Increased C-fos mRNA Expression Research Articles

Lu AF35700 reverses the phencyclidine-induced disruption of thalamo-cortical activity by blocking dopamine D1 and D2 receptors

Antipsychotic drugs of different chemical/pharmacological families show preferential dopamine (DA) D2 receptor (D2-R) vs. D1 receptor (D1-R) affinity, with the exception of clozapine, the gold standard of schizophrenia treatment, which shows a comparable affinity for both DA receptors. Here, we examined the ability of Lu AF35700 (preferential D1-R>D2-R antagonist), to reverse the alterations in thalamo-cortical activity induced by phencyclidine (PCP), used as a pharmacological model of schizophrenia. Lu AF35700 reversed the PCP-induced alteration of neuronal discharge and low frequency oscillation (LFO, 0.15–4 Hz) in thalamo-cortical networks. Likewise, Lu AF35700 prevented the increased c-fos mRNA expression induced by PCP in thalamo-cortical regions of awake rats. We next examined the contribution of D1-R and D2-R to the antipsychotic reversal of PCP effects. The D2-R antagonist haloperidol reversed PCP effects on thalamic discharge rate and LFO. Remarkably, the combination of sub-effective doses of haloperidol and SCH-23390 (DA D1-R antagonist) fully reversed the PCP-induced fall in thalamo-cortical LFO. However, unlike with haloperidol, SCH-23390 elicited different degrees of potentiation of the effects of low clozapine and Lu AF35700 doses. Overall, the present data support a synergistic interaction between both DA receptors to reverse the PCP-induced alterations of oscillatory activity in thalamo-cortical networks, possibly due to their simultaneous blockade in direct and indirect pathways of basal ganglia. The mild potentiation induced by SCH-23390 in the case of clozapine and Lu AF35700 suggests that, at effective doses, these agents reverse PCP effects through the simultaneous blockade of both DA receptors.

Specific inhibition of α5 subunit-containing GABAA receptors enhances locomotor activity and neuronal activity in the motor cortex.

Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the central nervous system (CNS). This study examined the effect of specific inhibition of α5 subunit-containing GABAA receptors (α5GABAAR) on the behavioral profile and neuronal activity of the CNS using a compound called L-655,708, which is a selective negative allosteric modulator of α5GABAAR. L-655,708 administration significantly increased locomotor activity without anxiety-related behavior. Furthermore, L-655,708 administration significantly increased c-Fos mRNA expression (a neuronal activity marker) in motor area of the cerebral cortex, whereas it hardly altered c-Fos mRNA expression in the sensory cortex, hippocampus, and spinal cord. This study revealed for the first time that alteration of neuronal activity with specific inhibition of α5GABAAR differs depending on each CNS region. α5GABAAR could be a potential target for modulating CNS excitability and behavioral activity.

Chronic Stress Alters Behavior in the Forced Swim Test and Underlying Neural Activity in Animals Exposed to Alcohol Prenatally: Sex- and Time-Dependent Effects.

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) stress response has been suggested to play a role in vulnerability to stress-related disorders, such as depression. Prenatal alcohol exposure (PAE) may result in HPA dysregulation, which in turn may predispose individuals to the effects of stress exposure throughout life, and increase their risk of developing depression compared to unexposed individuals. We examined the immediate and delayed effects of chronic unpredictable stress (CUS) in adulthood on behavior of PAE animals in the forced swim test (FST) and the neurocircuitry underlying behavioral, emotional, and stress regulation. Adult male and female offspring from PAE and control conditions were tested for 2 days in the FST, with testing initiated either 1 day (CUS-1; immediate) or 14 days (CUS-14; delayed) post-CUS. Following testing, c-fos mRNA expression of the medial prefrontal cortex (mPFC), amygdala, hippocampal formation, and the paraventricular nucleus of the hypothalamus was assessed. Our results indicate that PAE and CUS interact to differentially alter FST behaviors and neural activation of several brain areas in males and females, and effects may depend on whether testing is immediate or delayed post-CUS. PAE males showed decreased time immobile (Day 1 of FST) following immediate testing, while PAE females showed increased time immobile (Day 2 of FST) following delayed testing compared to their respective control counterparts. Moreover, in males, PAE decreased c-fos mRNA expression in the lateral and central nuclei of the amygdala in the non-CUS condition, and increased c-fos mRNA expression in the CA1 in the CUS-14 condition. By contrast in females, c-fos mRNA expression in the Cg1 was decreased in PAE animals (independent of CUS) and decreased in all mPFC subregions in CUS-14 animals (independent of prenatal treatment). Constrained principal component analysis, used to identify neural and behavioral networks, revealed that PAE altered the activation of these networks and modulated the effects of CUS on these networks in a sex- and time-dependent manner. This dysregulation of the neurocircuitry underlying behavioral, emotional and stress regulation, may ultimately contribute to an increased vulnerability to psychopathologies, such as depression, that are often observed following PAE.

