Effects of long-term food restriction on genital reflexes in paradoxically sleep-deprived male rats

The purpose was to ascertain whether the different schedules of long-term food restriction (FR) exert influence on genital reflexes (penile erection-PE and ejaculation-EJ) induced by paradoxical sleep deprivation (PSD) in male rats. Diet restriction began at weaning with 6 g/day and food was increased by 1 g per week until reaching 15 g/day by adulthood. Rats submitted to FR and those fed ad libitum were distributed into PSD or maintained as control groups and challenged with saline or cocaine. The results indicated that PSD+saline induced PE and EJ in both ad libitum and FR groups, but cocaine only potentiated reflexes in ad libitum group. In an attempt to revert the effects of FR on genital reflexes, we provided food ad libitum to the restricted group during the PSD period (4 days). When compared to FR rats, an increase in the frequency of PE was observed in the FR group fed ad libitum during PSD (both groups were challenged with cocaine). Further, we sought to investigate motivational behavior by placing food within the behavioral cage during the evaluation of genital reflexes. The FR PSD+saline group challenged with food did not display genital reflexes but when injected with cocaine the responses were similar to those observed in FR PSD+cocaine rats not challenged with food. Our data suggest that the facilitatory effect of PSD on genital reflexes did not override the inhibitory effect of FR on erectile function, but different schedules of FR produce distinct effects on genital reflexes. Further studies are warranted to dissect the effect of food restriction on sexual behavior.     

Influence of paradoxical sleep deprivation and cocaine on development of spontaneous penile reflexes in rats of different ages

Recent studies have established that paradoxical sleep deprivation (PSD) and cocaine administration induce genital reflexes (penile erection and ejaculation) in adult and old rats. To determine whether the same effects would induce spontaneous genital reflexes in rats of different ages (30-90 days old), we administered with cocaine (7 mg/kg) or saline to rats after a 4-day period of PSD, or at the equivalent time-point in control animals, and penile erection and ejaculation were then evaluated. In PSD rats administered cocaine, erection was observed from 30 days old to 90 days old, when both genital reflexes reached a peak. Animals submitted to PSD and saline injection showed erection from 60 to 90 days old. None of the control (saline and cocaine) groups of any age displayed these behaviors. The effects of PSD on steroid hormone levels showed that, although testosterone levels increased with age, PSD caused a marked decrease in testosterone at all ages evaluated. Progesterone and corticosterone levels were higher in PSD groups than in the respective control groups. These findings suggest that the interaction of PSD and cocaine probably enhances dopaminergic transmission in the brain and may accelerate the development of genital reflexes in male rats.     

Association of paradoxical sleep deprivation and ecstasy (MDMA) enhances genital reflexes in male rats

Ecstasy ((±)3,4-methylenedioxymethamphetamine, MDMA) is a psychostimulant and a synthetic derivative of amphetamine that, according to its consumers, promotes the enhancement of sexual pleasure. This study sought to investigate the effects of ecstasy in the genital reflexes of paradoxical sleep deprived (PSD) male rats. Distinct groups of PSD rats were administered with saline or different doses of ecstasy. The incidence of genital reflexes was verified for 100 min. The four doses that were used induced genital reflexes in PSD animals and these significantly differed from their respective treated control groups. Under the influence of two intermediary doses (2.5 and 5 mg/kg), all animals displayed erection and ejaculation. The frequency of genital reflexes was also significantly greater than in relation to the PSD-saline group. The comparison between cocaine and ecstasy in PSD rats revealed that ecstasy induced more erections and ejaculations than cocaine. Thus, the present results showed a great enhancement of the genital reflexes of PSD rats that might have occurred due to serotoninergic alterations induced by this illicit substance when associated to sleep deprivation.     

