Slices Of Rat Caudate Nucleus Research Articles

Sodium channel blockade unmasks two temporally distinct mechanisms of striatal dopamine release during hypoxia/hypoglycaemia in vitro

Massive striatal dopamine release during cerebral ischaemia has been implicated in the resulting neuronal damage. Sodium influx is an early event in the biochemical cascade during ischaemia and blockade of sodium channels may increase resistance to ischaemia by reducing energy demand involved in compensation for sodium and potassium fluxes. In this study, we have determined the effects of opening and blockade of voltage-gated sodium channels on hypoxia/hypoglycaemia-induced dopamine release. Slices of rat caudate nucleus were maintained in a slice chamber superfused by an oxygenated artificial cerebrospinal fluid containing 4 mM glucose. Ischaemia (hypoxia/hypoglycaemia) was mimicked by a switch to a deoxygenated artificial cerebrospinal fluid containing 2 mM glucose and dopamine release was measured using fast cyclic voltammetry. In drug-free (control) slices, there was a 2–3 min delay after the onset of hypoxia/hypoglycaemia followed by a rapid dopamine release event which was associated with anoxic depolarization. In slices treated with the Na + channel opener, veratridine (1 μM), the time to onset of dopamine release was shortened (101±20 s, compared with 171±8 s in controls, P<0.05). Conversely, phenytoin (100 μM), lignocaine (200 μM) and the highly selective sodium channel blocker, tetrodotoxin (1 μM) markedly delayed and slowed dopamine release vs paired controls. In the majority of cases, dopamine release was biphasic after sodium channel blockade: a slow phase preceded a more rapid dopamine release event. The latter was associated with anoxic depolarization. Neither the fast nor the slow release events were affected by pretreatment with the selective dopamine uptake blocker GBR12935 (0.2 μM), suggesting that uptake carrier reversal did not contribute to these events. In conclusion, sodium channel antagonism delays and slows hypoxia/hypoglycaemia-induced dopamine release in vitro. Furthermore, sodium channel blockade delays anoxic depolarization and its associated neurotransmitter release, revealing an earlier dopamine release event that does not result from reversal of the uptake carrier.

Dynamic observation of dopamine autoreceptor effects in rat striatal slices.

Fast-scan cyclic voltammetry has been used to measure dopamine (DA) synaptic overflow in slices of rat caudate nucleus induced by electrical stimulation with one-, two-, and 50-pulse, 10-Hz trains. Synaptic overflow in this preparation is shown to be the result of the competing effects of release and cellular uptake. Release caused by all pulses was attenuated by the D2 agonist quinpirole (1 microM). The rapid time response of the measurements (100 ms) allows the autoinhibition induced by endogenous, released DA to be resolved in real time. The concentration of DA released during the second pulse of a train was 58% of that released by the first pulse, an effect that is partially blocked by the addition of 2 microM sulpiride, a D2 antagonist, to the perfusion buffer. DA release during the first stimulus pulse is unaffected by 2 microM sulpiride, suggesting that autoreceptors are not normally occupied in this preparation. Release caused by the third pulse was 14% of the first pulse and also could be partially enhanced by 2 microM sulpiride. The duration of the inhibition of release induced by endogenous DA was estimated by varying the interval between one-pulse stimulations until the overflow of DA induced by the second pulse was equal to that on the first; a half-time of approximately 17 s was found. The addition of picrotoxin (100 microM) and glutamate (10 microM) to the perfusion buffer did not affect stimulated release of DA, although the addition of atropine (100 microM) attenuated overflow for all the trains tested.

Simultaneous measurement of oxygen and dopamine: Coupling of oxygen consumption and neurotransmission

Fast-scan cyclic voltammetry was used to simultaneously measure increases in dopamine concentration and decreases in O 2 concentration evoked by brief electrical stimulation (two pulses at 10 Hz) in slices of rat caudate nucleus. Dopamine concentration began increasing immediately after the first pulse and reached a maximum within 200 ms of stimulation. The O 2 concentration began to decrease 300–700 ms after onset of stimulus. Responses for both dopamine and O 2 were dependent on external Ca 2+ and were Cd 2+ and tetrodotoxin sensitive. Only the O 2 response was sensitive to CN − (0.15 mM). At short times after exposure to 50 μM ouabain, electrically stimulated dopamine overflow was increased by 150% and electrically stimulated changes in O 2 concentration were unaffected. Maximum dopamine concentration was increased 28% by sulpiride (2 μM), 78% by l-DOPA (60 μM), 105% by nomifensine (10 μM) and unaffected by nialamide (10 μM). Maximum decrease in O 2 concentration was increased by 25% by sulpiride and unaffected by nialamide, l-DOPA, or nomifensine. The decreases in O 2 concentration are indicative of increased O 2 consumption and are a measure of oxidative energy production evoked by electrical stimulation. The increase in dopamine is due to the release of dopamine balanced by uptake and serves as an indication of neurotransmitter activity. The results indicate that increases in oxidative energy production following electrical stimulation are dependent on external Ca 2+ entry through Cd 2+-sensitive channels. Possible mechanisms for this coupling are discussed.

