Genetic differences in mechanisms involving neuroregulators

Behavioral and genetic interrelationships between locomotor activity and brain biogenic amines

1. Spontaneous locomotor activity of four mouse strains, the albino ICR, BALB/C, the black C57 BL/6 and the brown CDF-I, was studied in conjunction with whole brain content of select biogenic amines and major metabolites. The ICR and C57BL/6 mice scored the highest and lowest motility among the strains studied, respectively. 2. The ICR mice motility were the most sensitive to experimental stress among the mouse strains evaluated. 3. Brain dopamine concentrations were greater in ICR and CDF-I mice than the other two mouse strains. This is compared to high serotonin and 5-hydroxyindole acetic acid levels determined in C57BL/6. 4. A relationship between the ICR mouse strain with a high motility and the ratios of brain dopamine:homovanillic acid and between serotonin:5-hydroxyindole acetic acid was established. 5. An inverse relationship between ICR mice motility and the ratio of metanephrine and normetanephrine:3-methoxy-4-hydroxyphenylglycol (MHPG) was determined. 6. It is concluded that genetic predisposition may account for a relationship between motor activity and brain biogenic amines which may give insight into the susceptibility of different patients to the development of certain extrapyramidal diseases.

Behavioral genetic analysis of regional mouse brain biogenic amines, acidic metabolites and motor activity

1. Comparative analyses of regional brain biogenic amines and spontaneous locomotor activity of three mouse strains suggest a genotype dependent relationship. 2. A positive correlation between striatal dopamine and locomotor activity was determined in the inbred albino BALB/c mouse strain. 3. An inverse relationship between some brain regions serotonin and motility was found in the inbred black C57BL/6 mouse strain. 4. No correlation could be established between brain monoamines and motor activity in the hybrid CDF-1 mouse strain. 5. The results suggest that inbred BALB/c and C57BL/6 mouse strains may be useful animal models for studying dopaminergic and serotonergic acting agents, respectively.

Effect of amantadine on motility of reserpinized mice as a function of brain biogenic amines and mouse strains

The effect of amantadine, reserpine or both on locomotor activity and whole brain content of selected biogenic amines and major metabolites was studied as a function of mouse strain. Successive administration of small dose regimens of reserpine, 0.2 mg/kg IP, did not alter motility from corresponding saline control. Administration of amantadine, 100 mg/kg, IP, prior to each of the reserpine treatments produced either stimulation of motor activity in the albino ICR and black C57BL/6 mice or caused inhibition from reserpine in the albino BALB/C and the brown CDF-1 mouse strains. This suggests a genotype strain sensitivity to the amantadine and reserpine interaction on the motor behavior of the mouse. The amantadine treatment did not alter brain dopamine concentration but increased its immediate acid metabolite, 3,4-dihydroxyphenylacetic acid, in the C57BL/6 mice as contrasted with reduction of the same in the BALB/C mouse strain. Both BALB/C and C57BL/6 mice showed changes in brain normetanephrine levels as a consequence of the pharmacologic intervention used which suggest catecholaminergic sensitivity. The only changes produced by the agents studied in brain serotonin or 5-hydroxyindoleacetic acid levels were confined to the BALB/C mouse strain. No changes occurred in brain levels of the compounds measured from corresponding controls in the CDF-1 mice. The results indicate differential sensitivity of the serotonergic and dopaminergic systems to drug-drug interaction studied which appears to be strain dependent.

Baseline exploratory activity predicts anxiolytic responsiveness to diazepam in five mouse strains

Inbred mouse strains showing variability in spontaneous exploratory behaviors displayed differential responsiveness to diazepam in an anxiety-related exploration model. C57B1/6J, BALB/cJ, Swiss Webster/NIH, Swiss Webster/Harlan Sprague-Dawley, and CF-1 mice demonstrated a significant correlation between baseline exploratory activity and maximal percentage increase in exploratory behavior induced by diazepam. No correlation was seen between those behavioral responses and the characteristics of brain benzodiazepine binding sites in the different strains. Anti-anxiety responsiveness appears to be a function of some genetically-determined substrate for spontaneous exploratory behaviors which may have multiple neurochemical substrates.

