Effect of desipramine and amphetamine on noradrenergic neurotransmission: electrophysiological studies in the rat brain

How Is the Norepinephrine System Involved in the Antiepileptic Effects of Vagus Nerve Stimulation?

Vagus Nerve Stimulation (VNS) is an adjunctive treatment for patients suffering from inoperable drug-resistant epilepsy. Although a complete understanding of the mediators involved in the antiepileptic effects of VNS and their complex interactions is lacking, VNS is known to trigger the release of neurotransmitters that have seizure-suppressing effects. In particular, norepinephrine (NE) is a neurotransmitter that has been associated with the clinical effects of VNS by preventing seizure development and by inducing long-term plastic changes that could restore a normal function of the brain circuitry. However, the biological requisites to become responder to VNS are still unknown. In this review, we report evidence of the critical involvement of NE in the antiepileptic effects of VNS in rodents and humans. Moreover, we emphasize the hypothesis that the functional integrity of the noradrenergic system could be a determining factor to obtain clinical benefits from the therapy. Finally, encouraging avenues of research involving NE in VNS treatment are discussed. These could lead to the personalization of the stimulation parameters to maximize the antiepileptic effects and potentially improve the response rate to the therapy.

Role of central serotonin and noradrenaline interactions in the antidepressants' action: Electrophysiological and neurochemical evidence

The development of antidepressant drugs, in the last 6 decades, has been associated with theories based on a deficiency of serotonin (5-HT) and/or noradrenaline (NA) systems. Although the pathophysiology of major depression (MD) is not fully understood, numerous investigations have suggested that treatments with various classes of antidepressant drugs may lead to an enhanced 5-HT and/or adapted NA neurotransmissions. In this review, particular morpho-physiological aspects of these systems are first considered. Second, principal features of central 5-HT/NA interactions are examined. In this regard, the effects of the acute and sustained antidepressant administrations on these systems are discussed. Finally, future directions including novel therapeutic strategies are proposed.

Pharmacotherapy for attention-deficit/hyperactivity disorder: from cells to circuits

Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent disorder of childhood and adulthood, with a considerable impact on public health. There is a substantial pharmacopoeia available for safe and effective treatment of ADHD, and newly available agents diversify the treatment options. With the burgeoning scientific literature addressing the genetic, neurochemical, and neural systems basis for this condition, increasing attention is directed at establishing the neural basis for the efficacy of existing treatments. ADHD remains the only highly prevalent, nondegenerative neuropsychiatric disorder for which effective medications remediate the principal cognitive disturbances in concert with clinical efficacy. Therefore, deeper insight into the neural mechanisms of cognitive remediation may serve to advance treatment development not only in ADHD, but across a wide range of neuropsychiatric disorders in which cognitive dysfunction is a cardinal feature and a strong predictor of clinical outcome. To date, all effective medications for ADHD act on 1 or both of the major catecholamine neurotransmitter systems in the brain. These 2 systems, which arise from subcortical nuclei and use norepinephrine (NE) or dopamine (DA) as transmitters, exert strong modulatory effects on widely distributed cortical-subcortical neural circuits, with important effects on cognition, mood, and behavior, in both health and illness. The present review outlines the actions of ADHD medications from subcellular effects to effects on neural systems and cognition in ADHD patients. This is a very active area of investigation at all phases of the translational cycle, and near-term work is poised to firmly link cellular neuropharmacology to large-scale effects, and point the way toward advances in treatment.