Effects of enantiomers of MDA, MDMA and related analogues on [ 3H]serotonin and [ 3H]dopamine release from superfused rat brain slices

The primary amines 3,4-methylenedioxyamphetamine (MDA), and 1-(1,3-benzodioxol-5-yl)-2-butanamine (BDB) were measured for efficacy in release of [ 3H]serotonin (5-HT) from rat hippocampal slices, and release of [ 3H]dopamine (DA) from rat caudate nucleus slices. The N-methyl derivatives of MDA and BDB, MDMA and MBDB, respectively, and the optical antipodes of these four agents were compared in this paradigm. All of the test compounds demonstrated a similar efficacy of [ 3H]5-HT release in the micromolar concentration range. No significant stereoselectivity was seen in measurements of 5-HT release. However, striking differences were found between the test compounds when [ 3H]DA release was studied. N-methylation of racemic MDA resulted in a decreased ability to release DA, while side chain extension from α-ethyl completely abolished this activity. Stereoselectivity for the S-(+)-isomers of MDA and MDMA was also demonstrated in the DA release studies. Correlation of these biochemical findings with human subjective reports indicates that serotonin release may play a more important role in the mechanism of action than does dopamine release.

Somatostatin and cholecystokinin octapeptide differentially modulate the release of [ 3H]acetylcholine from caudate nucleus but not cerebral cortex: Role of dopamine receptor activation

The effects of somatostatin (SOM) and cholecystokinin octapeptide (CCK-8) on basal and potassium-induced release of acetylcholine (ACh) were investigated in slices of rat caudate nucleus (CN) and, for comparison, cerebral cortex (CX). Potassium (5–55 mM) produced a concentration-dependent increase in the release of [ 3H]ACh in the presence of extracellular Ca 2+. SOM (1 μ), CCK-8 (1 μM) and the dopamine (DA) receptor agonist, apomorphine (APO, 30 μM) inhibited the K +-induced (35 mM) release of [ 3H]ACh by 26–32% from CN, but did not affect ACh release from CX. Other peptides (1 μM), such as Met-enkephalin, vasoactive intestinal peptide, thyrotropin-releasing hormone and substance P, had no effect on release of [ 3H]ACh in CN or CX. Sulpiride (SULP), a dopamine receptor antagonist, prevented the effects of APO and SOM, but not CCK-8, to inhibit [ 3H]ACh release. The results indicate that: (1) SOM and CCK-8 inhibit the release of [ 3H]ACh in CN, but not CX; and (2) the inhibitory effect of SOM, but not CCK-8, on [ 3H]ACh release is mediated by dopaminergic mechanisms.

Somatostatin and CCK-8 modulate release of striatal amino acids: Role of dopamine receptors

The effects of somatostatin (SOM) and cholecystokinin octapeptide (CCK-8) on basal and potassium-evoked release of neurotransmitter amino acids were investigated in slices of rat caudate nucleus (CN) and, for comparison, cerebral cortex (CX). Endogenous aspartate (Asp), glutamate (Glu), glycine (Gly), and gamma-aminobutyric acid (GABA) were measured by high performance liquid chromatography. In both CN and CX, potassium (5–55 mM) produced a concentration-dependent increase in the release of Asp, Glu, Gly, and GABA in the presence of extracellular Ca 2+. CCK-8 (1 μM) stimulated in CN the basal and K +-evoked release of Gly to 231% and 160% of control, respectively; this effect was blocked by sulpiride (SULP), a dopamine receptor antagonist. In contrast, SOM (1 μM) inhibited the K +-evoked release of Glu in CN by 26%, an effect that was not blocked by SULP. SOM and CCK-8 did not significantly affect the basal or K + (35 mM)-evoked release of other amino acids in the CN or of any amino acids in CX. The results indicate that: (a) CCK-8 facilitation of Gly release is dependent on dopamine receptor activation, whereas the inhibition by SOM of Glu release is not; and (b) the effects of SOM and CCK-8 are specific with respect to the brain region affected.

