Induction of c-fos in rat brain by acute cocaine and fenfluramine exposure: a comparison study

Effects of isoflurane and ethanol administration on c-Fos immunoreactivity in mice

Noninvasive functional imaging holds great promise for the future of translational research, due to the ability to directly compare between preclinical and clinical models of psychiatric disorders. Despite this potential, concerns have been raised regarding the necessity to anesthetize rodent and monkey subjects during these procedures, because anesthetics may alter neuronal activity. For example, in studies on drugs of abuse and alcohol, it is not clear to what extent anesthesia can interfere with drug-induced neural activity. Therefore, the current study investigated whole-brain c-Fos activation following isoflurane anesthesia as well as ethanol-induced activation of c-Fos in anesthetized mice. In the first experiment, we examined effects of one or three sessions of gaseous isoflurane on c-Fos activation across the brain in male C57BL/6J mice. Isoflurane administration led to c-Fos activation in several areas, including the piriform cortex and lateral septum. Lower or similar levels of activation in these areas were detected after three sessions of isoflurane, suggesting that multiple exposures may eliminate some of the enhanced neuronal activation caused by acute isoflurane. In the second experiment, we investigated the ability of ethanol injection (1.5 or 2.5g/kgi.p.) to induce c-Fos activation under anesthesia. Following three sessions of isoflurane, 1.5g/kg of ethanol induced c-Fos in the central nucleus of amygdala and the centrally-projecting Edinger-Westphal nucleus (EWcp). This induction was lower after 2.5g/kg of ethanol. These results demonstrate that ethanol-induced neural activation can be detected in the presence of isoflurane anesthesia. They also suggest, that while habituation to isoflurane helps reduce neuronal activation, interaction between effects of anesthesia and alcohol can occur. Studies using fMRI imaging could benefit from using habituated animals and dose-response analyses.

Self-regulation therapy to reproduce drug effects: a suggestion technique to change personality and the DRD3 gene expression

This study proposes a strategy, based on self-regulation therapy, to change personality and its biological substrate, the DRD3 gene expression. It has been demonstrated that acute doses of stimulating drugs, like methylphenidate, are able to change personality and the expression of certain genes in the short term. On the other hand, self-regulation therapy has been proven to reproduce the effects of drugs. Thus, it is feasible to hope that self-regulation therapy is equally effective as methylphenidate in changing personality and the gene expression. This is a preliminary study with a single-case experimental design with replication in which 2 subjects participated. The results and potential implications for research and psychotherapy are discussed.

Addiction-related gene regulation: risks of exposure to cognitive enhancers vs. other psychostimulants

The psychostimulants methylphenidate (Ritalin, Concerta), amphetamine (Adderall), and modafinil (Provigil) are widely used in the treatment of medical conditions such as attention-deficit hyperactivity disorder and narcolepsy and, increasingly, as "cognitive enhancers" by healthy people. The long-term neuronal effects of these drugs, however, are poorly understood. A substantial amount of research over the past two decades has investigated the effects of psychostimulants such as cocaine and amphetamines on gene regulation in the brain because these molecular changes are considered critical for psychostimulant addiction. This work has determined in some detail the neurochemical and cellular mechanisms that mediate psychostimulant-induced gene regulation and has also identified the neuronal systems altered by these drugs. Among the most affected brain systems are corticostriatal circuits, which are part of cortico-basal ganglia-cortical loops that mediate motivated behavior. The neurotransmitters critical for such gene regulation are dopamine in interaction with glutamate, while other neurotransmitters (e.g., serotonin) play modulatory roles. This review presents (1) an overview of the main findings on cocaine- and amphetamine-induced gene regulation in corticostriatal circuits in an effort to provide a cellular framework for (2) an assessment of the molecular changes produced by methylphenidate, medical amphetamine (Adderall), and modafinil. The findings lead to the conclusion that protracted exposure to these cognitive enhancers can induce gene regulation effects in corticostriatal circuits that are qualitatively similar to those of cocaine and other amphetamines. These neuronal changes may contribute to the addiction liability of the psychostimulant cognitive enhancers.

5-HT(2A) receptor blockade and 5-HT(2C) receptor activation interact to reduce cocaine hyperlocomotion and Fos protein expression in the caudate-putamen

Both the 5-HT(2A) receptor (R) antagonist M100907 and the 5-HT(2C) R agonist MK212 attenuate cocaine-induced dopamine release and hyperlocomotion. This study examined whether these drugs interact to reduce cocaine hyperlocomotion and Fos expression in the striatum and prefrontal cortex. We first determined from dose-effect functions a low dose of both M100907 and MK212 that failed to alter cocaine (15 mg/kg, i.p.) hyperlocomotion. Subsequently, we examined whether these subthreshold doses given together would attenuate cocaine hyperlocomotion, consistent with a 5-HT(2A)/5-HT(2C) R interaction. Separate groups of rats received two sequential drug injections 5 min apart immediately before a 1-h locomotion test as follows: (1) saline + saline, (2) saline + cocaine, (3) 0.025 mg/kg M100907 + cocaine, (4) 0.125 mg/kg MK212 + cocaine, or (5) cocktail combination of 0.025 mg/kg M100907 and 0.125 mg/kg MK212 + cocaine. Brains were extracted for Fos immunohistochemistry 90 min after the second injection. We next examined the effects of 0.025 mg/kg M100907 and 0.125 mg/kg MK212, alone and in combination, on spontaneous locomotor activity. While neither drug given alone produced any effects, the M100907/MK212 cocktail attenuated cocaine hyperlocomotion as well as cocaine-induced Fos expression in the dorsolateral caudate-putamen (CPu), but had no effect on spontaneous locomotion. The findings suggest that 5-HT(2A) Rs and 5-HT(2C) Rs interact to attenuate cocaine hyperlocomotion and Fos expression in the CPu, and that the CPu is a potential locus of the interactive effects between these 5-HT(2) R subtypes on behavior. Further research investigating combined 5-HT(2A) R antagonism and 5-HT(2C) R agonism as a treatment for cocaine dependence is warranted.