Diurnal variation in the genital reflexes and hormone levels induced by paradoxical sleep deprivation and cocaine in male rats

The purpose was to ascertain whether the genital reflexes induced by paradoxical sleep deprivation (PSD) in male rats show diurnal variation, and whether the hormonal rhythm of testosterone and progesterone is involved in these behaviors. Genital reflexes (penile erection – PE, and ejaculation – EJ) and hormone levels were assessed during a 24 h period at four testing times (0900, 1600, 2100 and 0400 h) in PSD rats injected with saline or cocaine. Results indicated that PE in PSD rats given saline or cocaine did not show diurnal variation while EJ responses were significantly reduced at 0400 h in the PSD-cocaine group. The home-cage control group testosterone concentrations were lower at 1600, 2100 and 0400 h than at 0900 h. At 0900 h, testosterone levels were significantly lower in the PSD groups than in the control group. In contrast, progesterone levels were significantly higher in PSD groups in relation to the control group at the four testing times. Thus, we observed strong diurnal variation in testosterone and progesterone in control rats whereas only EJ responses in PSD-cocaine seemed to be influenced by the time of day. These results suggest that progesterone may influence the modulation of male genital reflexes displayed by sleep-deprived rats.     

Involvement of dopamine receptors in cocaine-induced genital reflexes after paradoxical sleep deprivation

Previous work has demonstrated that paradoxical sleep deprivation (PSD) potentiates cocaine-induced genital reflexes in male rats. To examine the possibility that this effect might involve alterations in binding to the DA transporter (DAT), we examined [3H] WIN 35,248 binding in brain after 96 h of PSD. No changes were found in any of the 11 brain regions examined. Since we had previously identified changes in D2 receptor binding after PSD, we next examined the effects of DA receptor subtype antagonists on cocaine-induced reflexes in sleep-deprived rats. Separate groups of PSD rats received saline, haloperidol (0.4, 0.8 or 1.6 mg/kg), SCH 23390 (0.25, 0.5, 1 mg/kg) or sulpiride (50, 100, 200 mg/kg) 60 min prior to acute cocaine (7 mg/kg). In saline pretreated rats, cocaine-induced penile erection (PE) in 100% of SD rats. This percentage was not significantly reduced by haloperidol at any dose, but was significantly reduced in rats pretreated with SCH 23390 (1 mg/kg) or sulpiride (100 or 200 mg/kg). In addition, acute cocaine-induced ejaculation in 80% of SD rats. This effect was not affected by haloperidol at any dose, but was significantly reduced by all doses of SCH 23390 and by the 200 mg/kg dose of sulpiride. These results suggest that the potentiating effects of cocaine on penile erection and ejaculation are likely due to PSD-induced changes in DA postsynaptic receptor sensitivity rather than alterations in DA transporter. They further suggest that both D1 and D2 receptors may play a role in these effects.     

卒中后抑郁与炎症因子的关系研究

目的分析卒中后抑郁(post-stroke depression,PSD)大鼠血清IL-17A水平、海马IL-1β、TNF-α mRNA表达的变化,探讨PSD的病理生理机制。方法将30只成年的无特定病原体级SD雄性大鼠随机分为假手术组、卒中组、PSD组,对各组大鼠进行基线行为学评估,其中卒中组和PSD组大鼠行大脑中动脉闭塞(middle cerebral artery occlusion,MCAO)缺血再灌注处理,1周后对PSD组大鼠行慢性轻度刺激(chronic unpredictable mild stress,CUMS),每天给予1~2种刺激,连续4周,CUMS刺激4周后对各组大鼠进行行为学评估。评估结束后采用尼氏染色观察各组大鼠海马区神经元形态,使用ELISA方法检测大鼠血清中IL-17A水平,实时荧光定量PCR检测大鼠海马IL-1β、TNF-α mRNA表达。观察PSD情况下,血清及海马神经元炎症因子的表达水平及海马损伤情况。结果假手术组、卒中组和PSD组大鼠血清的IL-17A水平分别为18.56±2.56 pg/mL、40.78±4.13 pg/mL和52.10±5.22 pg/mL,三组比较差异有统计学意义;假手术组、卒中组、PSD组大鼠海马区IL-1βmRNA相对表达水平分别为0.570±0.322、2.617±0.128和3.189±0.107,三组比较差异有统计学意义;假手术组、卒中组、PSD组大鼠海马区TNF-α mRNA基因相对表达水平分别为0.999±0.007、1.258±0.042和1.623±0.041,三组比较差异有统计学意义;尼氏染色提示卒中组、PSD组海马区CA1区神经元存在损伤,以PSD组最明显。结论 PSD组大鼠血清IL-17A水平上调,海马IL-1β、TNF-αmRNA高表达,提示PSD发生的病理生理机制中可能有炎症反应参与。     

