Thomas G. Reigle

Brain norepinephrine and metabolites after treadmill training and wheel running in rats.

Regional changes in concentrations of brain norepinephrine [NE] and its metabolites after chronic exercise have not been described for exercise protocols not confounded by other stressors. We examined levels of [NE], 3-methoxy-4-hydroxyphenylglycol [MHPG], and 3,4-dihydroxyphenylglycol [DHPG] in the frontal cortex, hippocampus, pons-medulla, and spinal cord after 8 wk of exercise. Male Sprague-Dawley rats (N = 36) were randomly assigned to three conditions: 1) 24-h access to activity wheel running (WR), 2) treadmill running (TR) at 0 degrees incline for 1 h.d-1 at 25-30 m.min-1, or 3) a sedentary control group (C). Levels (nmol.g-1) of [NE], [MHPG], and [DHPG] were assayed by high performance liquid chromatography with electrochemical detection. Planned contrasts (P < 0.05) indicated that exercise training increased succinate dehydrogenase activity (mmol cytochrome C reduced.min-1.g-1 wet weight) in soleus muscle for TR compared with WR or C. [NE] was higher in the pons-medulla and spinal cord for both TR and WR compared with C. [DHPG] was higher in the pons-medulla for TR compared with C, and [MHPG] was higher in the frontal cortex and in the hippocampus for TR compared with C. Our results suggest that treadmill exercise training is accompanied by brain noradrenergic adaptations consistent with increased metabolism of NE in areas containing NE cell bodies and ascending terminals, whereas treadmill running and wheel running are accompanied by increases in levels of NE in the areas of NE cell bodies and the spinal cord, independently of an exercise training effect.

Activity wheel running reduces escape latency and alters brain monoamine levels after footshock

We examined the effects of chronic activity wheel running on brain monoamines and latency to escape foot shock after prior exposure to uncontrollable, inescapable foot shock. Individually housed young (approximately 50 day) female Sprague-Dawley rats were randomly assigned to standard cages (sedentary) or cages with activity wheels. After 9-12 weeks, animals were matched in pairs on body mass. Activity wheel animals were also matched on running distance. An animal from each matched pair was randomly assigned to controllable or uncontrollable inescapable foot shock followed the next day by a foot shock escape test in a shuttle box. Brain concentrations of norepinephrine (NE), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), 5-hydroxytryptamine (5-HT), and 5-hydroxyindole acetic acid (5-HIAA) were assayed in the locus coeruleus (LC), dorsal raphe (DR), central amygdala (AC), hippocampus (CA1), arcuate nucleus, paraventricular nucleus (PVN), and midbrain central gray. After prior exposure to uncontrollable foot shock, escape latency was reduced by 34% for wheel runners compared with sedentary controls. The shortened escape latency for wheel runners was associated with 61% higher NE concentrations in LC and 44% higher NE concentrations in DR compared with sedentary controls. Sedentary controls, compared with wheel runners, had 31% higher 5-HIAA concentrations in CA1 and 30% higher 5-HIAA concentrations in AC after uncontrollable foot shock and had 28% higher 5-HT and 33% higher 5-HIAA concentrations in AC averaged across both foot shock conditions. There were no group differences in monoamines in the central gray or in plasma prolactin or ACTH concentrations, despite 52% higher DA concentrations in the arcuate nucleus after uncontrollable foot shock and 50% higher DOPAC/DA and 17% higher 5-HIAA/5-HT concentrations in the PVN averaged across both foot shock conditions for sedentary compared with activity wheel animals. The present results extend understanding of the escape-deficit by indicating an attenuating role for circadian physical activity. The altered monoamine levels suggest brain regions for more direct probes of neural activity after wheel running and foot shock.

Schedule-Controlled Operant Behavior of Rats During 1,1,1-Trichloroethane Inhalation: Relationship to Blood and Brain Solvent Concentrations1

The central nervous system is the principal target of 1,1,1-trichloroethane (TRI), and several studies of this volatile solvent have demonstrated effects on learned animal behaviors. There have been few attempts, however, to quantitatively relate such effects to blood or target organ (brain) solvent concentrations. Therefore, Sprague-Dawley rats trained to lever-press for evaporated milk on a variable interval 30-s reinforcement schedule were placed in an operant test cage and exposed to clean air for 20 min, followed by a single concentration of TRI vapor (500-5000 ppm) for 100 min. Additional rats were exposed to equivalent TRI concentrations for 10, 20, 40, 60, 80, or 100 min to determine blood and brain concentration vs. time profiles. Inhalation of 1000 ppm slightly increased operant response rates, whereas 2000, 3500, and 5000 ppm decreased operant response rates in a concentration- and time-dependent manner. Accumulation of TRI in blood and brain was rapid and concentration dependent, with the brain concentration roughly twice that of blood. Plots of blood and brain TRI concentrations against operant performance showed responding in excess of control rates at low concentrations, and decreasing response rates as concentrations increased. Linear regression analyses indicated that blood and brain concentrations, as well as measures of time integrals of internal dose, were strongly correlated with operant performance. Neurobehavioral toxicity in laboratory animals, as measured by changes in operant performance, can therefore be quantitatively related to internal measures of TRI exposure to enhance its predictive value for human risk assessment.