Acetylcoenzyme A and acetylcholine in slices of rat caudate nuclei incubated with (-)-hydroxycitrate, citrate, and EGTA.

The effects of (-)-hydroxycitrate (OHC) and citrate on the concentration of acetylcoenzyme A (acetyl-CoA) and acetylcholine (ACh) in the tissue and on the release of ACh into the medium were investigated in experiments on slices of rat caudate nuclei incubated in media with 6.2 or 31.2 mM K+, 0 or 2.5 mM Ca2+, and 0, 1, or 10 mM EGTA. OHC diminished the concentration of acetyl-CoA in the slices under all conditions used; in experiments with 2.5 mM OHC, the concentration of acetyl-CoA was lowered by 25-38%. Citrate, in contrast, had no effect on the level of acetyl-CoA in the tissue. Although both OHC and citrate lowered the concentration of ACh in the slices during incubations with 6.2 mM K+ and 1 mM EGTA, they had different effects on the content of ACh during incubations in the presence of Ca2+. The concentration of ACh in the slices was increased by citrate during incubations with 2.5 mM Ca2+ and 31.2 or 6.2 mM K+, but it was lowered or unchanged by OHC under the same conditions. The release of ACh into the medium was lowered or unchanged by OHC and lowered, unchanged, or increased by citrate. It is concluded that most effects of OHC on the metabolism of ACh can be explained by the inhibition of ATP-citrate lyase; with glucose as the main metabolic substrate, ATP-citrate lyase appears to provide about one-third of the acetyl-CoA used for the synthesis of ACh. Experiments with citrate indicate that an increased supply of citrate may increase the synthesis of ACh. The inhibitory effect of citrate on the synthesis of ACh, observed during incubations without Ca2+, is interpreted to be a consequence of the chelation of intracellular Ca2+; this interpretation is supported by the observation of a similar effect caused by 10 mM EGTA.

Effects of choline and glucose on atropine-induced alterations of acetylcholine synthesis and content in the caudate nuclei of rats

Atropine-induced decrease in the concentration of acetylcholine (ACh) in the brain can be diminished by pretreating the animals with a large dose of choline 72,73. The injected choline might act by improving the supply of substrate for the synthesis of ACh, or by competing with atropine for presynaptic muscarinic receptors and thus decreasing the release of ACh. Since, under in vitro conditions, changes in the release of ACh are reflected by changes in its synthesis, experiments have been performed on slices of rat caudate nuclei to check whether an increase in the extracellular concentration of choline causes a decrease in the atropine-induced stimulation of ACh synthesis. The rate of [ 14C]ACh synthesis from [ 14C]glucose was faster in the presence of 530 μM than 30 μM choline, and 5 μM atropine stimulated the synthesis of [ 14C]ACh more at 530 μM than at 30 μM choline in the medium. These observations substantiate the view that the administration of choline in vivo acts by supporting the synthesis of ACh, rather than by inhibiting its release. In subsequent experiments on rats in vivo, an attempt has been made to influence the ACh-depleting action of atropine by pretreatment with a large dose of glucose as a distant precursor of acetyl-CoA, the second substrate for the synthesis of ACh. The administration of atropine (25 mg/kg) diminished the content of ACh in the caudate nuclei by 48%; if the injection of atropine followed after an injection of glucose (20.2 mmol/kg), the content of ACh was diminished by only 25%. It appears likely that glucose acted by improving the availability of acetyl-CoA for the synthesis of ACh and that the supply of either precursor of ACh (i.e. choline and acetyl-CoA) may become rate-limiting when the demands on the synthesis of ACh in the brain are increased.

Acetyl coenzyme A and acetylcholine in slices of rat caudate nuclei incubated in the presence of metabolic inhibitors.

Acetyl coenzyme A and acetylcholine in slices of rat caudate nuclei incubated in the presence of metabolic inhibitors.

Utilization of citrate, acetylcarnitine, acetate, pyruvate and glucose for the synthesis of acetylcholine in rat brain slices.

