In vivo changes in responsiveness of the caudate nucleus to L-dopa infusion as a function of the estrous cycle

In the present experiment we measured changes in the responsiveness of the nigrostriatal dopaminergic system to L-DOPA as a function of the estrous cycle in the freely behaving animal with push-pull perfusion. Intact female rats were implanted with a push-pull cannula directed at the caudate nucleus and perfused repetitively on each day of their estrous cycle. During the perfusion, the response of the caudate nucleus was tested with two successive increasing doses of L-DOPA (1.0 and 10 microM) infused directly through the push side of the cannula. In response to 1.0 microM L-DOPA, significantly greater dopamine release was obtained for female rats perfused on proestrus, with all 6 females showing maximal responsiveness at this estrous cycle stage. There was an overall 3-4 fold greater increase in dopamine release to the 10 microM L-DOPA infusion, regardless of estrous cycle day. However, with the use of this 10 microM L-DOPA dose, the significant effect at proestrus was maintained. These results demonstrate that the responsiveness of the caudate nucleus to L-DOPA is maximal at proestrus. These data together with previous work from our laboratory indicate that the natural physiological changes which occur in hormone levels, in particular changes in progesterone during proestrus, exert a substantial influence upon this extra-hypothalamic central nervous system site.     

Striatal dopamine release is altered by glucose and insulin during push-pull perfusion of the rat's caudate nucleus

An individual site in the caudate-putamen complex of the unrestrained, fasted rat was tritium-labeled with 1.0 μCi of either³H-DA or ³H-NE. The amine was microinjected in a volume of 0.5 μl through a permanently implanted 20 ga guide cannula. Then 30 min later, a push-pull cannula assembly was lowered through the guide and the labeled site was perfused with an artificial CSF solution at a rate of 25 μl/min. Each perfusion lasted for 5 min with a 10 min interval between successive perfusions. At the mid-point of a sequence of seven perfusions, one of two experimental procedures was introduced: (1) the rat was offered food pellets which were readily consumed; or (2) one of three compounds was added to the CSF perfusate: (a) 55 μg/gml of D-glucose; (b) 4 mU/μl of insulin; or (c) 10 μg/μl of 2-DG. The results showed that the efflux of³H-DA increases as the rat feeds and during the subsequent perfusions. An immediate rise occurs in the output of the amine also when insulin is added to the perfusate; conversely, a slight suppression in ³H output is caused by glucose during its perfusion but a consistent elevation of radioactivity follows thereafter. 2-DG has no effect on the kinetics of catecholamine activity in the caudate-putamen. The patterns of release of ³H-NE are similar to those of ³H-DA under the same experimental conditions; however, the magnitude of the change is substantially attenuated. Although catecholamine activity within the caudate-putamen is usually implicated in motor control, our results support the possibility that dopamine in this structure may play a functional role in the regulation of food intake.     

Disulfiram alters dopamine metabolism at sites in rat's forebrain as detected by push-pull perfusions

WEINER, H., C. W. SIMPSON, J. A. THURMAN AND R. D. MYERS. Disulfiram alters dopamine metabolism atsites in rat's forebrain as detected by push-pull perfusions. BRAIN RES. BULL. 3(5) 541–548, 1978.—The effect of tetraethylthiuramdisulfide (disulfiram) on the catabolism of dopamine within discrete regions of the brain was investigated in the unrestrained rat. After a guide cannula had been implanted stereotaxically, a given subcortical site was radiolabeled with ¹⁴C-dopamine (DA) by microinjecting 2.0 μCi in 2.0 μl. Successive push-pull perfusates collected from each tissue were assayed by paper electrophoresis for the separation of DA metabolites. When disulfiram, a potent aldehyde dehydrogenase (ALDH) inhibitor, was given intragastrically in a clinically efficacious dose of 200 mg, the formation of the acids DOPAC and HVA was inhibited within perfusates of the caudate nucleus and nucleus accumbens. However, following disulfiram treatment, the proportion of alcohol metabolites did not differ from the control level in the untreated rat. The level of ALDH decreased by approximately 50% in these subcortical nuclei following the inhibition of the enzyme by disulfiram. Conversely, in samples of perfusate obtained from ¹⁴C-labeled sites within inferofrontal cortex, periform cortex, diagonal band of Broca, lateral-posterior caudate nucleus, tuberculum olfactorium, lateral olfactory tract or the olfactory nuclear complex, the proportion of DA metabolites remained stable. Generally, a low rate of deamination of the exogenously injected DA occurred within perfusion sites in the ventrobasal forebrain, whereas an intermediate rate of deamination was noted in samples collected at more dorsal loci. Thus, clearcut regional differences in DA catabolism occur in the brain of the living animal, which may depend upon the characteristics of the dopaminergicrich area of the rat's brain.     

