Tadashi Saigusa

The non-peptidic delta opioid receptor agonist TAN-67 enhances dopamine efflux in the nucleus accumbens of freely moving rats via a mechanism that involves both glutamate and free radicals.

The activation of the delta-opioid receptors in the nucleus accumbens is known to induce a large and rapid increase of accumbal dopamine efflux. (+/-)-TAN-67 (2-methyl-4a(alpha)-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12a(alpha)-octahydro-quinolino[2,3,3,-g]isoquinoline) is a centrally acting non-peptidic delta opioid receptor agent which has recently become available. Interestingly, the (+) enantiomer of TAN-67 induces hyperalgesia in contrast to the (-) enantiomer of TAN-67 that produces profound antinociceptive effects in mice; the latter effects are mediated through delta-1 receptor stimulation. Using the microdialysis technique, the ability of the enantiomers of TAN-67 to alter the release of accumbal dopamine in vivo was analyzed. Like the 25-min infusion of the selective delta-1 opioid receptor agonist (D-[Pen2,5]-enkephalin) DPDPE (50 nM) and the delta-2 opioid receptor agonist deltorphin II (50 nM), the 25-min infusion of both (-)-TAN-67 (25 and 50 nM) and (+)-TAN-67 (25 and 50 nM) into the nucleus accumbens produced a similar transient dose-dependent increase in the accumbal extracellular dopamine level. Naloxone (1 mg/kg i.p., given 25 min prior to the drugs), namely a treatment that is known to inhibit the increase of dopamine induced by DPDPE and deltorphin II, did not affect the transient increase in the accumbal dopamine level produced by infusion of the enantiomers of TAN-67. The DPDPE and deltorphin II-induced increase in accumbal dopamine level, but not that of (-)-TAN-67 and (+)-TAN-67, was eliminated by subsequently perfused tetrodotoxin (2 microM) into the nucleus accumbens. The increase in accumbal dopamine level produced by an infusion of (-)-TAN-67 and (+)-TAN-67 was not altered by a Ca2+-free Ringers solution. The (-)-TAN-67 and (+)-TAN-67-induced accumbal dopamine efflux was strongly prevented by reserpine (5 mg/kg i.p., given 24 h earlier) or alpha-methyl-para-tyrosine (250 mg/kg i.p., given 2 h earlier). The effects of the enantiomers of TAN-67 on the accumbal dopamine were nullified by combined treatment with reserpine and alpha-methyl-para-tyrosine. The (-)-TAN-induced dopamine efflux was significantly reduced by the N-methyl-D-aspartate (NMDA) receptor antagonists ifenprodil (20 mg/kg i.p., 20 min before) and MK-801 (0.5 mg/kg i.p., 20 min before), respectively. The effects of (-)-TAN-67 on the dopamine efflux were also inhibited by the free radical scavenger N-2-mercaptopropionyl glycine (100 mg/kg i.p., 20 min before). These results show that both enantiomers of TAN-67 enhance the release of reserpine sensitive, vesicular dopamine and alpha-methyl-p-tyrosine sensitive, cytosolic dopamine from dopaminergic nerve terminals in the nucleus accumbens in a way that is independent of neural activity; activation of delta opioid receptors plays no role in these events. All together, the results suggest that (-)-TAN-67 can generate a burst of free radicals that in turn trigger a release of glutamate that ultimately via activation of NMDA receptors enhances the release of dopamine from dopaminergic nerve terminals in the nucleus accumbens.

Endomorphin-2 and Endomorphin-1 Promote the Extracellular Amount of Accumbal Dopamine via Nonopioid and Mu-Opioid Receptors, Respectively

Activation of mu-opioid receptors in the nucleus accumbens (NAc) is known to increase accumbal dopamine efflux in rats. Endomorphin-2 (Tyr-Pro-Phe-Phe-NH2; EM-2) and endomorphin-1 (Tyr-Pro-Trp-Phe-NH2; EM-1) are suggested to be the endogenous ligands for the mu-opioid receptor. As the ability of EM-2 and EM-1 to alter the accumbal extracellular dopamine level has not yet been studied in freely moving rats, the present study was performed, using a microdialysis technique that allows on-line monitoring of the extracellular dopamine with a temporal resolution of 5 min. A 25 min infusion of either EM-2 or EM-1 into the NAc (5, 25, and 50 nmol) produced a dose-dependent increase of the accumbal dopamine level. The EM-2 (50 nmol)- and EM-1 (25 and 50 nmol)-induced dopamine efflux were abolished by intra-accumbal perfusion of tetrodotoxin (2 μM). Intra-accumbal perfusion of the mu-opioid receptor antagonist CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH2; 3 nmol) failed to affect the EM-2 (50 nmol)-induced dopamine release, whereas it significantly inhibited the EM-1 (25 and 50 nmol)-induced dopamine release. The EM-1 (50 nmol)-induced accumbal dopamine efflux was significantly reduced by the systemic administration of the putative mu1-opioid receptor antagonist naloxonazine (15 mg/kg, intraperitoneally (i.p.), given 24 h before starting the perfusion). Systemic administration of the aspecific opioid receptor antagonist naloxone (1 mg/kg, i.p., given 10 or 20 min before starting the perfusion) also failed to affect the EM-2 (50 nmol)-induced dopamine efflux, whereas it significantly inhibited the EM-1 (25 and 50 nmol)-induced dopamine efflux. The present study shows that the intra-accumbal infusion of EM-2 and EM-1 increases accumbal dopamine efflux by mechanisms that fully differ. It is concluded that the effects of EM-2 are not mediated via opioid receptors in contrast to the effects of EM-1 that are mediated via mu1-opioid receptors in the NAc.

