Cerebral decortication reverses the effect of amphetamine on striatal D2 dopamine binding site density

Concurrent choice for social interaction and amphetamine using conditioned place preference in rats: effects of age and housing condition

BACKGROUND

Social interaction can serve as a natural reward that attenuates drug reward in rats; however, it is unknown if age or housing conditions alter the choice between social interaction and drug.

METHODS

Individually- and pair-housed adolescent and adult male rats were tested using conditioned place preference (CPP) in separate experiments in which: (1) social interaction was conditioned against no social interaction; (2) amphetamine (AMPH; 1mg/kg, s.c.) was conditioned against saline; or (3) social interaction was conditioned against AMPH.

RESULTS

Social interaction CPP was obtained only in individually-housed adolescents, whereas AMPH CPP was obtained in both individually-housed adolescents and adults; however, the effect of AMPH was not statistically significant in pair-housed adults. When allowed to choose concurrently between compartments paired with either social interaction or AMPH, individually-housed adolescents preferred the compartment paired with social interaction, whereas pair-housed adolescents preferred the compartment paired with AMPH. Regardless of housing condition, adults showed a similar preference for the compartments paired with either social interaction or AMPH.

CONCLUSIONS

Although some caution is needed in interpreting cross-experiment comparisons, the overall results suggest that individually-housed adolescents were most sensitive to the rewarding effect of social interaction, and this hypersensitivity to social reward effectively competed with AMPH reward.

Knocking out the dopamine reuptake transporter (DAT) does not change the baseline brain arachidonic acid signal in the mouse

BACKGROUND

Dopamine transporter (DAT) homozygous knockout (DAT(-/-)) mice have a 10-fold higher extracellular (DA) concentration in the caudate-putamen and nucleus accumbens than do wildtype (DAT(+/+)) mice, but show reduced presynaptic DA synthesis and fewer postsynaptic D(2) receptors. One aspect of neurotransmission involves DA binding to postsynaptic D(2)-like receptors coupled to cytosolic phospholipase A(2) (cPLA(2)), which releases the second messenger, arachidonic acid (AA), from synaptic membrane phospholipid. We hypothesized that tonic overactivation of D(2)-like receptors in DAT(-/-) mice due to the excess DA would not increase brain AA signaling, because of compensatory downregulation of postsynaptic DA signaling mechanisms.

METHODS

[1-(14)C]AA was infused intravenously for 3 min in unanesthetized DAT(+/+), heterozygous (DAT(+/-)), and DAT(-/-) mice. AA incorporation coefficients k* and rates J(in), markers of AA metabolism and signaling, were imaged in 83 brain regions using quantitative autoradiography; brain cPLA(2)-IV activity also was measured.

RESULTS

Neither k* nor J(in) for AA in any brain region, or brain cPLA(2)-IV activity, differed significantly among DAT(-/-), DAT(+/-), and DAT(+/+) mice.

CONCLUSIONS

These results differ from reported increases in k* and J(in) for AA, and in brain cPLA(2) expression, in serotonin reuptake transporter (5-HTT) knockout mice, and suggest that postsynaptic dopaminergic neurotransmission mechanisms involving AA are downregulated despite elevated DA in DAT(-/-) mice.

Chronic d-amphetamine depresses an imaging marker of arachidonic acid metabolism in rat brain

Acute d-amphetamine (d-Amph) administration to rats leads to the release of arachidonic acid (AA, 20:4n-6) as a second messenger following indirect agonism at dopamine D2-like receptors in the brain. We hypothesized that chronically administered d-Amph in rats also would alter brain AA metabolism and signalling. To test this, adult male rats were injected i.p. daily for 2 wk with saline or 2.5 mg/kg d-Amph. After a 1-d washout, the unanaesthetized rats were injected acutely with i.v. saline, 1 mg/kg quinpirole (a D2-like receptor agonist) or 5.0 mg/kg SKF-38393 (a D1-like receptor agonist), followed by i.v. [1-14C]AA. The AA incorporation coefficient k* (brain radioactivity/integrated plasma radioactivity), a marker of AA signalling and metabolism, was quantified using autoradiography in each of 62 brain regions. Compared with chronic saline, chronic d-Amph widely decreased baseline values of k* in brain regions having D2-like receptors. On the other hand, chronic amphetamine did not alter the k* responses to quinpirole seen in chronic saline-treated rats. SKF-38393 had minimal effects on k* in both chronic saline-treated and amphetamine-treated rats, consistent with D1-like receptors not being coupled to AA signalling. The ability of chronic d-Amph after 1-d washout to down-regulate baseline values of k* probably reflects neuroplastic changes in brain AA signalling, and may correspond to depressive behaviours noted following withdrawal from chronic amphetamine in humans and in rats.