The effect of acetylcholine and dopamine on the caudate spindle in cats

Electrocortical activity was reacorded in cats whose caudate nuclei were perfused and electrically stimulated using a push-pull cannula. Electric stimulation invariably induced spindles (10-14 Hz) in the ipsilateral frontal cortex. Perfusions of acetylcholine together with physostigmine reduced the number of spontaneous spindles, the response to electric stimulation and induced behavioural arousal. This effect was atropine-sensitive. Perfusions of dopamine with or without tranylcypromine had no significant effect on the number of spontaneous spindles or the response to electric stimulation. Injections of both acetylcholine and dopamine into the cuadate nucleus invariably induced spontaneous spindles and slow waves. The significance of acetylcholine and dopamine in the caudate nucleus intiating caudate spindles and their significance in controlling arousal is discussed.     

Region specific increase of dopamine receptor D1/D2 mRNA expression in the brain of μ-opioid receptor knockout mice

Previous pharmacological studies have indicated the possible existence of functional interactions between opioidergic and dopaminergic neurons in the CNS. In this study, the expression of mRNAs encoding dopamine receptor D1/D2 was examined to investigate whether there is a change in the dopamine pathway of mice lacking the μ-opioid receptor by in situ hybridization technique. In the μ-opioid receptor knockout mice, the expression of dopamine receptor D1 mRNA was increased in the olfactory tubercle, nucleus accumbens, caudate putamen, and the layer VI of the neocortex compared with that of wild-type mice. The expression of dopamine receptor D2 mRNA was also increased in the olfactory tubercle, caudate putamen, and the nucleus accumbens of μ-opioid receptor knockout mice. These results indicate that there are compensational changes in the dopaminergic systems of μ-opioid receptor knockout mice.     

Progesterone enhances L-dopa-stimulated dopamine release from the caudate nucleus of freely behaving ovariectomized-estrogen-primed rats

In the present experiment we examined the effect of progesterone upon dopamine (DA) release induced by a direct infusion of unlabeled L-dihydroxyphenylalanine (L-DOPA) into the caudate nucleus of freely behaving rats. Ovariectomized rats were implanted with a push-pull cannula directed at the caudate nucleus and subjected to perfusion under 3 different hormonal conditions: (1) following 4 days of treatment with estradiol benzoate (EB), (2) following 4 days of treatment with estradiol benzoate plus progesterone at 4-6 h prior to perfusion (EB + P-4-6 h) and (3) following 4 days of treatment with estradiol benzoate plus progesterone at 28 h prior to perfusion (EB + P-28 h). During each perfusion session and under each of the 3 hormonal treatment conditions, L-DOPA was infused through the push side of the cannula. Three increasing doses of L-DOPA (10(-6), 10(-5) and 10(-4) M) were infused with a 45-75 min interval between infusions. Regardless of hormonal treatment condition, a clear dose-response increase in DA and 3,4-dihydroxyphenylacetic acid (DOPAC), but not 5-HIAA, output was observed in response to the increasing doses of L-DOPA infusion. For each of the 3 doses of L-DOPA, maximal DA output was observed for animals tested under the EB + P-4-6 h hormonal condition, with statistically significant differences in the areas under the L-DOPA-stimulated DA response curves obtained following the 10(-6) and 10(-5) M doses of L-DOPA infusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Peptide-induced grooming behavior and caudate nucleus dopamine release

We simultaneously measured the display of grooming behavior and, by monitoring the extracellular dopamine concentration via transversal microdialysis, the release of dopamine in the caudate nucleus in freely moving rats after i.c.v. administration of 1 μg adrenocorticotropic hormone-(1–24) (ACTH-(1–24)). During a period of 1 h after administration of the peptide, the incidence of excessive grooming behavior was increased. Concomitantly, the concentration of dopamine in the caudate nucleus dialysates was significantly increased (maximal effect 151% of basal release) whereas that of its metabolite DOPAC was unchanged. The potent α-melanocyte stimulating hormone (α-MSH) receptor agonist, [Nle⁴,D-Phe⁷]α-MSH, induced grooming behavior and stimulated caudate nucleus dopamine release (maximal effect 148% of basal release) whereas ACTH-(7–16)-NH₂ did neither induce grooming behavior nor cause an increase in caudate nucleus dopamine release. Single-dose tolerance was observed for ACTH-induced grooming but not for ACTH-induced dopamine release. These data are in support of the proposed involvement of brain dopamine systems in grooming behavior of the rat but at the same time suggest that the effect of ACTH/MSH-like peptides on dopaminergic transmission in the caudate nucleus is proximal to the final neural pathway involved in ACTH-induced grooming behavior.     