Slices of rat caudate nuclei were incubated in saline media containing choline, paraoxon, unlabelled glucose, and [1,5-14C] citrate, [1-14C-acetyl]carnitine, [1-14C]acetate, [2-14C]pyruvate, or [U-14C]glucose. The synthesis of acetyl-labelled acetylcholine (ACh) was compared with the total synthesis of ACh. When related to the utilization of unlabelled glucose (responsible for the formation of unlabelled ACh), the utilization of labelled substrates for the synthesis of the acetyl moiety of ACh was found to decrease in the following order: [2-14C]pyruvate greater than [U-14C]glucose greater than [1-14C-acetyl]carnitine greater than [1,5-14C]citrate greater than [1-14C]acetate. The utilization of [1,5-14C]citrate and [1-14C]acetate for the synthesis of [14C]ACh was low, although it was apparent from the formation of 14CO2 and 14C-labelled lipid that the substrates entered the cells and were metabolized. The utilization of [1,5-14C]citrate for the synthesis of [14C]ACh was higher when the incubation was performed in a medium without calcium (with EGTA); that of glucose did not change, whereas the utilization of other substrates for the synthesis of ACh decreased. The results indicate that earlier (indirect) evidence led to an underestimation of acetylcarnitine as a potential source of acetyl groups for the synthesis of ACh in mammalian brian; they do not support (but do not disprove) the view that citrate is the main carrier of acetyl groups from the intramitochondrial acetyl-CoA to the extramitochondrial space in cerebral cholinergic neurons.

Inhibition of the synthesis of acetylcholine in rat brain slices by (-)-hydroxycitrate and citrate.

Abstract: Slices of rat caudate nucleus were incubated in a solution of 123 mM‐NaCl, 5 mM‐KCl, 1.2 mM‐MgCl2, 1.2 mM‐NaH2PO4, 25 mM‐NaHCO3, 0.2 mM‐choline chloride, 0.058 mM‐paraoxon, 1 mM‐EGTA, and oxidizable substrates. (−)‐Hydroxycitrate, a specific inhibitor of ATP‐citrate lyase (EC 4.1.3.8), used at a concentration of 2.5 mM, inhibited the synthesis of acetylcholine (ACh) from [1,5‐14C]citrate by 82–86%, but that from [U‐14C]glucose by only 33%, from [2‐14C]pyruvate by 24% and from [1‐14C‐acetyl]carnitine by 8%; the production of 14CO2 from these substrates was not substantially changed. The synthesis of ACh from glucose and pyruvate was in hibited also by citrate; 2.5 mM‐ and 5 mM‐citrate diminished it by 43% and 66%, respectively; the production of from [U‐14C]glucose and from [1‐14C]pyruvate was not affected. The mechanism of the inhibitory effect of citrate on the synthesis of ACh is not clear; the possibility is discussed that citrate alters the intracellular milieu in cholinergic neurons by chelating the intracellular Ca2+ and decreases the supply of mitochondrial acetyl‐CoA to the cytosol. The results with (−)‐hydroxycitrate indicate that the cleavage of citrate by ATP‐citrate lyase is not responsible for the supply of more than about one‐third of the acetyl‐CoA which is used for the synthesis of ACh when glucose or pyruvate are the main oxidizable substrates. This proportion may be even smaller, since (−)‐hydroxycitrate possibly affects the synthesis of ACh from glucose and pyruvate by a mechanism (unknown) similar to that of citrate, rather than by the inhibition of ATP‐citrate lyase.

A comparison of the effects of methylphenidate and amphetamine on the simultaneous release of radiolabelled dopamine and p- or m-tyramide from rat striatal slices

The release of [ 14C]dopamine (DA) from slices of rat caudate nucleus was studied simultaneously with the release of either [ 3 H]para- tyramine (pTA) or [ 3 H]meta- tyramine (mTA). Amphetamine (10 −5 M) caused a large concurrent release of [ 14C]DA and [ 3H]pTA; similar results were obtained when [ 14C]DA and [ 3H]mTA release were studied. The release of all three amines by amphetamine was quantitatively similar. In contrast, methylphenidate caused a release of [ 3H]pTA similar to that seen with amphetamine, but only a very small simultaneous release of [ 14C]DA. [ 3H]mTA was also strongly released by methylphenidate concurrent with a minimal release of [ 14C]DA. The inclusion of reserpine in the incubation medium had no detectable effect on the release of any of the three amines by amphetamine. Methylphenidate-induced release of tritiated mTA and pTA was also unaffected by reserpine. However, the release of [ 14C]DA by methylphenidate was potentiated in the presence of reserpine. The uptake of radiolabelled pTA, mTA and DA was inhibited by both amphetamine and methylphenidate, although amphetamine was a stronger inhibitor of the uptake of all three amines. It is suggested that release of endogenous tyramines may be involved in mediating some actions of psychomotor stimulant drugs.

