Lewis S. Freedman

Brain and adrenal tyrosine hydroxylase activity after chronic footshock stress.

Rats subjected to 9 daily sessions of electric footshock stress showed marked increases in tyrosine hydroxylase activity in various brain regions and in the adrenal gland. The activity of the brain enzyme was elevated in the cerebral cortex, hypothalamus, locus coeruleus and the pons-medulla indicating a widespread effect of stress throughout the brain. Anatomical specificity of the response was indicated by a greater percent increase in the locus coeruleus, a nucleus containing noradrenergic cell bodies, than in the hypothalamus, cortex and pons-medulla, areas that contain noradrenergic terminals.

Reversal of cycloheximide-induced amnesia by adrenergic receptor stimulation.

Amnesia for a multiple trial appetitive spatial dicrimination habit induced by the protein synthesis inhibitor cycloheximide (CXM) was reversed by peripheral injections of both alpha (clonidine) and beta (isoproterenol) norepinephrine receptor stimulators. Stimulation of dopamine receptors with piribedil and acetylcholine receptors with pilocarpine was ineffective in reversing amnesia. The clonidine-induced recovery was blocked by phentolamine and the isoproterenol recovery by propranolol. Examination of the temporal parameters of clonidine-induced recovery indicated that the amnesia was prevented if the agonist was injected either before training and CXM treatment, up to 1 hr after training and up to 3 hr prior to testing. Clonidine also alleviated amnesia induced by another protein synthesis inhibitor anisomycin, for a shock motivated brightness discrimination habit. These data suggest that the transient amnesia induced by CXM may be a consequence of disruption of adrenergic mechanisms and more specifically that norepinephrine may play an important role in memory retrieval.

Serum Dopamine-β-Hydroxylase Activity in Neuroblastoma

Abstract The activity of dopamine-β-hydroxylase, the enzyme that catalyzes the conversion of dopamine to norepinephrine, was measured in the serum of 22 patients with neuroblastoma and of 27 control subjects. Twelve patients with neuroblastoma had serum values in the range of the control subjects, whereas 10 had extremely high values. Patients with high serum dopamine-β-hydroxylase activity also excreted large amounts of the norepinephrine metabolite, vanillymandelic acid. There was no correlation between the serum dopamine-β-hydroxylase activity and the urinary excretion levels of dopamine and its metabolite, homovanillic acid. The assay of serum levels of the enzyme may be useful for diagnosis of neuroblastomas.

A radioimmunoassay of human circulatory dopamine-β-hydroxylase☆

Abstract A procedure for the radioimmunoassay of human circulatory dopamine-β-hydroxylase (DβH) using antibodies directed toward human DβH is described. A significant correlation between serum DβH activity and the amount of serum immunoreactive (IR) DβH was found in the analyzed population. The radioimmunoassay of serum DβH could be used in monitoring changes of sympathetic activity in various physiological and pathological states.

Clonidine reverses the amnesia induced by dopamine beta hydroxylase inhibition.

The role of noradrenergic (NE) mechanisms in amnesia induced by the dopamine-beta-hydroxylase (DBH) inhibitor, diethyldithiocarbamate (DEDTC) was examined by studying the antiamnestic characteristics of the alpha-NE receptor stimulator clonidine. DEDTC (250 mg/kg) administered 3 hr prior to training to C57BL/6J mice resulted in marked deficits when retention of a multiple trial food motivated spatial discrimination task was measured 24 hr after learning. Investigation of the temporal aspects of recovery indicated that the agonist was an effective antiamnestic agent when administered 0, 1, 3, 21 and 23 hr after training. No recovery was observed when the drug was administered 6 and 18 hr posttraining. A dose response study of the effectiveness of clonidine administered 1 hr prior to testing indicated recovery of memory at doses ranging from 10-500 microgram/kg. The clonidine induced recovery was not a result of general performance facilitation, but specific to the memory tested. In addition, the clonidine effect was pharmacologically specific to its actions on NE receptors, as recovery was blocked by pre-treatment with the alpha-NE antagonist, phentolamine. No recovery from DEDTC induced amnesia was seen with post-training or pre-test injection of d-amphetamine.

