Machteld E. Carstens

Maternal separation in rats leads to anxiety-like behavior and a blunted ACTH response and altered neurotransmitter levels in response to a subsequent stressor.

Adverse early life experiences can have a negative impact on behavior later in life. We subjected rat pups to maternal separation and determined the effects thereof on adult behavior. We removed rat pups from their mothers for 3 h daily from postnatal days 2 to 14. While controls were reared normally on day 60, the behaviors of the rats were tested using the elevated plus-maze. Some rats were subsequently subjected to restraint stress for a 10-min period. Trunk blood was collected for basal, as well as 15- and 60-min postrestraint stress ACTH determinations. Neurotransmitter levels (noradrenaline (NA), serotonin (5HT), and their metabolites, MHPG and 5HIAA, respectively) were also determined at basal, immediately and 15-min post-restraint stress in the hypothalamus, hippocampus, and frontal cortex in another group of animals. The amount of entries into the arms of the elevated plus-maze was significantly reduced in the separated animals, indicating decreased locomotion. They spent significantly more time in the closed arms of the maze. A significant increase in defecation frequency was noted. These observations suggested anxious behavior. Basal ACTH levels were significantly higher in separated animals. At 15-min post-restraint stress, the ACTH levels were significantly lower than controls, indicating a blunted stress response. A decrease in noradrenaline was noted first in limbic regions and an increase in 5HIAA levels was found in the frontal cortex and hippocampus. We conclude that maternal separation induced abnormal behaviors and stress responses that were associated with altered neurotransmitter levels.

Increased frequency of the transferrin C2 subtype in Alzheimer's disease

Several genetic variants of transferrin can be separated by polyacrylamide gel isoelectric focusing. Studies by other workers have revealed that the genetic type Tf C2 has an increased frequency in certain malfunctions which are associated with the formation of free radicals, suggesting that the iron binding of Tf C2 promotes the formation of hydroxyl radicals. In our study population of 20 patients with Alzheimers disease, 13 had the C2 genetic subtype. Since the frequency of C2 in the South African population is 0.136 (14%), this represents a significant increase (p < 0.005) in the appearance of this genetic subtype.

Evidence that lithium induces a glutamatergic: Nitric oxide-mediated response in rat brain

Studies have indicated the involvement of a glutamatergic mechanism in lithium (Li+) action. Glutamatergic agonists, such as kainic acid, are known to promote the synthesis of nitric oxide (NO) and to increase cGMP, while Li+ has displayed a similar, yet unexplained, ability to increase cGMP. NO synthesis is regarded as the principal prodromal event leading to the activation of the guanyl cyclase-cGMP transduction mechanism. In the present study, the involvement of the NO:cGMP pathway in the action of Li+ was examined, while the possibility of a glutamatergic mechanism in this response was also investigated. Parameters examined included cortical accumulation of cGMP and the stable oxidative metabolites of NO, viz. NO2− and NO3−, collectively expressed as NO2−. A significant positive correlation was observed in the in vivo cGMP and NO2− data throughout all the groups. Chronic treatment of rats with LiCl (0.3% m/m) engendered a significant increase in cGMP levels which was inhibited by the NO-synthase (NOS) inhibitor, N-nitro-l-arginine methyl ester (L-NAME). Acute administration of kainic acid resulted in an increased accumulation of NO2−, also prevented by concomitant L-NAME administration. In addition, a synergistic stimulatory response on cortical NO2− was observed in the combination of LiCl and kainic acid. Collectively, these data implicate an involvement of a glutamatergic-mediated NO:cGMP transduction mechanism in the action of Li+.

Beta-adrenoceptors on lymphocytes of patients with major depressive disorder

3H-Dihydroalprenolol binding to lymphocyte membranes of patients with primary, unipolar major depressive disorder was compared to that of a normal, healthy control population. No significant difference could be demonstrated between the Kd values of the two different groups, but the Bmax values of the depressed patients were significantly lower than those of the controls. Positive correlations were observed between the lymphocyte beta-adrenoceptor Bmax values of the patients and their Beck self-evaluation and Hamilton depression ratings. We propose that decreased lymphocyte beta-adrenoceptor Bmax values may be used as a biological marker for major depressive disorder.

Alpha2-adrenoceptor levels on platelets of patients with major depressive disorders

Abstract 3 H- p -Aminoclonidine binding to platelets of patients with primary, unipolar major depressive disorder was compared to that of a normal healthy control population. The variances of platelet α 2 -adrenoceptor K d and B max values in patients were significantly greater than in the control group. No significant difference could be demonstrated between the K d values of the two different groups, but the B max value of the depressed group was significantly lower than that of controls. We propose that an abnormal platelet α 2 -adrenoceptor density may be used as a biological marker for major depressive disorder.