Modes of adaptation of peripheral neuroendocrine mechanisms of the sympatho-adrenal system to short-term stress as studied in two inbred rat strains

Alterations in mechanisms involved in catecholamine (CA) and corticosterone (B) regulation following short periods of stress have been investigated in two inbred rat strains: a strain more reactive to stress, Wistar-Kyoto (WK), and a less reactive strain, Brown-Norway (BN). Measurements after decapitation stress alone and after decapitation following different periods of immobilization stress, indicate that: (a) plasma CA levels immediately after severe stress (i.e. decapitation) are directly related to the behavioral reactivity of the two rat strains to stress but inversely related to adrenal gland size, their content of CA and biosynthetic enzymes, and to plasma levels of MHPG; (b) levels of B in adrenal glands and in plasma after stress are similar in both strains, in spite of different gland sizes; (c) CAT activity in presynaptic sympathetic terminals is directly related to plasma CA after short-term stress; and (d) liver COMT activity is directly related to plasma CA levels after stress, but inversely plasma levels of MHPG. The implications of the findings are discussed further in the text and lead to the conclusion that the BN strain represents a mode of a slower response to stressful stimuli than WK.

Central and peripheral norepinephrine metabolism in rat strains selectively bred for differences in response to stress

Rats of the Maudsley nonreactive (MNRA) strain were found to contain higher levels of norepinephrine in heart, spleen, and hypothalamus than animals of the Maudsley reactive (MR) strain. Total adrenal catecholamines were also greater in nonreactive animals. There was a trend toward higher endogenous norepinephrine concentration in MR rats in brainstem and telencephalon, but this was not statistically significant. Turnover measurements calculated from the fall of norepinephrine at 1 and 4 hours after a single dose of levo-alpha-methylparatyrosine showed no significant strain differences in telencephalon or brainstem, but MNRA animals had a faster rate of norepinephrine decline in heart than had MR rats. Possibly indicative of a higher rate of norepinephrine metabolism, the percentage of 3H-non-catechol metabolites relative to total counts was higher in brainstem of MNRA rats 90 min after intraventricular injection of 3H-norepinephrine. However, the disagreement between this estimate of norepinephrine metabolism and that provided by the alpha-methyl-paratyrosine technique prevents a conclusive statement about norepinephrine metabolism in the two strains. The results are discussed in the light of the established differences in behavior between the strains as well as other work exploring relationships between catecholamine metabolism and emotionality.

Genetic differences in ethanol drinking of the rat following injection of 6-OHDA, 5,6-DHT or 5,7-DHT into the cerebral ventricles

The preference characteristics for ethanol of four different strains of rats were determined in a two-choice situation by offering water and ethanol in a concentration which was increased from 3 to 30% over a 12-day test sequence. Using stereotaxic procedures, 50 mug 5,6-dihydroxytryptamine (5,6-DHT), 200 mug 6-hydroxydopamine (6-OHDA) or 100 mug 5,7-dihydroxytryptamine (5,7-DHT) were then injected acutely into the lateral cerebral ventricle in a 20 mul volume. Rats of the Sprague-Dawley strain increased their ethanol preference following the lesioning of the serotonergic system by 5,6-DHT, whereas similar destruction of catecholaminergic neurons by 6-OHDA markedly suppressed ethanol intake; Long-Evans rats displayed a similar trend in ethanol drinking patterns. However, animals of the Holtzman strain manifested the increased drinking after 5,6-DHT, but showed no suppression of drinking following 6-OHDA. The preference of rats of the Wistar strain was unaffected by 5,6-DHT but attenuated by 6-OHDA. 5,7-DHT had little or no effect on ethanol consumption in any of these strains. These findings thus suggest that genetic factors are an important determinant in an animal's response to a drug that affects 5-HT or NE systems in the brain, particularly when ethanol selection is investigated.

[Psychiatry, morphology and behaviour genetics (author's transl)]

No organic substrate is known for endogenous psychoses, neuroses and behaviour disorders. Therefore genetic studies have to depart from the behavioural level. This approach has yielded the empirical risk figures which depend on genetic and environmental factors. Beyond this level behaviour genetics endeavours to clarify the genetic mechanisms underlying normal and abnormal behaviour. In the schizophrenias f.i. several stretegies have been developed to approach the genetic basis: Mathematial models as to the mode of inheritance; use of modified classificatory and diagnostic criteria for genetic analysis; search for phenomena representing steps between genotype and phenotype and showing a clear mode of inheritance, f.i. biochemical or electrophysiological characters. In case the neurotransmitters are not changed in quality or total quantity but in compartmentation in the genetic defect might be localized in the pre- or postsynaptic membranes or receptors. Genetic factors are also involved in nonpsychotic behaviour disorders but to a lesser degree. They can be demonstrated even in psychoses with somatic background.