Source Of Chemical Signals Research Articles

Seasonal ultrastructural changes in apocrine gland cells in back skin of male brown bears (Ursus arctos).

Oily secretions from the back skin are involved in the marking behavior of male brown bears (Ursus arctos), and apocrine glands in back skin are activated during the breeding season. Here, we investigated seasonal changes in the intracellular organelles of apocrine gland cells in the back skin of male brown bears using transmission electron microscopy (TEM) and osmium-maceration scanning electron microscopy (OM-SEM). The morphological features of mitochondria and intracellular granules, and secretory mechanisms obviously differed between breeding and non-breeding seasons. The TEM findings showed that contents of low-density granules were released into the glandular lumen by frequent exocytosis, and sausage-shaped mitochondria were located in the perinuclear region during the non-breeding season. In contrast, high-density granules appeared in the apical region and in projections during the breeding season, and swollen mitochondria and lysosome-like organelles separating into high-density granules were located in the perinuclear region. The OM-SEM findings revealed swollen mitochondria with only a few partially developed cristae, and small mitochondria with cristae shaped like those in swollen mitochondria in the apical regions during the breeding season. These findings indicated that the small mitochondria corresponded to the high-density granules identified by TEM. These findings suggested that mitochondria in apocrine gland cells swell, degenerate, fracture into small pieces, and are finally released by apocrine secretions during the breeding season. Small mitochondria released in this secretory manner might function as the source of chemical signals in the oily secretions of brown bears during the breeding season.

Evaluation of sexual dimorphism of histochemical activity of phosphatases of the plantar glands of Norway rats (Rattus norvegicus)

The activity of acid phosphatase, alkaline phosphatase and adenosine triphosphatase in the eccrine and sebaceous glands of the skin of the soles of the paws of male and female Norway rats was studied by histochemiсal methods. Using the methods of qualimetric analysis, we presented a digitalized form of the enzyme activity, which made it possible to calculate sexual dimorphism indices, reflecting quantitative differences in the enzymatic activity of the skin glands in males and females of Norway rats. For acid phosphatase activity, the sexual dimorphism index was equal to 0.50 in the eccrine glands and equal to 0.33 in the sebaceous glands. For alkaline phosphatase activity, values of sexual dimorphism indices were equal to –0.25 and 0.33 correspondingly, and for adenosine triphosphatase values of sexual dimorphism indices were equal to –0.33 and 0.50. Digital analogues of the histoenzymatic activity of the skin glands were presented as coordinates in three-dimensional space. Using the methods of analytical geometry, we calculated the values of intersexual distances (1.73 for eccrine glands and 1.73 for sebaceous glands), reflecting the cumulative differences in the activity of three types of phosphatases, which can be considered as an integral indicator of sexual dimorphism. Histochemical activity entropy is significant in the eccrine glands. Male entropy value (0.842 bit) was less than female entropy value (0.915 bit), because total actual activity of the males’ phosphatases was greater (220% of 300%) than total actual activity of the females’ phosphatases (200% of 300%). High entropy level of phosphatase activity was typical for male sebaceous glands (0.998 bit), where the general level of enzymatic activity was significantly reduced (160% of 300%). Because of the highest total actual phosphatase activity of female sebaceous glands (220% of 300%), entropy value was the lowest (0.842 bit). The obtained results show not only sexual dimorphism by histochemical parameters but show different communicational levels of male and female Norway rats, taking into account the important role of the plantar glands as sources of chemical signals determining the character of marking behaviour.

Symbiotic skin bacteria as a source for sex-specific scents in frogs

Amphibians are known to possess a wide variety of compounds stored in their skin glands. While significant progress has been made in understanding the chemical diversity and biological relevance of alkaloids, amines, steroids, and peptides, most aspects of the odorous secretions are completely unknown. In this study, we examined sexual variations in the volatile profile from the skin of the tree frog Boana prasina and combined culture and culture-independent methods to investigate if microorganisms might be a source of these compounds. We found that sesquiterpenes, thioethers, and methoxypyrazines are major contributors to the observed sex differences. We also observed that each sex has a distinct profile of methoxypyrazines, and that the chemical origin of these compounds can be traced to a Pseudomonas sp. strain isolated from the frog's skin. This symbiotic bacterium was present in almost all individuals examined from different sites and was maintained in captive conditions, supporting its significance as the source of methoxypyrazines in these frogs. Our results highlight the potential relevance of bacteria as a source of chemical signals in amphibians and contribute to increasing our understanding of the role that symbiotic associations have in animals.

The MrCYP52 Cytochrome P450 Monoxygenase Gene of Metarhizium robertsii Is Important for Utilizing Insect Epicuticular Hydrocarbons

Fungal pathogens of plants and insects infect their hosts by direct penetration of the cuticle. Plant and insect cuticles are covered by a hydrocarbon-rich waxy outer layer that represents the first barrier against infection. However, the fungal genes that underlie insect waxy layer degradation have received little attention. Here we characterize the single cytochrome P450 monoxygenase family 52 (MrCYP52) gene of the insect pathogen Metarhizium robertsii, and demonstrate that it encodes an enzyme required for efficient utilization of host hydrocarbons. Expressing a green florescent protein gene under control of the MrCYP52 promoter confirmed that MrCYP52 is up regulated on insect cuticle as well as by artificial media containing decane (C10), extracted cuticle hydrocarbons, and to a lesser extent long chain alkanes. Disrupting MrCYP52 resulted in reduced growth on epicuticular hydrocarbons and delayed developmental processes on insect cuticle, including germination and production of appressoria (infection structures). Extraction of alkanes from cuticle prevented induction of MrCYP52 and reduced growth. Insect bioassays against caterpillars (Galleria mellonella) confirmed that disruption of MrCYP52 significantly reduces virulence. However, MrCYP52 was dispensable for normal germination and appressorial formation in vitro when the fungus was supplied with nitrogenous nutrients. We conclude therefore that MrCYP52 mediates degradation of epicuticular hydrocarbons and these are an important nutrient source, but not a source of chemical signals that trigger infection processes.