Changes in striatal D2-receptor density following chronic treatment with amphetamine as assessed with PET in nonhuman primates

Recent brain imaging studies suggest that schizophrenia may be related to abnormally high amphetamine-induced dopamine release. It is known that repeated use of amphetamine may cause paranoid psychosis and persisting stereotypies. The biochemical background for these signs and symptoms has not been clarified. In this study, positron emission tomography and [11C]raclopride were used to determine central D2-dopamine receptor density (Bmax) and apparent affinity (K(D)app) in Cynomolgus monkeys before and after 14 days of treatment with d-amphetamine sulphate (2 mg/kg/day; s.c.). One day after withdrawal from amphetamine, K(D)app was increased, suggesting [11C]raclopride competition with elevated concentration of dopamine. At 7 and 14 days after withdrawal, there was a 19-26% decrease in Bmax but no change in K(D)app as compared to baseline. Although this study was performed on two monkeys only, there was thus no support for the view that chronic intermittent hyperactivity of the dopamine system may be related to an upregulation of striatal D2-dopamine receptors. Repeated administration of amphetamine may, rather, cause a long-lasting downregulation of the D2-receptor density, which may be a neurochemical correlate to the abnormal movements, anhedonia, anxiety, and depression seen in psychostimulant abusers.

Differences in D2 dopamine receptor binding in the neostriatum between cats hemidecorticated neonatally or in adulthood

In order to study differences in response to neocortical injury sustained at different ages at the neurotransmitter level, we examined the density in D2 dopamine receptors in the neostriatum of cats hemidecorticated neonatally (N = 4) or in adulthood (N = 4), as well as in intact brains (N = 6). Receptor densities were measured using quantitative autoradiography and [3H]-spiperone binding in 12 regions of the neostriatum and nucleus accumbens septi. We found that the anterior lateral caudate nucleus on both sides of the brain contained a higher D2 receptor density in neonatal-lesioned as compared to adult-lesioned brains. Ipsilateral to the lesion, the increase was 101% (P < 0.05) and contralaterally it amounted to 77% (P < 0.05). Moreover, this region of the ipsilateral caudate nucleus of neonatal-lesioned cats tended to be more densely labeled than that of intact brain by 58% (P < 0.1). D2 receptor densities in adult-lesioned cats did not differ from that of intact controls. Comparison of these data with those of a former morphological study using the same animals suggested that this bilateral elevation of D2 receptor density in neonatally lesioned brains represents a higher mean density of binding sites per neuron. The elevation in the neonatal-lesioned cats might be a response of the striatum to neuroplastic changes in the striatal neuropil, including the corticostriatal afferents, since such changes are different in neonatal- as compared to adult-lesioned cats.

Lamotrigine in the treatment of nocturnal myoclonus syndrome (NMS): two case reports

In previous investigations we found an increase of D2 dopamine receptors in the striatum of patients with nocturnal myoclonus syndrome (NMS) after treatment with dopamimetics. Under the hypothesis, that, according to animal experiments, the glutamatergic system could be involved in this atypical dopaminergic up-regulation in NMS. The glutamate release inhibitor lamotrigine was tested in up to now two NMS patients. The results and the success of this approach and its implications are discussed.

Single photon emission tomography (SPET) imaging of dopamine D2 receptors in the course of dopamine replacement therapy in patients with nocturnal myoclonus syndrome (NMS)

Single photon emission tomography (SPET) permits the in vivo measurements of regional cerebral radioactivity in the human brain following the administration of compounds labeled with photon-emitting isotopes. According to our SPET findings of a reduced binding of [123I]labeled (S)-2-hydroxy-3-iodo-6-methoxy-([1-ethyl-2-pyrrolidinyl]methyl) benzamide (IBZM) (a highly selective CNS D2 dopamine receptor ligand) to D2 dopamine receptors in striatal structures in untreated patients with nocturnal myoclonus syndrome (NMS) it seemed to be of interest to investigate whether there are changes in D2 receptor binding under dopamine replacement therapy or not. We studied the uptake and distribution of [123I]IBZM before and in the course of dopamine replacement therapy in four patients with severe insomnia caused by a nocturnal myoclonus syndrome (NMS). We found an increase of the IBZM binding to D2 receptors in the course of treatment, which was associated with an improvement of sleep quality. Reasons for this are discussed. The [123I]IBZM SPET technique in conclusion offers an intersting tool for in vivo investigations of functional changes in the dopaminergic neurotransmitter system in longitudinal studies.

Tonic D2-mediated attenuation of cortical excitation in nucleus accumbens neurons recorded in vitro

The effects of dopamine D1 and D2 selective drugs on the responses evoked in accumbens neurons by stimulation of cortical afferents were studied in an in vitro brain slice preparation. The D2-specific antagonist sulpiride (1-10 microM) increased, whereas the D2 agonist quinpirole (1-20 microM) occasionally attenuated the amplitude of stimulation-evoked EPSPs recorded in accumbens neurons. Administration of the D1 agonist SKF 38393 (3-10 microM) or the D1 antagonist SCH 23390 (10 microM) did not alter the EPSP amplitude, although an apparent change in the time course of the EPSP was often observed. In slices obtained from dopamine (DA)-depleted animals, sulpiride failed to induce changes in the amplitude of the EPSPs, whereas quinpirole produced a highly significant suppression of EPSP amplitude that was only occasionally observed in control slices. These results indicate that DA modulates the response of accumbens neurons to cortico-accumbens fiber stimulation via D2 receptors. Furthermore, these D2 receptors appear to be located presynaptically on the cortical afferent terminals, since this action of DA was not accompanied by changes in membrane potential, input resistance, or time constant, and was not modified by changes in the membrane potential. These data provide evidence for a tonic basal level of D2 receptor stimulation in the accumbens slice preparation.

