Dopamine receptor-coupled modulation of the K+-depolarized overflow of 3H-acetylcholine from rat striatal slices: alteration after chronic haloperidol and alpha-methyl-p-tyrosine pretreatment

Carbachol and naloxone synergistically elevate dopamine release in rat striatum: an in vivo microdialysis study

Striatal dopamine (DA) release increased to 184% of baseline after 10-20 min of continuous intrastriatal perfusion with 10 mM carbachol, dropping to 124% after 30-40 min. The addition of 100 microM naloxone amplified (to 236% of baseline) and prolonged the increase in DA release, but naloxone alone (up to 1 mM) had no effect. These data suggest that activation of opiate-releasing striatal neurons suppresses cholinergic stimulation of DA release.

Effect of selective opiate antagonists on striatal acetylcholine and dopamine release

We investigated the effect of selective opiate antagonists on striatal acetylcholine (ACh) and dopamine (DA) release. The mu-receptor antagonist beta-funaltrexamine (beta-FNA), the delta-antagonist naltrindole (NTI), and the kappa-antagonist norbinaltorphimine (nor-BNI) were used to selectively block different subtypes of opiate receptors. The experiments were carried out on isolated superfused striatal slices of rats, loaded with [3H]choline or [3H]dopamine. beta-FNA and NTI significantly enhanced the electrical field stimulation-evoked release of ACh but only if the dopaminergic input had been impaired either by chemical denervation or D2 dopamine receptor blockade. By contrast, neither the selective nor nonselective antagonists had any modulatory effect on the release of dopamine. It is concluded, therefore, that the release of ACh is tonically controlled by endogenous opioid peptide(s) through the stimulation of mu- and delta-opiate receptors located on cholinergic axon terminals, in addition to the tonic control by DA.

Effect of nicotine on dopaminergic-cholinergic interaction in the striatum

We have investigated the effect of nicotinic receptor stimulation on acetylcholine (ACh) release measured by radioassay in rat striatal slices. Since the release of ACh in the striatum is tonically inhibited by endogenous dopamine and nicotine enhances the release of dopamine, we studied the release of ACh when the dopaminergic input was impaired. We used chemical denervation (6-hydroxydopamine pretreatment) or D2-receptor-blockade by sulpiride to remove the dopaminergic control of the cholinergic neurons. In our experiments nicotine failed to increase ACh release from striatal slices taken from rats whose dopaminergic-cholinergic interaction was not impaired but it enhanced the release of ACh from slices dissected from 6-hydroxydopamine pretreated rats or in the presence of sulpiride. Our results provide neurochemical evidence for the existence of nicotinic receptors on striatal cholinergic interneurons. Since the spontaneous release of ACh enhanced by nicotine was inhibited by tetrodotoxin it seems very likely that (-)-nicotine acts on the somatodendritic part of cholinergic interneurons.

Decreased striatal release of acetylcholine following withdrawal from long-term treatment with haloperidol: modulation by cholinergic, dopamine-D1 and -D2 mechanisms

The effect of chronic treatment with haloperidol (2.7-5.3 mumol/kg/day) on K(+)-evoked release of [3H]acetylcholine (ACh) from superfused slices of the striatum was assessed. Acute injections of haloperidol (0.7-13.3 mumol/kg) produced 5-54% increases in the release of [3H]ACh in the striatum. Chronic treatment with haloperidol for 2.5 and 5 months also resulted in enhanced release of [3H]ACh in the striatum (28-35%). However, withdrawal from 2.5 and 5 months of treatment produced 34 and 38% decreases in K(+)-evoked release of [3H]ACh in the striatum, respectively. The drug SKF 38393 (D1-agonist), produced concentration-dependent (0.1-10 microM) increases (24-59%) in the release of [3H]ACh in the striatum which were blocked by the selective D1-antagonist, SCH 23390. The effect of stimulation of D1-receptors was significantly reduced after 2.5 or 5 months of chronic treatment with haloperidol. Both LY171555 (D2-agonist) and carbachol (muscarinic agonist) produced concentration-dependent (0.1-10 microM) inhibitions of the release of [3H]ACh in the striatum (LY171555: 28-62%; carbachol: 23-63%). Long-term treatment with haloperidol (2.5 and 5 months) elicited increases in sensitivity to the effect of LY171555, while the effect of carbachol was diminished only after the 5-month treatment period. These findings demonstrate that withdrawal from chronic exposure to haloperidol in the rat results in a reduction in the release of acetylcholine in the striatum. This effect is accompanied by (1) attenuated dopaminergic D1 mechanisms which ordinarily facilitate evoked release of ACh, (2) enhanced D2 mechanism which elicits inhibition of the release of ACh in the striatum, and (3) diminished muscarinic inhibitory influence which regulates the release of ACh.