Effects of sustained administration of quetiapine alone and in combination with a serotonin reuptake inhibitor on norepinephrine and serotonin transmission

Quetiapine is now used in the treatment of unipolar and bipolar disorders, both alone and in combination with other medications. In the current study, the sustained administration of quetiapine and N-Desalkyl quetiapine (NQuet) in rats in a 3 : 1 mixture (hQuetiapine (hQuet)) was used to mimic quetiapine exposure in patients because rats do not produce the latter important metabolite of quetiapine. Sustained administration of hQuet for 2 and 14 days, respectively, significantly enhanced the firing rate of norepinephrine (NE) neurons by blocking the cell body α₂-adrenergic autoreceptors on NE neurons, whether it was given alone or with a serotonin (5-HT) reuptake inhibitor. The 14-day regimen of hQuet enhanced the tonic activation of postsynaptic α₂- but not α₁-adrenergic receptors in the hippocampus. This increase in NE transmission was attributable to increased firing of NE neurons, the inhibition of NE reuptake by NQuet, and the attenuated function of terminal α₂-adrenergic receptors on NE terminals. Sustained administration of hQuet for 2 and 14 days, respectively, significantly inhibited the firing rate of 5-HT, whether it was given alone or with a 5-HT reuptake inhibitor, because of the blockade of excitatory α₁-adrenergic receptors on 5-HT neurons. Nevertheless, the 14-day regimen of hQuet enhanced the tonic activation of postsynaptic 5-HT(1A) receptors in the hippocampus. This increase in 5-HT transmission was attributable to the attenuated inhibitory function of the α₂-adrenergic receptors on 5-HT terminals and possibly to direct 5-HT(1A) receptor agonism by NQuet. The enhancement of NE and 5-HT transmission by hQuet may contribute to its antidepressant action in mood disorders.

In vivo comparison of norepinephrine and dopamine release in rat brain by simultaneous measurements with fast-scan cyclic voltammetry

Brain norepinephrine and dopamine regulate a variety of critical behaviors such as stress, learning, memory, and drug addiction. In this study, we demonstrate differences in the regulation of in vivo neurotransmission for dopamine in the anterior nucleus accumbens (NAc) and norepinephrine in the ventral bed nucleus of the stria terminalis (vBNST) of the anesthetized rat. Release of the two catecholamines was measured simultaneously using fast-scan cyclic voltammetry at two different carbon-fiber microelectrodes, each implanted in the brain region of interest. Simultaneous dopamine and norepinephrine release was evoked by electrical stimulation of a region where the ventral noradrenergic bundle, the pathway of noradrenergic neurons, courses through the ventral tegmental area/substantia nigra, the origin of dopaminergic cell bodies. The release and uptake of norepinephrine in the vBNST were both significantly slower than for dopamine in the NAc. Pharmacological manipulations in the same animal demonstrated that the two catecholamines are differently regulated. The combination of a dopamine autoreceptor antagonist and amphetamine significantly increased basal extracellular dopamine whereas a norepinephrine autoreceptor antagonist and amphetamine did not change basal norepinephrine concentration. α-Methyl-p-tyrosine, a tyrosine hydroxylase inhibitor, decreased electrically evoked dopamine release faster than norepinephrine. The dual-microelectrode fast-scan cyclic voltammetry technique along with anatomical and pharmacological evidence confirms that dopamine in the NAc and norepinephrine in the vBNST can be monitored selectively and simultaneously in the same animal. The high temporal and spatial resolution of the technique enabled us to examine differences in the dynamics of extracellular norepinephrine and dopamine concurrently in two different limbic structures.

Postsynaptic alpha-2 adrenergic receptors are critical for the antidepressant-like effects of desipramine on behavior