Changes in the β-endorphin content of discrete hypothalamic nuclei during the estrous cycle of the rat

Concentrations of β-endorphin were measured in discrete brain nuclei of 4-day cycling rats on each day of the estrous cycle. On the afternoon of proestrus β-endorphin levels were significantly higher in median eminence and suprachiasmatic nucleus, and lower in arcuate nucleus, when compared to levels found on other days of the cycle. These changes coincided with the peak of plasma prolactin, which was blocked by prior administration of naloxone.     

Peristaltic versus syringe pumps for push-pull perfusion: tissue pathology and dopamine recovery in rat neostriatum

The characteristics of performance were compared for two types of pump, peristaltic and infusion-withdrawal, commonly used for localized push-pull perfusion of brain tissue. Guide cannulae were stereotaxically implanted bilaterally in the caudate-putamen complex of the rat at homologous sites in the coronal plane. Consecutive 5.0 min push-pull perfusions were carried out simultaneously with one pump perfusing ipsilaterally while the other pump perfused the contralateral caudate nucleus. 3H-dopamine (DA) diluted with an artificial CSF was used as the radiotracer and was perfused at a rate of 25 microliters/min. Following the collection of 7-8 samples, the brain was fixed, removed, and histological sections taken through the sites of perfusion. Microscopic examination of the perfusion site showed that the circumscribed lesion at the tip of the cannula connected to either pump was generally indistinguishable. A comparison of the values of 3H-DA recovery in samples obtained with the peristaltic and infusion-withdrawal pumps demonstrated that: (1) the respective uptakes of the catecholamine into caudate tissue paralleled one another in most experiments, and (2) the content of 3H-DA in push-pull perfusates recovered from sample to sample varied independently of the pump used. Based on the results of histopathological examination and DA radioactivity values, it is concluded that the peristaltic pump as well as the syringe-driven push-pull pump can yield valid experimental observations which are comparable to one another.     

Further Studies on the Suppression of Luteinizing Hormone Release Due to Activation of Medial Preoptic-Anterior Hypothalamic Area μ-Opioid Receptors

Our laboratory has previously demonstrated that specific activation of μ-opioid receptors in the medial preoptic-anterior hypothalamic area with [D-Ala², N Me-Phe⁴, Gly-ol⁵]-enkephalin (DAGO) suppresses luteinizing hormone secretion in the ovariectomized rat [29]. In the present study, three experiments were undertaken to ascertain whether changes in the activity of norepinephrine or dopamine neurons modulate the decrease in luteinizing hormone release in response to DAGO. The first experiment utilized push-pull perfusion in conjunction with HPLC to assess in vivo norepinephrine release in the medial preoptic-anterior hypothalamic area in response to perfusion of this site with DAGO (5 μg/h). DAGO significantly decreased luteinizing hormone release, but perfusate norepinephrine levels did not change. In the second experiment, push-pull perfusion in the medial preoptic-anterior hypothalamic area with cerebrospinal fluid (CSF) or CSF containing DAGO was done in rats pretreated with the norepinephrine synthesis inhibitor, FLA-63. This drug pretreatment had no effect on the DAGO-induced suppression of luteinizing hormone secretion. In Experiment 3, push-pull perfusion in the medial preoptic-anterior hypothalamic area with CSF followed by CSF containing DAGO was done in rats pretreated with vehicle, or a dopamine receptor antagonist, either pimozide or d-butaclamol. Neither dopamine receptor antagonist had any effect on the DAGO-induced suppression of luteinizing hormone release. Thus, these studies do not support a role for alterations in the activity of norepinephrine or dopmaine neurons in mediating the suppression of luteinizing hormone release in response to activation of μ-opioid receptors in the medial preoptic-anterior hypothalamic area in the ovariectomized rat. Copyright © 1997 Elsevier Science Inc.     