Differential effects of relaxin-3 and a selective relaxin-3 receptor agonist on food and water intake and hypothalamic neuronal activity in rats

The neuropeptide relaxin-3 (RLN3) binds with high affinity to its cognate receptor, relaxin-family peptide receptor 3 (RXFP3), and with lower affinity to RXFP1, the cognate receptor for relaxin. Intracerebroventricular (icv) administration of RLN3 in rats strongly increases food and water intake and alters the activity of the hypothalamic-pituitary-adrenal (HPA) and gonadal (HPG) axes, but the relative involvement of RXFP3 and RXFP1 in these effects is not known. Therefore, the effects of icv administration of equimolar (1.1 nmol) amounts of RLN3 and the RXFP3-selective agonist RXFP3-A2 on food and water intake, plasma levels of corticosterone, testosterone, and oxytocin and c-fos mRNA expression in key hypothalamic regions in male rats were compared. Food intake was increased by both RLN3 and RXFP3-A2, but the orexigenic effects of RXFP3-A2 were significantly stronger than RLN3, 30 and 60min after injection. Water intake and plasma corticosterone and testosterone levels were significantly increased by RLN3, but not by RXFP3-A2. Conversely, RXFP3-A2 but not RLN3 decreased oxytocin plasma levels. RLN3, but not RXFP3-A2, increased c-fos mRNA levels in the parvocellular (PVNp) and magnocellular (PVNm) paraventricular and supraoptic (SON) hypothalamic nuclei, in the ventral medial preoptic area (MPAv), and in the organum vasculosum of the lamina terminalis (OVLT). A significant increase in c-fos mRNA expression was induced in the perifornical lateral hypothalamic area (LHApf) by RLN3 and RXFP3-A2. These results suggest that RXFP1 is involved in the RLN3 stimulation of water intake and activation of the HPA and HPG axes. The reduced food intake stimulation by RLN3 compared to RXFP3-A2 may relate to activation of both orexigenic and anorexigenic circuits by RLN3.

Pulsatile kisspeptin effectively stimulates gonadotropin-releasing hormone (GnRH)-producing neurons

Hypothalamic kisspeptin is integral to the hypothalamic–pituitary–gonadal axis by stimulating gonadotropin-releasing hormone (GnRH) release. GnRH is released from the hypothalamus in a pulsatile manner and determines the output of the gonadotropins. However, the effect of kisspeptin on GnRH-secreting cells remains unknown. In an experiment using static cultures of GT1-7 cells, kisspeptin did not significantly increase GnRH mRNA expression. However, when kisspeptin was administered to the cells in a pulsatile manner, GnRH mRNA expression was significantly increased. Primary cultures of fetal rat brain containing GnRH-expressing neurons responded to kisspeptin and increased GnRH mRNA expression by 1.65 ± 0.27-fold in the static condition. When cells were stimulated with kisspeptin in a pulsatile manner, GnRH mRNA expression was increased by up to 2.40 ± 0.21-fold. In perifused GT1-7 cells, pulsatile, but not continuous kisspeptin stimulation, effectively stimulated GnRH mRNA expression. To assess the level of stimulation of GnRH neurons by kisspeptin, the expression of c-fos was examined. In GT1-7 cells, kisspeptin stimulation in the static condition failed to increase c-fos mRNA expression. However, pulsatile kisspeptin stimulation increased c-fos mRNA by 2.31 ± 0.47-fold. Similar to the phenomenon observed in GT1-7 cells, pulsatile, but not static, kisspeptin stimulation significantly increased c-fos mRNA expression in the primary cultures of fetal rat brain. These observations suggest that pulsatile kisspeptin more effectively stimulates GnRH-producing cells to increase the production of GnRH.