The antidepressant desipramine inhibits the reuptake of norepinephrine (NE), leading to activation of both pre- and postsynaptic adrenergic receptors, including alpha-1, alpha-2, beta-1, and beta-2 subtypes. However, it is not clear which adrenergic receptors are involved in mediating its antidepressant effects. Treatment of mice with desipramine (20 mg/kg, i.p.) produced an antidepressant-like effect, as evidenced by decreased immobility in the forced-swim test; this was antagonized by pretreatment with the alpha-2 adrenergic antagonist idazoxan (0.1-2.5 mg/kg, i.p.). Similarly, idazoxan, administered peripherally (0.5-2.5 mg/kg, i.p.) or centrally (1-10 microg, i.c.v.), antagonized the antidepressant-like effect of desipramine in rats responding under a differential-reinforcement-of-low-rate (DRL) 72-s schedule, ie, decreased response rate and increased reinforcement rate. By contrast, pretreatment with the beta-adrenergic antagonists propranolol and CGP-12177 or the alpha-1 adrenergic antagonist prazosin did not alter the antidepressant-like effect of desipramine on DRL behavior. The lack of involvement of beta-adrenergic receptors in mediating the behavioral effects of desipramine was confirmed using knockout lines. In the forced-swim test, the desipramine-induced decrease in immobility was not altered in mice deficient in beta-1, beta-2, or both beta-1 and beta-2 adrenergic receptors. In addition, desipramine (3-30 mg/kg) produced an antidepressant-like effect on behavior under a DRL 36-s schedule in mice deficient in both beta-1 and beta-2 adrenergic receptors. As antagonism of presynaptic alpha-2 adrenergic receptors facilitates NE release, which potentiates the effects of desipramine, the present results suggest that postsynaptic alpha-2 adrenergic receptors play an important role in its antidepressant effects.

Effect of long-term administration of the antidepressant drug milnacipran on serotonergic and noradrenergic neurotransmission in the rat hippocampus

The effect of a long-term administration of the antidepressant milnacipran on the function of the serotonergic (5-HT) and noradrenergic (NE) systems was studied using single cell recording of CA3 hippocampal pyramidal cells in chloral hydrate-anesthetized male Sprague-Dawley rats, and in vitro [3H]5-HT release measurement from hippocampal slices. The sensitivity of neither the extrasynaptic nor that of the postsynaptic 5-HT1A receptors of the pyramidal neurons was altered, as indicated by their unchanged responsiveness to the microiontophoretic application of 5-HT, and by the unchanged effect of the electrical stimulation at low frequency of the ascending 5-HT bundle, respectively. Increasing the frequency of stimulation (from 1 to 5 Hz) decreased its efficacy in control rats; the milnacipran treatment abolished this phenomenon. This cannot be attributed to a desensitisation of the terminal 5-HT1B autoreceptor, since the suppressive effect of 5-HT agonist 5-carboxyamidotryptamine on [3H]5-HT release was enhanced in milnacipran-treated rats. As for the NE system, the unchanged suppressing effect of microiontophoretic applications of NE and that of the 5 Hz stimulation in the locus coeruleus (LC) on the firing activity of pyramidal neurons indicates that the milnacipran treatment not altered the sensitivity of extrasynaptic alpha2- and postsynaptic alpha1-adrenergic receptors on pyramidal cells, as well as that of the presynaptic alpha2-autoreceptor on NE terminals. The decreased inhibitory effect of NE on the [3H]5-HT release in milnacipran-treated rats revealed that this treatment results in a desensitisation of the presynaptic alpha2-heteroreceptor located on serotonergic terminals. Taken together with the decreased suppressive effect of a low frequency of stimulation of the NE tract, the present results suggest that long-term milnacipran treatment enhances the efficacy of the 5-HT and reduces that of the NE neurotransmission.

Dual serotonin and noradrenaline reuptake inhibitors: Focus on their differences

There are three non-tricyclic dual serotonin (5-HT) and noradrenaline (NA) reuptake inhibitors (SNRIs) currently used in human therapeutics for psychiatric disorders. These medications differ in their in vitro potency to inhibit 5-HT and NA reuptake with differential ratios of activity. Using in vivo studies carried out in laboratory animals, which better reflect human physiology than experiments using lysed tissue in a test tube, venlafaxine is about three times more potent on 5-HT than NA reuptake, duloxetine five times, and milnacipran is about twice more potent on NA than 5-HT reuptake. Sustained administration of SNRIs induces different adaptive effects on presynaptic 5-HT and NA receptors controlling the function of 5-HT and NA neurons, suggesting that they may differentially affect transmission of these two neuronal systems. In the treatment of depression, SNRIs appear to have similar effectiveness and when compared to selective 5-HT reuptake inhibitors, they generally exert a superior antidepressant effect. Taken together, these observations suggest that individual patients not responding to a SNRI may present a favourable response to another agent within that family. SNRIs have different pharmacokinetic properties and exert distinct effects on the activity of liver metabolic enzymes. These features of SNRIs can help clinicians tailor treatment to individual patients.