Potential anxiogenic effects of cannabinoid CB1 receptor antagonists/inverse agonists in rats: comparisons between AM4113, AM251, and the benzodiazepine inverse agonist FG-7142

Cannabinoid CB1 inverse agonists suppress food-motivated behaviors, but may also induce psychiatric effects such as depression and anxiety. To evaluate behaviors potentially related to anxiety, the present experiments assessed the CB1 inverse agonist AM251 (2.0-8.0mg/kg), the CB1 antagonist AM4113 (3.0-12.0mg/kg), and the benzodiazepine inverse agonist FG-7142 (10.0-20.0mg/kg), using the open field test and the elevated plus maze. Although all three drugs affected open field behavior, these effects were largely due to actions on locomotion. In the elevated plus maze, FG-7142 and AM251 both produced anxiogenic effects. FG-7142 and AM251 also significantly increased c-Fos activity in the amygdala and nucleus accumbens shell. In contrast, AM4113 failed to affect performance in the plus maze, and did not induce c-Fos immunoreactivity. The weak effects of AM4113 are consistent with biochemical data showing that AM4113 induces little or no intrinsic cellular activity. This research may lead to the development of novel appetite suppressants with reduced anxiogenic effects.

Differential effects of stress and amphetamine administration on Fos-like protein expression in corticotropin releasing factor-neurons of the rat brain

Corticotropin releasing factor (CRF) appears to be critical for the control of important aspects of the behavioral and physiological response to stressors and drugs of abuse. However, the extent to which the different brain CRF neuronal populations are similarly activated after stress and drug administration is not known. We then studied, using double immunohistochemistry for CRF and Fos protein, stress and amphetamine-induced activation of CRF neurons in cortex, central amygdala (CeA), medial parvocellular dorsal, and submagnocellular parvocellular regions of the paraventricular nucleus of the hypothalamus (PVNmpd and PVNsm, respectively) and Barrington nucleus (Bar). Neither exposure to a novel environment (hole-board, HB) nor immobilization (IMO) increased Fos-like immunoreactivity (FLI) in the CeA, but they did to the same extent in cortical regions. In other regions only IMO increased FLI. HB and IMO both failed to activate CRF+ neurons in cortical areas, but after IMO, some neurons expressing FLI in the PVNsm and most of them in the PVNmpd and Bar were CRF+. Amphetamine administration increased FLI in cortical areas and CeA (with some CRF+ neurons expressing FLI), whereas the number of CRF+ neurons increased only in the PVNsm, in contrast to the effects of IMO. The present results indicate that stress and amphetamine elicited a distinct pattern of brain Fos-like protein expression and differentially activated some of the brain CRF neuronal populations, despite similar levels of overall FLI in the case of IMO and amphetamine.

Cocaine‐induced locomotor activity and Fos expression in nucleus accumbens are sensitized for 6 months after repeated cocaine administration outside the home cage

Induction of the immediate early gene protein product Fos has been used extensively to assess neural activation in the striatum after repeated cocaine administration to rats in their home cages but rarely after repeated administration outside the home cage, which produces more robust locomotor sensitization. In the present study, we found cocaine-induced Fos expression in nucleus accumbens, but not caudate-putamen, was enhanced 1 and 6 months after repeated drug administration in locomotor activity chambers. Double-labelling of Fos protein and enkephalin mRNA indicated that Fos expression in nucleus accumbens was enhanced in enkephalin-positive, but not enkephalin-negative, medium spiny neurons. In contrast, cocaine-induced Fos expression was absent altogether in nucleus accumbens and unaltered in caudate-putamen 1 month after repeated cocaine administration in the home cage. As cocaine-induced locomotor activity was also enhanced 1 and 6 months after repeated cocaine administration in locomotor activity chambers, we wanted to confirm that neuronal activity in nucleus accumbens mediates cocaine-induced locomotor activity using our particular treatment regimen. Bilateral infusions of the GABA agonists baclofen and muscimol (1 microg/side) into nucleus accumbens of sensitized rats blocked cocaine-induced Fos expression and locomotor activity. Thus, while neuronal activity in both D1- and D2-type neurons in nucleus accumbens can mediate acute cocaine-induced locomotor activity, the enhanced activation of enkephalinergic D2-type neurons suggests that these latter neurons mediate the enhancement of cocaine-induced locomotor activity for up to 6 months after repeated drug administration outside the home cage.

Topography of methylphenidate (ritalin)-induced gene regulation in the striatum: differential effects on c-fos, substance P and opioid peptides

Dopamine action alters gene regulation in striatal neurons. Methylphenidate increases extracellular levels of dopamine. We investigated the effects of acute methylphenidate treatment on gene expression in the striatum of adult rats. Molecular changes were mapped in 23 striatal sectors mostly defined by their predominant cortical inputs in order to determine the functional domains affected. Acute administration of 5 and 10 mg/kg (i.p.) of methylphenidate produced robust increases in the expression of the transcription factor c-fos and the neuropeptide substance P. Borderline effects were found with 2 mg/kg, but not with 0.5 mg/kg. For 5 mg/kg, c-fos mRNA levels peaked at 40 min and returned to baseline by 3 h after injection, while substance P mRNA levels peaked at 40-60 min and were back near control levels by 24 h. These molecular changes occurred in most sectors of the caudate-putamen, but were maximal in dorsal sectors that receive sensorimotor and medial agranular cortical inputs, on middle to caudal levels. In rostral and ventral striatal sectors, changes in c-fos and substance P expression were weaker or absent. No effects were seen in the nucleus accumbens, with the exception of c-fos induction in the lateral part of the shell. In contrast to c-fos and substance P, acute methylphenidate treatment had minimal effects on the opioid peptides dynorphin and enkephalin. These results demonstrate that acute methylphenidate alters the expression of c-fos and substance P preferentially in the sensorimotor striatum. These molecular changes are similar, but not identical, to those produced by other psychostimulants.

