Decreased receptor-binding sites for kainic acid in brains of patients with Huntington's disease

The specific binding of (3H)kainic acid (KA) to high- and low-affinity receptor sites was assayed in postmortem samples from the brains of patients affected with Huntington's disease (HD) and age-matched controls. Treatment of rat brain with conditions that closely mimic the temperature gradient occurring in postmortem human brain only slightly but not significantly decreased receptor binding by 12 hr after death. In HD brains, total specific binding of (3H)KA was reduced in the caudate nucleus by 51%, putamen by 77%, and frontal cortex by 47%. Specific binding to the high-affinity site was virtually undetectable in the caudate nucleus and was reduced by 90% in the putamen from HD brains. No significant alterations in specific binding of (3H)KA were noted in the insular or temporal cortex, hippocampus, or cerebellum. Thus, losses of KA receptor binding were mainly localized to those regions of the HD brain that are most severely affected by neuronal degeneration, and the high-affinity receptor site appeared more affected.

Chemical pathology of Huntington's disease

Huntington's disease (HD), a dominantly inherited disorder of the nervous system, is usually manifest about middle age by dance-like movements. The disorder may occur in children, when epilepsy and rigidity may be the predominant signs. Degeneration of neurons occurs throughout the whole brain, but this is most marked in the basal ganglia. Neurochemical examination of postmortem brain frozen at the time of autopsy has been collected from patients dying with HD and compared with postmortem brain from psychotic patients and cases without neuropsychiatric disease. A number of alterations in neurotransmitters and their biosynthetic enzymes have been found. There are decreased concentrations of the neuroinhibitory transmitter gamma aminobutyric acid and this is associated with increased concentrations of dopamine and serotonin in the basal ganglia. In addition, there is decreased activity of glutamic acid decarboxylase, choline acetyltransferase, angiotensin-converting enzyme, as well as a decreased concentration of the neuropeptide substance P. Various pharmacologic agents have been tried based on the neurochemical alterations, but nothing has been found to be superior to the various neuroleptics in common use.

Distribution of beta-endorphin in normal and schizophrenic human brains

beta-Endorphin was measured by radioimmunoassay in post-mortem human brains. Samples of brain were taken from five discrete areas, both from control brains and brains of schizophrenic patients. No difference in beta-endorphin levels was found in these two groups of brains. beta-Endorphin was confirmed to be widely distributed in the brain, but there were considerable differences in the concentrations in different areas.

Abnormalities of neurotransmitter enzymes in Huntington's chorea

The activities of L-glutamate decarboxylase (GAD), GABA-transaminase (GABA-T), choline acetyltransferase (CAT), and cysteic and cysteinesulfinic acids decarboxylase (CAD/CSAD) in putamen and frontal cortex in both Huntington's chorea and normal tissues were measured. The greatest difference between Huntington's and normal tissues occurred in putamen, in which the apparent CSAD activity was reduced by 85%, while no difference was observed in frontal cortex. GAD, CAD, and CAT activities were also reduced in putamen by 65%, 63%, and 42%, respectively (P less than 0.05). Slight reduction in the enzyme activities was also observed in frontal cortex. However, these reductions appeared to be statistically insignificant (P greater than 0.05 in all cases). GABA-T showed little difference in both putamen and frontal cortex in Huntington's chorea and normal tissues. GAD and GABA-T from Huntington's tissues were indistinguishable from those obtained from normal tissues by double diffusion test and by microcomplement fixation test, which is capable of distinguishing proteins with a single amino acid substitution. Furthermore, the similarity of the complement fixation curves for GAD from Huntington's and normal tissues suggests that the decrease in GAD activity is probably due to the reduction in the number of GAD molecules, presumably through the loss of neurons, and not due to the inhibition or inactivation of GAD activity by toxic substances which might be present in Huntington's chorea.

Antipsychotic drug action in schizophrenic patients: effect on cortical dopamine metabolism after long-term treatment

In the brains of deceased schizophrenics who underwent long-term treatment with antipsychotic drugs, the concentration of homovanillic acid (a dopamine metabolite) was significantly increased in the orbital frontal, cingulate, and temporal tip areas of the cortex, but not in the putamen or the nucleus accumbens. The concentration of homovanillic acid was normal in the brains of schizophrenics who were not treated with drugs.

Increased dopamine concentration in limbic areas of brain from patients dying with schizophrenia

Dopamine, noradrenaline, glutamate decarboxylase (GAD) and choline acetyl-transferase (CAT) were measured in post-mortem brain samples from more than 50 patients dying with a hospital diagnosis of schizophrenia and an equal number of controls. GAD was measured in 14 different brain regions, and was significantly lower in both control and schizophrenia patients who died following a protracted illness. If GAD values from patients who died suddenly were compared, no significant differences were observed between the control and schizophrenia groups. There was also no differences between the CAT values measured in 13 different brain regions in the two groups. Noradrenaline values were not different in the two groups in most limbic areas or in the caudate nucleus, but were elevated in the schizophrenic group in nucleus accumbens and in anterior perforated substance. These differences were not, however, statistically significant. On the other hand dopamine concentrations in nucleus accumbens and in anterior perforated substance were significantly elevated (by 34 and 95 per cent, respectively) in the schizophrenia group as compared with controls, although dopamine values were not different in caudate nucleus, putamen, septal nuclei or amygdala. The finding of elevated concentrations of dopamine in certain areas of the limbic forebrain in schizophrenia is discussed in relation to current hypotheses of the involvement of dopamine in this illness, and the difficulties of determining whether the observed changes are related to chronic treatment with antischizophrenic drugs.

