Long-term administration of cocaine or serotonin reuptake inhibitors results in anatomical and neurochemical changes in noradrenergic, dopaminergic, and serotonin pathways

The catechol and indole pathways are important components underlying plasticity in the frontal cortex and basal ganglia. This study demonstrates that administering rats either cocaine or a selective serotonin (or 5-hydroxytryptamine; 5-HT) reuptake inhibitor (SSRI) for 16 weeks results in reduced density of dopaminergic and noradrenergic terminals in the striatum and olfactory bulb, respectively, reflecting pruning of the terminal arbor of ventral midbrain dopaminergic and locus coeruleus noradrenergic neurones. In the striatum of cocaine-treated animals, basal dopamine levels, as well as cocaine-induced dopamine release, is diminished compared with controls. In contrast, serotonergic fibers, projecting from the raphe, sprout and have increased terminal density in the lateral septal nucleus and frontal cortex, following long-term cocaine or SSRI treatment. This is associated with elevated basal 5-HT and enhanced cocaine-induced 5-HT release in the frontal cortex. The anatomical and neurochemical changes in serotonergic fibers following cocaine or SSRI treatment may be explained by attenuated 5-HT_1A autoreceptor function in the raphe. This study demonstrates extensive plasticity in the morphology and neurochemistry of the catechol and indole pathways that contribute to drug-induced plasticity of the corticostriatal (and other) projections. Moreover, our data suggest that drug-induced plastic adaptation is anatomically widespread and consequently, likely to have multiple and complex consequences.     

Behavioral and neurochemical changes in the zebrafish leopard strain

The zebrafish leopard phenotype (leo) displays abnormal pigmentation and shows increased anxiety‐like behavior. The neurochemical changes associated with this anxious phenotype are not known. Here, we demonstrate that leo show increased anxiety‐like behavior in the light/dark box and in the novel tank test. This anxious phenotype is rescued by acute treatment with a dose of a serotonin reuptake inhibitor, fluoxetine, that is inactive in wild‐type animals. Moreover, leo show decreased tissue levels of serotonin, increased serotonin turnover and slightly increased monoamine oxidase activity. These results suggest that the anxious phenotype observed in leo zebrafish is caused by a decrease in serotonin uptake. This work could open an important avenue in defining the neurochemical underpinning of natural variation in anxiety disorders .     

Supersensitivity of sigma receptors after repeated administration of cocaine.

We investigated the role of sigma receptors in the expression of behavioral sensitization induced by cocaine. Rats received intraperitoneal injections of either 20 mg/kg cocaine or saline once daily for 14 consecutive days. Cocaine-treated rats became sensitized. After a 5-day abstinence period, a challenge dose of (+)-3-[3-hydroxyphenyl]-N-(1-propyl)piperidine ((+)-3-PPP), a sigma receptor agonist, was administered. (+)-3-PPP at doses of 12 and 24 mg/kg induced significantly more frequent rearing and more potent stereotypy consisting of repetitive head movement and sniffing in cocaine-sensitized rats than in saline-pretreated rats. These enhanced responses to (+)-3-PPP lasted for at least a month. The enhanced responses to (+)-3-PPP were attenuated by 30 mg/kg BMY 14802, a putative sigma antagonist, and also attenuated by 100 mg/kg (+/-)-sulpiride, a D2 dopamine antagonist. These findings show that repeated administration of cocaine produces lasting supersensitivity of simga receptors, which may induce subsequent activation of dopaminergic transmission.     

Subchronic steroid administration induces long lasting changes in neurochemical and behavioral response to cocaine in rats

The abuse of anabolic androgenic steroids (AASs), such as nandrolone, is not only a problem in the world of sports but is associated with the polydrug use of non-athletes. Among other adverse effects, AAS abuse has been associated with long term or even persistent psychiatric problems. We have previously found that nandrolone decanoate treatment could produce prolonged changes in rats’ brain reward circuits associated to drug dependence. The aim in this study was to evaluate whether AAS-induced neurochemical and behavioral changes are reversible.The increases in extracellular dopamine (DA) and serotonin (5-HT) concentration, as well as stereotyped behavior and locomotor activity (LMA) evoked by cocaine were attenuated by pretreatment with nandrolone. The recovery period, which was needed for the DA system to return back to the basic level, was fairly long compared to the dosing period of the steroid. In the 5-HT system, the time that system needed to return back to the basal level, was even longer than in the DA system. The attenuation was still seen though there were no detectable traces of nandrolone in the blood samples.Given that accumbal outflow of DA and 5-HT, as well as LMA and stereotyped behavior are all related to reward of stimulant drugs, this study suggests that nandrolone decanoate has significant, long-lasting but reversible effects on the rewarding properties of cocaine.     