Activation of the cGMP pathway in dopaminergic structures reduces cocaine-induced EGR-1 expression and locomotor activity

Nitric oxide (NO) and the C-type natriuretic peptide (CNP) exert their action on brain via the cGMP signaling pathway. NO, by activating soluble guanylyl cyclase, and CNP, by stimulating membrane-bound guanylyl cyclase, cause intracellular increases of cGMP, activating cGMP-dependent protein kinases (PKGs). We show here that injection of CNP into the rat ventral tegmental area strongly reduced cocaine-induced egr-1 expression in the nucleus accumbens in a dose-dependent manner. The effect of CNP was reversed by the previous injection of a selective PKG inhibitor, KT5823. Activation of PKG by 8-bromo-cGMP reduced, like CNP, cocaine-induced gene transcription in dopaminergic structures. To confirm the involvement of PKG, this was overexpressed in either the mesencephalon or the caudate-putamen. Using the polyethyleneimine delivery system, an active protein was expressed by injecting a plasmid vector containing the human PKG-Ialpha cDNA. PKG was overexpressed in dopaminergic and GABAergic neurons when the plasmid was injected in the ventral tegmental area, whereas overexpression was observed in medium spiny GABAergic neurons and in both cholinergic and GABAergic interneurons when the PKG vector was injected into the caudate-putamen. Activation of the overexpressed PKG reduced cocaine-induced egr-1 expression in dopaminergic structures and affected behavior (i.e., locomotor activity). These effects were again reversed by previous injection of the selective PKG inhibitor. The current data suggest that NO and the neuropeptide CNP are potential regulators of cocaine-related effects on behavior.

Nitric oxide in health and disease of the respiratory system

During the past decade a plethora of studies have unravelled the multiple roles of nitric oxide (NO) in airway physiology and pathophysiology. In the respiratory tract, NO is produced by a wide variety of cell types and is generated via oxidation of l-arginine that is catalyzed by the enzyme NO synthase (NOS). NOS exists in three distinct isoforms: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS). NO derived from the constitutive isoforms of NOS (nNOS and eNOS) and other NO-adduct molecules (nitrosothiols) have been shown to be modulators of bronchomotor tone. On the other hand, NO derived from iNOS seems to be a proinflammatory mediator with immunomodulatory effects. The concentration of this molecule in exhaled air is abnormal in activated states of different inflammatory airway diseases, and its monitoring is potentially a major advance in the management of, e.g., asthma. Finally, the production of NO under oxidative stress conditions secondarily generates strong oxidizing agents (reactive nitrogen species) that may modulate the development of chronic inflammatory airway diseases and/or amplify the inflammatory response. The fundamental mechanisms driving the altered NO bioactivity under pathological conditions still need to be fully clarified, because their regulation provides a novel target in the prevention and treatment of chronic inflammatory diseases of the airways.

Morphine induction of c-fos expression in the rat forebrain through glutamatergic mechanisms: role of non-n-methyl-D-aspartate receptors

Acute injection of morphine induces expression of the immediate-early genes c-Fos and JunB in several forebrain regions of the rat, in part through an N-methyl-D-aspartate (NMDA) receptor-dependent mechanism. Because membrane depolarization through (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors is believed to be necessary for full activation of NMDA receptors, we determined the role of AMPA receptors in morphine-induced c-Fos expression. Rats were given the AMPA receptor antagonist GYKI-52466 (12.9 mg/kg, i.p.) 15 min before morphine (10 mg/kg, s.c.), or the AMPA receptor enhancer CX516 (30 mg/kg, i.p.) 5 min after morphine. The c-Fos response was attenuated by the antagonist and augmented by the enhancer. Using double immunocytochemistry, we found that morphine induced c-Fos in neurons containing the GluR2/3, but not the GluR1 and rarely the GluR4, subunits of the AMPA receptor. Double immunocytochemistry for mu opioid receptor and c-Fos showed that c-Fos expression was mainly absent in the patch compartment of the striatum, which is enriched in mu opioid receptors. The glutamatergic synapse often contains metabotropic receptors as well as ionotropic receptors. Type I metabotropic glutamate receptors are coupled to activation of protein kinase C, which has also been shown to mediate the immediate-early gene response to morphine. To determine if activation of metabotropic glutamate receptors is involved in rapid effects of morphine on the brain, rats were given the type I metabotropic glutamate receptor antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA; 0.2 mg/kg, i.p.) or vehicle 30 min before morphine treatment. Pretreatment with AIDA completely blocked morphine-induced c-Fos expression in the caudate-putamen.Taken together, these results demonstrate involvement of both AMPA and type I metabotropic glutamate receptors in the acute effects of morphine on the forebrain, supporting an important role for glutamatergic neurotransmission mediated by non-NMDA glutamate receptors in morphine's actions.

Repeated methylphenidate treatment in adolescent rats alters gene regulation in the striatum

Methylphenidate is a psychostimulant which inhibits the dopamine transporter and produces dopamine overflow in the striatum, similar to the effects of cocaine. Excessive dopamine action is often associated with changes in gene expression in dopamine-receptive neurons. Little is known about methylphenidate's effects on gene regulation. We investigated whether a methylphenidate treatment regimen known to produce behavioural changes would alter gene expression in the striatum. Using in situ hybridization histochemistry, we assessed the effects of acute and repeated methylphenidate treatment on the expression of immediate-early genes (c-fos, zif 268) and neuropeptides (dynorphin, substance P, enkephalin) in adolescent rats. Acute methylphenidate treatment (0-10 mg/kg, i.p.) produced a dose-dependent increase in the expression of c-fos and zif 268. These effects were most pronounced in the dorsal striatum at middle to caudal striatal levels, and were found for doses as low as 2 mg/kg. Repeated treatment with methylphenidate (10 mg/kg/day, 7 days) increased the expression of dynorphin, which was highly correlated with the acute immediate-early gene response across different striatal regions. Moreover, after repeated methylphenidate treatment, cocaine-induced expression of c-fos and zif 268, as well as of substance P, was significantly attenuated throughout the striatum. These effects of repeated methylphenidate treatment mirror those produced by repeated treatment with cocaine or other psychostimulants and are considered to reflect drug-induced neuroadaptations. Thus, our findings demonstrate that acute and repeated methylphenidate treatment can produce molecular alterations similar to other psychostimulants.