Hypothalamic microinjection of norepinephrine (NE) elevates and prolongs basal efflux of unmetabolized NE from injection site

The effect of a microinjection of norepinephrine (NE) into the diencephalon of the rat was examined in terms of the subsequent endogenous activity of this amine. A push-pull guide cannula was first implanted stereotaxically with the tip resting in the rat's hypothalamus. Several days later, NE in a dose of 20 ng, 95 ng or 3.2 μg was microinjected in a volume of 0.5 μl into the perifornical region. After a 30 min interval, the injection site was perfused, by means of push-pull cannulae with an artificial CSF at a rate of 25 μl/min. The samples of perfusate collected one hour after the microinjection were analyzed by HPLC with electrochemical detection. The results indicate that an unexpectedly high level of unmetabolized NE can be detected at the perfusion site. This NE is greater than the picogram quantities of NE present endogenously in the rat's hypothalamus. The persistent presence of the exogenously applied amine within a microinjection site could explain the longevity of a given pharmacological effect of an amine often seen with this injection procedure. Also, it suggests that the local metabolic degradation of the amine is not as rapid as one would expect.     

Differentiation of basal ganglia dopaminergic involvement in behavior after hippocampectomy

Large bilateral aspiration lesions of the hippocampus in rats lead to a variety of changes in spontaneous behavior measured in an open field/hole board, relative to sham and neocortically lesioned controls. These changes include increased locomotion, and decreased grooming frequency and rearing bout duration. When animals were injected with the dopamine (DA) agonist 3,4-dihydroxyphenylamino-2-imidazoline (DPI: 0.5, 1.0 and 5.0 μg) into the nucleus accumbens one week after surgery, the behavior of hippocampally lesioned rats was restored to levels not different from control lesioned rats. Haloperidol injections (0.05, 0.1 and 0.5 μg) into the caudate nucleus were not able to do this. Further, DPI injected into the caudate nucleus one month after surgery was also able to attenuate some of the effects of hippocampal damage. On the other hand, haloperidol injections into the nucleus accumbens did not influence behavior. The results are interpreted in terms of hippocampal lesion-induced alteration of a balance in basal ganglia DA systems, indicated by modified response to pharmacological intervention and which mediate the behavioral effects of the lesion.     

Cyclic nucleotides in the rat neostriatum: Push-pull perfusion studies

A push-pull perfusion technique was employed for in vivo study of adenosine 3',5'-monophosphate (cAMP) and guanosine 3',5'-monophosphate (cGMP) in the rat caudate nucleus. Addition of dopamine to the perfusion fluid elicited dose-dependent increases of both cAMP and cGMP perfusate concentrations. In separate experiments, it was found that pretreatment of animals with the dopamine antagonist, pimozide, significantly depressed both nucleotide responses to dopamine perfusion over the dose range studied. Mechanistic interpretations of the observations are considered. The push-pull perfusion technique appears to provide an extremely useful means of examining extracellular cyclic nucleotide levels in a discrete brain region, in vivo, under dynamic conditions.     

Chronic cocaine alters brain mu opioid receptors

The possibility that dopamine may modulate the expression of opioid receptors was investigated by determining the effects of chronic cocaine administration on the density of μ opioid receptors. Quantitative in vitro autoradiography with the highly selective μ opioid ligand [³H]DAMGO was used to measure and localize changes in μ opioid receptors in the brains of rats administered cocaine or saline three times daily for 14 days. Significant increases in [³H]DAMGO binding were measured in areas of the cingulate cortex, nucleus accumbens, caudate putamen, and basolateral amygdaloid nucleus of the cocaine-treated animals. These results demonstrate that μ opioid receptors undergo upregulation in response to chronic cocaine exposure and suggest that dopamine activity can regulate the expression of μ opioid receptors.     

Changes in catecholamine content in discrete brain nuclei during the estrous cycle of the rat

Norepinephrine (NE) and dopamine (DA) concentrations were measured in discrete brain nuclei in female rats at different stages of the 4-day estrous cycle. In the medial preoptic and paraventricular nuclei, NE levels were reduced on the days of proestrus and estrus as compared to metestrus-diestrus. NE levels sharply increased between estrus and metestrus in the lateral septal nucleus but did not vary significantly at other times. In the mesencephalic central gray catecholamine area, NE levels were elevated on metestrus as compared to all other days of the cycle.DA concentrations also varied in certain nuclei during the estrous cycle. In the lateral septum, DA levels were highest during diestrus, and in the nucleus of the tractus diagonalis, DA levels were highest on metestrus. The DA concentration of the caudate nucleus decreased between proestrus and estrus and remained low through metestrus. DA in the medial preoptic nucleus showed a similar pattern of change as did NE. In the median eminence DA levels increased significantly from proestrus afternoon to estrus, but did not vary on the other days.It is concluded that cyclic activity of catecholamines in a few discrete areas of the brain may be related to the fluctuations of the gonadotropins and ovarian hormones to influence ovulation and mating behavior.     