Conditioned posture changes in dogs after systemic administration of dopaminergic agents

Influence of systemic injection of some dopaminergic drugs on conditioned postural rearrangement prior to instrumental movement realization and on other motor components of instrumental reaction as well as on the performance of the instrumental task itself--was studied in chronic experiments in 5 dogs on a model of instrumental defensive reflexes connected with maintenance of a certain posture. Drugs were used influencing the nigrostriate dopaminergic system, i.e. dopamine agonist L-DOPA and haloperidol blocking dopamine striate receptors. All the motor components of the instrumental reaction and first of all conditioned postural rearrangement were modified by systemic haloperidol injection. Initial components of the postural rearrangement were modified to the greatest extent, in particular the period of preparation of the animal to the posture change increased. On the contrary, the latency of initiation of postural rearrangement was sharply shortened by systemic injection of L-DOPA. On the other hand, the main component of the postural change, i.e. redistribution of body mass among the bearing limbs (the values of which significantly increased after preliminary stimulation of the head of the caudate nucleus) changed insignificantly during modulation of the striatum dopamine level.     

Prenatal cocaine exposure disrupts the dopaminergic system and its postnatal responses to cocaine

Impaired attention is the hallmark consequence of prenatal cocaine exposure (PCE), affecting brain development, learning, memory and social adaptation starting at an early age. To date, little is known about the brain structures and neurochemical processes involved in this effect. Through focusing on the visual system and employing zebrafish as a model, we show that PCE reduces expression of dopamine receptor Drd1, with levels reduced in the optic tectum and other brain regions, but not the telencephalon. Organism‐wide, PCE results in a 1.7‐fold reduction in the expression of the dopamine transporter (dat), at baseline. Acute cocaine administration leads to a 2‐fold reduction in dat in drug‐naive larvae but not PCE fish. PCE sensitizes animals to an anxiogenic‐like behavioral effect of acute cocaine, bottom‐dwelling, while loss of DAT due to genetic knockout (DATKO) leads to bottom‐dwelling behavior at baseline. Neuronal calcium responses to visual stimuli in both PCE and DATKO fish show tolerance to acute cocaine in the principal regions of visual attention, the telencephalon and optic tectum. The zebrafish model can provide a sensitive assay by which to elucidate the molecular mechanisms and brain region‐specific consequences of PCE, and facilitate the search for effective therapeutic solutions.     

Changes in rat hypothalamo-neurohypophyseal system after repeated ethanol administration]

The histochemical, immunohistological and histoenzymatic study of the hypothalamo-neurohypophysial system of the rat shows that chronic ethanol administration induces: a temporary blockage of vasopressin synthesis, a vasoconstriction of the neurohypophysial capillaries, a dendritic storage of immunoreactive vasopressin. In our experimental conditions, a long ethanol treatment disturbs the balance between vasopressin synthesis and release.     

Correlation of behavioral and neurochemical effects of acute administration of cocaine in rats.

Effects of cocaine were investigated on spontaneous motor activity (SMA) and stereotypy as well as on the concentrations of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and acetylcholine (ACh) in the discrete brain areas, such as the caudate nucleus (CN), diencephalon-midbrain (DM) and pons-medulla (PM) in rats up to 90–120 min following its injection in single doses (15–20 mg/kg, i.p.). After cocaine administration, the SMA was increased usually reaching its peak between 10–20 min, and then decreased gradually. Stereotypy and its components gradually increased to their maximum at about 50–60 min and remained at that level during rest of 120 min sessions. NE levels slightly increased in the DM and PM at 10 min post-drug after which they were decreased at 20 min. DA levels in the CN and DM were increased markedly at 20 min post-drug and decreased at 40 min. 5-HT levels in DM and PM decreased gradually up to 20 min, then began to increase. ACh level in the CN was gradually increased at 40 min and then decreased. It appears that cocaine-induced hyperactivity and stereotypy followed release of NE and DA after their accumulation in the respective brain areas.     