Effects of acute and chronic administration of cocaine on striatal uptake, compartmentalization and release of [3H]dopamine

The effects of acute and repetitive administration of cocaine were studied on several parameters associated with the uptake and release of [3H]dopamine ([3H]DA) in the striatum. It was found that repetitive administration of cocaine followed 7 days later by acute challenge with cocaine, produced an increase in the Vmax with no change in the affinity of the uptake carrier for either dopamine (DA) or cocaine. The intracellular compartmentalization of [3H]DA in synaptosomes was not altered by either acute or repeated treatment with cocaine. However, chronic administration of cocaine abolished the stimulatory effect that 1 microM amphetamine normally has on the efflux of [3H]DA from the fast pool in untreated synaptosomes. The K(+)-stimulated release of [3H]DA from slices of striatum was not affected by acute or chronically administered cocaine; however, chronically administered cocaine, plus acute challenge with cocaine potentiated the effect of amphetamine on the K(+)-induced release of [3H]DA. This was accompanied by a reduction of the effect of amphetamine on the spontaneous release of DA. In addition, chronically administered cocaine plus acute challenge with cocaine increased K(+)-stimulated release of [14C]acetylcholine [( 14C]ACh). These data suggest that repetitive administration of cocaine, in a regimen that elicits behavioral sensitization, alters the substrates through which amphetamine exerts its effects on the subcellular distribution and release of [3H]DA, and further, that challenge with cocaine of sensitized rats produces a compensatory increase in the uptake of [3H]DA that is correlated with increased depolarization-induced release of [14C]ACh.

Effect of the inhibition of dopamine uptake on the dopamine- and dimethyldopamine-induced-inhibition of the potassium-evoked release of [3H]acetylcholine from striatal slices

1. Dimethyldopamine was eight times more potent than dopamine in activating the D2 receptor that inhibits the potassium-evoked release of [3H]acetylcholine from striatal slices. 2. Cocaine and mazindol produced an eight-fold shift in the concentration-response curve for dopamine, but not for dimethyldopamine. 3. The IC50 of dimethyldopamine for the inhibition of [3H]dopamine uptake was thirty times greater than that for dopamine. 4. Dopamine may be less potent than dimethyldopamine at the D2 receptor because dopamine has a higher affinity for the dopamine uptake system, resulting in its rapid removal from the vicinity of the receptor.

Serotonin inhibits acetylcholine release from rat striatum slices: evidence for a presynaptic receptor-mediated effect

Rat brain striatum slices were incubated with [3H]choline, perfused with a physiological buffer, and stimulated by perfusion with a K+-enriched buffer for 2 min. The tritium overflow evoked by K+ was decreased by 5-hydroxytryptamine (serotonin, 5-HT) (maximal inhibition 10(-6) M). This effect of 5-HT was mimicked by several agonists (5-methoxytryptamine, N,N-dimethyl-tryptamine, bufotenin) and blocked by serotonergic antagonists (methiothepin, methysergide, cinanserin) but not by haloperidol; methiothepin and methysergide alone slightly increased the K+-evoked overflow of tritium (3H). Inhibition of the tritium release by 5-HT was not suppressed in the presence of tetrodotoxin (TTX) (10(-6) M). These results suggest that 5-HT tonically inhibits acetylcholine (ACh) release from striatal cholinergic neurons by acting on a presynaptic receptor localized on cholinergic terminals.

