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Biomedical subjects

J A Severson

Publications and source records attributed to J A Severson.

At least 19 recordsLinked to original sources
PubMed1990

Behavioral sensitization following a single apomorphine pretreatment--selective effects on the dopamine release process.

Once daily subchronic pretreatments with the dopamine (DA) agonist apomorphine (APO) increase striatal DA synthesis and metabolism. Such changes imply that adaptations to APO do not dissipate completely within 24 h. In the present report we evaluated the effects of a single APO treatment 24 h prior to euthanasia on behavior and on striatal DA synthesis, metabolism, release and receptor binding. The single APO pretreatment reduced DA release from striatal synaptosomes. In contrast, striatal DA synthesis, metabolism, and the high-affinity binding of DA to the D2 receptor were unaltered 24 h after agonist pretreatment. At this time the stereotypic response to a subsequent APO challenge was enhanced. This adaptive pattern is different from that observed 60 min following an acute APO pretreatment, when high-affinity D2 binding is reduced. The pattern 24 h following a single APO pretreatment is also different from that observed following subchronic agonist dosing, when stereotypic behavior is enhanced, while basal DA synthesis and metabolism are increased.

Animals↗
PubMed1990

Behavioral sensitization following subchronic apomorphine treatment--possible neurochemical basis.

Subchronic treatment with the dopamine agonist apomorphine produces a sensitization to the stereotypic effects of subsequent apomorphine challenge. The present study investigated the effects of this subchronic treatment on apomorphine induced stereotypic behavior and striatal dopamine synthesis, release, metabolism, and D2 receptor binding. The pretreatment, which enhanced the behavioral response to apomorphine challenge, also elevated basal dopamine synthesis and metabolism, but left the ability of a challenge dose of apomorphine to inhibit dopamine synthesis and metabolism unaltered. Thus, ongoing dopamine synthesis and extracellular levels of metabolites would be higher following apomorphine challenge in animals treated subchronically with the agonist. In contrast, neither synaptosomal dopamine release in response to depolarizing stimuli nor the density of D2 dopamine receptors was altered by the treatment. Overall, the results suggest that, while we did not find evidence of autoreceptor desensitization per se, apomorphine treatment may result in enhanced extracellular dopamine levels following dopamine agonist challenge to provide a greater stimulation of an intact dopamine receptor system.

Animals↗
PubMed1990

Single apomorphine pretreatment results in a rapid decline in high-affinity dopamine binding to the striatal dopamine D-2 receptor.

The formation of a ternary complex of agonist, receptor, and G-protein precedes inhibition of adenylate cyclase and is associated with high-affinity agonist binding. The present experiment was conducted to determine if a single direct dopamine (DA) agonist, apomorphine (APO), pretreatment could produce a rapid uncoupling of the striatal DA D-2 receptor from its G-proteins. APO (30 mg/kg, i.p.) and saline were administered once, with killing 60 or 90 min following the APO or vehicle treatment. APO pretreatment resulted in a reduction in the high-affinity binding of DA to the striatal DA D-2 receptor without altering total agonist binding. The total density of antagonist-defined D-2 receptors (Bmax) was not altered by the treatment. The present results represent, to our knowledge, the first demonstration of changes in high-affinity agonist binding to the DA D-2 receptor following a single in vivo pretreatment of a direct DA agonist.

Animals↗
PubMed1990

Methodological issues in the preparation and assay of platelet 3H-imipramine binding.