Increased neuronal nitric oxide synthase (nNOS) activity triggers picrotoxin-induced seizures in rats and evidence for participation of nNOS mechanism in the action of antiepileptic drugs

Increased neuronal nitric oxide synthase (nNOS) activity was observed during the prodromal period of seizures in various rat brain regions following administration of GABA(A) receptor antagonist, picrotoxin (PCT). Pretreatment with the selective nNOS inhibitor 7-nitroindazole (7-NI), dose- and time-dependently delayed the onset of clonus with a corresponding decrease in nNOS activity. The threshold dose of antiepileptic drugs (AEDs; diazepam, phenobarbitone and gabapentin) have potentiated the anticonvulsant action by pretreatment with graded doses of 7-NI. The increase in efficacy of anticonvulsant action correlated with a corresponding decrease of PCT-evoked increase in nNOS activity. The present data support a role for abnormal nNOS activity in mechanisms that trigger seizures and suggest a possible NO-mediated interplay between GABA(A) and glutamate receptors. The results of the present study provide evidence for a trigger role of neuronally produced NO in epileptogenesis induced by PCT and the participation of nNOS inhibitory mechanisms in the action of AEDs.

Rat strain differences to fluoxetine in striatal Fos-like proteins

Humans afflicted with mood disorders respond differently to antidepressant drug therapy. Different responses to psychoactive drugs are also observed in rats, and specific strains exhibit substantial differences in gene expression following synaptic activity. We examined the effects of fluoxetine on the induction of Fos-like proteins in Long-Evans and Sprague-Dawley rat brains. Fluoxetine elicited a strong induction of Fos in the striatum of Long-Evans but not Sprague-Dawley rats following acute drug exposure. This effect was specific to fluoxetine as two highly selective serotonin reuptake inhibitors, HD-31 and HD-50, as well as treatment with fenfluramine failed to replicate the observed differences in Fos. These differences in Fos expression between rat strains may represent variability in post-receptor pathways that ultimately mediate the therapeutic actions of fluoxetine.

Differential rat brain expression of EGR proteins and of the transcriptional corepressor NAB in response to acute or chronic cocaine administration

Members of the Egr family of early genes are known to play a prominent role in neuronal plasticity. Using in situ hybridization, we report the induction in the rat forebrain of the immediate early gene egr-1 and of the transcriptional repressor NAB2 in response to acute or repeated cocaine administration. A single exposure to cocaine enhanced the expression of egr-1 in dopaminergic brain areas. Chronic cocaine treatment was not followed by induction of egr-1 mRNA initially, but only 12 h following the last injection, whereas Egr-1 binding activity was maintained elevated at 2 h and was increased again at 12 h. Expression of the Egr corepressor NAB2, but not NAB1, was rapidly and transiently stimulated by cocaine. Both acute and chronic cocaine treatment displayed biphasic NAB2 mRNA expression. It appears that NAB2 operates as an inducible regulator of gene expression in postmitotic neurons. Egr-3 displayed an expression profile similar to that of Egr-1 in response to acute cocaine injection and was expressed slightly earlier upon repeated cocaine treatment. Regulation of Egr transcription factors during chronic cocaine treatment appears to differ from that of the AP1 transcription factor, since Egr-1 and Egr-3 were induced after both acute and repeated cocaine administration, and that neither Egr-2 nor Egr-3 substituted for Egr-1 after chronic cocaine treatment. Our data suggest that Egr-1, Egr-3, and NAB2 are the key members of their families that regulate expression of Egr target genes.

The nitric oxide releasing agent sodium nitroprusside modulates cocaine-induced immediate early gene expression in rat brain

The nitric oxide (NO)/cGMP pathway triggers key events in synaptic phenomena involved in learning and memory. Using in situ hybridization, the present report demonstrates that NO released by sodium nitroprusside regulates egr-1, c-fos, and junB immediate early gene expression in rat forebrain. These genes, which are rapidly and transiently induced in response to diverse extracellular stimulation, coordinate alterations in gene expression underlying neuronal plasticity. Intracerebroventricular injection of sodium nitroprusside induced immediate early gene expression, which was highest in the nucleus accumbens. On the other hand, sodium nitroprusside abolished the cocaine-induced early gene expression in the dopaminergic projection fields nucleus accumbens, caudate-putamen, and frontal cortex. Further studies are warranted to explore the potential of the NO/cGMP/cGMP-dependent protein kinase pathway to modify cocaine-related behavioral effects.

Induction of the immediate early genes egr-1 and c-fos by methamphetamine in mouse brain

Methamphetamine (METH) is one of the most commonly abused psychostimulant, and is known to induce dopaminergic neurotoxicity by generating oxidative stress and free radicals. In the present study we investigated the effects of METH on egr-1 and c-fos immediate early gene induction in different regions of mouse brain, at different doses and different time courses. We also measured the tissue levels of monoamines in order to correlate their changes with gene expression. A single injection of METH (40 mg/kg) significantly increased egr-1 and c-fos mRNA expression within 30 min in frontal cortex, nucleus accumbens, caudate putamen, septum and CA1 region of hippocampus. Time course studies showed that in most cases, both genes were expressed within 30 min and decreased after 60 min. METH produced a significant decrease in striatal dopamine level, reaching a very low level after 24 h. Striatal serotonin level significantly increased and returned to control levels after 2 h. These data show that METH induced egr-1 and c-fos mRNA expression in selective brain areas, which correlated with an alteration in monoamines.