Biophysical modeling of tonic cortical electrical activity in attention deficit hyperactivity disorder

Psychophysiological theories characterize Attention Deficit Hyperactivity Disorder (ADHD) in terms of cortical hypoarousal and a lack of inhibition of irrelevant sensory input, drawing on evidence of abnormal electroencephalographic (EEG) delta-theta activity. To investigate the mechanisms underlying this disorder a biophysical model of the cortex was used to fit and replicate the EEGs from 54 ADHD adolescents and their control subjects. The EEG abnormalities in ADHD were accounted for by the model's neurophysiological parameters as follows: (i) dendritic response times were increased, (ii) intrathalamic activity involving the thalamic reticular nucleus (TRN) was increased, consistent with enhanced delta-theta activity, and (iii) intracortical activity was increased, consistent with slow wave (<1 Hz) abnormalities. The longer dendritic response time is consistent with the increase in the activity of inhibitory cells types, particularly in the TRN, and therefore reduced arousal. The increase in intracortical activity may also reflect an increase in background activity or cortical noise within neocortical circuits. In terms of neurochemistry, these findings may be accounted for by disturbances in the cholinergic and/or noradrenergic systems. To the knowledge of the authors, this is the first study to use a detailed biophysical model of the brain to elucidate the neurophysiological mechanisms underlying tonic abnormalities in ADHD.

Stimulant drug action in attention deficit hyperactivity disorder (ADHD): inference of neurophysiological mechanisms via quantitative modelling

OBJECTIVE

To infer the neural mechanisms underlying tonic transitions in the electroencephalogram (EEG) in 11 adolescents diagnosed with attention deficit hyperactivity disorder (ADHD) before and after treatment with stimulant medication.

METHODS

A biophysical model was used to analyse electroencephalographic (EEG) measures of tonic brain activity at multiple scalp sites before and after treatment with medication.

RESULTS

It was observed that stimulants had the affect of significantly reducing the parameter controlling activation in the intrathalamic pathway involving the thalamic reticular nucleus (TRN) and the parameter controlling excitatory cortical activity. The effect of stimulant medication was also found to be preferentially localized within subcortical nuclei projecting towards frontal and central scalp sites.

CONCLUSIONS

It is suggested that the action of stimulant medication occurs via suppression of the locus coeruleus, which in turn reduces stimulation of the TRN, and improves cortical arousal. The effects localized to frontal and central sites are consistent with the occurrence of frontal delta-theta EEG abnormalities in ADHD, and existing theories of hypoarousal.

SIGNIFICANCE

To our knowledge, this is the first study where a detailed biophysical model of the brain has been used to estimate changes in neurophysiological parameters underlying the effects of stimulant medication in ADHD.

Comparative study of the effects of desipramine and reboxetine on locus coeruleus neurons in rat brain slices