Noradrenergic function and hypothalamic-pituitary-adrenal axis activity in primary unipolar major depressive disorder

Plasma levels of cortisol, norepinephrine (NE), and 3-methoxy-4-hydroxyphenylglycol (MHPG) were found to be significantly higher in 16 drug-free patients with primary, unipolar major depressive disorder than in 20 controls. Plasma free MHPG and basal cortisol levels showed a significant positive correlation in the controls, but not in the patients. There were, however, significant positive correlations between cortisol and NE, as well as between NE and free MHPG levels in the patients. No correlations were observed between patient plasma NE levels and platelet alpha 2-adrenoceptor or lymphocyte beta-adrenoceptor Kd or Bmax values. These peripheral measures of noradrenergic function are proposed as useful markers for patients with primary, unipolar major depressive disorder with melancholia.

Imipramine binding sites on platelets of patients with major depressive disorder.

3H-Imipramine binding to platelets of patients with primary, unipolar major depressive disorder was investigated and compared to that of a normal, healthy control population. No significant differences could be demonstrated between either the Kd or the Bmax values of the two groups. A negative correlation was observed between imipramine Bmax values and the Hamilton anxiety ratings of the depressed patients. Patients who displayed psychomotor retardation tended to have lower platelet imipramine Bmax values than patients with psychomotor agitation. It is suggested that platelet imipramine Bmax values may be a biological marker for subtypes of depression.

Biological markers in juvenile depression

3H-p-Aminoclonidine binding to platelets of children and adolescents with major depressive disorder was compared to that of a healthy control population. Significantly higher alpha 2-adrenoceptor Kd and Bmax values were observed in the patient population. 3H-Dihydroalprenolol binding to lymphocyte membranes of the same patient population showed significantly higher beta-adrenoceptor Bmax values than controls. Control females had significantly higher beta-adrenoceptor Kd values than control males, and the female patients had significantly lower beta-adrenoceptor Kd values than control females. 3H-Imipramine binding to platelets of these patients showed significantly higher imipramine Kd values in patients with a suicide attempt, whereas the imipramine Bmax values were significantly increased in patients with major depressive disorder with or without a suicide attempt. We propose that increased platelet alpha 2-adrenoceptor Kd and Bmax values, together with increased platelet imipramine Kd values, may serve as possible biological markers for children and adolescents with major depressive disorder and a tendency toward suicide. Elevated platelet imipramine and lymphocyte beta-adrenoceptor Bmax values may be biological markers for juvenile depression, and decreased beta-adrenoceptor Kd values may be a biological marker for depression in young females.

Lithium modulation of cortical cyclic nucleotides: evidence for the Yin-Yang hypothesis

Rats were subjected to chronic treatment with lithium chloride (0.2-0.3%) over a period of 3 weeks. The activity of cortical phosphodiesterase (EC 3.1.4.17) was determined simultaneously with cyclic AMP and cyclic GMP content and compared to control, untreated animals. Lithium, at therapeutic serum concentrations was found to suppress cyclic AMP levels with a concomitant increase in cyclic AMP-phosphodiesterase activity. A simultaneous two-fold increase in cyclic GMP was observed. Through the alteration of cortical cholinergic activity with physostigmine and the use of cyclic GMP as a cholinergic marker, we were able to demonstrate a novel cholinotropic property of lithium to stimulate synthesis of cyclic GMP. This effect appears to be linked, in a Yin-Yang mechanism, to the observed suppression of cyclic AMP induced by lithium through activation of cyclic AMP-phosphodiesterase.

Central effects of the preservative, methylparaben: In vivo activation of cAMP-specific phosphodiesterase and reduction of cortical cAMP

The phenolic preservative, methylparaben (MPB), has in the past been demonstrated to harbour definite pharmacological effects. In an attempt to examine the possible central effects of MPB, notably on cyclic nucleotides and cyclic nucleotide phosphodiesterase (PDE; EC 3.1.4.17), rats were orally treated with the drug (0.4% in rat food) for 3 weeks with cortex extracts being used for the various determinations. Three isozymes were identified by DEAE-cellulose anion exchange chromatography, namely the calmodulin/calcium-stimulated form or PDE I (peak I), the cGMP-stimulated form or PDE II (peak II), and an independent form not affected by either calmodulin or cGMP also known as PDE IV (peak III). The presence of MPB induced a significant decrease in cortical cAMP, as well as strongly stimulating the activity of PDE IV (peak III). In addition, a small, yet significant, increase in cGMP levels was observed. Since no increase in cGMP hydrolysis was observed, we conclude that chronic ingestion of MPB induces a preference for cAMP hydrolysis, which was confirmed by the increase in PDE IV (peak III) activity. PDE IV is a membrane-bound, low Km PDE exhibiting high selectivity for cAMP hydrolysis. While there was an increase in cGMP, we failed to observe an increase in the activity of the cGMP-stimulated PDE (PDE II). These data are discussed with reference to the possible membrane effects of MPB allowing it to alter both the kinetic properties of PDE IV with the resultant effects on cAMP, as well as a means whereby it may activate guanyl cyclase and increase cGMP.