T.D. Reisine

In vivo release of met-enkephalin in the cat brain

Abstract Push-pull cannulae were implanted into the globus pallidus (anterior part), the caudate nucleus (medio-dorsal part) and the substantia nigra of halothane-anaesthesized cats to study the characteristics of the in vivo release of met-enkephalin. Met-enkephalin was measured by radioimmunoassay (sensitivity: 0.1 pg) and identified by Bio-Gel P 2 chromatography and high-pressure liquid chromatography. Under resting conditions, met-enkephalin was detected in perfusates from these three regions; in the globus pallidus, the rate of spontaneous release of met-enkephalin was 5–6 times higher than that observed in the caudate nucleus and the substantia nigra. The local application of either an excess (60 mM) of K + or of glutamate (10 μM) produced a marked increase in the rate of met-enkephalin release both from the globus pallidus and the caudate nucleus. Further analyses in the globus pallidus indicated that the depolarizing agents, veratridine (50 μM) and batrachotoxin (0.1 μM), produced a large increment in the rate of met-enkephalin release; this effect was completely prevented by the local application of tetrodotoxin (2 μM). The chemical (with 60 mM K + or 10 μM glutamate), electrical or mechanical stimulation of the dorsomedial part of the caudate nucleus failed to significantly alter the rate of met-enkephalin release in the ipsilateral globus pallidus, in spite of the high sensitivity of enkephalinergic nerve terminals in the globus pallidus itself to local stimuli. This observation argues against the existence of a major caudatopallidal enkephalinergic pathway.

A role for striatal beta-adrenergic receptors in the regulation of dopamine release

Abstract The effect of (−) isoproterenol on the spontaneous release of [3H]dopamine ([3H]DA) continuously formed from [3H]tyrosine has been studied both in vitro using rat striatal slices and in vivo in halothane-anaesthetized cats implanted with push-pull cannulae in each caudate nucleus and each substantia nigra. In vitro, (−) isoproterenol (10−6M) stimulated [3H]DA release. This effect was stereospecific since (+) isoproterenol (10−6M) was without effect. (±) Propranolol (10−6M), which did not block the acetylcholine (10−5M)-induced release of [3H]DA, completely prevented the stimulatory effect of (−) isoproterenol on [3H]DA release. (±) Practolol (10−5M) significantly reduced the (−) isoproterenol-induced release of [3H]DA whereas phentolamine (10−5M) was uneffective. These results suggest that (−) isoproterenol acts on [3H]DA release through β1-receptors. Since the adrenergic agonist still stimulated [3H]DA release in the presence of tetrodotoxin, the β-receptors involved may be located on DA terminals. Confirming in vitro results, (−) isoproterenol (10−6M) enhanced the local release of [3H]DA when applied into one caudate nucleus. This effect was biphasic and prevented by (±) propranolol (10−6M). The β-antagonist by itself slightly reduced [3H]DA spontaneous release suggesting that noradrenergic neurons which may innervate the caudate nucleus could exert a tonic facilitatory influence on DA release. No change in [3H]DA release occured in other structures studied during the application of (−) isoproterenol into one caudate nucleus. These various results indicate that striatal β-adrenergic receptors play a role in the regulation of DA release from DA nerve terminals and suggest an interaction between noradrenergic and dopaminergic neurones in the caudate nucleus.

Loss of rat cerebral cortical opiate receptors following chronic desimipramine treatment

The characteristics of central opiate and beta-adrenergic receptors were studied after giving the tricyclic antidepressant desimipramine (DMI) to rats. Administration of DMI for 1 or 7 days did not alter cortical opiate or beta-adrenergic receptors. However, after 21 days of treatment there was a significant subsensitivity of both these receptors in the cortex. A specific loss of receptor sites for opiate binding was detected with no change in affinity. After a similar time of treatment, opiate receptors in the corpus striatum and hippocampus were the same as the controls. The data suggest that change in cortical opiate receptors may be important in the mechanism of action of antidepressants.

Effects of various opiates including specific delta and mu agonists on dopamine release from nigrostriatal dopaminergic neurons in vitro in the rat and in vivo in the cat

Abstract The effect f various opiates on the release of newly synthesized 3H-dopamine (3H.DA) was studied both in vitro in rat striatal slices and in vivo in caudate nuclei and substantiae nigrae of halothane anaesthetized cats, using a push pull cannula technique. The hexapeptide Tyr-D-Ser -Gly-Phe-Leu-Thre (DSTLE) which acts preferentially on δ receptors stimulates 3H.DA release in vitro and produces a biphasic increase of the local 3H-amine outflow when applied in the cat caudate nucleus in vivo . Similar effects were induced by D Ala2-met-enkephalinamide. By contrast, morphine, fentanyl and the potent μ agonist Tyr-D-Ala-Gly-NH-C6-H13 (Trimu 4) did not affect 3H.DA release in vitro . In vivo their effects differ from those of the δ agonists and from each other: morphine produced a delayed long lasting increase in 3H.DA release while fentanyl and Trimu 4 induced an immediate increase of the 3H-amine outflow followed by a delayed inhibition. The local effects of δ and μ agonists also differed as regard to their sensitivity to naloxone but in addition, when co-applied with the opiate antagonist, D-Ala2-met-enkephalinamide and morphine induced changes in 3H.DA release in the contralateral caudate nucleus and the contralateral or ipsilateral substantia nigra respectively. Therefore, in the striatum, some opiates may, under certain circumstances, act directly or indirectly upon striatal efferences involved in the control of the contralateral nigro-striatal dopaminergic neurons. In conclusion, thanks to the use of recently developed opiate agonists exhibiting a high preference for either δ or μ receptors it has been shown that these receptors are involved in different mechanisms regulating the striatal dopaminergic transmission. In addition, these results suggest that less specific agents, by interacting with several types of receptors, induce a unique combination of events responsible for local and distal control of DA release from nigro-striatal dopaminergic neurons.