Cholinergic/dopaminergic interaction in the rat striatum assessed from drug-induced repetitive oral movements

The role of striatal dopaminergic/cholinergic interactions in the regulation of oral behaviour in rats was studied using methods which resolve distinct patterns of jaw movements, allowing a more accurate quantitative and qualitative analysis. Both dopamine and acetylcholine receptor agonists given either systemically or into the ventral striatum induced repetitive oral movements. However, the cholinergic movements differed from dopaminergic movements as to pattern of activity. Oral movements induced by apomorphine (0.2 mg/kg i.v.) were potentiated by carbachol (0.1 microgram/0.2 microliters) injected into the dorsal striatum, while inhibition was observed when carbachol was injected into the ventral striatum. Pilocarpine (4 mg/kg)-induced oral movements were reduced by injecting flupentixol (10 micrograms/0.2 microliters), but not a combination of SKF 38393 (3 micrograms)+quinpirole (10 micrograms/0.2 microliter), into either the dorsal or the ventral striatum. Oral movements induced by the injection of carbachol (1 microgram/0.2 microliter) into the ventral striatum were enhanced by previous injection of this combination of dopamine receptor agonists into the same site and were inhibited by flupentixol. These results suggest that cholinergic and dopaminergic oral movements are separate behaviors and that the striatal dopamine/acetylcholine interaction in their regulation is neither simply antagonistic or synergistic, nor reciprocal.

Dopamine efflux in the rat nucleus accumbens evoked by dopamine receptor stimulation in the entorhinal cortex is modulated by oestradiol and progesterone

This study compared the effects of dopamine receptor stimulation in the entorhinal cortex on dopamine release in the nucleus accumbens, measured by in vivo microdialysis in conscious Sprague‐Dawley rats, with and without oestradiol and progesterone priming. Nonselective dopamine receptor stimulation with apomorphine reduced dopamine release in the nucleus accumbens, an effect which was prevented by injection of cis‐flupenthixol into the entorhinal cortex. Selective D1 receptor stimulation with SKF38393 increased dopamine release, whereas selective D2 receptor stimulation with quinpirole did not affect dopamine release. Combined administration of oestradiol and progesterone potentiated the response to apomorphine and prevented the response to SKF38393. The effects of single hormone administration on the response to apomorphine suggested that the modulation was primarily due to oestradiol enhancing effects of progesterone. Experiments with high [K+] suggested these hormonal effects were exerted predominantly in the entorhinal cortex. The present experiments have demonstrated that dopaminergic modulation of transmission in a cortico‐striatal loop linking temporal and prefrontal cortex is regulated by oestradiol and progesterone. Dysfunction in this system in humans may give rise to affective and cognitive symptoms which may, if initiated by a postpartum fall in oestrogen and progesterone concentrations, constitute the core pathophysiology of puerperal psychosis. Synapse 25:37–43, 1997.

Dissimilarities between cholinergic and dopaminergic turning elicited by nucleus accumbens stimulation in freely moving rats