Several methodological factors in the preparation of platelets and the determination of platelet 3H-imipramine (3H-IMI) binding were examined. The ionic composition of the assay significantly affected platelet 3H-IMI binding. Approximately 25% of the specific binding of 3H-IMI to intact platelet preparations was retained in the absence of sodium and chloride ions. The addition of sodium ions enhanced the specific binding of 3H-IMI, but the addition of chloride in the presence of sodium had a more pronounced effect, enhancing binding approximately five-fold over that observed with the addition of sodium. Sodium was the only cation tested that enhanced binding. Only halides enhanced binding in the presence of sodium with the following order of potency: Cl- greater than Br- greater than I- = F-. Ions increased the density of binding sites (Bmax) and did not affect the affinity of the binding sites for 3H-IMI. In the presence of sodium and chloride, the use of serotonin (5HT) to define nonspecific binding in saturation experiments resulted in lower binding densities (Bmax) than when desipramine was used to define nonspecific binding. The component of binding that was insensitive to 5HT was roughly equal to the Bmax of 3H-IMI binding obtained in the absence of sodium and chloride using desipramine to define nonspecific binding. Overall, these data suggest that not all 3H-IMI binding that is displaced by desipramine is related to serotonergic mechanisms, and suggest that 5HT is a better choice than desipramine for the determination of the nonspecific binding of 3H-IMI. In addition, the binding of 3H-IMI to different platelet preparations was compared. The binding of 3H-IMI to intact platelets was less than that obtained using lysed platelet membranes when data were expressed per mg protein. The Coomassie Blue dye-binding method to determine platelet protein resulted in greater Bmax values than were obtained with the Folin phenol reagent method. The method of platelet preparation that is commonly used to prepare platelets for 3H-IMI binding resulted in similar binding values when compared to a method that prepares the entire platelet population. The results suggest that some, but not all, variations in laboratory methods used to prepare platelets and assay for platelet 3H-IMI binding may affect clinical studies examining this measure.

Adult↗
PubMed1989

Aging does not alter the voltage-dependent release of endogenous dopamine from mouse striatal synaptosomes.

Striatal synaptosomes isolated from 3-, 12-, and 24-month-old C57B1/6J mice were exposed to low (5 mM) and high (30 mM) concentrations of potassium of 1, 3, 5, 15 and 30 s. There were no age-related differences in the total intrasynaptosomal content of dopamine among the three age groups of mice. The basal release of endogenous dopamine from synaptosomes isolated from 24-month-old animals was significantly greater than that from synaptosomes isolated from 3-month-old animals at all time points tested. Similarly the potassium stimulated release of dopamine from 24-month-old animals was also higher than that from the 3-month-old group, but this increase was not statistically significant. The net voltage-dependent release of dopamine (stimulated minus basal) was similar for all groups at all time points measured. The increase in basal dopamine release in the 24-month-old animals may reflect an increased fragility or leakiness of the synaptosomal preparation.

Aging↗
PubMed1988

Platelet tritiated imipramine binding and MAO activity in Alzheimer's disease patients with agitation and delusions.

Decreased platelet 3H-imipramine binding density and decreased monoamine oxidase (MAO) activity have been considered as biological characteristics of several neuropsychiatric disorders, and may be related to central serotonin defects. Since serotonin system defects occur in Alzheimer's disease (AD), and decreased brain 3H-imipramine binding density, and increased brain and platelet MAO activity are reported also, we studied platelet 3H-imipramine binding density (Bmax) and platelet MAO activity in AD outpatients without antecedent psychiatric disorder. AD subjects with significant symptomatic behavioral disorder, predominantly agitation and delusions, and AD subjects without symptomatic behaviors were compared with controls. Age, sex, mini-mental state examination score, and illness duration did not distinguish the two AD groups. The agitated/delusional group showed significantly lower Bmax values than uncomplicated AD subjects or controls. MAO activity was significantly increased among female AD subjects without symptomatic behaviors compared to those who were agitated or to controls. These results indicate that 3H-imipramine binding and MAO activity may distinguish AD subjects with agitation or delusions from those without symptomatic behaviors, and suggest the existence of a biologically based Alzheimer's behavioral subtype.

Aged↗
PubMed1988

Electrocardiographic changes with nortriptyline and 10-hydroxynortriptyline in elderly depressed outpatients.

Pharmacokinetic factors may contribute to altered nortriptyline effects in the elderly. Plasma concentrations of nortriptyline's principal metabolite, E-10-hydroxynortriptyline, tend to be greater than nortriptyline, increase with age, and may contribute to cardiotoxicity. Electrocardiogram changes were evaluated in 21 ambulatory, elderly, depressed outpatients who were treated with therapeutic doses of nortriptyline. Resting electrocardiograms were obtained before and after 6 weeks of treatment. Plasma samples were assayed simultaneously for nortriptyline, E-, and Z-10-hydroxynortriptyline. Three subjects developed a first degree atrioventricular block and one developed a right bundle branch block during treatment. Mean daily nortriptyline dose and steady state plasma level in these subjects did not differ from those who did not develop conduction defects, but E-10-hydroxynortriptyline levels were significantly higher. Overall, there were significant correlations between changes in the PR interval and QRS duration with plasma concentrations of nortriptyline, E-10-hydroxynortriptyline, Z-10-hydroxynortriptyline, and the sum of nortriptyline and its 10-hydroxynortriptyline metabolites. Multiple regression analyses suggested that increases in PR interval were associated with increasing nortriptyline concentration, while increases in QRS duration and Q-Tc intervals were associated with increasing Z-10-hydroxynortriptyline concentration. E- and Z-10-hydroxynortriptyline may contribute substantially to the cardiac conduction effects of nortriptyline treatment and may be of particular importance in the elderly.

