol, peak effects relative to baseline were decreased in younger animals, but unchanged in older animals (postnatal day 45 and 60). Results indicate that there is a key developmental transition in the ability of rats to adapt to the effects of repeated ethanol exposure, which occurs between postnatal day 35 and 45. This alteration may explain the increased addiction vulnerability observed in individuals who initiate alcohol use during early adolescence.     

Brain regional changes of guanine nucleotide binding protein-inhabitant 2 in acute and chronic morphine-tolerant and -dependent rats★

BACKGROUND： Drug addiction involves two main central nervous systems, namely the dopamine and noradrenaline systems. These systems are primarily distributed in five brain regions： the ventral tegmental area, the nucleus accumbens, the prefrontal cortex, the hippocampus, and the locus coeruleus.
OBJECTIVE： To investigate regional changes of guanine nucleotide binding protein-inhabitant 2 （Gi2） in dopaminergic and noradrenergic neurons in brains of morphine-tolerant and -dependent rats.
DESIGN, TIME, AND SETTING： A randomized control study was performed at the Department of Neurobiology in the Second Military Medical University of Chinese PLA （Shanghai, China） between September 2002 and March 2004.
MATERIALS： Thirty-six, healthy, male, Sprague-Dawley （SD） rats were used to establish morphine-dependent models. Morphine hydrochloride was a product of Shenyang First Pharmaceutical Factory （China）; naloxone hydrochloride was a product of Beijing Four-Ring Pharmaceutical Factory （China）; and α subunit of Gi2 antibody was offered by Santa Cruz Biotechnology, lnc （USA）.
METHODS： Thirty-six SD rats were randomly divided into six groups （n = 6）： （1） acute morphine-dependent group, （2） acute abstinent group, （3） acute control group, （4） chronic morphine-dependent group, （5） chronic abstinent group, and （6） chronic control group. Rats in the acute morphine-dependent and the acute groups were injected with morphine （5 mg/kg）, one injection every two hours, for a total of eight injections. In the acute and chronic morphine-dependent rat models, morphine withdrawal syndrome was precipitated by an injection of naloxone （5 mg/kg）. Rats in the acute control group were given a peritoneal injection of physiological saline at the same administration time as the above two groups. Rats in the chronic morphine-dependent and chronic abstinent groups were injected with morphine three times per day. The administration dose on day 1 was initially 5 mg/kg at 20     

Brain regional changes of guanine nucleotide binding protein-inhabitant 2 in acute and chronic morphine-tolerant and-dependent rats

BACKGROUND:Drug addiction involves two main central nervous systems,namely the dopamine and noradrenaline systems.These systems are primarily distributed in five brain regions:the ventrai tegmental area,the nucleus accumbens,the prefrontal coaex,the hippocampus,and the locus coeruleus.OBJECTIVE:To investigate regional changes of guanine nucleotide binding protein-inhabitant 2(Gi2)in dopaminergic and noradrenergic neurons in brains of morphine-tolerant and-dependent rats.DESIGN,TIME,AND SETTING:A randomized centrel study was performed at the Department of Neurobiology in the Second Military Medical University of Chinese PLA(Shanghai,China) between September 2002 and March 2004.MATERIALS:Thirty-six,healthy, male, Sprague-Dawley (SD) rats were used to establish morphine-dependent models.Morphine hydrochloride was a product of Shenyang First Pharmaceutical Factory (China);naloxone hydrochloride was a product of Beijing Four-Ring Pharmaceutical Factory (China);and α subunit of Gt2 antibody was offered by Santa Cruz Biotechnology,Inc(USA).METHODS:Thirty-six SD rats were randomly divided into six groups(n=6):(1)acute morphine-dependent group,(2)acute abstinent group,(3)acute control group,(4)chronic morphine-dependent group,(5)chronic abstinent group,and(6)chronic control group.Rats in the acute morphine-dependent and the acute groups were injected with morphine(5 mg/kg),one injection every two hours,for a total of eight injections.In the acute and chronic morphine-dependent rat models,morphine withdrawal syndrome was precipitated by an injection of naloxone (5 mg/kg).Rats in the acute control group were given a peritoneal iniection of physiological saline at the same administration time as the above two groups.Rats in the chronic morphine-dependent and chronic abstinent groups were injected with morphine three times per day.The administration dose on day 1 was initially 5 mg/kg at 20:00,which increased by 5 mh/kg at 8:00,12:00,and 20:00 until day 7.On day 13,the dose continuously increased bv 10 mg/kg until a chronic morphine-dependent rat model was successfully induced.Aflerwards.the rats presented with withdrawal syndromes on naloxone (5 mg/kg)at 8:00 on the same day.Rats in the chronic centrel group were injected with physiological saline at the same time of the two chronic groups.MAIN OUTCOME MEASURES:The concentration of Gl2 protein in the five brain regions(ventral tegmental area,nucleus accumbens,prefrontal cortex,locus coeruleus,and hippocampus)was detected by immunohistochemistry.RESULTS:In the acute morphine-dependent and acute abstinent groups,Gl2 protein concentration was significantly decreased in the nucleus accumbens,compared to the acute control group(P<0.01),while no obvious changes were detected in other brain regions.In the chronic morphine-dependent and chronic abstinent groups,Gl2 protein concentration was significantly decreased in the nucleus accumbeas,but significantly jncreased in the Iocus coeruleus(P<0.01)compared to the chronic centrel group.CONCLUSION:Morphine dependence and tolerance may induce obvious reductions of Gi2 protein levels in the nucleus accumbens of rats.Chronic morphine dependence desensitizes the homologous neurons.     

Age-specific effects of 6-hydroxydopamine lesions of the rat medial prefrontal cortex on stress-induced c-fos expression in subcortical areas

As adolescence is a critical period when dopaminergic neuronal maturation peaks, we hypothesized that 6-hydroxydopamine (OHDA) lesions of the medial prefrontal cortex (mPFC) in adolescent rats would have more negative effects than lesions in adult rats. Therefore, we investigated the effects of 6-OHDA lesions of the mPFC in adolescent and adult rats on stress-induced c-fos expression in the brain. Adolescent and adult Sprague–Dawley rats, aged 4 and 7 weeks on arrival, respectively, were studied. 6-OHDA (8.0 µg) for the lesion groups and ascorbic acid for the sham groups were injected bilaterally into the mPFC. All animals were pretreated with desipramine 30 min before being anesthetized. The control group did not undergo any surgery-related procedure except the desipramine injection. After recovery for 1 week, the rats were subjected to restraint stress for 1 h. Immediately after the stress, the rats were killed and c-fos immunohistochemistry was examined. The c-fos expression in the nucleus accumbens core (AcbC), nucleus accumbens shell (AcbSh), CA1, CA3, dentate gyrus (DG), central amygdaloid (Ce), basolateral amygdaloid (BL), and temporal cortex (Tc) was compared. Adolescent rats with 6-OHDA lesions subjected to restraint stress had greater c-fos expression in the AcbC, AcbSh, DG, Ce, BL, and Tc, compared to the sham and control groups, whereas these differences were not observed among the adult groups. These results suggest that a hypodopaminergic state in the mPFC of adolescent rats, but not adult rats, is related to increased sensitivity to stress, suggesting that damage to or maldevelopment of dopaminergic neurons during adolescence has an age-specific effect. Further research is warranted to investigate the mechanism of the age-specific effect of 6-OHDA lesions of the mPFC.