Endocrine and neurochemical actions of cocaine

The endocrine and neurochemical actions of cocaine in human and animal studies are reviewed. In humans, cocaine has been shown to influence plasma prolactin and growth hormone, as well as the dexamethasone suppression of cortisol and the thyroid-stimulating hormone response to thyroid-releasing hormone. In rats, cocaine affects plasma prolactin, luteinizing hormone, and testosterone, and can lead to adrenocortical hypertrophy. Behavioral sensitization to cocaine in rats has been shown to be related to the gender of the animals and appears to be modulated by vasopressin. A review of the neurochemical actions of cocaine indicates the important role of dopamine systems in the euphoric effects of the drug, as well as its withdrawal symptoms. Cocaine is a potent dopamine uptake inhibitor, as shown by its competition with [3H]GBR-12935 (a specific ligand for the dopamine uptake sites) for striatum binding sites. However, it does not acutely affect the high-affinity agonist sites of the D-2 dopamine receptors, which are suggested to be the active form of the presynaptic receptor. Using microdialysis techniques, cocaine is shown to rapidly cause a large increase of rat striatal dopamine levels, while its metabolites dihydroxyphenylacetic acid and homovanillic acid are slightly decreased and increased, respectively.     

Transient changes of cortical interhemispheric responses after repeated caffeine administration in immature rats

Repeated postnatal caffeine treatment of rat pups led to transient developmental changes in cortical epileptic afterdischarges. To know if physiological cortical functions are also affected transcallosal evoked potentials were studied. Rat pups of the Wistar strain were injected daily with caffeine (10 or 20 mg/kg s.c.) from postnatal day (P) 7 to P11, control siblings received saline. Cortical interhemispheric responses were tested at P12, 18, 25 and in young adult rats. Amplitude of initial monosynaptic components was evaluated in averaged responses. Single pulses as well as paired and frequency (five pulses) stimulations were used. Developmental rules - highest amplitude of responses in 25-day-old rats, potentiation with paired and frequency stimulation present since P18 - were confirmed. Caffeine-treated rats exhibited transient changes: single responses were augmented in P25 if high stimulation intensity was used, paired-pulse and frequency responses were higher in experimental than in control animals at P12, the opposite change was observed in 18- and more markedly in 25-day-old rats. No significant changes were found in adult animals, monosynaptic transcallosal responses represent a simple and robust system. The developmental profile of described changes did not exactly correspond to changes in epileptic afterdischarges supporting the possibility that afterdischarges did not arise from early monosynaptic components of responses. In spite of transient nature of changes they can reflect delayed or more probably modified brain development.     

Dieldrin-induced oxidative stress and neurochemical changes contribute to apoptopic cell death in dopaminergic cells.

We examined the acute toxicity of dieldrin, a possible environmental risk factor of Parkinson's disease, in a dopaminergic cell model, PC12 cells, to determine early cellular events underlying the pesticide-induced degenerative processes. EC(50) for 1 h dieldrin exposure was 143 microM for PC12 cells, whereas EC(50) for non-dopaminergic cells was 292-351 microM, indicating that dieldrin is more toxic to dopaminergic cells. Dieldrin also induced rapid, dose-dependent releases of dopamine and its metabolite, DOPAC, resulting in depletion of intracellular dopamine. Additionally, dieldrin exposure caused depolarization of mitochondrial membrane potential in a dose-dependent manner. Flow cytometric analysis showed generation of reactive oxygen species (ROS) within 5 min of dieldrin treatment, and significant increases in lipid peroxidation were also detected following 1 h exposure. ROS generation was remarkably inhibited in the presence of SOD. Dieldrin-induced apoptosis was significantly attenuated by both SOD and MnTBAP (SOD mimetic), suggesting that dieldrin-induced superoxide radicals serve as important signals in initiation of apoptosis. Furthermore, pretreatment with deprenyl (MAO-inhibitor) or alpha-methyl-L-p-tyrosine (TH-inhibitor) also suppressed dieldrin-induced ROS generation and DNA fragmentation. Taken together, these results suggest that rapid release of dopamine and generation of ROS are early cellular events that may account for dieldrin-induced apoptotic cell death in dopaminergic cells.     