Aged↗
PubMed1986

Chronic antidepressant treatment and mouse brain 3H-imipramine binding.

Chronic pretreatment of mice with the monoamine oxidase type B inhibitor (-)deprenyl resulted in an increase in the density of cerebral cortical 3H-imipramine binding sites and a decrease in the density of cerebral cortical beta-adrenergic receptors. In contrast, pretreatment of mice with the tricyclic antidepressants imipramine and desipramine did not alter the density of cerebral cortical 3H-imipramine binding sites. Imipramine and desipramine treatment decreased the density of beta-adrenergic receptors. Haloperidol pretreatment resulted in an increase in the density of striatal D-2 dopamine receptors, but did not alter the density of cerebral cortical 3H-imipramine binding sites or beta-adrenergic receptors. These data suggest that brain 3H-imipramine binding sites can be regulated by pharmacological pretreatment, but that this regulation may not occur for all antidepressants.

Animals↗
PubMed1986

Subdivision of mouse brain [3H]imipramine binding based on ion dependence and serotonin sensitivity.

The specific binding of [3H]imipramine to mouse brain membranes in an assay containing 120 mM NaCl and 5 mM KCl was similar in regional distribution and pharmacological specificity to that reported previously in rat and human brain. However, the absence of ions decreased the density of the specific binding of [3H]imipramine and did not affect the equilibrium dissociation constant. Sodium was the only cation, and halides were the only anions tested that enhanced the specific binding of [3H]imipramine. Chloride did not increase the density of binding in the absence of sodium. The ion-sensitive binding of [3H]imipramine was regionally dependent and was highly correlated with the uptake of 5-hydroxytryptamine (5-HT, serotonin) into synaptosomes from brain regions. 5-HT did not inhibit the binding of [3H]imipramine in the absence of ions. Antidepressants inhibited binding in the absence and presence of ions, but in the presence of ions inhibition curves were shifted to the left and the apparent complexity of inhibition was increased. Quantitative analysis of the inhibition of [3H]imipramine binding by antidepressants conducted in the presence of ions was consistent with two binding sites. Lesion of the serotonergic input to the cerebral cortex by 5,7-dihydroxytryptamine suggested that both the 5-HT-sensitive and ion-sensitive binding of [3H]imipramine were associated with serotonergic nerve terminals. [3H]Imipramine binding displaced by desipramine, but insensitive to 5-HT and ions, was not affected by the lesion. Thus, the binding of [3H]imipramine that is displaced by desipramine, the most common assay for [3H]imipramine binding, includes a component that is not associated with brain serotonergic nerve terminals and 5-HT uptake, and, in addition, a separable component that is highly correlated with serotonergic function. These data have important implications for studies of serotonergic neurons and for the interpretation of imipramine binding data.

Animals↗
PubMed1986

Genetic influence on the regulation of beta adrenergic receptors in mice.

The regulation of beta adrenergic receptors was investigated in inbred mouse strains in which previous studies revealed differences in the regulation of dopamine receptors. The density of beta adrenergic receptors in the cerebral cortex of BALB/J mice was about one-third of that in CBA/J and C57BL/6J mice. Strain differences in the binding of [125I]iodohydroxypindolol to beta adrenergic receptors were due to changes in the density of beta-1 adrenergic receptors. Chronic administration of propranolol did not result in an increase in the density of beta adrenergic receptors receptors in cortices of C57BL/6J and BALB/cJ mice were observed. In contrast, pretreatment with 6-hydroxydopamine resulted in increases in the density of beta adrenergic receptors in the cerebral cortex of all three strains. Analysis of the effects of these treatments on the subtypes of beta adrenergic receptors revealed that the changes were restricted to changes in the density of beta-1 receptors. The failure to observe a response to propranolol in CBA/J mice expands the extent of deficits reported previously in this strain for striatal dopamine receptor supersensitivity after chronic treatment with haloperidol (Severson et al., Brain Res. 210: 201-215, 1981). CBA/J mice may be a useful model for genetic analysis of mechanisms for the control of receptor sensitivity and to investigate the impairments of the regulation of catecholaminergic receptors observed in aged rodents.