Differential effects of central administration of relaxin-3 on food intake and hypothalamic neuropeptides in male and female rats.

Relaxin-3 (RLN3) is an orexigenic neuropeptide that produces sex-specific effects on food intake by stronger stimulation of feeding in female compared with male rats. This study determined which hypothalamic nuclei and associated neuropeptides may be involved in the sex-specific orexigenic effects of RLN3. Relaxin-3 (800 pmol) or vehicle was injected into the lateral ventricle of female and male rats. Food and water intake were measured after the first injection, and rats were euthanized after the second injection to determine the mRNA expression of the hypothalamic neuropeptides. Food but not water intake showed sex-specific effects of RLN3. Stimulation of food intake by RLN3 was significantly higher in female than in male rats. No effect of RLN3 injection was found on c-fos mRNA expression in the arcuate, dorsomedial and ventromedial hypothalamic nuclei. Increased c-fos mRNA expression was observed in the paraventricular hypothalamic nucleus (PVN) in both sexes and in the lateral hypothalamic area (LHA) in female rats. Relaxin-3 injections led to a sex-nonspecific increase in the expression of oxytocin mRNA in the magnocellular PVN. Conversely, RLN3-induced expression of anorexigenic neuropeptide arginine vasopressin (AVP) was significantly higher in the parvocellular PVN in male compared with female rats. Finally, RLN3 administration significantly increased the expression of orexin (ORX) mRNA in the LHA in female but not in male rats. Stronger expression of anorexigenic AVP in the PVN in male rats and increased expression of ORX in the LHA in female rats may contribute to stronger orexigenic effects of RLN3 in female rats compared with male rats.

Extinction of conditioned taste aversion is related to the aversion strength and associated with c-fos expression in the insular cortex

Taste aversion learning is a type of conditioning where animals learn to associate a novel taste (conditioned stimulus; CS) with a stimulus inducing symptoms of poisoning or illness (unconditioned stimulus; US). As a consequence animals later avoid this taste, a reaction known as conditioned taste aversion (CTA). An established CTA extinguishes over time when the CS is repeatedly presented in the absence of the US. However, inter-individual differences in CTA extinction do exist. Using a model of behavioral conditioning with saccharin as CS and the immunosuppressant cyclosporine A as US, the present study aimed at further elucidating the factors underlying individual differences in extinction learning by investigating whether extinction of an established CTA is related to the strength of the initially acquired CS–US association. In addition, we analyzed the expression of the neuronal activation marker c-fos in brain structures relevant for acquisition and retrieval of the CTA, such as the insular cortex and the amygdala. We here show that animals, displaying a strong CS–US association during acquisition, maintained a strong CTA during unreinforced CS re-exposures, in contrast to animals with moderate CS–US association. Moreover, the latter animals showed increased c-fos mRNA expression in the insular cortex. Our data indicate that CTA extinction apparently depends on the strength of the initially learned CS–US association. In addition, these findings provide further evidence that the memory for the initial excitatory conditioning and its subsequent extinction is probably stored in those structures that participate in the processing of the CS and the US.

5-HT2C receptor desensitization moderates anxiety in 5-HTT deficient mice: from behavioral to cellular evidence.