Application ofl-glutamic acid and substance P to the substantia nigra modulates in vivo [3H]serotonin release in the basal ganglia of the cat

L-Glutamic acid or substance P were applied to the caudate nucleus (CN) or substantia nigra (SN) and their effects on local, spontaneous, in vivo [3H]serotonin ([3H]5-HT) release as well as [3H]5-HT release in the contralateral CN and SN were studied using cats implanted with push-pull cannulae. L-Glutamic acid (5 x 10(-5) M), when applied to the CN or SN inhibited the local release of [3H]5-HT but did not affect release in the contralateral CN and SN. In the SN, the L-glutamic acid effect was blocked by L-glutamic acid diethylester. Substance P (10(-7) M) applied to the SN induced an increase in [3H]5-HT release that was delayed in onset. Furthermore, [3H]5-HT release was elevated in the contralateral CN immediately upon the application of substance P to the SN. These results suggest that L-glutamic acid and substance P may control 5-HT transmission in the basal ganglia.

In vivo evidence for gabaergic control of serotonin release in the cat substantia nigra

Push-pull cannulae were used for estimating the release of endogenously synthesized [3H]serotonin in both substantia nigra and caudate nuclei of halothane-anaesthetized cats. The unilateral nigral application of GABA (10-5 M) reduced the local release of [3H]serotonin picrotoxin induced an opposite effect. Both treatments failed to modify [3H]serotonin release in the caudate nuclei or in the contralateral substantia nigra. These results suggest that GABAergic neurons innervating the substantia nigra may regulate nigral serotonin transmission. The possibility that such a regulation could be presynaptic (direct or through other nigral neurotransmitters) or related to a change in the activity of the nigro-raphe projection is discussed.

Evidence for a dopaminergic innervation of the cat lateral habenula: its role in controlling serotonin transmission in the basal ganglia.

The presence of a dopaminergic innervation of the cat lateral habenula and its possible role in modulating serotonin transmission within the basal ganglia were investigated using both in vitro and in vivo approaches. A high density of [3H]spiroperidol binding sites with similar affinities for domperidone and apomorphine as those present in the cat striatum were found in the habenula. By means of the push-pull cannula technique, a substantial release of [3H]dopamine continuously formed from [3H]tyrosine was detected in the lateral habenula of halothane-anesthetized cats since the amount of [3H]catecholamines was enhanced in the presence of benztropine, an inhibitor of dopamine uptake into dopaminergic nerve terminals. Furthermore, in anesthetized animals with a push-pull cannula implanted in each caudate nucleus and substantia nigra habenular applications of dopamine (10(-7) M) reduced nigral but not striatal release of [3H]serotonin continuously formed from [3H]tryptophan. This change was prevented either by the delivery of domperidone to the lateral habenula or by the blockade of GABAergic transmission (picrotoxin 10(-5) M) in the dorsal raphe. These data support the involvement of habenulo-raphe pathways in the regulation of serotonin transmission in the cat basal ganglia and indicate that dopaminergic inputs to the lateral habenula participate in such a control.

Striatal Dopamine Release In Vitro: A β‐Adrenoceptor‐Regulated Response Not Mediated Through Cyclic AMP

Abstract: The effects of (‐)isoproterenol(106 M), dibutyryl cyclic AMP (10−2 M), and the phosphodiesterase inhibitor 3‐isobutyl‐1‐methylxanthine (IBMX) (10−4 M) on in vitvo [3H]dopamine ([3H]DA) cllux and synthesis were studied in rat striatal slices continuously superfused with [3H]tyrosine. The β‐adrenoceptor agonist (‐)isoproterenol induced an immediate and significant facilitation of [3H]DA efflux but did not alter [3H]DA synthesis as measured by [3H]H2O formation. In contrast, both dibutyryl cyclic AMP and IBMX enhanced [3H]DA synthesis as well as efflux. The presence of IBMX in the superfusing medium did not potentiate the augmentation of [3H]DA efflux caused by (‐)isoproterenol. Additionally, the blockade of [3H]DA synthesis by α‐methyl‐p‐tyrosine (10−1 M) completely prevented the action of dibutyryl cyclic AMP on [3H]DA efflux. However, under similar conditions, (‐)so proterenol was still able to increase [3H]DA efflux. The results suggest that (‐)isoproterenol can modify striatal DA release through a mechanism not involving cyclic AMP.