SCHEDULE-CONTROLLED OPERANT BEHAVIOR OF RATS FOLLOWING ORAL ADMINISTRATION OF PERCHLOROETHYLENE: TIME COURSE AND RELATIONSHIP TO BLOOD AND BRAIN SOLVENT LEVELS

Previous studies have indicated that human exposure to perchloroethylene (PCE) produces subtle behavioral changes and other neurological effects at concentration at or below the current occupational exposure limit. Since comparable effects in animals may be reflected by changes in schedule-controlled operant behavior, the ability of orally administered PCE to alter fixed-ratio (FR) responding for a food reward was investigated in male Sprague-Dawley rats. Furthermore, since behavioral effects of solvents are likely to be more closely related to blood or target tissue (i.e, brain) concentrations than administered dose, the relationship between the pharmacokinetic distribution of PCE and its effects on operant responding was also evaluated. Rats trained to lever-press for evaporated milk on an FR-40 reinforcement schedule were gavaged with 160 or 480 mg/kg PCE and immediately placed in an operant test cage for 90 min. Separate animals gavaged with equivalent doses of PCE were used to determine profiles of blood and brain concentrations versus time. Perchloroethylene produced changes in responding that varied not only with dose but also among animals receiving the same dose. Changes in the response rates of rats receiving 160 mg/kg PCE were either not readily apparent, restricted to the first 5 min of the operant session, or attributable to gavage stress and the dosing vehicle. However, 480 mg/kg produced either an immediate suppression of responding for 15-30 min before a rapid recovery to control rates or a complete elimination of lever-pressing for the majority of the operant session. Although the two doses of PCE produced markedly different effects on operant behavior during the first 30 min of exposure, differences in brain concentrations of PCE were minimal. Furthermore, the majority of animals receiving 480 mg/kg PCE fully recovered from response suppression while blood and brain levels of the solvent continued to rise. Thus, relationships between blood and brain PCE levels and performance impairment were not discernible over the monitored time course. Since the rapid onset of response suppression suggests that the precipitating event occurs within the first few minutes of exposure, it is possible that altered responding is related to the rate of increase in blood or brain concentrations rather than the absolute solvent concentrations themselves. The relationship between the pharmacokinetic distribution of solvents and their effects on the central nervous system is obviously complex and may involve acute neuronal adaptation as well as the dynamics of solvent distribution among the various body compartments.

Increased brain norepinephrine metabolism correlated with analgesia produced by the periaqueductal gray injection of opiates

Dose-dependent increases in 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MOPEG-SO4), a major metabolite of norepinephrine, were produced in the limbic forebrain and cerebral cortex 30 min after the bilateral injection of morphine into the periaqueductal gray (PAG). These effects were also elicited by similar injections of levorphanol. Highly significant correlations were obtained between the concentrations of MOPEG-SO4 and the analgesic effect of the opiates and opiate actions were antagonized by systemic naloxone. These results indicate that activation of opiate receptors in the PAG may elicit the involvement of noradrenergic systems in distant brain regions in the mediation of analgesia.

Effects of morphine and other centrally acting drugs on 3,4-dihydroxyphenylethylene glycol sulfate (DOPEG-SO4) in rat brain

Brain concentrations of DOPEG-SO4 were measured fluorometrically 0, 0.5, 1, 2, 4 and 8 hr after i.p. injections of morphine sulfate (20 mg/kg), d-amphetamine sulfate (5 mg/kg), desmethylimipramine HCl (25 mg/kg), or reserpine (5 mg/kg) in order to observe the effects of these drugs on intraneuronal norepinephrine degradation. No change in brain levels of DOPEG-SO4 was found until 8 hr after morphine, at which time the metabolite was significantly (p<.01) decreased. d-Amphetamine and desmethylimipramine significantly (p<.01) decreased the metabolite at all observed timepoints after 0 hr. Brain DOPEG-SO4 after reserpine was significantly (p<.01) increased at 0.5 and 1 hr, and significantly (p<.01) decreased at 4 and 8 hr. DOPEG-SO4 remained unchanged 0–8 hr after saline injections. These results, together with previous measurements of brain 3-methoxy-4-hydroxyphenylethylene glycol sulfate (MOPEG-SO4), indicate that the mechanism of morphine action on noradrenergic neurons differs from those of the other drugs examined and that morphine may cause central norepinephrine release.