Background:Desensitization and blockade of 5-HT2C receptors (5-HT2CR) have long been thought to be central in the therapeutic action of antidepressant drugs. However, besides behavioral pharmacology studies, there is little in vivo data documenting antidepressant-induced 5-HT2CR desensitization in specific brain areas.Methods:Mice lacking the 5-HT reuptake carrier (5-HTT-/-) were used to model the consequences of chronic 5-HT reuptake inhibition with antidepressant drugs. The effect of this mutation on 5-HT2CR was evaluated at the behavioral (social interaction, novelty-suppressed feeding, and 5-HT2CR–induced hypolocomotion tests), the neurochemical, and the cellular (RT-qPCR, mRNA editing, and c-fos–induced expression) levels.Results:Although 5-HTT-/- mice had an anxiogenic profile in the novelty-suppressed feeding test, they displayed less 5-HT2CR–mediated anxiety in response to the agonist m-chlorophenylpiperazine in the social interaction test. In addition, 5-HT2CR–mediated inhibition of a stress-induced increase in 5-HT turnover, measured in various brain areas, was markedly reduced in 5-HTT-/- mutants. These indices of tolerance to 5-HT2CR stimulation were associated neither with altered levels of 5-HT2CR protein and mRNA nor with changes in pre-mRNA editing in the frontal cortex. However, basal c-fos mRNA production in cells expressing 5-HT2CR was higher in 5-HTT-/- mutants, suggesting an altered basal activity of these cells following sustained 5-HT reuptake carrier inactivation. Furthermore, the increased c-fos mRNA expression in 5-HT2CR–like immune-positive cortical cells observed in wild-type mice treated acutely with the 5-HT2CR agonist RO-60,0175 was absent in 5-HTT-/- mutants.Conclusions:Such blunted responsiveness of the 5-HT2CR system, observed at the cell signaling level, probably contributes to the moderation of the anxiety phenotype in 5-HTT-/- mice.

Peripheral α2-β1 adrenergic interactions mediate the ghrelin response to brain urocortin 1 in rats.

SummaryThe autonomic nervous system (ANS) conveys neuronal input from the brain to the stomach. We investigated mechanisms through which urocortin 1 (UCN1) injected intracerebroventricularly (ICV, 300 pmol/rat) inhibits circulating ghrelin in rats. This was achieved by assessing (1) the induction of c-fos gene expression as a marker of neuronal activation in specific hypothalamic and caudal brainstem regulating ANS; (2) the influence of vagotomy and pharmacological blockade of central and peripheral α- and β-adrenergic receptor (AR) on ICV UCN1 -induced reduction of plasma ghrelin levels (determined by ELISA); and (3) the relevance of this pathway in the feeding response to a fast in rats. UCN1 increased c-fos mRNA expression in key brain sites influencing sympathetic activity namely the hypothalamic paraventricular and ventromedial nuclei, locus coeruleus, nucleus of the solitary tract, and rostral ventrolateral medulla, by 16-, 29-, 6-, 37-, and 13-fold, respectively. In contrast, the dorsal motor nucleus of the vagus had little c-fos mRNA expression and ICV UCN1 induced a similar reduction in acylated ghrelin in the sham-operated (31%) and vagotomized (41%) rats. An intraperitoneal (IP) injection of either a non-selective α- or selective α2-AR antagonist reduced, while a selective α2-AR agonist enhanced ICV UCN1-induced suppression of plasma acylated ghrelin levels. In addition, IP injection of a non-selective β- or selective β1-AR agonist blocked, and selective β1-AR antagonist augmented, the ghrelin response to ICV UCN1. The IP injections of a selective α1- or non-selective β or β2-AR antagonists, or any of the pretreatments given ICV had no effect. ICV UCN1 reduced the 2-h food intake in response to a fast by 80%, and this effect was partially prevented by a selective α2-AR antagonist. These data suggest that ICV UCN1 reduces plasma ghrelin mainly through the brain sympathetic component of the ANS and peripheral AR specifically α2-AR activation and inactivation of β1-AR. The α2-AR pathway contributes to the associated reduction in food intake.

Tachykinin (NK1, NK2 and NK3) receptor, transient receptor potential vanilloid 1 (TRPV1) and early transcription factor, cFOS, mRNA expression in rat tissues following systemic capsaicin treatment