Age Factors↗
PubMed1985

Genotypic variation in striatal calmodulin content.

CBA/J and BALB/cJ mice have quantitative differences in the nigrostriatal projection. The number of nigral tyrosine hydroxylase reactive neurons, nigral and striatal tyrosine hydroxylase activity and the density of striatal D-2 dopamine receptors are all less in the CBA/J compared to the BALB/cJ mouse. An unrelated strain, the C57BL/6J, has a striatal D-2 dopamine receptor density that is intermediate to that of CBA/J and BALB/cJ mice. CBA/J mice also show deficits in the ability of brain monoaminergic receptor systems to develop supersensitivity. Calmodulin may participate in several striatal dopaminergic receptor mechanisms. Thus, striatal calmodulin was examined in CBA/J, C57BL/6J and BALB/cJ mice. Striatal calmodulin was greater in CBA/J mice than in C57BL/6J or BALB/cJ. In all three strains, cerebral cortical calmodulin was similar. The percent distribution of total striatal calmodulin between soluble and particulate fractions was similar in the three strains. Calcium redistributed soluble striatal calmodulin into the particulate fraction and EGTA shifted calmodulin from the particulate into the soluble fraction. The percent of total striatal calmodulin redistributed by either treatment was similar in all three strains. Gel filtration chromatography of heat-treated soluble extracts from CBA/J and BALB/cJ striatum was similar in elution pattern, although more calmodulin was observed in extracts from the CBA/J. Possible mechanisms for the strain differences in calmodulin are discussed along with their relationship to strain differences in striatal dopamine receptor subtypes.

Animals↗
PubMed1985

Elevated density of [3H]imipramine binding in aged human brain.

Aging was associated with an increase in the density of specific binding sites for [3H]imipramine in postmortem specimens of human hypothalamus, frontal cortex, and parietal cortex. In general, [3H]imipramine binding was not affected by factors considered difficult to control in postmortem studies, i.e., time from death to autopsy and cause of death. The in vitro regulation of [3H]imipramine binding by sodium was impaired with age in hypothalamic homogenates. In vitro regulation of [3H]imipramine binding by chloride was intact. Determination of the concentrations of 5-hydroxytryptamine (serotonin) and 5-hydroxyindoleacetic acid in hypothalamus and frontal cortex indicated no apparent age-related changes in indole metabolism. The age-related increase in brain [3H]imipramine binding and impairment in the in vitro regulation of binding by ions are similar to changes observed previously in aged mouse brain. The increase in brain antidepressant binding sites is discussed in relationship to other indices of brain serotonergic function in aging and to the relationship of [3H]imipramine binding and depression.

Adolescent↗
PubMed1985

D-2 dopamine receptors in aging mouse striatum: determination of high- and low-affinity agonist binding sites.

Striatal D-2 dopamine receptors in homogenates from aged male C57BL/6J mice were examined for high and low-affinity agonist binding. High-affinity dopamine binding requires the ternary complex of the D-2 receptor and a guanine nucleotide binding regulatory protein (N). Thus, changes in the interaction of D-2 and N could contribute to previously reported changes in agonist binding in aged rodents and humans. Qualitative experiments indicated no age-change in the ability of guanine nucleotides to reduce the apparent potency of dopamine at D-2 receptors. Also, no age differences were observed in the ability of guanine nucleotides to decrease N-[3H]propylnorapomorphine binding, suggesting that the ability of guanine nucleotides to dissociate D-2 and N was similar with age. Quantitative determination of the high- (RH) and low-affinity (RL) agonist binding components of striatal D-2 dopamine receptors in the absence of guanine nucleotides indicated differences in the density of RH, and the percentage of D-2 receptors measured as RH, between the ages of 3 and 12 months. No changes in RH or percentage of RH occurred after midlife. In contrast, the total D-2 receptor population, [3H]spiperone maximum binding, declined progressively from 3 to 24 months. Age-changes were restricted to D-2 receptor density; the dissociation constants for agonist and antagonist binding were similar across age. The data suggest that age-changes in striatal D-2 dopamine receptors can occur in the density of the D-2 receptor and in the mechanism that confers the property of high-affinity agonist binding upon the D-2 receptor.