The effect of acute and chronic swim stress on dopamine-β-hydroxylase activity

Abstract The acute and chronic swim stress led to an increase in serum dopamine-β-hydroxylase activity in rats. The elevated serum dopamine-β-hydroxylase levels found after stress probably reflect the balance between the rate of release and the rate of disappearance of the enzyme from the circulation. The acute, but not the chronic swim stress resulted in a decrease in dopamine-β-hydroxylase activity in the mesenteric arteries. The changes in dopamine-β-hydroxylase in the arteries following stress probably reflect the balance between the rate of release of the enzyme from the terminals and the rate of replenishment of the enzyme from the cell bodies. The chronic, but not the acute stress resulted in an increase in enzyme activity in the cervical ganglia and in adrenal glands. This finding is consistent with the idea that chronic stress induces the de novo enzyme-protein synthesis.

Effect of γ-glutamyl cycle inhibitors on brain amino acid transport and utilization

Two inhibitors of the γ-glutamyl cycle, methionine sulfoximine (MSO) and 2-imidazolidone-4-carboxylic acid (ICA) were administered to C57BL/6J mice. Both agents resulted in a reduced rate of transport of tyrosine from blood to brain and a decreased rate of incorporation of tyrosine from plasma into brain protein. MSO administration also diminished the concentrations of brain tyrosine, dopamine, and norepinephrine. MSO decreased the transport rate of valine by brain as well as the rate of its incorporation into protein when expressed in relation to the plasma specific activity. The results demonstrate a significant role for the γ-glutamyl cycle in the transport of large neutral amino acids from blood to brain.

Serum dopamine-β-hydroxylase levels in Down's syndrome

Serum dopamine‐β‐hydroxylase (DBH) and serum immunoreactive (IR) DBH levels were measured in patients with Downs syndrome. Serum DBH activity was markedly reduced in Downs syndrome patients as compared with age matched, normal controls or non‐mongoloid, disturbed children. Serum IR‐DBH levels were also markedly reduced in Downs syndrome. The possible factors responsible for the observed reduction in serum DBH levels (active and inactive enzyme levels) in Downs syndrome were investigated.

Effects of cycloheximide, a protein synthesis inhibitor, on mouse brain catecholamine biochemistry.

Cycloheximide (CXM), a protein synthesis inhibitor, has been shown to result in a marked inhibition of central catecholamine (CA) synthetic mechanisms at doses that cause amnesia in animals. Unlike other inhibitors of CA synthesis no significant depletion of whole brain NE or DA concentrations was observed 0.75, 1, 2, 3, 4, 6, 17, or 24 hours after administration of CXM (120 mg/kg) to C57BL/6J mice. In order to investigate the underlying basis of maintenance of CA levels in face of CA synthesis inhibition, the effects of CXM on in vitro release of 3H-NE was studied in mouse hypothalamic slices. CXM, in a dose related manner, significantly inhibited the potassium stimulated release of NE from hypothalamic slices. Anisomycin, another protein synthesis inhibitor, similarly inhibited NE release. These studies further document the effects of protein synthesis inhibitors on CA mechanisms and suggest that disruption of CA biochemistry may play a role in the amnesia observed after administration of protein synthesis inhibitors.

Some characteristics of amnesia induced by FLA-63 an inhibitor of dopamine beta hydroxylase.

The amnesic effects of FLA-63, a potent dopamine-beta-hydroxylase (DBH) inhibitor, were investigated in a food motivated spatial discrimination task. Groups of C57BL/6J mice were injected with either 5 mg/kg, 15 mg/kg, 25 mg/kg, 35 mg/kg or physiological saline 4 hr prior to training. Amnesia was observed 24 hr following training at all dose levels except 5 mg/kh. The performance deficit was specific to memory of the discrimination and not the result of state-dependency. Training conditions which produce an increase in habit strength prevented the amnestic effects of FLS-63. Spontaneous recovery of memory occurred 48 hr following drug administration. Recovery from amnesia was also induced by injections of a monoamine oxidase inhibitor, pargyline, administered 2 hr prior to the retention test. These data suggest that amnesia induced by norpinephrine (NE) depletion is the result of impairment of mechanisms necessary for memory retrieval.