Capsaicin, the pungent component of chilli pepper, stimulates TRPV1-expressing cells which are followed by desensitisation to subsequent exposure to capsaicin and other TRPV1 activators. At high systemic doses (>125mg/kg), capsaicin produces long-term changes in both tachykinin receptor and TRPV1 expression and function in rats. However, whether desensitising (low) doses of capsaicin (~50mg/kg) affect tachykinin receptor and TRPV1 gene expression in the short term has yet to be investigated. The aim of the present study was to compare tachykinin receptor (NK1, NK2 and NK3) and TRPV1 mRNA expression 24h after administration of capsaicin (50mg/kgs.c.). Tachykinin receptor and TRPV1 mRNA were detected in all tissues studied with expression levels differing by up to 2500-fold between tissues. The highest expression of TRPV1 and NK1 mRNA was observed in the salivary gland, whereas NK2 mRNA expression was highest in the urinary bladder and NK3 mRNA expression in the frontal cortex. In the cervical spinal cord of rats treated with capsaicin, NK1 and NK3 mRNA expression were reduced by 56% and 80%, respectively (P<0.05), whereas NK2 and TRPV1 mRNA expression were increased 2.2- and 1.4-fold, respectively (P<0.05). NK1 and NK2 mRNA expression were decreased (P<0.05) in the urinary bladder and gastric fundus, respectively, following capsaicin treatment. There was a marked 100-fold increase in cFOS mRNA expression and 100-fold decrease in NK2 mRNA expression in the whole blood of capsaicin-treated rats. In conclusion, these studies show that tachykinin receptor and TRPV1 mRNA expression undergo significant changes within 24h of systemic low-dose capsaicin administration.

Galantamine as a Preventive of Diisopropylphosphorofluoridate Toxicity Effects in Rat Brain

Diisopropylfluorophosphate exerts its toxic effect by irreversibly inhibiting acetylcholinesterase. This results in over-stimulation of central and peripheral cholinergic activity. The aim of the present study was to evaluate the possible preventive effects of acute treatment with reversible acetylcholinesterase inhibitor galantamine against the signs of cholinergic toxic syndrome provoked by diisopropylfluorophosphate, such as hypothermia, muscular fasciculations, oral dyskinesia and decreased locomotor performance in a rat model of intoxication. The effects of these two anticholinesterases on acetylcholinesterase activity and on the expression of mRNA of the immediate early response gene c-fos in the brain were assessed by histochemical acetylcholinesterase staining and by in situ hybridization, respectively. Diisopropylfluorophosphate induced rapidly progressing hypothermia, muscular fasciculations, oral dyskinesia and decreased locomotor performance. The increased cholinergic cortical and hippocampal activity due to irreversible acetylcholinerase inhibition were indicated by the increased c-fos mRNA autoradiographic signal and by the inhibition of acetylcholinesterase staining, respectively. Galantamine by itself provoked transient and relatively weak inhibition of the acetylcholinesterase staining, while it did not induce increased c-fos mRNA expression or significant behavioural signs of cholinergic toxicity. Galantamine significantly reduced the rate of the onset, but not the maximal hypothermia induced by diisopropylfluorophosphate. Importantly, all the above-mentioned behavioural and neurochemical effects of diisopropylfluorophosphate were significantly reduced by galantamine. These results indicate that the acute pre-treatment with galantamine may have prophylactic effects against the intoxication by diisopropylfluorophosphate.

Unconditioned freezing is enhanced in an appetitive context: Implications for the contextual dependency of unconditioned fear

It has been well established that expression of conditioned fear is context independent, but the context dependency of unconditioned fear expression has rarely been explored. A recent study reported that unconditioned freezing in rats is enhanced in a familiar context, which suggests that unconditioned fear expression can be modulated by contextual processing. In order to further explore this possibility we examined unconditioned freezing in novel, familiar, and appetitive contexts; and attempted to identify brain regions critical for context-related changes in unconditioned freezing by measuring c-Fos mRNA levels in emotional circuits. Unconditioned freezing was enhanced in the appetitive context, and this enhancement was accompanied by increased c-Fos mRNA expression in the medial amygdala and hippocampus, but attenuated expression in the medial prefrontal cortex. In the appetitive context, expectation of a reward coupled with detection of threat may have enhanced unconditioned fear expression, which suggests that unconditioned fear expression can be modulated by contextual factors. Context-related expectancy mismatch may explain the enhancement of unconditioned fear expression seen in this study and warrants further examination.

