Ross F. Lane

Chemically modified electrode for in vivo monitoring of brain catecholamines.

A chemically modified graphite paste electrode was developed to allow catecholamines to be electrochemically distinguished from ascorbic acid and the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC). Interference from 5-hydroxyindoles is eliminated through appropriate choice of electrode potential. The electrode gives linear current responses with increasing concentrations of catecholamines unaffected by the presence of ascorbic acid or DOPAC and exhibits long-term response stability in brain tissue. Examples are provided demonstrating the selectivity of the electrode to changes in extracellular dopamine in the rat striatum.

Chronic treatment with classical and atypical antipsychotic drugs differentially decreases dopamine release in striatum and nucleus accumbens in vivo

In vivo electrochemical techniques were employed to demonstrate that repeated treatment with classical antipsychotic drugs reduced basal dopamine (DA) release in the striatum and nucleus accumbens, whereas repeated treatment with atypical antipsychotics decreased DA release only in accumbens. Administration of apomorphine temporarily reversed these decreases to values comparable to those measured in vehicle-treated controls. These results suggest that the delayed onset of antipsychotic efficacy and extrapyramidal side effects involve a decrease in DA release in mesolimbic and nigrostriatal DA terminal fields, respectively. The results further suggest that induction of depolarization block in DA neurons may be the mechanism underlying these effects.

Normal rats trained to circle show asymmetric caudate dopamine release

Caudate catecholamine release was monitored by bilateral in vivo electrochemical electrodes in male Sprague-Dawley rats trained to circle for sucrose/water reward. Baseline release of dopamine was equal from both sides of caudate. When reinforced circling began, 44 +/- 4 percent greater catechol release occurred from the caudate contralateral to the circling direction. As turning subsided, differential release returned to basal levels. Further evidence that the catecholamine metabolism was affected by turning was obtained by direct measurement of caudate dopamine and DOPAC at selected time points. Concentration data showed relative increases in dopamine and DOPAC in the contralateral caudate. These data provide evidence that dopamine is released asymmetrically from caudate in unlesioned rats during voluntary behavior.

In vivo electrochemical analysis of cholecystokinin-induced inhibition of dopamine release in the nucleus accumbens.

In vivo electrochemical techniques were used to study the effects of the sulfated (CCK8-S) and unsulfated (CCK8-US) forms of the cholecystokinin octapeptide on dopamine (DA) release in the nucleus accumbens. A dose-dependent inhibition of DA release was observed only with CCK8-S. This inhibitory effect was blocked by the CCK receptor antagonist proglumide, and was reversed by systemic injections of apomorphine. Given that apomorphine can hyperpolarize DA neurons, these data indicate that CCK may inhibit the release of DA by a process of depolarization block and suggest a mechanism by which CCK may regulate overactive mesolimbic DA transmission.

Electrochemistry in Vivo: Application to CNS Pharmacology

In vivo electrochemistry is a technique that shows great promise for the direct measurement of a variety of easily oxidized compounds in the brains of anesthetized, immobilized, or freely moving animals.’ This technique is being developed to provide information concerning the presence and concentration of these compounds in the brain extracellular fluid and, perhaps more importantly, to measure dynamic changes in the concentration of these compounds that occur in response to physiological and pharmacological stimuli and to behavioral changes. Of particular interest is the monitoring of catecholamines and 5-hydroxytryptamine, which are easily oxidized neurotransmitters. Several studies have shown that in vivo electrochemical techniques can measure changes in concentration of electro-oxidizable species that are related to biogenic amine neurotransmitter release.’ However, the major problem associated with in vivo voltammetric detection of brain catecholamines is one of selectivity. This arises from the fact that the catecholamines and their non-methoxylated metabolites, as well as ascorbic acid, all oxidize at very similar potentials at most electrodes, including the unmodified graphite electrodes frequently used for in vivo studies. The resulting lack of discrimination was recognized in the first papers on in vivo voltammetrf” and was pointed out as a primary disadvantage of electrochemical measurements in brain tissue. The basal extracellular concentrations of ascorbate and the dopamine (DA) metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the rat striatum and nucleus accumbens are much higher than DA concentration,a and therefore currents due to ascorbate and DOPAC oxidation mask the current due to oxidation of DA. More problematical, levels of extracellular ascorbate and DOPAC in the striatum can be increased following the administration of various dopaminergic These changes in ascorbate and DOPAC concentrations are sufficiently large so as to obscure the much smaller changes in extracellular DA, confusing the analysis of drug-induced changes in DA levels. In view of these limitations, the development of electrodes with improved selectivity for the catecholamines has been an active area of research interest. At present, a

Chronic haloperidol decreases dopamine release in striatum and nucleus accumbens in vivo: Depolarization block as a possible mechanism of action

The effects of chronic haloperidol administration on the basal release of endogenous dopamine (DA) in the intact rat striatum and nucleus accumbens were investigated using in vivo electrochemical techniques. Repeated (21 day) treatment with haloperidol produced marked decreases in the release of DA in both brain regions. Administration of apomorphine to vehicle-treated control animals rapidly reduced DA release, in accord with its inhibitory, hyperpolarizing actions on DA neurons. In contrast, apomorphine reversed the haloperidol-induced reductions in DA release to values that were not significantly different from those measured in control animals. The present study is the first report to demonstrate decreased DA release in response to chronic neuroleptic treatment and to present evidence for induction of depolarization block of DA cell firing as a possible mechanism underlying this effect.