Dopamine D2 receptor alteration in patients with periodic movements in sleep (nocturnal myoclonus)

Periodic movements in sleep (PMS) can cause severe sleep disturbances. We investigated the central dopamine D2 receptor density in patients with PMS with 123I-IBZM and single photon emission tomography (SPET). In PMS there was a lower 123I-IBZM binding in the basal ganglia compared to the control group. The results indicate a loss of central D2 receptors in PMS.

Autoradiographic studies of post-mortem human narcoleptic brain

Although the pathological basis for narcolepsy is unknown, studies of human and canine narcolepsy have suggested that monoamine and cholinergic metabolism may be altered. We used quantitative autoradiography to assess binding of dopaminergic, noradrenergic, and cholinergic ligands to basal ganglia and amygdala of five narcoleptic and 17 control human brains. Dopamine receptor studies revealed significant increases in D-1 and D-2 receptor binding in the caudate nucleus, as well as large but not significant increases of D-1 binding in the medial globus pallidus, and D-2 binding in the lateral globus pallidus and the lateral nucleus of the amygdala. Alpha-adrenergic receptor studies revealed a significant increase in alpha-2 receptor binding in the putamen and large but not significant increases of alpha-2 binding in the caudate nucleus, and basal and lateral nuclei of the amygdala. Alpha-1 receptor binding was decreased in several areas but the changes were not statistically significant. Studies of two narcoleptic brains revealed small but not statistically significant increases in muscarinic receptor binding in the caudate nucleus, putamen, and amygdala. Although we cannot exclude the possibility that stimulant medications used before death may be partly responsible for these findings, the results suggest that human narcolepsy is associated with upregulation of dopamine and alpha-2 adrenergic receptors in specific brain regions.

Recovery from lateralized neocortical damage: dissociation between amphetamine-induced asymmetry in behavior and striatal dopamine neurotransmission in vivo

It has been hypothesized that neocortical damage is accompanied by secondary changes in other brain areas (the shock or diaschisis of von Monakow), which contributes to initial non-specific behavioral depression. The relation between behavioral changes and dopamine (DA), serotonin (5-HT), and their metabolites, measured with intracerebral microdialysis in freely moving rats and by tissue assay postmortem, was examined during postsurgical recovery from unilateral hemidecortications. Rats were tested for rotational asymmetry and extracellular concentration of DA was measured both during rest and after amphetamine (1.5 mg/kg). It was found that: (1) during the first few postsurgical days the hemidecorticate rats rotated ipsilateral to their lesions after amphetamine but thereafter on tests given up to 121 days postsurgery concentration of DA or its metabolites at any time after surgery; (3) the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) was elevated acutely for a few days following surgery; (4) during the first 3 postoperative days, both baseline extracellular 3,4-dihydroxyphenylacetic acid (DOPAC) and amphetamine-induced DA release were significantly elevated bilaterally. These findings demonstrate that the acute behavioral asymmetry in rotation produced by hemidecortication is not related to unilateral changes in striatal DA activity and its metabolites. Thus, the behavioral asymmetries might be related to other striatal changes (i.e. 5-HIAA) or other damage, such as to the corticospinal projections of the lesioned hemisphere. Nevertheless, unilateral lesions did produce acute bilateral increases in DA levels, which may be a correlate of generalized neural shock produced by the lesion.

Food deprivation alters dopamine utilization in the rat prefrontal cortex and asymmetrically alters amphetamine-induced rotational behavior

The effects of 24 and 48 h of food deprivation on changes in the activity of dopaminergic (DAergic) neurons and D-amphetamine-induced rotational behavior were studied in male and female Long-Evans rats. Food deprivation selectively altered 3,4-dihydroxyphenylacetic acid (DOPAC) in the medial prefrontal cortex (PFC) but not in the nucleus accumbens or striatum: PFC DOPAC was significantly increased and decreased bilaterally after 24 and 48 h of food deprivation, respectively. Left greater than right hemispheric asymmetries were seen for DOPAC and DOPAC/DA in the control animals. In a separate experiment, 24 h of food deprivation enhanced right rotational behavior, while 48 h significantly increased left rotational behavior. The results are discussed in terms of food deprivation's effects on mesocortical DAergic neurons, previous work on cortical modulation of striatal function and how these effects on rotational behavior may be determined by brain asymmetry.

Striatal dopamine after cortical injury: a reexamination

We reevaluated the effects of unilateral sensorimotor cortex ablation on dopamine and dihydroxyphenylacetic acid concentration in the left and right neostriatum. We found no evidence for an asymmetry of either dopamine or dihydroxyphenylacetic acid in control or sham-operated animals and cortical ablation had no effect on dopamine or dihydroxyphenylacetic acid concentrations. These results suggest that the influence of sensorimotor cortex lesions on extrapyramidal function does not involve changes in striatal dopamine concentrations or turnover.