A critique of the contributions of immunoperoxidase cytochemistry to our understanding of pituitary cell function, as illustrated by our current studies of gonadotropes, corticotropes and endogenous pituitary GnRH and TRH

Summary The peroxidase-antiperoxidase technique has been used to study sites of pituitary hormone storage and binding. Some recent findings from our laboratory show that the technique can make intriguing contributions to our understanding of pituitary cell function. In serial ulbra-thin sections, one can identify two or three hormones in a given cell. During pre-pubertal development, gonadotropes may contain adrenocorticotropin immunoreactivity. Brain releasing hormones may be stored or sequestered in granules of cells they stimulate. This report includes a discussion andcritique of our recent findings and interpretations which must be considered before one draws any conclusions about their biological significance.     

Bioactive compounds produced by cyanobacteria

Cyanobacteria produce a large number of compounds with varying bioactivities. Prominent among these are toxins: hepatotoxins such as microcystins and nodularins and neurotoxins such as anatoxins and saxitoxins. Cytotoxicity to tumor cells has been demonstrated for other cyanobacterial products, including 9-deazaadenosine, dolastatin 13 and analogs. A number of compounds in cyanobacteria are inhibitors of proteases — micropeptins, cyanopeptolins, oscillapeptin, microviridin, aeruginosins- and other enzymes, while still other compounds have no recognized biological activities. In general cyclic peptides and depsipeptides are the most common structural types, but a wide variety of other types are also found: linear peptides, guanidines, phosphonates, purines and macrolides. The close similarity or identity in structures between cyanobacterial products and compounds isolated from sponges, tunicates and other marine invertebrates suggests the latter compounds may be derived from dietary or symbiotic blue-green algae.     

Local Interactions Lead to Pathogen-Driven Change to Host Population Dynamics

Individuals tend to interact more strongly with nearby individuals or within particular social groups. Recent theoretical advances have demonstrated that these within-population relationships can have fundamental implications for ecological and evolutionary dynamics [1], [2], [3], [4], [5], [6], [7], [8], [9], [10] and [11]. In particular, contact networks are crucial to the spread [12], [13] and [14] and evolution [8], [9], [11] and [15] of disease. However, the theory remains largely untested experimentally [16]. Here, we manipulate habitat viscosity and thereby the frequency of local interactions in an insect-pathogen model system in which the virus had previously been shown to have little effect on host population dynamics [16] and [17]. At high viscosity, the pathogen caused the collapse of dominant and otherwise stable host generation cycles. Modeling shows that this collapse can be explained by an increase in the frequency of intracohort interactions relative to intercohort interactions, leading to more disease transmission. Our work emphasizes that spatial structure can subtly mediate intraspecific competition and the effects of natural enemies. A decrease in dispersal in a population may actually (sometimes rather counterintuitively) intensify the effects of parasites. Broadly, because anthropological and environmental change often cause changes in population mixing, our work highlights the potential for dramatic changes in the effects of parasites on host populations.