Modulation of the endogenous acetylcholine release from rat striatal slices

The dopaminergic modulation of the acetylcholine release from rat striatal slices has been investigated using a chemiluminescent method. Dopamine, more efficiently than apomorphine, decreased the potassium-evoked release of acetylcholine. The effect of dopamine antagonists, haloperidol and sulpiride, has been studied, and haloperidol was a better antagonist than sulpiride to the dopamine effect. Haloperidol elicited an acetylcholine release from striatal slices at 0.1 nM, probably by removing endogenous dopamine from dopaminergic receptors.

Inhibition of the electrically evoked release of [3H]acetylcholine in rat striatal slices: an experimental model for drugs that enhance dopaminergic neurotransmission

The activation by endogenous dopamine of the inhibitory 3,4-dihydroxyphenylethylamine (dopamine) receptors modulating the electrically evoked release of [3H]acetylcholine [( 3H]ACh) and [3H]dopamine in rat striatal slices is a function of the concentration of dopamine accumulated in the synaptic cleft during electrical stimulation. When the release of 3H-neurotransmitters was elicited with a 2-min period of stimulation at a frequency of 1 Hz, neither dopamine autoreceptors nor dopamine receptors modulating [3H]ACh were activated by endogenously released dopamine. On the other hand, exposure to (S)-sulpiride facilitated the release of [3H]dopamine and [3H]ACh elicited when the 2-min stimulation was carried out at a frequency of 3 Hz but this effect was not observed at a lower frequency of stimulation (1 Hz). In the presence of amphetamine the dopamine receptors modulating the electrically evoked release of [3H]ACh can be activated by endogenous dopamine even at the lower frequency of stimulation (1 Hz). Similar effects can be obtained if the neuronal uptake of dopamine is inhibited by cocaine or nomifensine. The inhibition by amphetamine of the release of [3H]ACh elicited by electrical stimulation at 1 Hz involves dopamine receptors and can be fully antagonized by clozapine, haloperidol, chlorpromazine, or pimozide. The stereoselectivity of this antagonism can be demonstrated with the optical enantiomers of sulpiride and butaclamol. This inhibitory effect of amphetamine on cholinergic neurotransmission appears to be the result of the stimulation of dopamine receptors of the D2 subtype, as they were resistant to blockade by the preferential D1 receptor antagonist SCH 23390.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a sulfonium analog of dopamine on the depolarization-induced release of [3H]acetylcholine from mouse striatal slices

P3 have synthesized a chemical analog or dopamine in which the amino group has been replaced by a charged dimethylsulfonium group. The dopaminergic activity of this drug was evaluated by determining its ability to inhibit the depolarization-evoked release of [3H]acetylcholine from mouse striatal slices. The slices were preincubated with [3H]choline (0.1 microM) and then superfused in physiological medium. [3H]Acetylcholine release was induced by exposure of the slices to a high potassium medium (12.5 mM) for 5 min. The sulfonium analog of dopamine, dopamine, and apomorphine inhibited the evoked [3H]acetylcholine release with IC50 values of approximately 10, 2.0, and 0.3 microM respectively. The inhibition by the sulfonium analog was reversed by fluphenazine (1 microM), suggesting that the inhibition of [3H]acetylcholine release was due to the activation of dopaminergic receptors. The sulfonium analog also inhibited the uptake of [3H]dopamine into striatal slices and caused the release of exogenously taken up [3H]dopamine from these slices. The release of [3H]dopamine by the sulfonium analog was inhibited by cocaine (3 microM), suggesting that the drug-induced release of [3H]dopamine was dependent on the carrier-mediated uptake of the sulfonium analog into dopaminergic neurons. The inhibition of the evoked [3H]acetylcholine release by high concentrations (30 and 60 microM) of the sulfonium analog did not appear to be mediated by endogenous dopamine release, since the analog still inhibited [3H]acetylcholine release from slices after reserpine-alpha-methyl-p-tyrosine treatment. However, the inhibitory effect of the sulfonium analog at 10 microM was reduced by reserpine-alpha-methyl-p-tyrosine treatment, suggesting that the inhibition at lower concentrations was mediated through endogenous DA release. These results suggest that a charged compound can act as a substrate for the dopamine carrier and can activate the dopamine receptor regulating acetylcholine release. They also indicate that the nitrogen on the dopamine molecule is not essential for dopamine agonist activity.