Sources of Chemical Signals which Enhance Multiparasitism Preference by a Cleptoparasitoid

The cleptoparasitoid Eupelmus vuilleti recognizes and prefers laying on hosts parasitized by Dinarmus basalis to unparasitized hosts. This recognition is based on the perception of a chemical substance deposited on the surface of the seed. Dufour's gland secretion and cuticular hydrocarbons of D. basalis are attractive and may mediate the host discrimination. This activity is linked to a mixture of linear and methyl alkanes whose source is apparently the Dufour's gland.

Developing Brain as a Giant Multipotent Endocrine Gland

The brain of adult mammals is composed of neuronal ensembles, which are intergrated in the course of synaptic transmission by chemical signals (CSs). Among them, there are classical neurotransmitters, neuropeptides, etc. In addition, neurosecretory neurons secrete the same CSs to the blood vessels in the brain areas lacking the blood-brain barrier (BBB), though their spectrum is greatly limited. According to the conventional conception, the brain lacks the neuroendocrine function over the ontogenetic period lasting from the genesis of neuronal units to the development of neuron-to-neuron synaptic connections (synaptogenesis) and BBB. Nevertheless, some recent data contradict this concept making reasonable its that CSs and receptors are expressed in the neurons just after their origin and long before the establishment of BBB. During this period, CSs are considered diffusive inductors of the brain development, which provide the paracrine regulation of the neuronal differentiation. Although this regulation is beyond doubt, some data do not agree with the concept. For example, the receptors of CSs are transiently expressed in many areas of the developing brain, though there are no neuronal sources of the respective CSs in close vicinity. This might be explained by the CS transfer from the synthesizing neurons toward the target neurons via the circulation, i.e., due to the neuroendocrine autoregulation. According to our hypothesis, the neurons serve as endocrine cells, and the brain can be considered a giant multipotent endocrine gland providing the neuroendocrine regulation of the development of the brain itself and peripheral target organs over the period preceding synaptogenesis and the establishment of BBB. The term “giant multipotent” means that the spectrum of the brain-derived circulating CSs and their occupancy at the periphery in the developing organism should greatly exceed those in adulthood. Gonadotropin-releasing hormone (GnRH)-producing and dopaminergic neurons, the most representative populations of peptidergic and monoaminergic neurons were used for testing our hypothesis. According to the age dynamics of GnRH and dopamine (DA) in general circulation in rats, the concentrations of these agents were sufficiently great for the regulation of the target cells before the establishment of BBB, but they dropped to an undetectable level after the BBB appearance. Furthermore, the microsurgical lesion of most GnRH and DA-ergic neurons in the developing brain resulted in a dramatic drop of both CSs in the blood, confirming that the brain is the principal but not the only source of circulating CSs. Potential targets for the brain-derived circulating CSs, including GnRH and DA, should be neurons and peripheral cells. For example, the gonads begin to express the GnRH receptors simultaneously with the onset of GnRH synthesis in the brain in fetal rats. The DA-sensitive cells in the developing organism are, e.g., represented by neurons of the suprachiasmatic nucleus in the brain and epithelial cells of the kidney. Both cell types transiently express D2 receptors before the establishment of BBB and the related fall of circulating DA. Thus, differentiating neurons and the developing brain play roles of secretory cells and of the endocrine gland, respectively, before the development of interneuronal synaptic connections and maturation of BBB.

NEPHROPORE ROSETTE GLANDS OF THE LOBSTER HOMARUS AMERICANUS: POSSIBLE SOURCES OF URINE PHEROMONES

ABSTRACT This study examined the nephropore area of sexually mature lobsters for the presence of structures capable of producing chemical signals in conjunction with urine release. Urine signals are used for chemical communication in the lobster Homarus americanus. Male urine plays a role in the determination of dominance and female choice of dominant males, while female urine reduces the incidence of male aggressive behavior and induces male mating behavior. Masses of rosette glands were found, lateral and medial to the ureter of all animals examined. Staining properties and gland morphology suggest that nephropore rosettes are active in males and females, in all molt stages and at all times of the year. Rosette glands stained positively for protein and mucopolysaccharides. Gland complexes did not show histochemical evidence of phenoloxidase, a product of some crustacean rosette glands. Nephropore rosette glands were packaged into clusters, which in turn were organized into lateral and medial gland complexes lying alongside each ureter. Complexes were joined by a common duct terminating at the bladder, while rosettes in some anterior clusters were served by individual ducts passing through the nephropore sphincter and terminating outside the animal adjacent to the site of urine release. These two duct systems could allow gland complexes to release their products into the environment with or without concomitant urine release, and as such these glands are good candidates for sources of chemical signals.