Several studies have suggested that the locus coeruleus may play an important role in the pathophysiology of depression. The aim of this study was to characterize, using single-unit extracellular recordings, the in vitro effects of the noradrenaline reuptake inhibitors desipramine and reboxetine, on locus coeruleus neurons from control rats and from those chronically treated with desipramine. Bath application of desipramine (1-100 microM) and reboxetine (0.1-10 microM) decreased the firing rate of locus coeruleus neurons in a concentration-dependent manner and the alpha(2)-adrenoceptor antagonist RX 821002 (10 microM) reversed these effects. In addition, reserpine (5 mg/kg, 3 h before the experiment) almost completely blocked the inhibitory effect of desipramine. Both drugs (1 microM desipramine and 0.1 microM reboxetine) potentiated the inhibitory effect of noradrenaline (10 microM). A 7-day treatment with desipramine (3 mg/kg/12 h, i.p.) caused a decrease in sensitivity to the alpha(2)-adrenoceptor agonist bromoxidine (EC(50) increased by 3.3-fold), but not to noradrenaline or reboxetine. In contrast, this treatment potentiated the inhibitory effect of desipramine with respect to control. Moreover, 14-day treatment with desipramine (3 mg/kg/12 h, i.p.) or reboxetine (10 mg/kg/12 h, i.p.) also potentiated the in vitro effect of desipramine without modifying the in vitro effect of reboxetine. These results show that desipramine and reboxetine modulate the activity of locus coeruleus neurons by noradrenaline acting on alpha(2)-adrenoceptors, and reveal that alpha(2)-adrenoceptor-independent mechanisms may also underlie the action of noradrenaline uptake inhibitors.

Adrenoceptor mechanisms underlying imipramine-induced memory deficits in rats

The post-training administration of tricyclic antidepressant imipramine impairs memory consolidation in the passive avoidance task. The present study investigated the effects of intrahippocampal (i.h.) injection of adrenoceptor agents on imipramine-induced (2-8 microg/rat) amnesia. The administration of the alpha1-adrenoceptor agonist phenylephrine (0.05 microg/rat) and the alpha1-adrenceptor antagonist prazosin (0.5 microg/rat) did not alter the effect of imipramine. The lower doses of phenylephrine (0.005 and 0.015 microg/rat) impaired, while the higher dose of the drug (0.025 and 0.05 microg/rat) improved retention. The effect of phenylephrine was not altered by prazosin (0.5 and 1 microg/rat) pretreatment, although prazosin alone decreased retention latencies. The alpha2-adrenoceptor antagonist yohimbine (0.5 and 1 microg/rat) decreased the response induced by imipramine. However, the alpha2-adrenoceptor agonist clonidine (0.08 microg/rat) did not alter the effect of the drug. Clonidine (0.15 and 0.3 microg/rat) by itself decreased, while yohimbine (1 and 2 microg/rat) increased retention latencies. Yohimbine pretreatment attenuated the effect of clonidine. It is concluded that alpha2-adrenoceptor mechanism(s) may be involved in imipramine-induced impairment of memory.

Reboxetine attenuates forced swim test-induced behavioural and neurochemical alterations in the rat

The forced swim test is a behavioural paradigm that is predicative of antidepressant activity in rodents. Until recently, research has focused on the ability of antidepressant drugs to decrease immobility in the forced swim test paradigm, but the neurochemical sequelae induced by swim stress, or the neurochemical basis of antidepressant-induced behavioural changes have received little attention. In this regard, we have recently demonstrated that forced swim test exposure increases serotonergic activity in the amygdala, frontal cortex and hippocampus and dopamine turnover in the striatum. In addition, forced swim test-exposure activates the hypothalamic pituitary adrenal axis. The purpose of the present study was to examine the effect of treatment with the selective noradrenaline reuptake inhibitor reboxetine (3, 10 and 30 mg/kg; i.p.) on immobility and defaecation scores in the forced swim test, and on forced swim test-induced neurochemical and hypothalamic pituitary adrenal axis changes in the rat. Reboxetine treatment (10 and 30 mg/kg) significantly decreased immobility and defaecation in the forced swim test in dose dependent manner. Furthermore, reboxetine produced a dose dependent attenuation of forced swim test-induced increases in serotonin turnover in the amygdala and frontal cortex and dopamine turnover in the striatum. Reboxetine (30 mg/kg) produced a modest, but non-significant, attenuation of forced swim test-induced increases in serum corticosterone concentrations. These data demonstrate that, in addition to the behavioural activity of reboxetine in the rat forced swim test paradigm, a dose-dependent attenuation of swim stress-induced increases in serotonergic and dopaminergic activity occurred in a region specific manner. These are the first data to demonstrate that treatment with the selective noradrenaline reuptake inhibitor, reboxetine can impact on the activity of other neurotransmitter systems in response to stress. Moreover, these data further demonstrate that this paradigm is a valuable tool in studying the effect of antidepressants, on both behaviour and swim stress-related alterations in central neurotransmitter function and hypothalamic pituitary adrenal axis activity in the rat.

