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

Polygenic inheritance of Tourette syndrome, stuttering, attention deficit hyperactivity, conduct, and oppositional defiant disorder: the additive and subtractive effect of the three dopaminergic genes--DRD2, D beta H, and DAT1

Polymorphisms of three different dopaminergic genes, dopamine D2 receptor (DRD2), dopamine beta-hydroxylase (D beta H), and dopamine transporter (DAT1), were examined in Tourette syndrome (TS) probands, their relatives, and controls. Each gene individually showed a significant correlation with various behavioral variables in these subjects. The additive and substractive effects of the three genes were examined by genotyping all three genes in the same set of subjects. For 9 of 20 TS associated comorbid behaviors there was a significant linear association between the degree of loading for markers of three genes and the mean behavior scores. The behavior variables showing the significant associations were, in order attention deficit hyperactivity disorder (ADHD), stuttering oppositional defiant, tics, conduct, obsessive-compulsive, mania, alcohol abuse and general anxiety-behaviors that constitute the most overt clinical aspects of TS. For 16 of the 20 behavior scores there was a linear progressive decrease in the mean score with progressively lesser loading for the three gene markers. These results suggest that TS, ADHD, stuttering oppositional defiant and conduct disorder, and other behaviors associated with TS, are polygenic, due in part to these three dopaminergic genes, and that the genetics of other polygenic psychiatric disorders may be deciphered using this technique.

Decreased density of presynaptic alpha 2-adrenoceptors in postmortem brains of patients with Alzheimer's disease

The full agonist [3H]bromoxidine (UK 14304) was used to quantitate alpha 2-adrenoceptors in postmortem brains of patients with Alzheimer's disease. The effects of aging and human serum Cohn fraction IV on [3H]bromoxidine binding were also assessed. In patients with Alzheimer's disease, the binding capacity (Bmax) of [3H]bromoxidine was lower in the frontal cortex (37%), hypothalamus (33%), and cerebellum (52%) than in matched controls. In the hippocampus, amygdala, and head of caudate, the binding capacities (Bmax) were unchanged. Quantitative autoradiographic analyses with [3H]bromoxidine confirmed the existence of a marked reduction (55-60%) in alpha 2A-adrenoceptor density in the frontal cortex (layers I and III). In patients with dementia who did not meet neuropathological criteria for Alzheimer's disease, the density of alpha 2-adrenoceptors was unchanged. In control subjects, the density of alpha 2A-adrenoceptors in the frontal cortex showed a significant negative correlation with age at death. The inhibitory effect of human serum Cohn fraction IV on [3H]bromoxidine was very similar in control subjects and patients with Alzheimer's disease. The observed decrease in the density of brain alpha 2-adrenoceptors in Alzheimer's disease may represent direct biochemical evidence of a presynaptic location of this receptor on noradrenergic nerve terminals in the human CNS.

Selective attention in Alzheimer's disease: characterizing cognitive subgroups of patients

Picture recognition was studied in 20 patients with AD and in 20 control subjects, using a procedure that matched these groups for initial performance. The groups did not differ significantly in overall forgetting, although 10 patients displayed improved recognition performance 72 hr after learning. These same patients were impaired in a test of attentional focusing, as revealed by post hoc analyses. A predictive experiment involving 20 new patients with AD confirmed the initial findings: a subgroup of patients displayed improved recognition performance 72 hr after learning and impairments in attentional focusing. Neuropsychological tests thus identify a subgroup of patients with impaired selective attention, perhaps related to locus coeruleus neuropathology.

Attenuation of forgetting by pharmacological stimulation of aminergic neurotransmitter systems

Mice were trained in one-way active avoidance to a criterion of 3/4 avoidances and tested under extinction conditions one week later when substantial forgetting had occurred. Thirty min prior to testing animals were injected with either saline or different doses of drugs which activate the noradrenergic (phenylephrine, salbutamol, clonidine) dopaminergic (L-dopa(Sinemet) transdihydrolisuride, apomorphine) and serotonergic (fluoxetine, 5-methoxy DMT) neurotransmitter systems. Results showed that all agents alleviated forgetting in a dose dependent fashion. Untrained mice treated with the most effective dose of representative drugs from each class did not exhibit avoidance behavior at testing indicating that the improved performance of trained animals was probably not the result of increased activity or other non-memorial effects of the drugs. It was concluded that pharmacological agents which stimulate monoamine systems may improve memory retrieval by activating a non-specific neural system which controls arousal, attention and motor readiness.

Selective attention in Alzheimer's disease: CSF correlates of behavioral impairments

CSF levels of HVA, 5-HIAA, and free MHPG, the major metabolites of dopamine, serotonin, and norepinephrine respectively, were measured in 22 patients with AD. These 22 patients were also administered tests of picture-recognition and attentional focusing as part of an earlier experiment. A significant association between deficits in attentional focusing and reduced levels of free MHPG in CSF was noted. These results suggest that behavioral measures can identify patients with noradrenergic involvement.

A comparison of the effects of localized brain administration of catecholamine and protein synthesis inhibitors on memory processing

Protein synthesis inhibitors disrupt biosynthetic processes thought to control the formation of long-term memory. While the agents used (i.e. puromycin, acetoxycycloheximide, cycloheximide and anisomycin) do not selectively inhibit the synthesis of any particular class of protein, it has generally been hypothesized or assumed that the critical proteins(s) is structural and necessary for modification and/or growth of synapses. Recent reports indicated that all of the protein synthesis inhibitors causing amnesia inhibited tyrosine hydroxylase activity. Tyrosine hydroxylase is needed for the conversion of tyrosine to dopamine (DA) and norpinephrine (NE); altering the level of this enzyme could affect catecholamine (CA) turnover. Since drugs known to inhibit CA synthesis cause amnesia, it is of considerable interest whether amnesia induced by protein synthesis inhibitors depends basically on inhibition of CA synthesis.

Memory storage impairment or retrieval failure: pharmacologically distinguishable processes

The effects of reserpine and syrosingopine on retention of a passive avoidance task in mice were investigated. Following repeated exposure to the training apparatus, the amnesia induced with syrosingopine could be reversed, the amnesia induced with reserpine could not. The amnesia produced by these agents was still evident 35 days following training. The results were discussed in terms of the effects of these drugs on memory consolidation and/or retrieval.

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.