Cocaine-induced genital reflexes in paradoxical sleep deprived rats: Indications of mediation by serotonin receptors

As paradoxical sleep deprivation (PSD) modifies cocaine-induced genital reflexes (penile erection [PE] and ejaculation [EJ]) and since cocaine is a serotonin (5-HT) reuptake inhibitor, we hypothesized that 5-HT also plays a role in these genital reflexes in PSD male rats. After a 4-day period of PSD each group was administered with serotonergic drugs prior to cocaine and placed in observation cages. The selective 5-HT(1) agonist (8-OH-DPAT) completely abolished PE events whereas the antagonist (pindolol) did not produce significant effects in the number of animals displaying PE. It was found that both drugs reduce the frequency of PE. There were no significant effects on the number of animals that ejaculated or in its frequency after pindolol although both parameters were reduced by the agonist at the highest doses (2 and 4 mg/kg, SC). Pretreatment with the 5-HT(2) agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (0.12; 0.5 and 1 mg/kg, SC) significantly reduced the number of rats displaying PE and all doses reduced both PE and EJ frequencies. The number of animals displaying PE after 5-HT(2) antagonist (ketanserin) pretreatment at 1 and 2.5 mg/kg doses was significantly decreased in relation to vehicle rats and all doses reduced PE frequency. 5-HT(2) compounds at any dose did not affect the number of animals ejaculating, but the frequency was significantly reduced by all doses of DOI and by 1 to 5 mg/kg doses of ketanserin. Taken together, the results suggest that serotonergic receptors play an important role in genital reflexes induced by cocaine in sleep deprived males.     

Chronic cocaine exposure impairs progenitor proliferation but spares survival and maturation of neural precursors in adult rat dentate gyrus

Recent observations indicate that drugs of abuse, including alcohol and opiates, impair adult neurogenesis in the hippocampus. We have studied in rats the impact of cocaine treatment (20 mg/kg, daily, i.p.) on cell proliferation, survival and maturation following short-term (8-day) and long-term (24-day) exposure. Using 5'-bromo-2-deoxyuridine (BrdU) and Ki-67 as mitotic markers at the end of the drug treatments, we found that both short- and long-term cocaine exposures significantly reduced cell proliferation in the dentate gyrus (DG) of the hippocampus. By labelling mitotic cells with BrdU pulses before or during the early stages of the drug treatment, we determined that long-term cocaine exposure did not affect the survival of newly generated cells. In register with this finding, cocaine chronic exposure did not increase the number of apoptotic cells labelled by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling). Using doublecortin (DCX) immunocytochemistry and electron microscopy, we next examined the effects of cocaine exposure on the maturation of the neural precursors and on synaptic output to CA3. DCX immunocytochemistry showed that immature hippocampal cells of rats exposed to cocaine displayed normal arborization patterns and similar degrees of colocalization with BrdU at two different developmental stages. Moreover, cocaine did not produce significant morphological alterations of the mossy fibre projection system to stratum lucidum in the CA3 area of the hippocampus. The results presented demonstrate that chronic cocaine exposure impairs proliferation dynamics in the DG without significantly altering either the survival and growth of immature cells or the structural features of terminal projections to CA3.     