Phencyclidine-induced inhibition of striatal acetylcholine release: comparisons with mu, kappa, and sigma opiate agonists

The effects of phencyclidine (PCP) on ACh release were compared to those of morphine, ethylketocyclazocine (EKC), and N-allylnormetazocine (SKF10047) in a superfused striatal slice preparation. The (+)-isomer of the prototypic sigma opiate agonist, SKF10047, and the prototypic kappa opiate agonist, EKC, had essentially the same pharmacological profile as did PCP. That is, they each inhibited ACh release in a concentration dependent manner (with EKC being the most potent) and this effect was antagonized by 0.1 microM naloxone. Since morphine was without effect on ACh release, it is unlikely that these drugs inhibit ACh release by acting at mu receptors. In addition, we observed that the inhibitory effect of PCP, (+) SKF10047, and EKC on ACh release was reversed by 0.1 microM haloperidol. Given that PCP has been shown to stimulate basal DA release in this preparation, it is possible that PCP, EKC and (+) SKF10047 inhibit ACh release indirectly by stimulating DA release. The naloxone-induced blockade of the effect of PCP and these benzomorphans is discussed in relation to the effects of naloxone on other systems known to influence ACh release.

Action of apomorphine, bromocriptine and lergotrile on gamma-aminobutyric acid and acetylcholine release in nucleus accumbens and corpus striatum

The effect of three dopamine agonists, apomorphine, bromocriptine and lergotrile, was tested on the release of gamma-aminobutyric acid, (GABA) and acetylcholine (ACh) from tissue slices of rat nucleus accumbens and striatum. All three agents in vitro caused a dose dependent depression of the K+-evoked release of [14C]-GABA in corpus striatum. This effect was also obtained following in vivo drug application and when endogenous GABA release was determined. A similar depression of GABA release was obtained in the nucleus accumbens. Both dopamine and dibutyryl adenosine-3':5'-cyclic monophosphoric acid inhibited the K+-evoked release of [14C]-GABA in corpus striatum. This inhibitory effect was not reversed by sulpiride. Bromocriptine and lergotrile also depressed the K+-evoked release of [3H]-acetylcholine from tissue slices of corpus striatum but not nucleus accumbens, as has previously been demonstrated for dopamine and apomorphine. In contrast, sulpiride enhanced the release of [3H]-acetylcholine and molindone reversed the apomorphine inhibition of [3H]-acetylcholine release. These results indicate that dopaminergic agents may influence the release of both GABA and ACh in the corpus striatum but only GABA in the nucleus accumbens.

Frequency-dependent release of acetylcholine and dopamine from rabbit striatum: its modulation by dopaminergic receptors

The release of [3H]dopamine (DA) and [14C]acetylcholine (ACh) was monitored from single slices of the rabbit striatum. In all cases, the evoked overflow of ACh showed a higher peak and was of shorter duration than that of 3H products. For ACh, the release per pulse showed a marked decline with increasing frequency of stimulation, whereas flat frequency-release curves were obtained for DA. At 0.1 and 1 Hz the evoked overflows of ACh were 15 and 7 times greater, respectively, than those of DA. Haloperidol (0.03 microM) and sulpiride (1 microM) produced large increases in the evoked overflow of DA and ACh at 3 and 10 Hz; little effect was observed at lower frequencies. These results indicate that the frequency-release curves for DA and ACh are different and that at high frequencies the slope of the curves is modified by activation of pre- and postsynaptic DA receptors. Apomorphine inhibited in a concentration-dependent fashion the evoked overflow of DA and ACh; greater inhibition was obtained at lower frequencies of stimulation. At 0.3 Hz the DA agonist was two times more potent in inhibiting DA than ACh overflow (IC50: 12.0 +/- 2.2 versus 22.0 +/- 2.8 nM; p less than 0.01). The greater sensitivity of pre- than postsynaptic sites to apomorphine was also seen at higher frequencies (3 Hz). Benztropine (1 microM) reduced the evoked overflow of ACh at 10 Hz, and enhanced that of 3H products at all rates of stimulation (0.3-10 Hz). These results suggest that the release of DA and ACh is regulated by dopaminergic receptors. They also indicate that the effects of DA agonists and antagonists and of uptake inhibitors on DA and ACh release are highly dependent on the frequency of stimulation used.

