Farouk Karoum

Ibotenic acid lesion of the ventral hippocampus differentially affects dopamine and its metabolites in the nucleus accumbens and prefrontal cortex in the rat

To determine the influence of neurons of the ventral hippocampus on dopamine (DA) turnover in other limbic areas, spontaneous and amphetamine-induced locomotion as well as DA and its metabolites were assayed in nucleus accumbens, medial prefrontal cortex and anteromedial striatum, 14 and 28 days after bilateral ibotenic acid (IA) or sham lesions of the ventral hippocampus in the rat. Spontaneous locomotion was increased 28 days postoperatively, while D-amphetamine induced locomotion was augmented both 14 and 28 days postoperatively in IA lesioned animals. DA levels in the nucleus accumbens were decreased on the 14th, but increased on the 28th day after the lesion. Dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and the DOPAC/DA ratio in the medial prefrontal cortex (MPFC) were reduced 28 days postoperatively. Moreover, there was a significant negative correlation between the DOPAC/DA ratio in the MPFC and DA levels in the nucleus accumbens at this time point. These data indicate that a lesion of the ventral hippocampus can produce differential changes in cortical and limbic DA activity. Implications for an animal model of schizophrenia are considered.

Effect of ibotenic acid lesions of the medial prefrontal cortex on amphetamine-induced locomotion and regional brain catecholamine concentrations in the rat

To determine the influence of intrinsic medial prefrontal cortex (MPFC) neurons on regional brain catecholamine turnover, dopamine (DA) and its metabolites were assayed in several brain areas 14 and 28 days after bilateral ibotenic acid (IA) lesions of the MPFC in the rat. The locomotor response to D-amphetamine was also assessed. On the 14th postoperative day levels of DA, homovanillic acid concentrations and 3,4-dihydroxyphenylacetic acid were elevated in the anterior striatum of IA-lesioned animals. Spontaneous and amphetamine-induced locomotion were also increased. These changes disappeared by the 28th postoperative day. It is concluded that destruction of the efferents of the MPFC induces transient increases in DA turnover within the medial striatum and transiently increases spontaneous and amphetamine-induced locomotion.

Metabolism of (‐) deprenyl to amphetamine and methamphetamine may be responsible for deprenyl's therapeutic benefit A biochemical assessment

The urinary excretion of some important phenylethylamines, catecholamines, their metabolites, amphetamine, and methamphetamine were measured in parkinsonian patients on Sinemet (L-dopa plus carbidopa, a peripheral dopadecarboxylase inhibitor) and depressed patients after chronic (-) deprenyl treatment. Deprenyl was efficiently metabolized to amphetamine and methamphetamine. It increased the excretion of phenylethylamine and of m-and p-tyramine, and reduced the output of norepinephrine metabolites, but failed to alter the excretion of dopamine-deaminated metabolites. These changes were attributed more to amphetamine and methamphetamine than to inhibition of monoamine oxidase type B. Sinemet treatment alone increased the excretion of dopamine, 3-methoxytyramine, and their respective deaminated metabolites, 3, 4-dihydroxyphenylacetic acid and homovanillic acid. It is concluded that conversion of deprenyl to amphetamine and methamphetamine may contribute to some of the therapeutic benefits of deprenyl.

Brain concentrations of biogenic amine metabolites in acutely treated and ethanol-dependent rats.

1 Mass fragmentography was used to measure whole brain concentrations of some of the major metabolites of tyramine, octopamine, dopamine and noradrenaline in acutely treated and in ethanoldependent rats. 2 Treatments with ethanol, either acutely or chronically, failed to alter significantly brain concentration of p‐hydroxyphenylacetic and p‐hydroxymandelic acid (metabolites derived from tyramine and octopamine respectively). The effect on catecholamine metabolites was marked and therefore suggests that ethanol is selective in its effect on central metabolism of biogenic amines. 3 Acute ethanol treatment significantly increased brain concentration of homovanillic acid (HVA), 3,4‐dihydroxyphenylacetic acid (DOPAC) and 3‐methoxy‐4‐hydroxyphenylglycol (MHPG). Vanilmandelic acid (VMA) was not affected. All four metabolites (HVA, DOPAC, MHPG and VMA) were increased in the brains of rats rendered dependent on ethanol while still intoxicated (blood ethanol levels above 200 mg/dl). In ethanol‐dependent rats undergoing ethanol withdrawal syndrome (no ethanol present in blood), the brain concentrations of HVA and DOPAC were normal while those of MHPG and VMA continued to be elevated. 4 From the decline in the concentrations of HVA and DOPAC after 50 mg pargyline/kg in control rats and rats acutely treated with ethanol, it was concluded that ethanol has no effect on the transport of phenolic acids across the blood brain barrier. 5 No reversal in the metabolism of catecholamines from an oxidative to a reductive pathway, analogous to that produced by ethanol in the periphery, could be established in the brain. 6 The increase in catecholamine metabolite concentrations after ethanol treatment, either acute or chronic, were interpreted as manifestations of increases catecholamine turnover.