Immortalization and characterization of osteoblast cell lines generated from wild‐type and Nmp4‐null mouse bone marrow stromal cells using murine telomerase reverse transcriptase (mTERT)

Intermittent parathyroid hormone (PTH) adds new bone to the osteoporotic skeleton; the transcription factor Nmp4/CIZ represses PTH-induced bone formation in mice and as a consequence is a potential drug target for improving hormone clinical efficacy. To explore the impact of Nmp4/CIZ on osteoblast phenotype, we immortalized bone marrow stromal cells from wildtype (WT) and Nmp4-knockout (KO) mice using murine telomerase reverse transcriptase. Clonal lines were initially chosen based on their positive staining for alkaline phosphatase and capacity for mineralization. Disabling Nmp4/CIZ had no gross impact on osteoblast phenotype development. WT and KO clones exhibited identical sustained growth, reduced population doubling times, extended maintenance of the mature osteoblast phenotype, and competency for differentiating toward the osteoblast and adipocyte lineages. Additional screening of the immortalized cells for PTH-responsiveness permitted further studies with single WT and KO clones. We recently demonstrated that PTH-induced c-fos femoral mRNA expression is enhanced in Nmp4-KO mice and in the present study we observed that hormone stimulated either an equivalent or modestly enhanced increase in c-fos mRNA expression in both primary null and KO clone cells depending on PTH concentration. The null primary osteoblasts and KO clone cells exhibited a transiently enhanced response to bone morphogenetic protein 2 (BMP2). The clones exhibited lower and higher expressions of the PTH receptor (Pthr1) and the BMP2 receptor (Bmpr1a, Alk3), respectively, as compared to primary cells. These immortalized cell lines will provide a valuable tool for disentangling the complex functional roles underlying Nmp4/CIZ regulation of bone anabolism.

Antinociceptive effects of intrathecal landiolol injection in a rat formalin pain model.

Perioperative beta-blocker administration has recently been recommended for patients undergoing cardiac or other surgery due to the beneficial cardiovascular effects of these agents. In addition, some studies have reported that perioperatively administered beta-blockers also have analgesic effects. In this study, to investigate the antinociceptive effects and the analgesic profile of landiolol, we examined the effects of intrathecal landiolol administration on nociceptive pain behavior and c-fos mRNA expression (a neural marker of pain) in the spinal cord using a rat formalin model. We found that pain-related behavior was inhibited by intrathecal landiolol administration. Moreover, the increase in c-fos mRNA expression on the formalin-injected side was less pronounced in rats administered landiolol than in saline administered controls. Thus, intrathecal administration of landiolol exhibited antinociceptive effects. Further investigation of the antinociceptive mechanism of landiolol is required.

Blood-Borne Angiotensin II Acts in the Brain to Influence Behavioral and Endocrine Responses to Psychogenic Stress

This study elucidates the neural circuits by which circulating angiotensin II (ANGII) acts in the brain to influence humoral and behavioral responses to psychological stressors. To test the hypothesis that systemic ANGII mediates stress responding via the subfornical organ (SFO), we first found that the timing of increased systemic ANGII in response to 60 min restraint coincides with increased c-fos mRNA expression in the SFO. Next, we administered an anterograde neuronal tract tracer into the SFO and found that fibers originating there make appositions onto neurons in the paraventricular nucleus of the hypothalamus that are also c-fos positive following restraint stress. To determine whether circulating ANGII stimulates the release of stress hormones via activation of angiotensin type 1 receptors (AT1R) within the SFO, we delivered lentivirus to knockdown AT1R expression locally in the SFO. Inhibition of AT1R specifically within the SFO blunted the release of adrenocorticotrophin-releasing hormone and corticosterone in response to restraint stress and caused rats to spend more time in the open arms of an elevated-plus maze than controls, indicating that inhibition of AT1R within the SFO is anxiolytic. Collectively, these results suggest that circulating ANGII acts on AT1R in the SFO to influence responding to psychological stressors.