Increased brain dopamine and reduced glutamic acid decarboxylase and choline acetyl transferase activity in schizophrenia and related psychoses

Dopamine, glutamic acid decarboxylase (G.A.D.) and choline acetyltransferase (C.A.T.) were measured in four regions of post-mortem brains. 41 patients with the hospital diagnosis of schizophrenia (psychotic group) were compared with a control grout normal in the putamen. G.A.D. activity was significantly reduced in the psychotic group, by about 50% in the nucleus accumbens, amygdala and hippocampus, and by about 30% in the putamen. C.A.T. activity was significantly lower in nucleus accumbens from the psychotic group, but normal in other brain regions. From an assessment of case notes, "schizophrenia" was distinguished from "schizophrenia-like psychosis". The biochemical findings for these subgroups were essentially similar, although C.A.T. activity in nucleus accumbens and hippocampus from the schizophrenic group was significantly lower than in controls. It is of brain are associated with schizophrenia and schizophrenia-like psychoses, although whether such neurochemical abnormalities are related to the illness or are a consequence of prolonged treatment with neuroleptic drugs remains unclear.

Huntington's chorea: selective depletion of activity of angiotensin coverting enzyme in the corpus striatum

The activity of angiotensin converting enzyme, which transforms the relatively inactive decapeptide angiotensin I to the active octapeptide angiotensin II by removal of an L-histidyl-L-leucine residue, has been assayed in numerous region of the calf brain and of the brains of humans with Huntington's chorea and controls. In calf brain there are pronounced regional variations in enzyme activity, with highest activity in the globus pallidus and area postrema. In human brain, enzyme activity is highest in the corpus striatum, with similar levels in the caudate, putamen, and globus pallidus. Converting enzyme activity is reduced by 83 to 92% in the globus pallidus in Huntington's chorea. The caudate and putamen of choreic patients display 62 to 69% reductions in enzyme activity. Converting enzyme activity in two cerebral cortical regions from choreic brains is not significantly different from control.

Synchronous nyctohemeral rhythms in human blood melatonin and in human post-mortem pineal enzyme

Serum melatonin was measured by radioimmunoassay at 4-hourly intervals for 24 h in five normal men, and shown to exhibit nyctohemeral variations. The highest concentrations of serum melatonin occurred at 02.00 hours and the lowest concentrations at 14.00 hours. The synthetic enzymes for melatonin, serotonin-N-acetyl transferase (SNAT) and hydroxyindole-O-methyltransferase (HIOMT) were measured in post-mortem pineal organs from thirty-six men and women, and the activity of both enzymes was directly related to the time of death of the subject, resulting in a similar nyctohemeral curve as that observed with serum melatonin. The SNAT and HIOMT enzymes were stable when measured in pineal organs held under the usual post-mortem conditions. The observations indicated a nyctohemeral rhythm in human pineal function and suggests that any clinical interpretation of pineal dysfunction in disease states should take into consideration this normal rhythm.

Plasma glucose, non-esterified fatty acids and amino acids in Huntington's chorea

1. The metabolic responses to an oral glucose tolerance test (100 g) and an intravenous insulin provocation test (0-1 i.u./kg) were studied in nine control subjects and nine patients with Huntington's chorea. 2. Plasma glucose responses to these stimuli were identical in both groups. 3. High fasting concentrations of non-esterified fatty acid (NEFA) were recorded in the choreic patients when compared with control subjects. This difference was maintained under hypoglycaemic conditions. However, during hyperglycaemia the differences in NEFA concentrations between the groups was abolished. 4. Total plasma tryptophan concentrations were equal in the two groups. Free plasma tryptophan, however, was markedly reduced in the choreic group, and this appeared to be a result of a disturbed relationship between free tryptophan and NEFA concentrations. The abnormalities in free tryptophan values were sensitive to plasma glucose concentrations, as hyperglycaemic conditions markedly reduced the differences between the choreic and control group. 5. Patients with Huntington's chorea showed reduced fasting plasma concentrations of leucine, isoleucine and valine.

Huntington's chorea. Changes in neurotransmitter receptors in the brain

Neurotransmitter-receptor binding sites for apparent muscarinic cholinergic, beta-adrenergic, gamma-aminobutyric acid and serotonin receptors were measured in the caudate nucleus and frontal cerebral cortex from post-mortem brains of 16 patients with Huntington's chorea and 16 controls. In addition, the samples were assayed for the gamma-aminobutyric-acid-synthesizing enzyme, glutamic acid decarboxylase, and for the acetylcholine-synthesizing enzyme, choline acetyltransferase. In the caudate nucleus of choreic brain, both enzyme activities were markedly lower, with significant decreases in muscarinic cholinergic and serotonin receptor binding, whereas enzyme activities and receptor binding were unchanged in the cerebral cortex. By contrast, gamma-aminobutyric acid and beta-adrenergic receptor binding were not significantly different in choreic and control caudate nucleus or cortex, suggesting that, despite the loss of gamma-aminobutyric-acid-synthesizing ability in the corpus striatum, gamma-aminobuytric acid mimetic drugs might alleviate the movement disorders in Huntington's chorea.

Plasma growth hormone concentrations in Huntington's chorea

1. Growth hormone secretion was assessed in nine control subjects and nine patients with Huntington's chorea. 2. Early-morning fasting plasma samples from patients with Huntington's chorea contained abnormally high concentrations of growth hormone. 3. The suppression of growth hormone after oral glucose in choreic patients, unlike the control subjects, occurred at irregular intervals after the glucose was given and was followed, again at irregular intervals, by an exaggerated rebound phase. 4. The response to intravenous insulin was not markedly abnormal in choreic patients. However, there was a significant increase in the rate of rise of growth hormone concentration in the first half and hour after the insulin injection when compared with control subjects.