Comparison of changes in the extracellular concentration of noradrenaline in rat frontal cortex induced by sibutramine or d-amphetamine: modulation by alpha2-adrenoceptors

1. The effects of sibutramine (0.25 - 10 mg kg-1, i.p.) on extracellular noradrenaline concentration in the frontal cortex of halothane-anaesthetized rats were compared with those of d-amphetamine (1 - 3 mg kg-1, i.p.) using in vivo microdialysis. The role of presynaptic alpha2-adrenoceptors in modulating the effects of these drugs on extracellular noradrenaline concentration were also investigated by pretreating rats with the selective alpha2-adrenoceptor antagonist, RX821002. 2. Sibutramine induced a gradual and sustained increase in extracellular noradrenaline concentration. The dose-response relationship was described by a bell-shaped curve with a maximum effect at 0.5 mg kg-1. In contrast, d-amphetamine induced a rapid increase in extracellular noradrenaline concentration, the magnitude of which paralleled drug dose. 3. Pretreatment with the alpha2-adrenoceptor antagonist, RX821002 (dose 3 mg kg-1, i.p.) increased by 5 fold the accumulation of extracellular noradrenaline caused by sibutramine (10 mg kg-1) and reduced the latency of sibutramine to reach its maximum effect from 144 - 56 min. 4. RX821002-pretreatment increased by only 2.5 fold the increase in extracellular noradrenaline concentration caused by d-amphetamine alone (10 mg kg-1) and had no effect on the latency to reach maximum. 5. These findings support evidence that sibutramine acts as a noradrenaline uptake inhibitor in vivo and that the effects of this drug are blunted by indirect activation of presynaptic alpha2-adreno-ceptors. In contrast, the rapid increase in extracellular noradrenaline concentration induced by d-amphetamine is consistent with this being mainly due to an increase in Ca2+-independent release of noradrenaline.

Chronic treatment with desipramine induces an estrous cycle-dependent anxiolytic-like action in the burying behavior, but not in the elevated plus-maze test

The effect of chronic desipramine (DMI, 2.5 mg/kg x 21-26 days) treatment in female rats in two anxiety paradigms was assessed: the burying behavior (BB) and the elevated plus-maze (EPM) tests. In the BB test DMI produced a significant decrease in burying in ovariectomized rats, an effect considered as anxiolytic-like. In cycling females, DMI also reduced the cumulative BB most notably in proestrus rats. However, in diestrus rats no anxiolytic-like actions were observed. In addition, DMI increased BB latencies in proestrus and estrus rats. In the EPM test, DMI produced anxiolytic-like actions only in ovariectomized rats, while no significant actions were found in cycling females. Finally, the chronic treatment with DMI produced a general reduction in the ambulatory behavior of rats in all estrous cycle phases. Results are discussed on the basis of the differences between both anxiety paradigms and the probable relationship between the steroids secreted during proestrus and chronic DMI treatment.

Acute methamphetamine administration increases tyrosine hydroxylase mRNA levels in the rat locus coeruleus

Tyrosine hydroxylase (TH) mRNA levels in the rat substantia nigra (SN), ventral tegmental area (VTA) and locus coeruleus (LC) were measured by in situ hybridization histochemistry 1, 4, 6 and 24 h after a single injection of methamphetamine (MAP, 4 mg/kg, i.p.) or an equivalent volume of saline. TH mRNA levels in LC were transiently increased (130% of control saline group, P < 0.05) at 1 h after MAP injection, and returned to basal levels within 4 h. In contrast, acute MAP administration did not significantly affect TH mRNA levels in SN and VTA. These findings are the first to demonstrate TH mRNA expression in the different responses of catecholaminergic neurons to acute MAP administration.