Characterization of dopamine autoreceptor and [3H]spiperone binding sites in vitro with classical and novel dopamine receptor agonists

The specific D2 receptor agonist, LY 141865, but not the specific D1-receptor agonist, SK&F 38393, potently inhibited electrically evoked [3H]dopamine release from slices of the cat caudate. Similarly, LY 141865, but not SK&F 38393, inhibited [3H]spiperone binding to membranes of the cat caudate. The inhibition by dopamine receptor agonists of electrically evoked [3H]dopamine release was antagonized by the specific D2-receptor antagonist S-sulpiride. The inhibition of the electrically evoked release of [3H]dopamine by apomorphine was not, however, antagonized by the specific D1-receptor antagonist, bulbocapnine. Similarly, S-sulpiride but not bulbocapnine potently inhibited [3H]spiperone binding to membranes of the cat caudate. These results suggest that the dopamine autoreceptor modulating the depolarization-evoked release of [3H]dopamine, and the binding site of [3H]spiperone, are valid in vitro models for D2-dopamine receptors. Contrary to some previous reports, DPI was inactive in both in vitro dopamine receptor models. The IC50 values of a series of dopamine receptor agonists correlated very well in the two in vitro dopamine receptor models. One exception to this correlation was bromocriptine, which was more potent at [3H]spiperone binding sites than at the dopamine autoreceptor. With the exception of bromocriptine, all dopamine receptor agonists had one-hundred fold higher potency at the dopamine autoreceptor than at [3H]spiperone binding sites. [3H]Spiperone binding sites are localized primarily postsynaptic to dopamine terminals. Possible differences between the pharmacological properties of pre- and postsynaptic dopamine receptors should become apparent in the comparison of the two in vitro dopamine receptor models. However, the order of potency of dopamine receptor agonists with both in vitro models, dopamine autoreceptor and [3H]spiperone binding, was the same: N-n-propylnorapomorphine greater than TL-99 = 7-HAT greater than M-7 greater than Apomorphine greater than LY 141865.

Sex differences in dopaminergic and cholinergic activity and function in the nigro-striatal system of the rat

Possible sex differences in the balance between dopaminergic and cholinergic activity in the rat striatum were investigated. Female rat show a greater vulnerability to neuroleptic-induced catalepsy compared to male rats. This vulnerability to neuroleptics has a human counterpart in that women show an increased frequency of neuroleptic-induced extrapyramidal syndrome (EPS) compared to men. In humans, EPS can be alleviated by increasing dopaminergic activity or by decreasing cholinergic activity. Conversely, EPS can be precipitated by decreasing dopaminergic activity with neuroleptics, and pre-existing EPS can be made worse with cholinergic agonists. Thus, the presence of EPS in humans or catalepsy in animals, as a result of neuroleptic agents, appears to be related to low dopaminergic and/or high cholinergic activity. In the present studies of sex differences it was found that: (1) cycling female rats had fewer striatal dopamine receptors than did male rats. Estradiol treatment significantly reduced the number in males and also reduced the number, although not significantly in ovariectomized (OVX) rats; (2) cycling female rats had lower apomorphine-induced stereotypy during phases with high estrogen levels as compared to phases with low estrogen levels. Estrogen treatment of male or OVX rats resulted in attenuation of induced stereotypy compared to untreated male or OVX rats; (3) female rats had a significantly higher affinity of striatal cholinergic receptors of 3H-QNB than did males and also had higher choline acetyltransfease activity than male rats. The data from these experiments provide the first direct evidence that estrogen plays a role in shifting the balance toward cholinergic predominance in the striatum, a state that favors the development of cataleposy in female rats and EPS in women.