C-type natriuretic peptide (CNP) regulates cocaine-induced dopamine increase and immediate early gene expression in rat brain

The neuropeptide C-type natriuretic peptide (CNP) is the primary biologically active natriuretic peptide in brain. Using in situ hybridization, the present report demonstrates that CNP regulates egr-1, c-fos and junB immediate early gene expression in rat brain. In the frontal cortex, CNP induced immediate early gene expression whereas it inhibited dose-dependently the cocaine-induced early gene expression in the dopaminergic projection fields nucleus accumbens and caudate-putamen. CNP may produce its effect directly on dopaminergic neurons because we found that its receptor, guanylyl cyclase GC-B, was expressed in the mesencephalon where dopaminergic neurons originate, as well as in their projection fields. The inhibition by CNP of the early gene expression elicited by cocaine in the caudate-putamen is correlated with a CNP-evoked decrease in cocaine-induced rise in extracellular dopamine, measured by in vivo microdialysis experiments. The significance of the inhibition of cocaine-induced dopamine release and early gene induction by the endogenous peptide CNP is demonstrated by data indicating that CNP reduced the cocaine-induced spontaneous locomotor activation. By inhibiting dopaminergic neuronal activity, CNP represents a potential negative regulator of related behavioural effects of cocaine.

C-fos and egr-1 immediate-early gene induction by cocaine and cocaethylene in rat brain: a comparative study

The induction of immediate-early genes can now be considered as a tool to study neuronal activation in different brain structures. These genes, which are rapidly and transiently induced in response to diverse extracellular stimulation, coordinate alterations in gene expression underlying neuronal plasticity. Using in situ hybridization, we found that acute i.p. cocaine (20 mg/kg) injection produced a strong expression of egr-1 and c-fos genes in the nucleus accumbens, caudate-putamen, and frontal cortex in the rat. Cocaethylene is an active metabolite of cocaine that is formed when cocaine is consumed together with ethyl alcohol. Injection of cocaethylene at a dose equivalent to cocaine induced the expression of the two immediate-early genes in the same brain structures, but to a lesser extent. A high dose of ethanol increased egr-1 and c-fos expression in the frontal cortex and in the lateral part of the caudate-putamen. Since cocaine is known to potently inhibit both dopamine and serotonin transporters, whereas cocaethylene only inhibits the dopamine transporter, our results strongly suggest that the serotonergic system participates in the mode of action of cocaine in its ability to trigger immediate-early gene transcription.

Interaction between the serotoninergic and dopaminergic systems in d-fenfluramine-induced activation of c-fos and jun B genes in rat striatal neurons

To test for the relative contributions of the dopaminergic and serotoninergic systems in the striatum to the effects of d-fenfluramine, an indirect serotonin receptor agonist, we assessed the expression of Fos/Jun proteins induced by d-fenfluramine given alone or in the presence of dopaminergic or serotoninergic agents. To determine the neuronal targets of d-fenfluramine in the striatum, we identified the phenotypes of striatal neurons in which d-fenfluramine induced Fos expression. Our results demonstrated that d-fenfluramine evokes nuclear expression of Fos/Jun B proteins in the striatum, and that the Fos expression was dose-dependent and accompanied by transient induction of c-fos mRNA. Fos expression was blocked by p-chloroamphetamine, a serotoninergic neurotoxin. Pretreatment with SCH 23390, a D1-dopamine receptor antagonist, led to a marked decrease in Fos/Jun B expression in the caudoputamen, but not in the cortex, whereas pretreatment with methiothepin, a nonselective serotonin 5-HT1 receptor antagonist, blocked Fos expression completely in the cortex and only partially in the caudoputamen. The expression of Fos/Jun B in the striatum occurred mainly in dynorphin-containing neurons and in a subpopulation of striatal interneurons that exhibited NADPH-diaphorase activity. Most of the enkephalin-containing neurons of the striatum did not show Fos/Jun B staining. These results suggest that the mechanism by which d-fenfluramine induces c-fos and jun B expression in the rat caudoputamen depends at least in part on activation of the dopaminergic system by serotonin.

Fenfluramine-induced increase in preproenkephalin mRNA levels in the striatum: interaction between the serotonergic, glutamatergic, and dopaminergic systems

Fenfluramine (FE) is a halogenated amphetamine derivative that has been used in the treatment of obesity. It has been suggested that the effects of FE on the striatum are mediated by serotonergic mechanisms. However, several major afferent systems may be involved, and administration of FE may be useful to study interactions between these systems. In this work, the effects of FE on striatopallidal neurons and the possible involvement of the major striatal afferent systems were studied in rats by determination of FE-induced changes in striatal levels of preproenkephalin (PPE) mRNA using in situ hybridization. Injection of FE induced a significant increase (60%) in striatal levels of PPE mRNA. This increase was blocked by pretreatment with the D(1) dopamine receptor antagonist SCH-23390 or with the NMDA glutamate receptor antagonist MK-801, or by lesion of the serotonergic system with 5,7-dihydroxytryptamine or p-chlorophenylalanine. In 6-hydroxydopamine lesioned rats, the lesion-induced increase in PPE mRNA levels was not affected by injection of FE, but was reduced by simultaneous serotonergic deafferentation. The results suggest that the serotonergic, glutamatergic, and dopaminergic system interact to increase striatal PPE mRNA levels after FE administration.

Acute ibogaine injection induces expression of the immediate early genes, egr-1 and c-fos, in mouse brain

The aim of the present study was to evaluate if an acute injection of ibogaine (IBO) induces immediate early gene expression in different regions of mouse brain. Adult male C57 mice received a single injection of IBO and were perfused transcardially with 1% paraformaldehyde 30 min after the drug administration. A single injection of IBO produced a significant increase of egr-1 messenger RNA induction in nucleus accumbens (NAc), caudate-putamen (CPu), frontal cortex (FCx), septum, dentate gyrus (DG) and CA3 region of hippocampus, whereas c-fos gene was induced in CPu, FCx, DG, septum and CA1 region of hippocampus. This gene expression may be due, in part, to the stimulant properties of IBO, as we found with other psychostimulants.

