Normal levels of tryptophan hydroxylase immunoreactivity in the dorsal raphe of depressed suicide victims

A variety of evidence suggests that serotonin neurotransmission is altered in the brain of suicide victims and depressed patients. While numerous post-mortem studies have investigated serotonin transporters and receptors, few studies have examined the biosynthetic integrity of the rate-limiting enzyme, tryptophan hydroxylase (TPH), in post-mortem specimens of depressed suicide subjects. Therefore, the aim of the present study was to test the hypothesis that the levels of TPH immunoreactivity (IR) are altered in specific subnuclei of the dorsal raphe (DR) in depressed suicide victims. Suicide victims with a confirmed diagnosis of major depression were matched with non-psychiatric controls based on age, gender and post-mortem interval. Frozen tissue sections containing the DR were selected from two anatomical levels and processed for TPH radioimmunocytochemistry. The optical density corresponding to the regional levels of TPH-IR was quantified in specific subnuclei of the DR from the film autoradiographic images. No significant differences in the levels of TPH-IR were found in any DR subnuclei between depressed suicide victims and control subjects. The lack of change in TPH-IR levels does not necessarily imply that serotonin synthesis or neurotransmission is not altered in the brain of depressed subjects. Many factors influence and regulate serotonin synthesis, and it is conceivable that alterations exist at other levels of regulation of serotonin biosynthesis in depression. Our findings indicate that TPH biosynthesis, at least at the protein level, is not significantly altered in the DR of depressed suicide victims.     

Modulation of epidermal growth factor-dependent protein phosphorylation in cell membrane preparations by receptor down regulation

We have reported previously [6] that epidermal growth factor (EGF)-induced down regulation of EGF receptors in normal rat kidney (NRK) cells results in a selective decrease in the in vitro EGF-dependent ³²P-phosphorylation of two membrane phosphoproteins of Mr I70K and Mr I50K. In this report, we further characterized the modulation of ³²P-phosphorylation of the 170K- and 150K-dalton proteins by down regulation with EGF in NRK cells. While EGF binding to its receptors was a necessary condition to induce loss of EGF-dependent phosphorylation of the 170K- and 150K-dalton proteins, it was not sufficient. Thus, reduction in the temperature of the incubation of cells with EGF from 37°C to 4°C abolished the loss of EGF-dependent phosphorylation of the 170K- and 150K-dalton membrane proteins. When EGF was removed from the medium the EGF-dependent phosphorylation of the 170K- and l50K-dalton proteins was quickly replenished; by 3 hr one-half of the “down regulated” phosphorylation was restored. All EGF-dependent phosphorylating capacity of the 170K- and l50K-dalton protein bands returned by 6 hr after removal of the growth factor. The loss of EGF-dependent phosphorylation of the 170K- and I50K-dalton proteins occurred at physiological EGF concentrations (0.25–25 ng/ml) that span the concentration range which is mitogenic for NRK cells. Exposure of confluent nondividing NRK cells to 1 ng/ml EGF, followed by incubation for 5 hr at 37°C. led to a 50% reduction in the EGF-dependent phosphorylation of the 170K- and 150K-dalton proteins. Maximal reduction (～95%) in the EGF-dependent phosphorylation of the 170K- and 150K-dalton proteins was noted with 10 ng/ml EGF for 5 hr. The EGF-induced loss of EGF-dependent phosphorylation was specific: several other growth factors did not produce phosphorylation loss of the 170K-     

The association of α-actinin with the plasma membrane

The role of α-actinin in the attachment of actin to plasma membranes has been investigated. Specific antibody staining of SDS gels has indicated that α-actinin is a major component in isolated plasma membranes prepared from three different cell types by two different procedures. Using specific extraction conditions, most of the α-actinin can be selectively extracted from the membranes with relatively little parallel release of actin. This selective dissociation of α-actinin from the plasma membrane leads us to conclude that α-actinin is present in these membrane preparations, because it is bound to actin, and that α-actinin does not form a direct link between actin and the membrane.