Independent in vitro regulation by the D-2 dopamine receptor of dopamine-stimulated efflux of cyclic AMP and K+-stimulated release of acetylcholine from rat neostriatum

Two types of dopamine receptors whose stimulation affect cAMP efflux (and by inference formation) could be identified in rat neostriatum. One type of receptor, called D-1 receptor, increased cAMP efflux whereas stimulation of a second type of dopamine receptor, called D-2 receptor, was followed by a reduction in cAMP efflux induced by stimulation with a D-1 receptor agonist. D-2 receptor agonists inhibited the effects of D-1 receptor agonists on cAMP efflux in a non-competitive way. These inhibiting effects of D-2 receptor agonists occurred also in the absence of Ca2+-ions which could imply that some of the D-2 receptors are located on cells possessing D-1 receptors. The dopamine receptor mediating inhibition of the release of radiolabeled acetylcholine (ACh) in the neostriatum appeared to have the same pharmacological characteristics as the D-2 dopamine receptor mediating the inhibition of the D-1 receptor agonist induced cAMP efflux. Selective D-2 receptor agonists like LY 141865 and RU 24926 stimulated this receptor while the D-1 receptor agonist SKF 38393 was inactive. Effects of the selective D-2 receptor agonists could be antagonized by (-)-sulpiride, a selective D-2 receptor antagonist. Although the pharmacological characteristics of the dopamine receptors mediating inhibition of both ACh release and (D-1 dopamine receptor agonist induced) cAMP efflux appeared to be similar, drugs stimulating cAMP efflux did not affect ACh release or LY 141865 induced inhibition of ACh release from rat neostriatum. Therefore it is still questionable whether the dopamine receptor mediating inhibition of both ACh release and cAMP efflux is one and the same functional entity.

Dopamine inhibition of the release of endogenous acetylcholine from corpus striatum and cerebral cortex in tissue slices and synaptosomes: a presynaptic response?

The effect of dopamine on the release of endogenous acetylcholine from striatal slices and synaptosomes and from cerebral cortex synaptosomes was studied. K+ (56 mM) and veratrine (75 microM) increased the release of acetylcholine from striatal slices by 3.7 and 3.3 times the resting release, respectively. The effect of veratrine was completely abolished by tetrodotoxin (1 microM). Dopamine (10(-6) to 10(-3) M) reduced the K+-evoked release of acetylcholine from striatal slices in a dose-dependent manner. The resting release of acetylcholine was also significantly reduced by dopamine. Apomorphine (20 microM) significantly reduced the K+-evoked release of acetylcholine, and both this effect and the inhibition due to dopamine (1 mM) were significantly antagonised by chlorpromazine (20 microM). Dopamine had a similar effect on the release of acetylcholine from striatal synaptosome beds; the resting release was depressed 32% by the presence of dopamine (1 mM). A greater effect of dopamine was seen on the release of acetylcholine from cerebral cortex synaptosome beds, the resting release being reduced by 54% and the K+-evoked release by 29%. These results are discussed in terms of the possible role of presynaptic dopamine receptors in controlling the release of acetylcholine and the magnitude of their contribution compared with that of the postsynaptic dopamine receptor.

Modulation by endogenous dopamine of the release of acetylcholine in the caudate nucleus of the rabbit

Slices of the caudate nucleus of rabbits were preincubated with 3H-choline and then superfused. Stimulation by electrical pulses at 3 Hz or by 25 mmol/l potassium elicited an increase in tritium outflow which was calcium-dependent and, in the case of electrical stimulation, tetrodotoxin-sensitive. The dopamine receptor agonist apomorphine (0.01-1 mumol/l) decreased, whereas the antagonist haloperidol increased the electrically evoked overflow of tritium. Nomifensine and cocaine, used at concentrations known to inhibit the re-uptake of dopamine, also reduced the evoked overflow of tritium, and this reduction was antagonized by haloperidol. Combined pretreatment with reserpine and alpha-methyltyrosine methylester (alpha-MT), which lowered dopamine levels by 99.5%, increased the electrically evoked overflow, as did bretylium which is shown here to block action potential-induced release of dopamine. The facilitation by haloperidol and bretylium as well as the inhibition by nomifensine and cocaine were diminished or abolished after pretreatment with reserpine plus alpha-MT. Apomorphine decreased, and haloperidol increased, the potassium-evoked overflow of tritium; the effects were not changed by tetrodotoxin. The results indicate that the striatal dopamine receptors which, when activated, depress the release of acetylcholine, are akin to the D-2 type. Endogenous dopamine also acts on the receptors as shown by several manipulations with known effects on dopaminergic transmission. A large fraction of these dopamine receptors may be located on the cholinergic axon terminals.