Neuronal-type NO synthase: transcript diversity and expressional regulation

Of the three established isoforms of NO synthase, the gene for the neuronal-type enzyme (NOS I) is by far the largest and most complicated one. The genomic locus of the human NOS I gene is located on chromosome 12 and distributed over a region greater than 200 kb. The nucleotide sequence corresponding to the major neuronal mRNA transcript is encoded by 29 exons. The full-length open reading frame codes for a protein of 1434 amino acids with a predicted molecular weight of 160.8 kDa. However, both in rodents and in humans, multiple, tissue-specific or developmentally regulated NOS I mRNA transcripts have been reported. They arise from the initiation by different transcriptional units containing alternative promoters (at least eight in the human gene), cassette exon deletions or insertions, and/or the usage of alternate polyadenylation signals. Depending on the insertions and deletions, translation results in functional or nonfunctional proteins. The use of alternative promoters can influence gene expression by various means. Indeed, NOS I is not a static, constitutively expressed enzyme, but subject to expressional regulation by various compounds and conditions. The molecular mechanisms underlying these regulations are currently being studied in several laboratories including our own.

The 5-HT3 receptor antagonist, MDL 72222, dose-dependently potentiates morphine-induced immediate-early gene expression in the rat caudate putamen

Previous studies from this laboratory have demonstrated that acute administration of morphine induces the immediate-early genes (IEGs) c-Fos and JunB in the rat caudate putamen (CPu). In the present study, we tested the hypothesis that the serotonin-3 receptor (5-HT3R) is involved in morphine-induced IEG expression, using the selective antagonist to the 5-HT3R, MDL 72222. Rats were divided into three pretreatment groups: MDL 72222, 1 mg/kg or 10 mg/kg; or vehicle (DMSO). Thirty minutes following the pretreatment, the rats were administered either morphine (10 mg/kg) or vehicle. Morphine significantly induced c-Fos expression in the dorsomedial CPu, as we have reported previously. Whereas MDL 72222 alone did not induce c-Fos, it potentiated the morphine-induced c-Fos expression. Morphine also induced JunB expression in the same region of the dorsomedial CPu. At 1 mg/kg, MDL 72222 both induced JunB expression and potentiated the response induced by morphine. At 10 mg/kg, MDL 72222 had no effect on basal JunB levels, but augmented the response to morphine. These findings demonstrate that the 5-HT3R antagonist, MDL 72222, can positively modulate morphine-induced IEG expression in the rat CPu in a dose dependent manner, in contrast to the reported suppressive effect observed when this antagonist is administered prior to amphetamine.

Cocaine and fluoxetine induce the expression of the hVH-5 gene encoding a MAP kinase phosphatase

A novel class of immediate early genes that encode enzymes of the MAP kinase phosphatase family has recently been described. These enzymes are dual-specificity protein phosphatases and some show tissue-specific distribution, like the hVH-5 gene (homologue of vaccinia virus H1 phosphatase gene clone 5), which is expressed predominantly in the adult brain. In this paper, we investigated whether the hVH-5 gene is induced by psychostimulants in rat brain, as has been demonstrated for immediate early genes encoding transcription factors. Using in situ hybridization, we found that i.p. injection of cocaine, amphetamine and caffeine induced hVH-5 mRNA expression within 40 min in the nucleus accumbens (NAc), caudate putamen, frontal cortex and hippocampus, with a maximal effect in the NAc. The cocaine-induced hVH-5 gene induction involves the serotonergic system, since it was abolished in the NAc by lesioning serotonergic raphé projections with 5,7-dihydroxytryptamine. Moreover, the effect of cocaine was fully mimicked by the selective serotonin uptake inhibitor fluoxetine. In contrast to what has been described for c-fos and egr-1 immediate early genes, we found that hVH-5 mRNA expression in the NAc and hippocampus was as significant after repeated cocaine injections for 10 days as after a single injection. The considerable and prolonged induction of the MAP kinase phosphatase hVH-5 gene by psychostimulant drugs in postmitotic brain cells, particularly in the NAc, could indicate that MAP kinase substrates are involved in the reinforcing properties of drugs of abuse.

Behavioral sensitization to cocaine after a brief social stress is accompanied by changes in fos expression in the murine brainstem

The objective of the present study was to determine how c-fos gene expression in brainstem structures after a brief episode of social defeat stress is related to behavioral sensitization to cocaine challenge. Social stress was defined as defeat in a brief confrontation with an aggressive resident mouse and subsequent 20-min exposure to the resident's threats behind a protective screen. Mice were treated with cocaine (40 mg/kg, i.p.) immediately or 1 week after social defeat stress. Fos-like immunoreactive (Fos-LI) cell nuclei were analyzed in the ventral tegmental area (VTA), dorsal raphe nucleus (DR), periaqueductal grey area (PAG) and locus coeruleus (LC). One episode of social stress induced behavioral sensitization to cocaine as indicated by an augmented locomotor response to a challenge injection 7 days after a single defeat. In naive mice, social stress markedly increased the number of Fos-LI nuclei in the DR, PAG and LC, but not in the VTA. Similarly, cocaine administration resulted in a significantly increased number of Fos-LI nuclei in the same areas. Administration of cocaine immediately following social defeat significantly reduced the number of Fos-LI nuclei in the DR, PAG and LC. Cocaine-induced Fos expression returned in the PAG and DR, but not in the LC, 1 week after social stress. In conclusion, the present results suggest that the presence of brainstem Fos be related to the ability to express stress-induced behavioral sensitization to cocaine.

Patterns of c-fos expression induced by fluvoxamine are different after acute vs. chronic oral administration

Fluvoxamine is a selective serotonin (5-HT) reuptake inhibitor (SSRI) with a broad spectrum of behavioral and therapeutic effects, e.g. in depressive illness. We used the expression of c-fos, after both acute and chronic oral administration of fluvoxamine in the rat, to study its immediate and long-term effects, in relation to the distribution of Galanin (GAL) and Vasoactive Intestinal Polypeptide (VIP). After acute oral administration, most consistent increases were apparent in (parts of); the nucleus of the solitary tract, medial part; the lateral parabrachial nucleus, external part; the bed nucleus of the stria terminalis, dorsolateral part; and the central nucleus of the amygdala, lateral part. After chronic administration, distribution of Fos-IR was similar to acute administration, although numbers of Fos-IR neurons were no longer significantly different from control values. It is concluded that activation of 5-HT3-receptors in the caudal brainstem or gastro-intestinal afferents of the vagal nerve may play a role in the observed pattern of Fos-IR after fluvoxamine administration. The relationship with the antidepressant effects of fluvoxamine needs further investigations.