Risperidone reverses phencyclidine induced decrease in glutathione levels and alterations of antioxidant defense in rat brain

Perinatal phencyclidine (PCP) administration to rats represents one of the actual animal models of schizophrenia. Numerous data suggest redox dysregulation in this disease. We have previously demonstrated decreased content of the reduced glutathione (GSH) and complex disbalance of antioxidant enzymes in the brain of rats perinatally treated with PCP. The aim of this study was to elucidate whether chronic risperidone treatment can reverse these changes. The Wistar rats were perinatally treated with either PCP (10mg/kg; PCP, two groups) or saline (0.9% NaCl, two groups). At postnatal day (PN) 35, two groups of rats one NaCl and one PCP have started to receive risperidone in drinking water for nine weeks (NaCl-RSP and PCP-RSP groups). Animals were sacrificed on PN100 and the levels of GSH, the activities of γ-glutamate cysteine ligase (GCL), glutathione peroxidase (GPx), glutathione reductase (GR) and superoxide dismutase (SOD), as well as, the concentration of lipid peroxides were determined in the different brain structures. Risperidone restored decreased GSH levels, as well as decreased γ-GCL activity in cortex and hippocampus of animals perinatally treated with PCP. Alterations in GPx and GR activities caused by perinatal PCP treatment were also reversed by risperidone in most investigated brain structures. Furthermore, chronic risperidone treatment caused the decrease in SOD activity both in control and in PCP perinatally treated groups. Increased levels of lipid peroxides noticed in hippocampus and thalamus were reversed after chronic risperidone treatment. The results of the present study demonstrate that risperidone treatment restores GSH levels and to great measure reverses antioxidant defense alterations in the brain of perinatally PCP treated rats. Further studies are necessary in order to clarify the significance of risperidone influence on oxidative stress parameters in schizophrenia.     

Imipramine treatment increases the number of hippocampal synapses and neurons in a genetic animal model of depression

The aim was to investigate treatment effects of the antidepressant imipramine on the markers of neuronal plasticity. We investigated changes in neuron and synapse numbers in a rat strain that displays a genetic susceptibility to depressive behavior, the Flinders Sensitive and Resistant Lines (FSL/FRL). All rats were treated with imipramine (15 mg/kg) or saline (i.p) once daily for 25 days. The volume, neuron and synapse numbers in the hippocampus were estimated using design‐based stereological methods. Under untreated conditions, the volume and the number of neurons and synapses were significantly smaller in the FSL saline group (untreated “depressed” rats) compared with the FRL saline group (normal rats), showing correlation to the observed decreased immobility in the forced swim test. Imipramine treatment significantly increased the number of neurons in the granule cell layer (GCL) and spine synapses in the CA1 in the FSL imipramine group (treated “depressed” rats) compared with the FSL saline group. The neuron numbers in the GCL and Hilus showed no differences in the FSL imipramine group compared to the FRL saline group. In conclusion, baseline levels of the volume and the number of neurons and spine synapses in hippocampus were significantly smaller in the untreated FSL rats. Our findings indicate that chronic imipramine treatment reverses the suppression of neurogenesis and synaptogenesis in the hippocampus of the “depressed” FSL rats, and this occurs in correlation with behavioral effects. Our results support the neuronal plasticity hypothesis that depressive disorders may be related to impairments of structural plasticity and neuronal viability in hippocampus, furthermore, antidepressant treatment counteracts the structural impairments. © 2009 Wiley‐Liss, Inc.     

Downregulation of kappa-opioid receptors in basolateral amygdala and septum of rats withdrawn for 14 days from an escalating dose "binge" cocaine administration paradigm