p‐Chlorophenylalanine antagonism of the analgesia and increase in brain noradrenaline metabolism produced by morphine

approximately four times higher than those for 5-ASA. These levels are similar to those obtained from patients taking up to 3 g of sulphasalazine daily (Fischer & Klotz 1979). In the urine, the acetyl form predominated (98%). These low levels would suggest that the action of 5-ASA may be largely topical rather than systemic and it is probable that 5-ASA rather than the acetyl5-ASA is the active compound (Binder et al 1981). although both have anti-inflammatory activity. Renal damage due to 5-ASA has been reported in rats (Calder et al 1972) after intravenous administration of 14-57 mM kg which might be expected to give higher serum levels than those obtained by our enemas or sulphasalazine administration. As the levels of 5-ASA and acetyl 5-ASA documented after 5-ASA enema administration in our patients (most of whom had active inflammation and might be expected to absorb more of the drug) were low, this should be a safe and non-toxic preparation in man.

Analgesia and increases in limbic and cortical MOPEG‐SO4 produced by periaqueductal gray injections of morphine

Analgesia and changes in limbic and cortical concentrations of the major brain noradrenaline metabolite, 3‐methoxy‐4‐hydroxy‐phenylethylene glycol sulphate (MOPEG‐SO4), were investigated in rats following the bilateral injection of morphine into the periaqueductal gray (PAG). Morphine, at a dose of 5 μg per bilateral site, produced a significant antinociceptive effect within 15 min of injection. This effect, as measured by the tail flick analgesic test, remained constant at a level of approximately 75% of the maximum for 60 min. Significant increases in limbic and cortical MOPEG‐SO4 were also observed 15, 30 and 60 min after the 5 μg bilateral PAG injection of morphine. However, MOPEG‐SO4 concentrations exhibited a sharp peak in both brain areas at 30 min. Analgesia and the regional increases in MOPEG‐SO4 were antagonized by the prior systemic injection of naloxone (1 mg kg−1, i.p.). Thus, analgesia and increases in noradrenaline metabolism in two brain regions appear to be mediated by the specific activation of opiate receptors in the PAG. Although these findings indicate that brain noradrenergic systems may be involved in the mediation of morphine analgesia, the lack of a strict temporal relationship between antinociceptive action and increases in MOPEG‐SO4, suggests that analgesia cannot be totally attributed to changes in brain noradrenergic transmission.

Effects of acute inhalation exposure to isoamyl nitrite on the hypothalamo-pituitary-adrenal axis in male Sprague-Dawley rats

Isoamyl nitrite (IAN) is a member of the family of volatile organic nitrites that exert vasodilatory effects and have recently exhibited a considerable potential for inhalation abuse. In an effort to provide mechanistic insight into the neurotoxic effects and abuse potential of these agents, the present study was designed to evaluate the acute effects of IAN on the hypothalamo-pituitary-adrenal (HPA) axis. Attempts were also made to correlate the neuroendocrine effects of IAN with its pharmacokinetic profile. Male Sprague-Dawley rats were exposed to 600 or 1200 ppm IAN by inhalation for 10 or 30 min. Following exposure, adrenocorticotropic hormone (ACTH) and corticosterone in plasma and corticotropin-releasing factor (CRF) in three brain regions (hypothalamus, hippocampus, and frontal cortex) were determined by radioimmunoassay. Levels of IAN in the three brain regions as well as in blood were measured by gas chromatography to determine the target tissue concentrations responsible for neuroendocrine changes. Uptake of IAN into blood and all brain regions was very rapid, as stable concentrations were achieved within 10 min of exposure and maintained for 30 min of continuous inhalation. Plasma corticosterone decreased significantly after 10 min inhalation of both IAN doses, and returned to control levels after 30 min. Moreover, plasma ACTH was significantly increased by 10 and 30 min of exposure to 600 and 1200 ppm IAN, while hypothalamic CRF increased significantly after 30 min of exposure to the 600 ppm dose. These latter findings suggest activation of the hypothalamus and pituitary due to a reduction in negative feedback resulting from the initial decrease in corticosterone. Although plasma ACTH was greatly increased after 30 min, plasma corticosterone levels were unchanged, indicating that IAN primarily acts to inhibit the synthesis or secretion of adrenal steroids and that activation of the HPA axis is not involved in the behavioral manifestations of IAN inhalation. These compensatory effects of HPA axis regulation, and possibly the vasodilatory properties of IAN, also likely precluded the establishment of definitive relationships between observed changes in hormone levels and blood or regional brain concentrations of the inhalant.