Drugs of abuse and immediate-early genes in the forebrain

A diverse array of chemical agents have been self administered by humans to alter the psychological state. Such drugs of abuse include both stimulants and depressants of the central nervous system. However, some commonalties must underlie the neurobiological actions of these drugs, since the desire to take the drugs often crosses from one drug to another. Studies have emphasized a role of the ventral striatum, especially the nucleus accumbens, in the actions of all drugs of abuse, although more recent studies have implicated larger regions of the forebrain. Induction of immediate-early genes has been studied extensively as a marker for activation of neurons in the central nervous system. In this review, we survey the literature reporting activation of immediate-early gene expression in the forebrain, in response to administration of drugs of abuse. All drugs of abuse activate immediate-early gene expression in the striatum, although each drug induces a particular neuroanatomical signature of activation. Most drugs of abuse activate immediate-early gene expression in several additional forebrain regions, including portions of the extended amygdala, cerebral cortex, lateral septum, and midline/intralaminar thalamic nuclei, although regional variations are found depending on the particular drug administered. Common neuropharmacological mechanisms responsible for activation of immediate-early gene expression in the forebrain involve dopaminergic and glutamatergic systems. Speculations on the biological significance and clinical relevance of immediate-early gene expression in response to drugs of abuse are presented.

Quinpirole attenuates striatal c-fos induction by 5-HT, opioid and muscarinic receptor agonists

Pretreatment with the dopamine D2 receptor agonist quinpirole (0.025-2.5 mg/kg) produced a marked, dose-dependent, attenuation of the striatal Fos expression induced by the serotonin (5-Hydroxytryptamine, 5-HT) releasing agent fenfluramine (25 mg/kg). Quinpirole (2.5 mg/kg) was also able to drastically attenuate the striatal Fos response produced by injections of the direct 5-HT1/2 receptor agonist N-(3-trifluoromethylphenyl)piperazine hydrochloride (TFMPP) (5 mg/kg), the selective 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI) (6.64 mg/kg), the 5-HT1A/1B receptor agonist RU-24969 (5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl)1H-indole) (5 mg/kg), the mu-opioid receptor agonist morphine (5 mg/kg) and the muscarinic cholinergic receptor agonist pilocarpine (50 mg/kg). These results are in marked contrast to the previously reported ability of quinpirole to potentiate the response to D1 dopamine receptor agonists and demonstrate that stimulation of D2-like receptors can have differential effects on the Fos responses induced by various drugs.

Serotonin-1B agonists induce compartmentally organized striatal Fos expression in rats

The 5HT1B agonist RU24969 (2.5-5.0 mg/kg) and anpirtoline (2.0 mg/kg) induced a striking increase in striatal Fos-like immunoreactivity in rats. In the rostral and dorsal regions of the striatum staining was dense and relatively homogeneous. In the ventral region of the striatum at more caudal levels, however, both drugs induced staining in patches which were in register with the opiate receptor rich striosomes. The effects of RU24969 could not be antagonized by the selective 5HT1A antagonist p-MPPI and little or no striatal Fos expression could be observed after injections of the selective 5HT1A agonist 8-OHDPAT or the selective 5HT3 antagonist MDL-72222.

Interaction between the serotonergic, dopaminergic, and glutamatergic systems in fenfluramine-induced Fos expression in striatal neurons

Fenfluramine (FE) is a halogenated amphetamine derivative used in the treatment of obesity and thought to induce serotonin (5-HT) release from nerve terminals and to reduce re-uptake. However, other pathways may also be involved. In this work, the effects of FE on the major striatal afferent systems, and the possible interactions of these systems in FE-induced striatal expression of Fos, were studied by lesion of the serotonergic and/or dopaminergic system and administration of NMDA glutamate (MK-801) or D1 dopamine (SCH-23390) receptor antagonists. Both the D1 and NMDA receptor antagonists suppressed Fos expression in response to FE almost entirely. FE-induced Fos expression was also dramatically reduced 24 h after 6-hydroxydopamine (6-OHDA) lesion of the dopaminergic system. However, the reduction was not so marked after chronic 6-OHDA lesion, probably due to compensatory changes. Chronic (5,7-dihydroxytryptamine injection, 4 weeks before) or acute (p-chlorophenylalanine injection) lesion of the serotonergic system led to a marked reduction in Fos expression in response to FE (decrease of about 50%). After simultaneous chronic lesion of both serotonergic and dopaminergic systems, a considerable number of Fos-positive nuclei were still observed (decrease of about 70% in the dorsal and dorsomedial regions). The FE-induced expression of Fos was almost totally suppressed (decrease of about 95% in the dorsal and dorsomedial regions) after simultaneous acute lesion. Our results indicate that FE-induced striatal expression of Fos is due in large measure to DA release and dopaminergic stimulation of D1 receptors. However, concurrent stimulation of NMDA glutamate receptors also appears to be essential, and 5-HT release (although not indispensable) doubles striatal Fos expression.

The effect of lactation on induced Fos-like immunoreactivity in the rat hypothalamic paraventricular nucleus

Lactating rats display a period of blunted hypothalamo-pituitary-adrenal (HPA) response to a variety of stressors. This hyporesponsiveness is reported to be dependent upon continuous mother-pup interactions. In this study, computer-assisted densitometric methods were used to measure levels of induced Fos-like immunoreactivity (FLI) in the hypothalamic paraventricular nucleus (PVN) of lactating and non-lactating rats. Adrenalectomy (ADX) induces elevated levels of FLI in the PVN of non-lactating rats. We have observed that, between post-partum day (pd) 4 and pd 21, the level of ADX-induced FLI in the PVN of lactating rats follows a U-shaped distribution; that the persistence of this phenomenon is dependent upon continued mother-pup interaction and that sustained mother-pup interaction beyond the end of the normal suckling period (pd 21) does not extend the period of refractoriness. We have further determined that both the non-specific neural activator Metrazole, and the glutamate agonist N-methyl-D,L-aspartate (NMA), induced smaller increases in FLI in the PVN of lactating rats compared to non-lactating cohorts, and that the suppressing effect of lactation on Metrazole-induced FLI does not extend to all brain regions. These results suggest that mechanisms responsible for the onset and maintenance of the so-called lactational stress-hyporesponsive period (LSHRP) include altered function of glutamatergic pathways.