The serotonergic and noradrenergic systems of the hippocampus: their interactions and the effects of antidepressant treatments

Previous reviews have well illustrated how antidepressant treatments can differentially alter several neurotransmitter systems in various brain areas. This review focuses on the effects of distinct classes of antidepressant treatments on the serotonergic and the noradrenergic systems of the hippocampus, which is one of the brain limbic areas thought to be relevant in depression: it illustrates the complexity of action of these treatments in a single brain area. First, the basic elements (receptors, second messengers, ion channels, ...) of the serotonergic and noradrenergic systems of the hippocampus are revisited and compared. Second, the extensive interactions occurring between the serotonergic and the noradrenergic systems of the brain are described. Finally, issues concerning the short- and long-term effects of antidepressant treatments on these systems are broadly discussed. Although there are some contradictions, the bulk of data suggests that antidepressant treatments work in the hippocampus by increasing and decreasing, respectively, serotonergic and noradrenergic neurotransmission. This hypothesis is discussed in the context of the purported function of the hippocampus in the formation of memory traces and emotion-related behaviors.

Raphe-septal neurons changes in sensitivity to desipramine following an early septal lesion in the rat

1. The electrophysiological responsivity to desipramine (DMI) applied by systemic or local route was tested in Wistar female rats submitted to a wide lesion in the lateral septal area on the 8th day after birth. 2. One year after a septal lesion, the dorsal raphe nucleus (DRN) stimulation produced an initial brief response in lateral septal and CA1/CA3 neurons. In the control and sham-lesion groups, most recordings showed only this initial brief response (non-late responding neurons); however, in the lesion group most of the recorded neurons showed an afterdischarge. 3. DMI (2.14 mg/kg, 21 days, i.p.) increased the firing rate in septal and CA1/CA3 non-late responding neurons. In the equivalent septal neurons from lesion group, DMI produced the inverse effect, i.e., a decreased firing rate. 4. In septal non-late responding neurons, DMI (2 mM; 10-15 nAmps, 0.5 sec) applied by microiontophoresis increased the firing rate only after long-term systemic DMI impregnation. The response to locally applied DMI did not occur in the lesion group even after long-term DMI treatment. 5. In conclusion, an early lateral septal lesion canceled the response of intermediate-dorsal septal neurons to DMI applied by systemic and local routes.

Amphetamine and haloperidol modulatory effects on Purkinje cell activity and on EEG power spectra in the acute rat model of epilepsy

The modulation of cerebellar Purkinje cell activity and EEG from parietal cortex was studied in the rat model of epilepsy induced by penicillin under acute haloperidol and amphetamine treatment. The discharge pattern of Purkinje cells showed tendency towards inhibition and EEG power spectra increased after parenteral administration of penicillin (1000000 IU/kg, i.p.). Acute haloperidol treatment (1 mg/kg, i.p.), performed after the development of penicillin induced epileptic episodes, elicited a prominent excitation of Purkinje cell discharges associated with parallel increase in mean EEG power spectra. However, acute DL-amphetamine treatment induced marked suppression of Purkinje cell discharges as well as outstanding decrease of the mean EEG power spectra. These results indicate that cerebellar Purkinje cells may be important in the control of seizure activity and that noradrenergic influences are relevant.