Relation between the content of acetyl-coenzyme A and acetylcholine in brain slices

Slices of rat caudate nuclei were incubated in vitro in media containing, among other constituents, three different concentrations of glucose (0.5, 2 and 10 mM), 0.2 mM-choline, paraoxon as an inhibitor of cholinesterase, and 5 mM- or 30 mM-K+. After 30 and 60 min of incubation, the concentrations of acetyl-CoA, acetylcholine and choline in the tissue and of acetylcholine in the incubation medium were measured. The content of acetyl-CoA in the sliced varied in direct relation to the concentration of glucose in the incubation medium. The content of acetylcholine in the slices and, in experiments with high K+, also the amount of acetylcholine released into the incubation medium varied in direct relation to the concentration of glucose in the incubation medium and to the concentration of acetyl-CoA in the slices; the relation between the concentrations of acetyl-CoA and of acetylcholine in the slices was linear. It was concluded that the availability of acetyl-CoA had a decisive influence on both the rate of synthesis of acetylcholine and its steady-state concentration. The observations accord with the view that, at the ultimate level, the synthesis of acetylcholine is controlled by the Law of Mass Action.

Thyrotrophin releasing hormone stimulates release of [3H]-dopamine from slices of rat nucleus accumbens in vitro.

Thyrotrophin releasing hormone (TRH) (25 to 100 microM) was found to stimulate the efflux of [3Hu-dopamine from small slices of rat nucleus accumbens, but not from similar slices of rat caudate nucleus. Uptake inhibition was not responsible for this action, since at 10 and 50 microM TRH had no effect on the ability of small slices of nucleus accumbens to accumulate radioactivity when incubated with 10(-7) M [3H]-dopamine. In addition the hormone had no effect on basal or dopamine-stimulated adenylate cyclase, nor did it displace [3H]-spiperone binding, in membrane preparations from nucleus accumbens.

GABA modulates the release of dopamine and acetylcholine from rat caudate nucleus slices

The effects of GABA on depolarization-induced (26 mM K +) release of radiolabeled dopamine (DA) and acetylcholine (ACh) from slices of rat caudate nucleus were examined with a superfusion method. GABA, in concentrations of 10 −5–10 −3 M, dose-dependently enhanced the release of DA, either accumulated by high-affinity uptake or synthesized from 14-C-tyrosine. In contrast, the release of ACh was reduced by GABA. This reduction appeared to be caused by the increase in DA-release. These effects of GABA decreased from the caudal to rostral part within the caudate nucleus, an order which parallels the distribution of endogenous GABA and glutamic acid decarboxylase. However, GABA had little, if any, effect in the nucleus accumbens. Since it was difficult to antagonize the effects of GABA on DA and ACh release with bicuculline or picrotoxin, it remains uncertain whether these effects were mediated via GABA receptors. In view of the high endogenous GABA level in the caudate nucleus it is concluded that GABA may be one of the local factors involved in the control of the amount of transmitter that will be released from dopaminergic varicosities upon depolarization.

In vitro acetylcholine release from rat caudate nucleus as a new model for testing drugs with dopamine-receptor activity.

The effects of a number of dopamine-receptor agonists on depolarization-induced (26 mM K+) release of 3H-acetylcholine from slices of rat caudate nucleus were examined with a superfusion method. Apomorphine (10−6 M) and N,N-dipropyliso-ADTN (10−7 M) inhibited acetylcholine-release in vitro by about 50% and these inhibitory effects were antagonized by haloperidol. For N,N-dipropyl-iso-ADTN an EC50 of approximately 3×10−9 M was estimated from its dose-response curve. However, dopamine (10−6 M) itself and bromocriptine (10−6 M) inhibited acetylcholine-release less. Presumably: the weak effect of exogenous dopamine is due to its (partial) uptake in dopaminergic nerve terminals and to the fact that released endogenous dopamine already partially activates the receptors involved in the inhibition of acetylcholine-release.

Tetrahydropapaveroline induces small granular vesicles in brain dopamine fibres.