Contralateral turning was produced by unilateral injection of carbachol (0.5, 2.5, 5 micrograms) into the nucleus accumbens, but not into the dorsal or ventral striatum. This behaviour was inhibited by muscarinic M1 acetylcholine receptor blockade in the nucleus accumbens, and less effectively by blockade of muscarinic M2 and nicotinic acetylcholine receptors. Unilateral injection of a mixture of the dopamine D1 receptor agonist 1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 38393, 5 micrograms) and the dopamine D2 receptor agonist quinpirole (10 micrograms) also produced contralateral turning. The stepping pattern, however, completely differed from that induced by carbachol. The number of carbachol-induced turnings was reduced by dopamine D1 or D2 receptor blockade (8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol (SCH 23390) and l-sulpiride, respectively) in the nucleus accumbens. However, the reduction was due to a change in the turning pattern. Blockade of muscarinic acetylcholine receptors in the nucleus accumbens did not change the contralateral turning induced by unilateral injection of dopamine receptor agonists into the nucleus accumbens. The results demonstrate that there is no functional interaction between the cholinergic and dopaminergic substrates involved, although blockade of the dopamine receptors elicited behavioural deficits that competed with the turning elicited by carbachol. The contralateral turning elicited by carbachol injection into the nucleus accumbens requires an intact dopamine activity at the level of dopamine D1 and D2 receptors in the ipsilateral, but not contralateral, ventrolateral striatum.

Reevaluation of the two-component hypothesis for turning behaviour by manipulating activities in the striatum and the nucleus accumbens of intact rats

The role of dopamine D1 and D2 receptor stimulation in the production of turning behaviour in rats was studied. In rats pretreated with unilateral injections of the non-selective dopamine D1/D2 receptor antagonist, cis(Z)-flupentixol (10 micrograms/0.5 microliter), into the ventral striatum, quinpirole (1, 3, 5, 10 mg/kg i.p.), a selective dopamine D2 receptor agonist, induced dose-dependent turning behaviour, while SKF 38393 (1, 3, 5, 10 mg/kg i.p.), a selective dopamine D1 receptor agonist, did not. The effect of the two drugs together was much greater than the effect of quinpirole alone and was reduced by additional blockade of dopamine D1/D2 receptors in either the ipsilateral or contralateral nucleus accumbens. The role of the nucleus accumbens in turning behaviour was determined from the effects of unilateral injections of SKF 38393 and quinpirole into the nucleus accumbens. The results show that unilateral injections of a mixture of the two drugs (SKF 38393 5 micrograms + quinpirole 10 micrograms/0.5 microliter) into the nucleus accumbens produced turning while injections of single drugs did not. Turning was abolished by the blockade of dopamine D1/D2 receptors in the ipsilateral but not contralateral ventral striatum. Turning was also reduced by the blockade of the contralateral nucleus accumbens. Moreover, turning was not produced by injections of the drug mixture into the dorsal or ventral striatum.

Tyrosine-induced release of dopamine is under inhibitory control of presynaptic dopamine D2 and, probably, D3 receptors in the dorsal striatum, but not in the nucleus accumbens

Stimulation of dopamine D2-like receptors decreases extracellular dopamine in the dorsal striatum and the nucleus accumbens. It is unknown whether the role of these receptors differs from that of dopamine D3 receptors. It is also unknown to what extent the role of these two types of receptors varies across both structures. Using microdialysis, we therefore investigated whether intracerebrally administered quinpirole, a dopamine D2-like receptor agonist, and PD 128907, (S(+)-(4aR,10bR)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]-benzopyrano[4,3-b]-1,4-oxazin-9-ol, a dopamine D3 receptor preferring agonist, differentially alter the tyrosine-induced increase of extracellular dopamine in the dorsal striatum and the nucleus accumbens, respectively. Perfusion of tyrosine (100 microM) into the dorsal striatum and the nucleus accumbens enhanced extracellular dopamine in a physiological manner in both areas. Infusion of the Na(+) channel blocker tetrodotoxin (2 microM) suppressed the enhanced level of dopamine derived from exogenous tyrosine in both brain areas. Infusion of the dopamine D2-like receptor agonist quinpirole at a concentration (1 nM), which alone did not affect basal extracellular dopamine, reduced tyrosine-enhanced extracellular dopamine when infused into the dorsal striatum, but not into the nucleus accumbens; the preferential dopamine D3 receptor agonist, PD 128907, had similar effects. Haloperidol, a dopamine D2-like receptor antagonist, given systemically at a dose, which alone did not significantly affect basal dopamine levels (10 nmol/kg i.p.), enhanced extracellular dopamine derived from exogenous tyrosine. This haloperidol treatment antagonized only the quinpirole-induced, but not the PD 128907-induced reduction in dopamine levels seen in tyrosine-treated rats. The results show that extracellular dopamine derived from exogenous tyrosine is under inhibitory control of presynaptic dopamine D2-like receptors in the dorsal striatum, but not in the nucleus accumbens; to what extent the same holds for dopamine D3 receptors remains to be proven. Future studies are required to elucidate whether the noted difference is absolute or not.