Ontogeny of behavioral sensitization in the rat: effects of direct and indirect dopamine agonists

In the present study, the abilities of NPA (a direct DA receptor agonist) and amphetamine (an indirect DA receptor agonist) to induce short- and long-term behavioral sensitization were assessed in 11- and 17-day-old rats (age at initial injection). Rats were injected on 4 consecutive days with amphetamine (1.0, 2.5, or 5.0 mg/kg), NPA (1.0 mg/kg), or saline. A final test day occurred either 2 days (experiment 1) or 8 days (experiment 2) later. On the test day, rats given successive agonist injections received a single injection of the same agonist again; whereas rats given successive saline injections received either amphetamine or NPA for the first time. Five minutes after injection, locomotor activity (line-crosses), stereotyped sniffing, and vertical activity were measured during a 30-min testing session. The results showed that 11- and 17-day-old rats exhibited behavioral sensitization when tested with NPA or amphetamine after a 2-day interval. In contrast, neither NPA nor amphetamine was able to sensitize the behaviors of preweanling rats when measured 8 days after initial drug treatments. Therefore, these results show that both direct and indirect DA agonists are able to induce short-term behavioral sensitization in preweanling rats, but that the mechanisms responsible for mediating long-term behavioral sensitization have not yet matured.

Ontogenetic effects of EEDQ on amphetamine-induced behaviors of rats: role of presynaptic processes

Previous research has shown that the alkylating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) affects dopamine (DA) synthesis and metabolism in both preweanling and adult rats. In the present study, we attempted to determine the behavioral relevance of EEDQ's presynaptic actions. To that end, 17- and 90-day-old rats were injected with either EEDQ (7.5 mg/kg, IP) or its vehicle 30 min after half the rats were pretreated with the selective DA antagonists SCH 23390 and sulpiride. (SCH 23390/sulpiride pretreatment was used to protect D1 and D2 receptors from EEDQ-induced inactivation.) The behavioral effects of amphetamine (0, 0.1, 0.3 or 1.0 mg/kg, IP) were then assessed 1, 2, 4, and 8 days after EEDQ treatment. Amphetamine-induced behaviors were used to assess EEDQ's presynaptic actions, because amphetamine does not directly bind to the DA receptor, but rather releases DA from the presynaptic terminal. Further, since half of the EEDQ-treated rats had a full complement of DA receptors (i.e., those rats pretreated with SCH 23390/sulpiride), EEDQ's actions in the presynaptic terminal could be dissociated from actions at pre- and postsynaptic receptors. In general, the results showed that EEDQ blocked most of the amphetamine-induced behaviors of both 17- and 90-day-old rats. Surprisingly, pretreatment with SCH 23390 and sulpiride only protected the amphetamine-induced behaviors of adult rats, but not the behaviors of 17-day-old rat pups. When considered together, these results suggest that EEDQ's presynaptic effects are not behaviorally relevant to the adult rat, but may be responsible for eliminating amphetamine-induced behaviors in the 17-day-old rat pup.

Regional extracellular norepinephrine responses to amphetamine and cocaine and effects of clonidine pretreatment

Microdialysis in behaving animals was used to characterize the hippocampus (HP) and prefrontal cortex (PFC) norepinephrine (NE) responses to amphetamine (AMPH) and cocaine (COC). NE exhibited regionally similar dose- and time-dependent increases to each drug. However, peak NE concentrations were approximately 2-fold greater at behaviorally similar doses of AMPH compared with COC. To examine the role of noradrenergic impulse flow in the mechanism(s) by which these stimulants enhance extracellular NE, groups of animals were pretreated with the alpha 2 autoreceptor agonist, clonidine (CLON), prior to stimulant administration. CLON (50 micrograms/kg) administration completely blocked the NE response to both 20 and 30 mg/kg COC. By contrast, CLON decreased the NE response to 0.5 mg/kg AMPH by 75%, but became progressively less effective on the response as the dose was increased to 1.75 and 5.0 mg/kg. CLON also had no effect on the caudate dopamine responses to either AMPH or COC, consistent with the presumed specificity of this drug for alpha 2 receptors and suggesting the absence of any significant pharmacokinetic interactions. These results indicate that COC acts an uptake blocker at NE-containing neurons and suggest that AMPH increases extracellular NE through two consequences of its interaction with the neuronal transport carrier: (1) reuptake blockade which predominates at lower doses; and (2) release which becomes more prevalent at higher doses. Behavioral analyses revealed effects of CLON which varied as a function of stimulant and dose.