Nicotine Alters Limbic Function in Adolescent Rat by a 5-HT1A Receptor Mechanism

Epidemiological studies have shown that adolescent smoking is associated with health risk behaviors, including high-risk sexual activity and illicit drug use. Using rat as an animal model, we evaluated the behavioral and biochemical effects of a 4-day, low-dose nicotine pretreatment (60 μg/kg; intravenous) during adolescence and adulthood. Nicotine pretreatment significantly increased initial acquisition of cocaine self-administration, quinpirole-induced locomotor activity, and penile erection in adolescent rats, aged postnatal day (P)32. These effects were long lasting, remaining evident 10 days after the last nicotine treatment, and were observed when nicotine pretreatment was administered during early adolescence (P28-31), but not late adolescence (P38-41) or adulthood (P86-89). Neurochemical analyses of c-fos mRNA expression, and of monoamine transmitter and transporter levels, showed that forebrain limbic systems are continuing to develop during early adolescence, and that this maturation is critically altered by brief nicotine exposure. Nicotine selectively increased c-fos mRNA expression in the nucleus accumbens shell and basolateral amygdala in adolescent, but not adult animals, and altered serotonin markers in these regions as well as the prefrontal cortex. Nicotine enhancement of cocaine self-administration and quinpirole-induced locomotor activity was blocked by co-administration of WAY 100 635 (N-{2-[4-(2-methoxyphenyl)-1-piperazinyl] ethyl}-N-(2-pyridinyl)cyclohexanecarboxamide), a selective serotonin 1A (5-HT1A) receptor antagonist. Early adolescent pretreatment with the mixed autoreceptor/heteroceptor 5-HT1A receptor agonist, 8-OH-DPAT, but not the autoreceptor-selective agonist, S-15535, also enhanced quinpirole-induced locomotor activation. Nicotine enhancement of quinpirole-induced penile erection was not blocked by WAY 100 635 nor mimicked by 8-OH-DPAT. These findings indicate that early adolescent nicotine exposure uniquely alters limbic function by both 5-HT1A and non-5-HT1A receptor mechanisms.

The Vasopressin V1b Receptor Modulates Plasma Corticosterone Responses to Dehydration-Induced Stress

Vasopressin V1b receptor knockout (V1b⁻/⁻) mice were used to investigate a putative role for the V1b receptor (V1bR) in fluid regulation and in the hypothalamic-neurohypophysial system (HNS) and hypothalamic-pituitary-adrenal (HPA) axis responses to osmotic stress induced by water deprivation (WD). Male wild-type and V1b⁻/⁻ mice were housed in metabolic cages to allow determination of water intake and urine volume and osmolality. When provided with food and water ad lib., spontaneous urine volume and urine osmolality did not differ between genotypes. Similarly, WD for 24 h caused comparable decreases in urine volume and increases in urine osmolality irrespective of genotype. WD resulted in an increase in plasma corticosterone concentration in wild-type animals; however, this WD-induced increase in plasma corticosterone was significantly attenuated in V1b⁻/⁻ mice. Comparable increases in neuronal activation, indicated by increased c-fos mRNA expression, and in vasopressin mRNA expression occurred in both the supraoptic nucleus and paraventricular nucleus (PVN) of wild-type and V1b⁻/⁻ mice following WD; however, the WD-induced decrease in corticotrophin-releasing hormone mRNA expression seen in the PVN of wild-type mice was not observed in the PVN of V1b⁻/⁻ mice. These data suggest that, although the vasopressin V1bR is not required for normal HNS function, it is necessary for a full HPA-axis response to the osmotic stress of WD.

Repeated administration of methamphetamine blocked cholecystokinin-octapeptide injection-induced c-fos mRNA expression without change in capsaicin-induced junD mRNA expression in rat cerebellum

In the cerebellum, there are numerous cholecystokinin (CCK-8)-containing fibers. Since systemic CCK-8 injection-induced anxiety (psychological stress) activates the locus coeruleus cells that send mossy fiber inputs to the cerebellum, we examined whether systemic CCK-8 injections activate the rat and mouse cerebellum. First, injections of CCK-8 were found to induce c-fos mRNA expression in a vague patchy pattern that is different from single methamphetamine-induced Zebrin band-like c-fos mRNA expression, suggesting that the CCK-8 activating mossy fibers induce gene expression differently from the dopamine-containing mossy fibers in the ventral tegmental area. Second, since CCK-8 facilitates neural activity of dopamine in the midbrain, we examined whether repeated methamphetamine administration that induced behavioral sensitization had similar effects on the cerebellar CCK system. Repeated administration of methamphetamine suppressed the CCK-8-induced c-fos mRNA expression in the rat cerebellum. Third, capsaicin injections (physical stress) into a hind limb of the rat increased junD mRNA expression with no effect on c-fos mRNA expression, and repeated methamphetamine injections had no effect on the capsaicin-induced expression of junD mRNA. Fourth, either single injection of methamphetamine or CCK-8 to mice increased c-fos mRNA expression in the locus coeruleus, and so noradrenalin, but not dopamine, might interact with CCK-8-activating system. However, we considered the possibility unlikely. Thus, we conclude that repeated methamphetamine administration though dopamine selectively inhibits the c-fos mRNA expression after CCK-8 injection in the cerebellum.

