Calcium and Photoentrainment in Chick Pineal Cells Revisited: Effects of Caffeine, Thapsigargin, EGTA, and Light on the Melatonin Rhythm

Abstract: Chick pineal cells in dispersed cell culture display a persistent, photosensitive, circadian rhythm of melatonin production and release. Light pulses have at least two distinguishable effects on these cells, i.e., acute suppression of melatonin output and phase shifts (entrainment) of the underlying circadian pacemaker. Previous results linked calcium influx through voltage-sensitive calcium channels in the plasma membrane to acute regulation of melatonin synthesis but denied a role for such influx in entrainment. Those experiments did not, however, address the role of intracellular calcium metabolism. Here we describe the effects of pulses of caffeine, thapsigargin, and EGTA on the melatonin rhythm, and their interactions with the effects of light pulses. Caffeine had two distinguishable effects on these cells, acute enhancement of melatonin output (attributable to phosphodiesterase inhibition) and phase shifts of the circadian pacemaker with a light-like pattern (attributable to effects on intracellular calcium). Phase shifts induced by light and caffeine were not additive. Thapsigargin (which specifically blocks the pump that replenishes intracellular calcium stores, thereby increasing cytoplasmic calcium and depleting intracellular stores) had no phase-shifting effects by itself but reduced the size of the phase advances induced by caffeine or light. Low calcium solution acutely suppressed melatonin output without inducing phase shifts or affecting those induced by caffeine or light. However, addition of EGTA (which specifically chelates calcium, thereby lowering cytoplasmic calcium and depleting intracellular stores) did reduce the size of phase advances induced by caffeine or light, in normal medium or in low calcium solution, without inducing a phase shift by itself at that phase. Taken together, these results point toward a role for intracellular calcium fluxes in entrainment of the circadian pacemaker.     

Multiple occurrence of spontaneous AKR/J lymphomas with T and B cell characteristics.

Three Thy 1.1-positive and surface IgM-positive (Thy 1+, SIg+) AKR/J lymphoma lines are described. These doubly marked tumors arose spontaneously in the peripheral lymphoid organs of 14- to 16-month-old AKR/J mice that either had spontaneous thymus atrophy or had been thymectomized at 1 month of age. All lines bore surface Thy 1.1, Ly,Ig(micron-chain) and Fc receptor (FcR), detectable by immunofluorescence. Immune response region (Iak) antigen was present on the two lines tested. Persistence of Thy 1.1 antigen and SIg after long-term tissue culture provided evidence that these markers were not passively acquired. One of these tumor lines, AkTB-1 always grows in lymph nodes as Thy 1.1-positive,SIg-negative tumors cells, whereas tumor cells growing in the spleen are initially Thy 1.1 positive, SIg negative, but they rapidly acquire SIg, FcR, and 1a between 18 and 21 days of passage.     

PARTICULATE AND SOLUBILIZED FUCOSYL TRANSFERASES FROM MOUSE BRAIN

The transfer of [¹⁴C]fucose from GDP-[U-¹⁴C]fucose to endogenous and exogenous acceptors by particulate and solubilized preparations from mouse brain is described. Suspensions of brain microsomes incorporated [¹⁴C]fucose into a heterogenous group of glycoprotein products, which have a distribution on gel electrophoresis similar to those synthesized in vivo. Fucosyl transferase, extracted from brain microsomes by Triton X-100, transferred [¹⁴C]fucose from GDP-[U-¹⁴C]fucose to terminal galactose residues exposed by mild acid hydrolysis of porcine plasma glycoprotein. Comparison of the specific activities of the solubilized fucosyl transferase from a number of organs showed that, in the presence of the exogenous acceptor which was used, the transferase of brain was more active than the transferases from all other organs tested, with the exception of kidney. Examination of subcellular fractions of brain, with endogenous and exogenous acceptors, showed that activity was limited to fractions containing microsomal membranes, whereas synaptosomal and other fractions were virtually inactive.     

Regulation of lymphocyte trapping: the negative trap.

Suppression of 51Cr-labeled lymphocyte homing to the spleen occurs after administration of insoluble protein antigen and as a late sequela to the graft-vs-host response (GVHr). This decrease in splenic localization of labeled cells, termed "negative trapping," has elements of immunologic specificity in that tolerance induction or presensitization abrogates the negative trap. Increasing the dose of antigen accelerates the appearance of the negative trap, which is, however, evanescent, lasting from 24 to 48 hr. Synergistic and antergistic regulation of the GVHr-induced lymphocyte trap is produced by populations of 850 R-irradiated thymocytes and by F1 cortisone-resistant thymocytes. The time at which these subpopulations cause suppression or amplification of the lymphocyte trap correlates with the activity of the GVHr-producing inoculum. These findings suggest that regulation of lymphocyte traffic may provide a mechanism for control of immune responses in vivo.     

Resistance to transplantation of spontaneous AKR lymphoma cells by substrains of AKR mice. In vivo resistance and generation of an H-2 restricted CML response.

High leukemia incidence AKR/J (H-2k, Thy 1.1) and AKR/Cu (H-2k, Thy 1.2) substrains of AKR mice reject the reciprocal strains spontaneously arising lymphoma cells. In the course of rejection, splenic precursor cells are generated which, upon secondary stimulation in vitro, result in specific cytotoxic T-cells. The antigenic component of AKR cells resulting in this secondary CML response resides on both lymphoma and normal T- and B-cells, and is distinct from the Thy antigen. Primed AKR/J lymphocytes will respond to and only lyse immunogens and targets homologous at the K- and-or D-end of the MHC, while primed AKR/Cu cells require homology at the D-end of the MHC.     

Bioinformatics training in the USA

This paper provides an overview of the history and funding of bioinformatics training in the USA, and summarises some of the challenges and key features associated with bioinformatics training programmes at PhD level. The paper includes compilations of current PhD bioinformatics training programmes and sources of funding.