There is evidence showing that the opioid systems play an important role in cocaine addiction; fewer studies have examined their roles in cocaine withdrawal. This study was conducted to determine whether cocaine or chronic withdrawal from cocaine alters the receptor component of the kappa-opioid system. Male Fischer rats were injected with saline or cocaine (3x15 mg/kg/day for 4 days, 3x20 mg/kg/day for 4 days, 3x25 mg/kg/day for 4 days, and 3x30 mg/kg/day for 2 days), three times daily at 1-h intervals in an escalating dose paradigm for 14 days. Identically treated rats were withdrawn from cocaine or saline for 14 days. We performed quantitative autoradiographic mapping of kappa-opioid receptors (KOP-r) in the brains of rats treated with this escalating dose "binge" cocaine administration paradigm and of rats withdrawn from cocaine for 14 days. A significant condition (chronic/withdrawal) effect was shown across all regions analyzed. A significant increase in [3H]CI-977 binding to KOP-r was detected in the septum of rats treated with an escalating dose binge cocaine administration paradigm and killed 30 min after the last cocaine injection. In contrast, there was a decrease in KOP-r binding in the septum and the basolateral amygdala of rats withdrawn for 14 days from chronic escalating dose binge cocaine administration, compared to rats at the end of 14 days chronic escalating dose cocaine administration. These results reconfirm and extend that KOP-r undergoes upregulation in response to chronic binge cocaine administration here, with an escalating dose. The observed lowering in KOP-r binding, which was shown in two brain regions of cocaine withdrawn animals, might contribute to the persistent dysphoria reported a long time after the discontinuation of the drug.     

Involvement of nitric oxide in cocaine-induced erections and ejaculations after paradoxical sleep deprivation

OBJECTIVES: As nitric oxide (NO) is involved in penile erectile (PE) function and also influences the sleep-wake cycle, we speculated that NO could play a role in PE and ejaculation of paradonical sleep deprivation (PSD) rats. METHODS: Animals were pretreated with N(G)-nitro-L-arginine methyl ester (L-NAME, ip) and L-arginine (ip and icv) prior to saline or cocaine injection. RESULTS: Cocaine-induced PE in 90% of PSD rats, 60% of which ejaculated. L-NAME reduced the frequency of erection, but had no effect in the proportion of PSD-cocaine-injected rats displaying this response. L-NAME had no effect in saline groups. L-Arginine in PSD-saline rats reduced the proportion of animals displaying PE at the highest dose and reduced the frequency of PE at all doses in both saline and cocaine groups. The icv administration of L-arginine reduced PE only in PSD-cocaine rats. Results indicate that common to both drugs, whether it was NO synthase (NOS) inhibitor or NO precursor, was their capacity to strongly reduce PE frequency in cocaine-treated rats. Moreover, L-arginine (ip) played a relevant inhibitory role in the erection displayed by PSD rats. CONCLUSIONS: Our findings suggest that the stimulating effects of PSD associated or not with cocaine on erection can be modified by alterations in the NO system.     

Persistent upregulation of mu-opioid, but not adenosine, receptors in brains of long-term withdrawn escalating dose "binge" cocaine-treated rats

There is evidence showing that the opioid and adenosine systems play an important role in cocaine addiction; fewer studies have examined their roles in cocaine withdrawal. To determine whether cocaine and/or chronic withdrawal from cocaine alters the specific components of the opioid and adenosine systems, we carried out quantitative autoradiographic mapping of mu-opioid, A1 and A2A adenosine receptors in the brains of rats treated with an escalating dose "binge" cocaine administration paradigm and of rats chronically withdrawn from cocaine. Male Fischer rats were injected with saline or cocaine (15 x 3 mg/kg/day for 4 days, 20 x 3 mg/kg/day for 4 days, 25 x 3 mg/kg/day for 4 days and 30 x 3 mg/kg/day for 2 days) at 1-h intervals for 14 days. Similarly treated rats were withdrawn from that paradigm for 14 days. A significant increase in [(3)H]DAMGO binding to mu-receptors was detected in the frontal and cingulate cortex, as well as in the caudate putamen, of long-term withdrawn rats after an escalating dose "binge" cocaine administration paradigm and in chronic cocaine-treated rats. No significant cocaine-induced change was found in A1 or A2A receptor binding in any region analyzed. These results reconfirm that mu-opioid (MOP) receptors undergo upregulation in response to chronic escalating dose "binge" cocaine administration. This upregulation was shown for the first time to persist at least 14 days into withdrawal after escalating "binge" cocaine.     