Involvement of endogenous opioid system in scorpion toxin-induced antinociception in mice

The present study analyzes the involvement of the endogenous opioid system in the antinociceptive effects produced in mammals after α- or β- scorpion toxin injections. The analgesic effects on mice of the α-anatoxin Amm VIII, a weak modulator of Na v1.2 channel, and the depressant insect-selective β-toxin LqqIT2 were evaluated by intraperitoneal route. The two toxins increased hot plate and tail flick latencies in a dose-dependent manner. We also compared the effects of the toxins with those obtained after acetic acid administration or cold-water tail immersion, which both induce pain relief through the activation of diffuse noxious inhibitory controls (DNIC) and the release of endogenous opioids. The increased latencies obtained with the toxins, acetic acid, or cold-water tail immersion were partly reversed by the co-administration of the opioid receptor antagonist naloxone. Finally, AmmVIII, LqqIT2, or acetic acid, induced increased c-fos mRNA expression in spinal cord. This increase disappeared when the toxins were co-injected with acetic acid. In conclusion, we show for the first time that an α-anatoxin exhibits a potent analgesic activity and confirm that depressant β-toxins are able to reduce nociception. We hypothesize that pain relief induced by these scorpion toxins may implicate the activation of an endogenous opioid system and may be partly the result of a counter irritation phenomenon, which could be due to the activation of DNIC.

Effects of transection of cervical sympathetic trunk on left ventricular remodeling after acute myocardial infarction in rats

Objective To investigate the effects of right or left transaction of cervical sympathetic trunk (TCST) on left ventricalar remodeling (LVRM) after acute myocardial infarction in rats and the mechanism. Methods Sixty-four adult mule pathogen-free SD rats (230-250 g) were randomly divided into 4 groups (n=16 each): group Ⅰsham operation (group S) ; group Ⅱ LVRM; group Ⅲ left TCST and group Ⅳ right TCST. Myocardial infarct was induced by ligation of left anterior descending branch (LAD) of coronary artery in group Ⅱ, Ⅲ and Ⅳ. Left and right TCST were performed immediately after myocardial infarct was successfully induced in group Ⅲ and Ⅳ respectively. In group S LAD and cervical sympathetic trunk were exposed but not ligated and transected. The animals were killed at 4 weeks after ligation of LAD and TCST. The weight of left ventricle was measured and left ventricle weight index calculated, Left veatricular myocardial tissue volume (V_t), the volume density of myocardial cells (V_v) and myocardial cell volmne (V_c) were quantitatively analyzed by stereological method. The c-fos mRNA expression in myocardium was determined by RT-PCR. Results The left ventricle weight index, V_t, V_c and c-fos mRNA expression were significantly increased in group LVRM (Ⅱ), left and right TCST (Ⅲ, Ⅳ) as compared with group S. Left ventricle weight index, V_v, V_t, V_c and c-fos mRNA expression were all significantly decreased in fight TCST group (Ⅳ), while left ventricle weight index, V_t, V_c and c-fos mRNA expression were significantly increased in left TCST group (Ⅲ) as compared with LVRM group (Ⅱ). Conclusion Right TCST down-regulates the increase in c-fos mRNA expression after acute myocardial infarction and inhibits the left ventricular remodeling while left TCST up-regulates the c-fos mRNA expression and promotes the development of left ventricular remodeling. Key words: Ganglia; sympathetic; Sympathectomy; Myocardial infarction; Ventricular remodeling