Behavioral evidence for dopaminergic supersensitivity after chronic haloperidol

Chronic administration for 16 days of haloperidol (in increasing doses up to 20 mg/kg/day) results in a supersensitivity of dopamine receptors. This supersensitivity is manifested by an enhanced stereotypy and aggression in response to small, otherwise ineffective, doses of apomorphine. Maximum aggression is observed 7 days after the last dose of haloperidol when 2.5 mg/Kg of apomorphine is administered. In addition, “wet shakes”, reminiscent of withdrawal from morphine, are observed in these animals after the cessation of the haloperidol administration. These shakes are blocked by morphine. These results may be interpreted to mean that “wet shakes” and drug induced aggression are the results of hyperactivity of the dopaminergic system.     

Effects of acute and subacute cocaine administration on the CNS dopaminergic system in Wistar-Kyoto and spontaneously hypertensive rats: III. Dopamine uptake

The characteristics of dopamine uptake after acute and subacute cocaine administration were determined in striata from WKY and SHR. In acutely-treated (40 mg/kg, s.c.) rats, significant increases in the V_max of dopamine uptake were observed 30 min after the cocaine injection in both strains, without changes in K_m values. The in vitro IC₅₀ for cocaine was significantly decreased at 30 min in WKY and at 2 h in SHR. However, the in vitro IC₅₀ for GBR-12909 was significantly increased at 30 min and at 2 h in both strains following cocaine administration. In both strains, the density (B_max) of the [³H]GBR-12935 binding site was significantly increased at 30 min and at 2 h with no charges in K_d. In subacutely-treated (20 mg/kg, twice daily for 3 or 7 days) rats, a significant increase in the K_m for dopamine uptake was observed in 7 day treated SHR. The in vitro IC₅₀ for GBR-12909 was significantly increased in 3 day treated WKY. The results suggest that cocaine administration alters dopamine uptake and characteristics of dopamine uptake sites in the rat brain.     

Effects of acute and subacute cocaine administration on the CNS dopaminergic system in Wistar-Kyoto and spontaneously hypertensive rats: II. Dopamine receptors

The characteristics of D-1 and D-2 dopamine receptors after acute and subacute cocaine administration were determined in striata and nuclei accumbens from WKY and SHR. In striata from acutely treated rats, significant increases in D-2 receptor density were observed at 30 min, 2 or 24 h following cocaine injection in both strains without changes in affinities. The density of D-1 receptors was significantly decreased 30 min after the injection in WKY, but not in SHR. In striata from subacutely treated rats, the density of D-1 receptors was significantly increased in 3- and 7-day treated WKY, but not in SHR. The affinities of both binding sites remained unchanged. In nuclei accumbens, the changes in both D-1 and D-2 receptors after cocaine administration were similar to those observed in the striatum. The results suggest that cocaine administration alters dopamine receptor binding characteristics. Furthermore, D-1 and D-2 dopamine receptors appear to be differently regulated.     

Histological changes of the dopaminergic nigrostriatal system in aging

Although the maximum human lifespan has not increased in recent history, average life expectancy has risen dramatically since the beginning of the last century. Lengthening of lifespan has little merit if the quality of life is not preserved. In the elderly, the decline in memory and cognitive abilities is of great concern, as is motor weakening, which increases with age. The dopaminergic system mediates some aspects of manual dexterity, in addition to cognition and emotion, and may be especially vulnerable to aging. Therefore, the aging of this system has both clinical and vocational aspects. This review includes studies quantitating age-related changes of the nigrostriatal system, with emphasis on the use of stereological methods, and provides tables of stereological studies performed in the nigrostriatal system.We acknowledge the Danish Parkinson Foundation and the Foundation of Stockbroker Henry Hansen and wife for financial support     

The presence of cocaine and benzoylecgonine in rat cerebrospinal fluid after the intravenous administration of cocaine.

Cocaine hydrochloride, in doses of 0.5, 1.0, 2.0 and 4.0 mg/kg, iv, was administered to male Sprague-Dawley rats. Cerebrospinal fluid (CSF) was collected from the cisterna magna over a 20 min period and blood samples were obtained at 20 min after cocaine administration. In addition, blood samples for the 1 mg/kg dose of cocaine were collected at 2, 10, 20 and 30 min following drug injection. Gas chromatography/mass spectrometry was used for the analysis of cocaine and its metabolites in plasma and CSF. The disappearance of cocaine (1 mg/kg) from the plasma exhibited first order kinetics with a half-life of 18.11 +/- 3.22 min. Cocaine and benzoylecgonine were found in CSF and the concentrations of cocaine and benzoylecgonine increased in CSF as the doses of cocaine were increased. CSF flow rates were not altered by the iv administration of cocaine or benzoylecgonine. The CSF-to-plasma ratios for cocaine were quite similar to each other over the dosage range of cocaine that was administered; however, the CSF-to-plasma ratios for benzoylecgonine decreased as the concentrations of benzoylecgonine increased in plasma and CSF. When benzoylecgonine (2 mg/kg, iv) was given, the compound was detected in CSF indicating that benzoylecgonine can enter into the central nervous system from the peripheral blood. This investigation shows that cocaine and benzoylecgonine can be assayed in CSF and that the plasma levels of these compounds correlate with their concentrations in CSF.     