Somatostatin regulates dopamine release in rat striatal slices and cat caudate nuclei

The effects of somatostatin on the release of tritiated dopamine (DA) formed continuously from tritiated tyrosine were studied in vitro in superfused striatal slices and in vivo in both caudate nuclei and both substantiae nigrae of halothane-anesthetized cats using a push-pull cannula technique. Somatostatin (3 X 10(-10) to 3 X 10(-7) M) increased the spontaneous tritiated dopamine release from rat striatal slices. This effect was dose dependent and was completely prevented by tetrodotoxin (5 X 10(-7) M). When applied for 30 min in one cat caudate nucleus, somatostatin (10(-7) M) immediately increased the local release of tritiated DA, while a gradual inhibition of the tritiated amine's efflux was observed in the contralateral caudate nucleus. No changes in tritiated dopamine were seen in either substantia nigra during or after the peptide's application in the caudate nucleus. These results suggest that somatostatin in the striatum may play a role in the local and the distal control of dopamine release from the terminals of dopaminergic nigrostriatal neurons.     

Dopamine released from dendrites in the substantia nigra controls the nigral and striatal release of serotonin

Using push-pull cannulae, the release of endogenously synthesized [³H]serotonin was estimated in both substantia nigra and caudate nuclei of ‘encéphale isolé’ cats. The unilateral nigral application of dopamine (10⁻⁷ M) reduced [³H]serotonin release in ipsilateral structures whereas α-methylparatyrosine (10⁻⁴ M) induced opposite effects. Both treatments decreased [³H]serotonin release in the contralateral caudate nucleus but not in the contralateral substantia nigra. As a working hypothesis it is suggested that the effects of observed are related to changes in the activity of nigroraphe neurons regulated by dopamine released from dendrites of the nigrostriatal dopaminergic neurons. However it cannot vet be excluded that the local changes in [³H]serotonin release induced by the nigral application of dopamine or α-methylparatyrosine result from presynaptic modulation.     

In vivo modulations by GABA-related drugs of met-enkephalin release in basal ganglia of the cat brain

The influence of the intrapallidal application of GABA-related compounds on the release of Met-enkephalin in the globus pallidus and the caudate nucleus in the two hemispheres was investigated in vivo in the cat. For this purpose, the 4 structures were continously superfused with an artificial CSF through implanted push-pull cannulae and Met-enkephalin released in superfusates was determined using a specific radioimmunoassay.GABA (10–500 μM) reduced the local release of Met-enkephalin during its application but once the amino acid was removed from the superfusing fluid, an increase in the peptide release was observed. Diazepam (10 μM) induced only an inhibitory effect whereas muscimol (1 μM) stimulated Met-enkephalin release. Opposite changes in Met-enkephalin release were also seen with the GABA antagonists, bicuculline methiodide (1 μM) and picrotoxin (10 μM), suggesting that the local regulation of Met-enkephalin released by GABA related compounds ay be mediated by at least two types of GABA receptors.In several cases, the unilateral pallidal application of GABA agonists and antagonists induced significant changes in Met-enkephalin release at distant structures. The most striking effect was observed with diazepam which markedly reduced the peptide release in both caudate nuclei and pallida. These data suggest that GABAergic systems can contribute to some bilateral regulation of striato-pallidal enkephalinergic neurones.     

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 habenula-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.     

Rapid desensitization of presynaptic dopamine autoreceptors during exposure to exogenous dopamine

When nomifensine is employed to inhibit neuronal uptake, exposure to dopamine (DA) (0.1–0.3 μM) or apomorphine (0.01–0.1 μM) inhibited, in a concentration-dependent manner, the electrically evoked release of [³H]dopamine from slices of the rabbit caudate nucleus. Apomorphine inhibited transmitter release independently of the time of exposure to the drug (6–32 min). On the other hand, the inhibitory effect of exogenous dopamine occurred only if a short period (4–12 min) of exposure was employed. In studies on the electrically evoked release of [³H]acetylcholine in slices of the rabbit caudate nucleus there was no evidence for desensitization to apomorphine or exogenous dopamine at the level of the dopamine receptors that inhibit [³H]acetylcholine release. These results indicate that the dopamine autoreceptors modulating [³H]dopamine release in the caudate nucleus become subsensitive after a few minutes of exposure to exogenous dopamine. This effect does not occur at the level of the dopamine receptors which inhibit the release of [³H]acetylcholine.