Behavioral sensitization to cocaine: modulation by the cyclic AMP system in the nucleus accumbens

We have previously observed that chronic cocaine administration increases levels of adenylyl cyclase and cAMP-dependent protein kinase (PKA) in the nucleus accumbens (NAc). In the present work we directly examined the involvement of the cAMP system at the level of the NAc in cocaine-induced locomotor activity and sensitization. Groups of rats were pretreated on 3 consecutive days with cocaine (10 mg/kg, i.p.) concurrently with intraaccumbens infusion of saline, 8-bromo-cAMP (2 μg/side; a membrane permeant analogue of cAMP which activates PKA), or RP-CPT-cAMP (20 nmol/side; which inhibits PKA). In a separate experiment, control animals received local infusion of either 8-bromo-cAMP or saline plus i.p. saline. All animals were tested for locomotor activity on pretreatment days, and following an additional cocaine challenge on a subsequent day. Over pretreatment days, animals given 8-bromo-cAMP showed greater cocaine-induced activity, while animals given RP-CPT-cAMP tended to be less active, compared to saline infused animals. When subsequently challenged with cocaine, animals pretreated with intraaccumbens 8-bromo-cAMP showed greater locomotor activity during the last 30 min of the 60 min test session than animals pretreated with saline or RP-CRT-cAMP. No differences in locomotor activity were evident between the two control groups on pretreatment or challenge days. These data suggest that PKA activation at the level of the NAc may have a facilitative role with respect to acute and long-term stimulant-induced locomotor activity.     

Brain lesions induced by chronic cocaine administration to rats

Cocaine is a common drug of abuse, and its use has emerged as a major public health problem with neurological complications. In this work, the authors studied microscopic lesions produced in brain by chronic cocaine administration to rats. Twenty-five Wistar rats were exposed to 30 mg/kg/day ip of cocaine and sacrificed at 15, 30, 45, 60, and 90 days after treatment and compared to 25 control rats injected daily with saline. The parietal cortex (Cx), hippocampus (Hp), substantia nigra (SN), and cerebellum (Ce) were morphologically analyzed. The authors found progressive light microscopic lesions in all regions studied, including nuclear pyknosis and atrophy, interstitial edema, broken fibers, and necrosis. Results show that chronic treatment with cocaine in rats leads to selective severe lesions in different brain regions.     

Behavioral daily rhythmic activity pattern of adolescent female rat is modulated by acute and chronic cocaine

Cocaine is one of well-known drugs of abuse, and many children experience early exposure to cocaine. Because of an immature neuronal system in adolescents, they may react differently to repeated cocaine administration compared to adults. Most of the published papers report the effect of cocaine on adult male rats and this paper focused on the effects of cocaine on the 24 h locomotor activity rhythm patterns activity of adolescent Sprague Dawley (SD) female rats. Changes in the locomotor activity rhythm patterns could indicate that cocaine elicits long-term changes in the clock genes of the body that regulate different physiological processes. The objective of this study was to investigate whether cocaine in adolescent female rats modulated their daily activity pattern. Animals were divided into control (saline), 3.0, 7.5, 15.0 mg/kg cocaine groups. On experimental day 1 (ED 1), all groups were given saline injection. From ED 2 to ED 7, either saline or cocaine (3.0, 7.5, or 15.0 mg/kg) was given daily. ED 8 to ED 10 were the washout days, where no injection was given. On ED 11, the animals were injected with saline or with the same dose of cocaine as they were treated on ED 2 to ED 7. Each animal’s locomotor activities was recorded nonstop following saline or cocaine injection for 11 consecutive days using the open field assay. In conclusion, it was observed that all three groups receiving repeated cocaine administration (3.0, 7.5, and 15.0 mg/kg) displayed significantly altered locomotor activity rhythm patterns.     