Aging↗
PubMed1978

Adrenocortical function in response to myocardial necrosis in exercise-trained rats.

Plasma corticosterone concentrations and in vitro adrenal secretion of corticosterone was determined in exercise-trained rats. Virgin, male rats, 100 days of age, were trained for an 11-wk period by treadmill running. Following the training program, rats were subjected to two subcutaneous injections of l-isoproterenol 24 h apart and killed 24 h after the second injection. All exercise-trained rats survived isoproterenol treatment, while 44% of the control rats died. Plasma corticosterone concentrations were elevated only in exercise-trained rats treated with isoproterenol. Control rats treated with isoproterenol had plasma corticosterone concentrations similar to that in control and exercise-treated rats given placebo injections. Exercise training reduced adrenocortical responsiveness to ACTH in vitro, but isoproterenol treatment increased in vitro responsiveness to ACTH in exercise-trained and control rats. Total unstimulated corticosterone secretion rates in vitro were similar. The reason for better rat survival in exercise-trained rats is unknown; however, improved energy metabolism, depressed aldosterone secretion, or both are suggested as reasons for the better survival of exercise-trained rats.

Adrenal Cortex↗
PubMed1978

A histologic study of age changes in the adult human periodontal joint (ligament).

This study evaluated the histological age changes in 80 periodontal joints from 24 human cadavers ranging in age from 20 to 90 years. The limitations of such a descriptive study were reviewed to prevent overextrapolation of the findings to whole populations. In the young speciments, the bone surface of the tooth socket was smooth and regular with the insertion of Sharpey's fibers evenly distributed in the woven bone. Interstitial lamellae were found between secondary osteons in the alveolar bone. Copious periodontal fibers passed around small vascularized interstitial spaces to insert evenly into the cementum as Sharpey's fibers. Numerous cells, probably fibroblasts, were present within and between the fiber bundles. Like the bone surface, the cemental surface was smooth and regular. Both cellular and acellular cementum were present. Cemental splits were found both intracementally and at the cemento-dentinal junction. In the older specimens, the periodontal surface of the alveolar bone was jagged and uneven with Sharpey's fibers inserting irregularly into the woven bone. Subjectively an increased amount of internal remodeling was seen in the periodontal bone. A relative decrease in both suspensory fibers and cellular content was noted in the periodontal ligaments of the older specimens. Large vascularized interstitial spaces encroached upon areas formerly occupied by periodontal fibers and bone. Fat cells also were observed replacing the suspensory fibers. The cementum showed an irregular surface into which Sharpey's fibers were unevenly inserted. Both cellular and acellular cementum were present, and cemental splits were seen with the same frequency as in the young specimens. There was a tendency for greater cemental apposition, particularly in the apical region of the tooth. In many respects the aging periodontal joint showed atrophic and degenerative changes similar to those in cranio-facial sutures. However, these changes did not include either bony ankylosis or osteoporosis related to increasing age. In summary, the periodontal joints of the younger specimens were well organized while those of the older specimens showed a more irregular structure and a decrease in fiber and cellular content. Intermediate changes were seen in the intermediate age groups.

Adult↗
PubMed1977

Adrenocortical function in aging exercise-trained rats.

Plasma corticosterone concentrations and in vitro adrenal secretion of corticosterone were determined in exercise-trained rats. Rats, 100, 200, and 300 days of age, were trained for a 10-wk period by treadmill running. Following the training program, rats were subjected to an acute bout of swimming. Acute swimming elevated plasma corticosterone concentrations in all age groups. At 170 days of age, the plasma corticosterone concentration following swimming was higher in exercise-trained rats than in controls. The opposite was true of acutely swum rats at 270 and 370 days of age. Acute swimming elevated the in vitro adrenal gland response to adrenocorticotropic hormone stimulation in control rats at all ages and in trained rats at 170 days of age. The in vivo relationship of epinephrine and the pituitary adrenal system is suggested as a mechanism which could have caused this response. The relationship of secretion rates to plasma corticosterone concentrations indicated that extra-adrenal mechanisms, such as decreased turnover, were also responsible for the elevated plasma corticosterone levels observed in response to acute swimming.

Adrenal Cortex↗