Presence of free, sulfate and glucuronide conjugated 3-methoxy-4-hydroxyphenylglycol (MHPG) in human brain, cerebrospinal fluid and plasma

The concentration of the free, glucuronide and the sulfate conjugated forms of 3-methoxy-4-hydroxyphenylglycol (MHPG) were measured in human plasma, cerebrospinal fluid (CSF) and brain by mass fragmentography. All three forms of MHPG were detected in the media analyzed. Free MHPG was found to be the predominant form in both the brain and the CSF. The sulfate conjugate of MHPG constitutes about 15% of the total MHPG in the CSF while in the brain the percentage varies between 30% in the hypothalamus and cortex and 80% in the substantia nigra. The concentration of the glucuronide conjugate of MHPG measured in the brain and CSF represents about 5% of the total MHPG concentration. In the plasma free MHPG and its glucuronide and sulfate conjugates are present in about equal concentrations. The relative concentrations of the three forms of MHPG measured in plasma, CSF and brain were compared with their concentrations in the urine from previously published results. From this comparison the diagnostic significance of each of the three forms of MHPG in the clinical assessment of central norepinephrine metabolism is discussed.

MASS FRAGMENTOGRAPHY OF PHENYLETHYLAMINE, m‐ AND p‐TYRAMINE AND RELATED AMINES IN PLASMA, CEREBROSPINAL FLUID, URINE, AND BRAIN

—A mass fragmentographic method for the assay of phenylethylamine (PEA) and a number of related amines in several biological materials is described. The gas chromatographic column employed for this analysis is a 12ft 1/8 in. o.d. steel column packed with 0.5% OV22+ 2% SE54 + 1% OV210 coated on 80/100 mesh chromosorb W (HP). The mass spectral characteristics of these amines are illustrated, compared, and discussed.

Catecholamine content of intracerebral adrenal medulla grafts

The rotational behavior which is produced by substantia nigra lesions can be decreased by adrenal medulla grafts adjacent to the denervated striatum. Perhaps these grafts secrete dopamine that diffuses into the striatum. In the present study, we measured concentrations of catecholamines in adrenal medulla grafts as compared with the normal adrenal medulla. The grafts were found to have high but extremely variable concentrations of dopamine. In hosts with substantia nigra lesions, concentrations of dopamine in the adrenal medulla grafts were decreased. Substantia nigra lesions, however, tended to increase concentrations of epinephrine in the grafts, while norepinephrine and total catecholamine concentrations were not significantly affected. It is concluded that at least some adrenal medulla grafts contain concentrations of dopamine sufficient to account for their behavioral effects.

MASS FRAGMENTOGRAPHIC DETERMINATION OF SOME ACIDIC AND ALCOHOLIC METABOLITES OF BIOGENIC AMINES IN THE RAT BRAIN

—A mass fragmentographic procedure is described for the simultaneous quantification of a number of deaminated metabolites derived from tyramine, octopamine, dopamine, and norepinephrine. With this method, several of the metabolites were measured in normal rat brain. The results support the central nervous system origin of tyramine, octopamine and their metabolites. The concentration of the dopamine metabolite, homovanillic acid, in the rat brain was found to be about 15% higher than that of dihydroxyphenylacetic acid. As for the metabolites of norepinephrine, vanilmandelic acid concentration was found to be about 5% that of 3‐methoxy‐4‐hydroxyphenylglycol. The possible role of vanilmandelic acid in the CNS metabolism of norephrine is discussed.

Persistent elevations in dopamine and its metabolites in the nucleus accumbens after mild subchronic stress in rats with ibotenic acid lesions of the medial prefrontal cortex

This study assessed the possible influence of the medial prefrontal cortex (MPFC) on the response of subcortical dopamine (DA) systems to subchronic, mild stress. DA and its metabolites as well as noradrenaline were assayed in the nucleus accumbens and corpus striatum, 1 and 7 days after one week of daily intraperitoneal saline injections (Stress) or no handling (No stress), in rats with sham (Sham) or ibotenic acid (IA) lesions of the MPFC. One day after the last saline injection the level of dihydroxyphenylacetic acid (DOPAC) was elevated in the nucleus accumbens of IA/Stress rats in comparison to the Sham/No stress, Sham/Stress, and IA/No Stress groups. Levels of mesolimbic DA, DOPAC and homovanillic acid were still elevated 7 days after the last injection in IA/Stress animals in comparison to all other groups. There were no other significant differences between the groups. The data suggest that in rats with MPFC impairment, mild subchronic stress can induce alterations in mesolimbic DA activity that persist beyond the duration of the stress.

Urinary excretion of 4-hydroxy-3-methoxyphenylglycol and 4-hydroxy-3-methoxyphenylethanol in man and rat

Abstract A sensitive, reproducible, and specific gas Chromatographic method for the assay of urinary excretion of free and conjugated 4-hydroxy-3-methoxyphenylglycol (HMPG) and 4-hydroxy-3-methoxyphenylethanol (HMPE) is described. These metabolites are derivatized by reacting them with pentafluoropropionic anhydride. Quantification of these derivatives emerging from the Chromatographic column was by electron capture detection (GC/ECD) and by mass fragmentography. Mean and standard error of metabolites excreted from 9 men and 5 male rats are given. Results are expressed as excretion per day or against creatinine. Since the HMPE and HMPG were also found in the urine of rats fed on an artificial casein diet it is suggested that they are produced endogenously.