Biosynthesis of dopamine and serotonin in the rat brain after repeated cocaine injections: A microdissection mapping study

The purpose of the present study was to examine the effects of chronic cocaine on dopamine (DA) and serotonin (5-HT) synthesis in several rat brain regions implicated in drug reinforcement. Male rats were treated twice daily with cocaine (15 mg/kg, ip) or saline for 1 week. After 42 hr of abstinence, rats were challenged with either cocaine (15 mg/kg, ip) or saline, followed by the aromatic L-amino acid decarboxylase inhibitor 3-hydroxybenzylhydrazine (NSD-1015; 100 mg/kg, ip). Animals were decapitated 30 min after NSD-1015 and discrete brain regions were microdissected from 300 μm frozen sections. Postmortem tissue levels of 3, 4-dihydroxyphenylalanine (DOPA) and 5-hyroxytryptophan (5-HTP) were quantified by HPLC with electrochemical detection and used to estimate biosynthesis of DA and 5-HT, respectively. In chronic saline-treated rats, cocaine dramatically suppressed DA and 5-HT synthesis in all forebrain regions examined, including: medial prefrontal cortex, nucleus accumbens, caudate nucleus, olfactory tubercle, and basolateral amygdala. The degree of inhibition ranged from 35-65% and was more pronounced in 5-HT neurons compared to DA neurons in the same tissue sample. In general, chronic cocaine did not significantly alter basal levels of DOPA or 5-HTP; a notable exception was lateral hypothalamus, where chronic cocaine reduced basal DA synthesis to 75% of control. After repeated cocaine injections, the synthesisiinhibiting effect of a challenge injection of cocaine was attenuated in many brain areas. These data suggest that whereas acute cocaine decreases DA and 5-HT synthesis in forebrain, chronic cocaine is not neurotoxic to DA and 5-HT neurons. In addition, the mechanism(s) mediating cocaine-induced suppression of monoamine synthesis may become desensitized by chronic exposure to the drug. Published 1993 Wiley-Liss, Inc.     

Chronic nicotine alters cannabinoid-mediated locomotor activity and receptor density in periadolescent but not adult male rats

A significant number of youths use cigarettes, and more than half of the youths who smoke daily also use illicit drugs. The focus of these studies is on how exposure to nicotine affects subsequent responses to both nicotine and cannabinoids in adolescents compared with adults. We have shown previously that chronic treatment with nicotine produces sensitization to its locomotor-activating effects in female and adult rats but not male adolescent rats. To better understand the effects of nicotine on adolescent and adult rats, rats were injected with nicotine or saline for 7 days and, on day 8, either challenged with delta-9-tetrahydrocannabinol (Δ9-THC) or the cannabinoid agonist CP 55,940 and tested for locomotor activity, or the brains were removed for quantitative autoradiography studies of the cannabinoid₁ receptor. A separate group of rats was treated with nicotine plus the cannabinoid antagonist AM 251 and then challenged with CP 55,940. In adolescent male rats, nicotine administration led to sensitization to the locomotor-decreasing effects of both Δ9-THC and CP 55,940, but in adult male rats, the response to either drug was unchanged compared to controls. The effect of nicotine on CP 55,940-mediated locomotor activity was blocked by co-administration of AM 251 with the nicotine. Further, cannabinoid receptor density was increased in the prelimbic prefrontal cortex, ventral tegmental area, and select regions of the hippocampus in adolescent male rats pretreated with nicotine compared to vehicle-treated controls. There were no significant changes in cannabinoid receptor binding, however, in any of the brain regions examined in adult males pretreated with nicotine. The prelimbic prefrontal cortex and the hippocampus have been shown previously to be involved in stimulant reinforcement; thus it is possible that these changes contribute to the unique behavioral effects of chronic nicotine and subsequent drug administration in adolescents compared with adults.     