Behavioral and neurochemical investigation of circadian time-place learning in the rat

The ability to form an association between the time and the place of food availability, namely time-place learning, is presumably important for survival. The present study was designed to examine time-place learning and to identify exogenous and endogenous factors that may affect this behavior in rats. In an initial experiment, rats displayed poor time-place behavior and appeared to prefer the feeder that was closer to the center aisle and water supply. When these cues were minimized in a subsequent experiment, rats consistently displayed the time-place discrimination by exhibiting food anticipatory activity (FAA) at the correct location prior to each meal time. These rats also showed significant correlations between the level of FAA and the amount of dopamine turnover (the dihydroxyphenylacetic acid/dopamine ratio) in the nucleus accumbens and paraventricular nucleus of the hypothalamus, indicating possible involvement of regional dopaminergic activity in time-place behavior. No correlation was found for norepinephrine, epinephrine, or serotonin. In addition, the correlation between FAA and dopamine turnover was not found when rats were entrained to only one meal per day. Together, the data suggest that rats can learn the time-place discrimination under proper experimental conditions and that dopamine may play a role in the expression of this behavior.     

Effects of acute and subacute cocaine administration on the CNS dopaminergic system in Wistar-Kyoto and spontaneously hypertensive rats: I. Levels of dopamine and metabolites

Effects of acute and subacute cocaine administration on dopamine (DA) and its metabolites in striata and nucleus accumbens of nine week-old Wistar-Kyoto and spontaneously hypertensive rats were studied. Levels of DA,3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were determined by HPLC-EC. There were no differences in DA levels in striata and nucleus accumbens between control WKY and SHR. Levels of DA in two brain regions were unaffected in groups treated acutely with cocaine. Both strains showed a significant increase in striatal HVA 2 hr after cocaine injection. Seven day treatment declined DA levels in striatum of WKY and in nucleus accumbens of SHR. However, only WKY treated subacutely with cocaine showed significantly increased HVA either with or without changes in DOPAC in nucleus accumbens and striatum, respectively. Increased DOPAC/DA and HVA/DA ratios appeared only in striatum of WKY and in nucleus accumbens of SHR following subacute treatment. These results suggest that subacute cocaine administration affects DA levels in striata and nucleus accumbens differently between WKY and SHR.     

Behavioral and cross sensitization after repeated exposure to modafinil and apomorphine in rats

Repeated exposure to psychostimulant drugs has been known to produce behavioral sensitization, a phenomenon explicitly indexed by locomotion (LM) and stereotyped movements (SM). So far, no evidence has demonstrated that this phenomenon can be displayed following the administration of modafinil (MOD) in animal study. We, therefore, assessed the possibility of behavioral sensitization of MOD and a direct dopamine agonist, apomorphine (APO), and cross-sensitization of these two drugs with one other. Pretreatment with MOD (64 mg/kg) or APO (0.5 mg/kg or 1.0 mg/kg) for 10 consecutive days was followed by a short-term (3 days) or long-term (21 days) withdrawal. Rats were then challenged with the drug and reciprocally re-challenged with the counterpart drug. The results showed that following short-term and long-term washout periods, both MOD and APO successfully induced sensitization in LM and SM. There was no cross-sensitization; an even lesser magnitude in LM when MOD-sensitized rats were challenged with APO was observed. However, after both the short-term and long-term withdrawal periods, APO (1.0 mg/kg)-sensitized rats showed cross-sensitization in LM and SM to MOD (64 mg/kg) challenge. The magnitude of APO-MOD cross-sensitization was lesser than the behavioral sensitization induced by APO alone. Our results indicated behavioral sensitization could be induced in rats exposed to MOD. In addition, changes in dopaminergic receptor activities could be involved in cross-sensitization of APO to MOD but not vice versa.