Stimulation of acetylcholine or dopamine receptors in the nucleus accumbens differentially alters dopamine release in the striatum of freely moving rats

The present study examined whether unilateral stimulation of acetylcholine or dopamine receptors in the nucleus accumbens induces an asymmetry in dopamine transmission in the ventrolateral striatum. For this purpose, a microdialysis technique was used to measure dopamine release in both sides of the ventrolateral striatum following unilateral injections of carbachol (5 micrograms/0.5 microliter) or a mixture of dopamine D1 and dopamine D2 receptor agonists (1-phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine-7,8-diol 5 micrograms + quinpirole 10 micrograms/0.5 microliter) into the nucleus accumbens. The results show that carbachol injection increased dopamine release in the ipsilateral striatum without changing dopamine release in the contralateral striatum, whereas the dopamine D1/D2 receptor agonist mixture injected unilaterally into the nucleus accumbens produced an increase followed by a decrease in dopamine release in the ipsilateral striatum, but only a decrease in dopamine release in the contralateral striatum. The biochemical effects of the cholinergic treatment greatly outlasted the drug-induced contralateral turning, whereas the biochemical effects of the dopaminergic treatment showed a good correlation with the drug-induced contralateral turning. The present study provides biochemical evidence that unilateral stimulation of acetylcholine or dopamine receptors in the nucleus accumbens elicits an asymmetry in dopaminergic activity in the ventrolateral striatum. The present study also provides biochemical evidence that two distinct neural substrates are involved in the effects of cholinergic and dopaminergic manipulation of the nucleus accumbens.

Spiraling dopaminergic circuitry from the ventral striatum to dorsal striatum is an effective feed-forward loop

Central dopamine systems are key players in the cerebral organization of behavior and in various neurological and psychiatric diseases. We demonstrate the presence of a neurochemical feed-forward loop characterized by region-specific changes in dopamine efflux in serially connected striatal regions, providing evidence in favor of the existence of so-called spiraling striato-nigro-striatal connections. Using in vivo microdialysis of rats, we show that simultaneous stimulation of dopamine D1 and D2 receptors in the accumbal shell decreased dorsal striatal dopamine efflux via a direct or indirect feed-forward loop involving shell, core, ventrolateral and dorsal part of the striatum: simultaneous stimulation of dopamine D1 and D2 receptors in the shell decreased dopamine efflux in the core; flupenthixol-induced inhibition of dopamine D1 and D2 receptors in the core increased dopamine efflux in the ventrolateral part of the striatum, and simultaneous stimulation of dopamine D1 and D2 receptors in the ventrolateral part of the striatum decreased dopamine efflux in the dorsal part of the striatum. Finally, simultaneous stimulation of dopamine D1 and D2 receptors in the shell decreased dopamine efflux in the dorsal part of the striatum. Thus, distinct striatal regions act also in series, providing a better understanding of the neural mechanisms underlying dopamine-dependent behaviors and the progression of dopamine-dependent disorders such as depression, schizophrenia, attention deficit hyperactivity disorder (ADHD), and addiction.

The α1-, but not α2-, adrenoceptor in the nucleus accumbens plays an inhibitory role upon the accumbal noradrenaline and dopamine efflux of freely moving rats

In vivo microdialysis was used to analyse the role of the α(1)- and α(2)-adrenoceptor subtypes in the regulation of noradrenaline and dopamine efflux in the nucleus accumbens of freely moving rats. Intra-accumbal infusion of α(1)-adrenoceptor agonist methoxamine (24pmol) failed to alter the noradrenaline efflux, but decreased the dopamine efflux. The intra-accumbal infusion of α(1)-adrenoceptor antagonist prazosin (6, 600 and 6000pmol) produced a dose-related increase and decrease of the noradrenaline and dopamine efflux, respectively. An ineffective dose of prazosin (6pmol) counteracted the methoxamine (24pmol)-induced decrease of dopamine efflux. The prazosin (6000pmol)-induced increase of noradrenaline efflux, but not the decrease of dopamine efflux, was suppressed by the co-administration of an ineffective dose of methoxamine (0.024pmol). Neither the α(2)-adrenoceptor agonist clonidine (300pmol) and UK 14,304 (300pmol) nor the α(2)-adrenoceptor antagonist RX 821002 (0.6, 3, 600 and 6000pmol) significantly affected the accumbal noradrenaline and dopamine efflux. The doses mentioned are the total amount of drug over the 60-min infusion period. The present results show that (1) accumbal α(1)-adrenoceptors which are presynaptically located on noradrenergic nerve terminals inhibit the accumbal noradrenaline efflux, increasing thereby the accumbal dopamine efflux, (2) accumbal α(1)-adrenoceptors which are postsynaptically located on dopaminergic nerve terminals inhibit the accumbal dopamine efflux, and (3) accumbal α(2)-adrenoceptors play no major role in the regulation of accumbal efflux of noradrenaline and dopamine.