5-HT1A receptor agonist flesinoxan enhances Fos immunoreactivity in rat central amygdala, bed nucleus of the stria terminalis and hypothalamus

5-Hydroxytryptamine-1A (5-HT1A) receptor agonists, including flesinoxan, reduce anxiety and activate the hypothalamus-pituitary-adrenal (HPA) axis under basal conditions. In order to investigate the underlying neural mechanisms we investigated immunoreactivity for the immediate early gene protein product Fos (Fos-ir) in rat brains 1 h after flesinoxan treatment (0.0, 0.3 or 3.0 mg/kg p.o.). Typically, 5-HT1A receptor-containing brain areas, such as the dorsal raphe nuclei, hippocampus, septum, diagonal band and the cortical and basomedial amygdala, do not show Fos-ir. Apparently, binding of flesinoxan at the 5-HT1A receptor does not directly lead to activation of c-fos in the cell, probably due to its negative coupling to adenylate cyclase. However, in typically non-5HT1A receptor-containing brain areas Fos-ir is increased due to flesinoxan treatment, as in the paraventricular nucleus of the hypothalamus (PVN), the dorsolateral part of the bed nucleus of the stria terminalis (BNSTdl) and the central amygdala (CeA). Flesinoxan-treated rats also exhibited higher plasma corticosterone levels than vehicle-treated animals, which suggests the involvement of corticotropin-releasing hormone (CRH) or vasopressin in the hypothalamus. After double immunolabelling (Fos/CRH or Fos/vasopressin), every CRH neuron detected in the PVN also contained Fos. Moreover, a significant correlation existed between the number of Fos-ir neurons in the PVN and the plasma corticosterone level. Hardly any Fos/vasopressin double labelling was visible in the PVN. Accordingly, flesinoxan exerts its activating effects on the HPA axis via CRH neurons in the PVN. These effects are trans-synaptically mediated by other brain areas, such as the CeA and BNSTdl, which also show increased Fos-ir.

Fenfluramine-induced activation of the immediate-early gene c-fos in the striatum: possible interaction between serotonin and dopamine

DL-Fenfluramine, a serotonin (5-HT) releasing agent, induces rapid expression of Fos-like immunoreactivity (Fos-LI) in the striatum as well as in other brain structures receiving a dense 5-HT innervation. Fenfluramine-induced Fos-LI expression in the striatum may result directly from the activation of 5-HT receptors or may be the result of interactions between dopamine (DA) and 5-HT neurotransmitter systems. To discriminate between these two possibilities, various groups of rats were pretreated with different 5-HT antagonists or a DA D1 antagonist, 20 min before fenfluramine administration. Animals were killed 60 min later. In the striatum, fenfluramine-induced expression of Fos-LI was almost completely blocked by SCH 23390, methysergide and S(-)-propranolol. The immediate-early gene response to fenfluramine was only slightly affected by pretreatment with the 5-HT2A/2C antagonist ritanserin. Fenfluramine was also administered to sham-operated and to unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. In the 6-OHDA-lesioned rats, fen-fluramine-induced Fos-LI was decreased by 60% on the DA denervated side compared to the intact side and to sham-operated rats. To further probe the possibility of a direct activation of Fos-LI by 5-HT receptor subtypes, we evaluated the expression of Fos-LI after the administration of different 5-HT agonists. Our results demonstrate that neither 8-OH-DPAT, CGS-12066B, RU 24969 nor phenyl-biguanide was able to reproduce the effects of fenfluramine. Only a high dose of DOI (8.5 mg/kg) produced a moderate expression of Fos-LI in the dorsomedial part of the striatum. This contrasted with the Fos-LI expression in other brain areas where 8-OH-DPAT and DOI (2.5 and 8.5 mg/kg) reproduced the effects of the 5-HT releasing agent. Our results suggest that the release of 5-HT by fenfluramine induced Fos-LI expression predominantly in a striatal region related to associative functions and, that this c-fos response may be under the control of both 5-HT and DA. Moreover, the mechanism by which fenfluramine induces c-fos expression in the striatum differs from other brain regions.

The effects of the kappa agonist U-50,488 on cocaine-induced conditioned and unconditioned behaviors and Fos immunoreactivity

The ability of kappa opioid agonists to modulate dopamine-mediated behavior and Fos immunoreactivity was assessed in adult rats. It was predicted that kappa agonist treatment would block the unconditioned and conditioned behaviors produced by cocaine (an indirect dopamine agonist). In the initial experiments, cocaine-induced locomotor activity was assessed after either acute or chronic injections of the kappa receptor agonist U-50,488 (5 mg/kg, SC). As expected, U-50,488 decreased cocaine-induced activity, while leaving baseline activity levels unaffected. Interestingly, chronic treatment with U-50,488 did not induce behavioral tolerance. The conditioned effects of cocaine (20 mg/kg, IP) were assessed using the conditioned place preference (CPP) paradigm. As expected, rats showed a preference for the cocaine-paired compartment, an effect blocked by U-50,488 (5 mg/kg, SC). One hour after CPP testing, rats were killed and Fos immunoreactivity was assessed. Rats conditioned with cocaine, but not U-50,488, showed increased Fos activity in the anterior cingulate cortex, piriform cortex, lateral septal area, and olfactory tubercles. When considered together, these results suggest that U-50,488 was effective at blocking the unconditioned and conditioned effects of cocaine, as well as cocaine-induced neuronal activity (as measured by Fos induction).