TETRAHYDROISOQUINOLINES (TIQs) can be formed by the condensation of catecholamines with aldehydes. Their in vivo formation has been postulated as a possible mechanism to explain some long-term effects of ethanol on the central nervous system1,2. However, there have been several criticisms3,4 and reviews5,6 of this hypothesis. Although TIQ formation may not explain all the effects of ethanol, TIQs can influence behaviour7–9 and they do have transmitter-like properties: they can be formed in vivo10–12; they can be taken up and released in vivo from the adrenergic plexus of the rat iris13; they can be taken up into rat brain synaptosome fractions14; and TIQs applied exogenously have been localised in peripheral catecholamine tissues with both fluorescence13 and electron microscopy15. Thus, TIQs may accumulate in specific brain regions and influence behaviour by either acting as false transmitters13 or by displacing endogenous transmitters. Critical to this TIQ hypothesis is the demonstration of TIQ uptake and localisation into central neurone terminals. In the present study, slices of rat caudate nucleus were incubated with TIQs and then examined with the electron microscope. The results provide evidence for both the uptake and localisation of the TIQ, tetrahydropapaveroline (THP), into central dopamine fibres and terminals. This localisation may prove important in understanding the mechanism by which TIQs influence animal behaviour and any possible role for TIQs in chronic alcohol consumption.

ACTIVATION OF GLYCOGEN PHOSPHORYLASE IN RAT CAUDATE NUCLEUS SLICES BY l‐ISOPROPYLNOREPINEPHERINE AND DIBUTYRYL CYCLIC AMP

Abstract— l‐Isopropylnorepinepherine (IPNE), 3‐isobutyl‐1‐methylxanthine (IBMX) and N6,O2′‐dibutyryl cyclic AMP have been found to stimulate the conversion of glycogen phosphorylase (GPase) from b to a forms in rat caudate nucleus slices. The average percentage of total GPase in the a form in control incubations was 32%. The percentage of total GPase in the a form was increased to 1.5 times the control value in the presence of 1 mM‐IBMX, to twice the control value in the presence of 0.05 mM‐IPINE and to 2.5 times the control in the presence of 0.05 mM‐IPNE and 1 mM‐IBMX in combination. The increase in GPase activation correlated well with the elevation of cyclic AMP levels by these agents in caudate slices. The percentage of total GPase in the a form was also increased to 2.5 times the control by 1 mM dibutyryl cyclic AMP. Dopamine (DA) and 2‐chloroadenosine (2‐CI‐Ado), which also elevate cyclic AMP levels in rat caudate slices, were without significant effect on GPase. The results indicate that the β‐adrenergc adenylate cyclase in the rat caudate nucleus plays a role in the regulation of glycogen metabolism, while the DA‐stimulated adenylate cyclase is not significantly involved. 2‐CI‐Ado does have effects on glycogen metabolism in the caudate, but these effects do not appear to be mediated by GPase activation.

STIMULATION OF GLYCOGENOLYSIS IN RAT CAUDATE NUCLEUS SLICES BY L‐ISOPROPYLNOREPINEPHERINE, DIBUTYRYL CYCLIC AMP AND 2‐CHLOROADENOSINE

Abstract—Dopamine (DA), L‐isópropylnorepinepherine (IPNE), 2‐chloroadenosine (2‐Cl‐Ado), 3‐isobutyl, I‐methylxanthine (IBMX) and N6,O2′‐dibutyryl cyclic AMP have been investigated for their effects on glycogen levels in rat caudate nucleus slices. Incubation of slices with 1 mM‐dibutyryl cyclic AMP, or with 50 μM‐IPNE in the presence of 1mM‐IBMX, or with 5‐500 μM‐2‐Cl‐Ado reduced glycogen levels to about 50% of control. Incubation of slices with 1 mM‐IBMX alone, or with 50μM‐IPNE alone, or with 50μM‐DA either alone or in the presence of 1 mM‐IBMX was without significant effect on glycogen levels. The effect of IPNE + IBMX was completely abolished by the prior addition of 10 μM‐propranolol. The effect of 10 μM‐2‐Cl‐Ado was not effectively prevented by either 100 μM‐theophylline or 100 μM‐cordycepin. The results indicate that the β‐adrenergic adenylate cyclase in the rat caudate nucleus plays a role in the regulation of glycogen metabolism, while the DA‐stimulated adenylate cyclase is not significantly involved. The 2‐Cl‐Ado‐stimulated adenylate cyclase may be involved in the control of glycogen metabolism, but other mechanisms for the 2‐CI‐Ado action, such as interference with allosteric regulatory sites on glycogen phosphorylase, have not been ruled out.