Selective inhibition of mesolimbic dopamine release following chronic administration of clozapine: involvement of α1-noradrenergic receptors demonstrated by in vivo voltammetry

The release of dopamine (DA) in vivo was compared in the striatum and nucleus accumbens following chronic (21 day) administration of clozapine (CLOZ) and repeated coadministration of haloperidol (HAL) and the alpha 1-noradrenergic (NE) receptor antagonist prazosin. Treatment with HAL reduced basal DA release in both brain regions, whereas treatment with CLOZ decreased basal DA release only in the accumbens. Chronic coadministration of HAL and prazosin resulted in decreased DA release in accumbens but not striatum. These results suggest that the alpha 1-NE receptor blocking properties of CLOZ may, in part, mediate its differential actions on nigrostriatal and mesolimbic DA release, an effect which may in addition contribute to its paucity of extrapyramidal side effects.

Dynamics of noradrenergic circadian input to the chicken pineal gland

To analyze the dynamics of sympathetic input to the chicken pineal the concentrations of catecholamines, indoleamines and some of their metabolites were determined by high performance liquid chromatography with electrochemical detection (HPLC-EC) in the pineal glands of young chickens killed at different times of day. Rhythmic variations over 24 h were observed in tissue levels of dopamine (DA), 5-hydroxytryptamine (5-HT), N-acetylserotonin (NAS) and 5-hydroxyindoleacetic acid (5-HIAA), while norepinephrine (NE) concentrations exhibited no significant change. DA content peaked 2 h after onset of darkness and NAS was detectable only during the night. A bimodal pattern of 5-HT and 5-HIAA levels was observed with peak tissue levels occurring at dawn and dusk. To determine the possible differential effects of light on these biogenic amines, birds were sacrificed at midday, midnight and at midnight following a 1 h exposure to light, and their pineals processed for HPLC-EC. NE, DA and 5-HT levels were similar at midday and midnight, while 5-HIAA and NAS were elevated during the night. Midnight illumination decreased NE and NAS levels, increased 5-HT and 5-HIAA levels and had no effect on DA levels. Temporal variations in NE turnover were determined by pretreating young chickens with alpha-methyl-p-tyrosine, a tyrosine hydroxylase inhibitor, and measuring the rates of decline in NE content over 2 h at midday and midnight in birds held on light cycles and at mid-subjective day in birds held in constant darkness (DD).(ABSTRACT TRUNCATED AT 250 WORDS)

Direct in vivo electrochemical monitoring of dopamine release in response to neuroleptic drugs

The ability of stearate-modified graphite paste electrodes to monitor changes in dopamine (DA) release in response to haloperidol and chlorpromazine was examined in rat striatum. The increase in electrochemical signal produced by both neuroleptics was not reversed by pargyline and was abolished by 6-hydroxydopamine lesions of the substantia nigra. The electrodes did not respond to administration of ascorbic acid or promethazine. The results demonstrate that neuroleptic-induced release of DA can be directly monitored with these electrodes.

Melatonin-Induced Increases in Serotonin Concentrations in Specific Regions of the Chicken Brain

Day-night differences in the concentrations of melatonin and serotonin (5HT) were measured in several regions of the chicken brain, pineal gland and serum. Melatonin concentrations are higher at midnight than at midday in 8 of the 10 tissues studied although the amplitudes of these rhythms varied greatly. Day-night differences in the pineal, hypothalamus, thalamus, retina and pons-midbrain regions had the highest amplitudes. 5HT concentrations were rhythmic in only 3 of the tissues studied: the hypothalamus, thalamus and retina. These were also the areas of highest 5HT concentration. Exogenous melatonin, injected at midday, was taken up with similar patterns; the pineal, hypothalamus, thalamus and pons-midbrain contained more melatonin 20 min after injection than did other tissues. The rate of decline of melatonin concentration varied little among all tissues studied, suggesting that the differences among tissue concentrations were due to selective uptake mechanisms rather than specialized degradation pathways. The effects of exogenous melatonin on 5HT concentration were restricted to hypothalamus, thalamus, pons-midbrain, retina and pineal. No effect was seen in cerebellum, optic tectum, neostriatum, hippocampus and medulla oblongata. Together, these data strongly suggest that pineal (and exogenous) melatonin is selectively taken up primarily by three brain regions, hypothalamus, thalamus and pons-midbrain, in which it produces increases in 5HT concentrations. Regional selectivity of uptake may be the mechanism by means of which the effects of melatonin on 5HT-mediated function are restricted to specific brain areas.