Morphine pretreatment increases opioid inhibitory effects on maternal behavior

Ongoing maternal behavior in rats is under the inhibitory influence of opiates. Exposure to drugs of abuse may result in a progressive and enduring enhancement of their reinforcing effects. Little attention has been paid to the possibility that puerperal treatment with morphine may lead to sensitization to this drug, ultimately influencing the effects of opiates on maternal behavior. The aim of the present study was to investigate if the abrupt withdrawal of repeated treatment with morphine chlorhydrate (MC) during late pregnancy and early lactation may influence maternal behavior in lactating rats. The premise that a possible change in sensitivity to the inhibitory effect of MC on maternal behavior would last at least until day 17 of lactation without any reinforcement was tested. In addition, the hypothesis that the MC-induced inhibition would be reversed by the opioid antagonist naloxone was also tested. In all experiments female Wistar rats were treated with MC (5.0 mg/kg/day, subcutaneous [s.c.]) or saline for 7 days starting on the 17th day of pregnancy. After the abrupt discontinuation of long-term treatment, animals were acutely challenged with MC (5.0 mg/kg, s.c.) or saline and tested for maternal behavior in three different experimental situations: first, on days 5, 10, and 17 postpartum (Experiment 1); second, on day 17 postpartum (Experiment 2); third, on day 6 postpartum following naloxone pretreatment (1.0 mg/kg; Experiment 3). In Experiment 1, animals were treated for 7 days with morphine and acutely challenged with MC (group MM). Experimental MM animals showed significantly longer latencies for all maternal behavior parameters than all other groups during all observation days. The other groups (treated with MC for 7 days and acutely challenged with saline, group MS; treated with saline for 7 days and acutely challenged with MC, group SM; and treated with saline for 7 days and acutely challenged with saline, group SS) did not differ significantly from one another. In Experiment 2, in which rats were submitted to a single test on day 17 of lactation, the MM group showed significantly longer latencies for all behavioral parameters as compared to group SM. Previous acute naloxone treatment (Experiment 3) reversed the inhibitory effects of MC on maternal behavior in lactating rats. These data suggest that repeated administration of MC to female rats during late pregnancy sensitizes the animals to the inhibitory effects of opioids on rat ongoing maternal behavior.     

Impact of inhibition of erythropoietin treatment-mediated neurogenesis in the dentate gyrus of the hippocampus on restoration of spatial learning after traumatic brain injury

Our previous study demonstrates that delayed (initiated 24h post injury) erythropoietin (EPO) therapy for traumatic brain injury (TBI) significantly improves spatial learning. In this study, we investigated the impact of inhibition of EPO treatment-mediated neurogenesis on spatial learning after experimental TBI. Young male Wistar rats (318+/-7 g) were subjected to unilateral controlled cortical impact injury. TBI rats received delayed EPO treatment (5000 U/kg in saline) administered intraperitoneally once daily at 1, 2, and 3 days post injury and intracerebroventricular (icv) infusion of either a mitotic inhibitor cytosine-b-D-arabinofuranoside or vehicle (saline) for 14 days. Another 2 groups of TBI rats were treated intraperitoneally with saline and infused icv with either a mitotic inhibitor Ara-C or saline for 14 days. Animals receiving sham operation were infused icv with either Ara-C infusion or saline. Bromodeoxyuridine (BrdU) was administered to label dividing cells. Spatial learning was assessed using a modified Morris water maze test. Animals were sacrificed at 35 days after injury and brain sections stained for immunohistochemical analyses. As compared to the saline treatment, immunohistochemical analysis revealed that delayed EPO treatment significantly increased the number of BrdU-positive cells and new neurons co-stained with BrdU and NeuN (mature neuron marker) in the dentate gyrus in TBI rats. EPO treatment improved spatial learning after TBI. Ara-C infusion significantly abolished neurogenesis and spatial learning recovery after TBI and EPO treatment. Both EPO and Ara-C reduced the number of astrocytes and microglia/macrophages in the dentate gyrus after TBI. Our findings are highly suggestive for an important role of EPO-amplified dentate gyrus neurogenesis as one of the mechanisms underlying EPO therapeutic treatments after TBI, strongly indicating that strategies promoting endogenous neurogenesis may hold an important therapeutic potential for treatment of TBI.