Arvin F. Oke

Liquid chromatographic analysis of catecholamines routine assay for regional brain mapping

Abstract A thoroughly tested and highly reliable catecholamine assay is described which routinely determines 20–100 picograms of norepinephrine and dopamine in small punches of brain tissue weighing 0.50 to 50 mg. The assay was designed for regional brain mapping. It employs liquid chromatography with electrochemical detection and involves a minimum of sample pretreatment. Its realistic performance is illustrated by typical experimental data. Modifications for larger or whole brain samples as well as details of construction and operation of this system are given.

Nafion-coated electrodes with high selectivity for CNS electrochemistry

A major improvement in the selectivity of small graphite electrodes used for in vivo electrochemistry is described. The electrodes are coated with Nafion, a perfluorosulfonated polymer. This coating is practically impermeable to ascorbic acid and anionic biogenic amine metabolites and only slightly responsive to neutral metabolites. Thus it becomes selective for the cationic primary neurotransmitters, dopamine, norepinephrine and 5-hydroxytryptamine. Responses of Nafion-coated and untreated electrodes in vivo are compared.

Detailed mapping of ascorbate distribution in rat brain

Abstract Since only limited data were available on the distribution of ascorbic acid in rat brain, a detailed mapping was undertaken using a slice and semi-micro punching technique. The study provides new data on a number of rat brain regions; the most significant finding is that there are very marked gradients of ascorbate concentrations throughout the various nuclei. The possible correlation of the ascorbate levels with the various neurotransmitter systems is discussed.

Regional distribution of ascorbate in human brain

A comprehensive mapping of ascorbate distribution in human brain was carried out by liquid chromatography analysis. The data agree with earlier literature values where comparable and provide new information on several brain regions, including a detailed distribution in the thalamus. While ascorbate concentrations tend to be high in regions rich in catecholamines, there is no real correlation between the two.

Selective attention dysfunctions in adult rats neonatally treated with 6-hydroxydopamine ☆

Adult rats treated intracisternally with 6-hydroxydopamine during the perinatal period were trained on a black-white discrimination. Alterations in cue shape and cue location failed to selectively distinguish differences in response patterns for the treated animals. However, when irrelevant stimuli were added to the discriminative array, the 6-hydroxydopamine group evidenced marked impairment of performance throughout the period of distraction.

Simultaneous voltammetric and chemical monitoring of dopamine release in situ

The validity of voltammetric monitoring of stimulated dopamine (DA) release was tested by simultaneous chemical assay of the extracellular fluid region next to the tip of a selective Nafion-coated graphite voltammetric electrode. Micro alumina probes were positioned next to the recording electrode tip to adsorb released catecholamines. The catecholamines were desorbed into microvolumes of acid and analyzed by very sensitive HPLC assays to provide unequivocal chemical verification of the electrochemical signals. The results fully confirm that selective voltammetric electrodes can detect released DA and that the concentrations determined voltammetrically or chemically agree well.

Epinephrine localization in human brain stem.

A study was undertaken to determine the presence and possible localization of epinephrine (E) in the human brain stem. Three brain stems were analyzed, although detailed mapping was performed only on the third. E was found to be highly localized in the reticular formation and the aqueductal gray. The highest concentrations were found in the region of the floor of the fourth ventricle. Norepinephrine (NE) and dopamine (DA) determinations were included in the analyses. These catecholamines were also found to be localized in the same regions. The relative E concentrations ranged from about 1-10% of the total catecholamine content.

In Vivo Dynamics of Norepinephrine Release-Reuptake in Multiple Terminal Field Regions of Rat Brain

Abstract: Electrical stimulation of the ascending dorsal tegmental bundle of the locus ceruleus was used to elicit controlled release of norepinephrine. Real‐time in vivo monitoring in the brains of urethane‐anesthetized rats was observed with high speed chronocoulometry at rapidly responding carbon fiber electrodes. Using modeling similar to that developed for dopamine release, the electrochemical signals were characterized as the balance between norepinephrine release per electrical stimulation pulse and apparent Michaelis‐Menten reuptake parameters. Stimulation produced simultaneous overflow release at all terminal fields examined. The release and reuptake characteristics varied considerably in different regions. If the parameters are normalized to endogenous concentration in the terminal fields, release but not reuptake correlates with innervation density in several regions. Stimulated release results in norepinephrine overflow and transport in most brain regions with half‐lives of 1–3 s and overflow distances of 25–50 µm at most. A surprising exception occurs in the upper layers of cortex (cingulate and sensory) where half‐lives may be in the 10s of seconds and spatial reach may be up to 100 µm. The uptake in the outer cortical layers appears to be minimal and comparable with only nonspecific reuptake.

Epinephrine distribution in human brain.

The distribution of epinephrine (E) in human brain has been analyzed by a previously described [11] liquid chromatographic method. E, though detectable in most areas sampled, was found to be highly localized in those areas previously known to contain highest norepinephrine (NE) concentrations [4]. The regions found to be highest in E concentration were the ventromedial, dorsomedial, supraoptic and paraventricular nuclei of the hypothalamus.

Three-dimensional mapping of norepinephrine and serotonin in human thalamus.

Detailed quantitative information on catecholamines and 5-hydroxytryptamine (serotonin) in the human thalamus is much needed because of increasing interest in norepinephrine and serotonin as modulators of thalamic behavioral state control and overall information processing. This study provides three-dimensional distribution patterns of these monoamines in postmortem thalami from 13 normal subjects (no known neurological or psychiatric histories). The patterns come from a relatively fine-grained grid mapping procedure on successive coronal sections. Samples were analyzed by high performance liquid chromatography with electrochemical detection. The highest endogenous concentrations of norepinephrine are found in a ventromedial core that includes a number of the medial and intralaminar sub-nuclei but extends only slightly into the sensory regions of the lateral tier. The posterior portion of the thalamus, the pulvinar, contains low levels of norepinephrine. The distribution of 5-hydroxytryptamine is quite similar to that of norepinephrine in the rostral two-thirds of thalamus; however, in the pulvinar region, levels of serotonin are considerably increased and differ markedly between individual thalami. The study provides the first definitive mapping of serotonin levels in human thalamus. Consistent with many animal studies, there is no evidence for major dopaminergic innervation of human thalamus. By emphasizing the pattern distribution of the monoamines rather than the absolute values, it can be shown that the ambiguities of postmortem degradation frequently associated with biochemical assays are largely avoided. The terminal field distribution of norepinephrine is an essentially constant neurochemical signature in all thalami examined. The utility of the biochemical grid mapping procedure may be especially significant in terms of matching with data from functional neuroimaging techniques.