[
J Med Entomol,
1989]
Intracellular melanization responses to developing larvae of Brugia species (B. malayi (Buckley), B. pahangi (Buckley and Edeson), and B. patei (Buckley, Nelson, and Heisch] in the thoracic muscle fibers of eight strains of Anopheles quadrimaculatus Say were first observed 48 to 72 h after an infective blood meal. Three to 4 d later, large numbers of melanized first-stage larvae were found within the thoracic muscle fibers. These intracellular responses were in addition to the extracellular responses to microfilariae and microfilarial sheaths of B. pahangi in the abdominal hemocoel of An. quadrimaculatus described in literature. Simultaneously, normal development of larvae of the three Brugia species also was observed in all eight strains of An. quadrimaculatus. Comparisons of melanized first-stage larvae and normally developing larvae of the three Brugia species in the thoracic muscle fibers of the eight strains of An. quadrimaculatus showed that there were distinct variations in numbers of melanized and developing larvae and percentage of females with melanized and developing larvae in different strains. Numbers of melanized first-stage larvae reflected the extent of refractoriness of An. quadrimaculatus strains. Fully melanized larvae showed no abnormalities in parasite organelles, indicating that refractoriness is due to an enhanced ability of the host to recognize the living parasite. Further comparison among the strains suggested that the mutants, Yellow Larvae and Vero Beach Colony were significantly more susceptible, and Red Stripe was the most refractory to all three Brugia species. Thus, the gene(s) controlling susceptibility and refractoriness to all three Brugia species probably occurs on the same autosomal chromosome as the mutations in these strains. The significance of intracellular melanization of filarial larvae is discussed with reference to the melanization responses to different parasites in other mosquitoes.
[
J Parasitol,
1994]
Ultrastructural aspects of extracellular humoral encapsulation of microfilariae of Brugia malayi in the hemocoel of Anopheles quadrimaculatus were compared with those of intracellular encapsulation of first-stage larvae (L1) of the same parasite species, in the thoracic muscle cells of the same species of mosquito. The results showed that extracellular humoral encapsulation of microfilarial sheaths, and sheathed and exsheathed microfilariae, in the hemocoel of mosquitoes occurs around the parasite within the first 6 hr postingestion, apparently without initial participation of hemocytes. Hemocytes and their remnants were observed near the parasite during the first 6 hr postingestion. Within the next 24 hr, hemocytes attach to the initial humoral capsule. By contrast, intracellular encapsulation of L1S is initiated by the accumulation of a dense cytoplasmic layer derived from the infected thoracic muscle cell. Melanin deposits accumulate in this layer adjacent to the parasite cuticle, again without visible participation of hemocytes.
[
MicroPubl Biol,
2019]
We have identified a relationship between egg-laying and defecation behaviors in C. elegans. As shown in Figure 1A, the egg-laying and defecation motor circuits show synaptic connectivity. The HSN command neurons and VC motor neurons make and receive synapses from the excitatory GABAergic AVL and DVB motoneurons that regulate defecation (White, J.G. et al. 1986). Serotonin and Gao signaling, which regulate egg laying behavior, can also signal to inhibit defecation (Sgalat et al. 1995; Waggoner et al. 1998; Tanis et al. 2008). Because evidence shows that both the egg-laying active state and the defecation motor program (DMP) are both linked to changes in forward and reverse locomotion (Hardaker et al. 2001; Nagy et al. 2015), we reasoned there may be a similar relationship between expulsive behaviors that drive either egg laying or defecation. Our experiments document an association between HSN Ca2+ activity and a reduced frequency of defecation. Animals lacking HSNs have a reduced defecation frequency (Garcia and Collins 2019). We hypothesize that egg-laying and defecation behaviors are coordinated because they use the same internal hydrostatic pressure to drive expulsion of uterine or intestinal contents, respectively. Worms continuously internalize bacterial food via pumping of a muscular pharynx (Figure 1B; Avery and Horvitz, 1989). Despite this continuous intake of mass, worms maintain a relatively uniform size, shape, and an internal hydrostatic pressure of ~140 kPa (Knight et al. 2002; Gilpin et al. 2015; Fechner et al. 2018), releasing waste about once per minute and ~3-5 fertilized eggs (~20 pL each) about every 20 minutes (Liu and Thomas 1994; Waggoner et al. 1998). During defecation, sequential activity of the anterior and posterior body wall muscles contracts the animal, increasing internal pressure that drives expulsion of liquid waste through the anus (Thomas 1990; Reiner et al. 1995). Mutations that eliminate the defecation motor program still expel gut contents at much reduced frequency. This is thought to be caused by a gradual accumulation of internal pressure by ongoing pharyngeal pumping of food that eventually ejects waste through the anus independent of circuit activity or muscle contractility (Avery and Thomas 1997). Our recent data suggest egg-laying behavior is regulated by a stretch-dependent homeostat. Feedback from embryo accumulation in the uterus activates the postsynaptic muscles which drives burst-firing in the presynaptic HSNs as visualized by Ca2+ imaging in behaving animals (Ravi et al. 2018a; b). Animals lacking HSNs still enter active states with strong vulval muscle contractions driving release of embryos which additionally supports this model (Collins et al. 2016). Electrical silencing of the postsynaptic muscles renders animals egg-laying defective with embryos often hatching inside the mother (Reiner et al. 1995). Unlike gut contents which are more fluid, fertilized embryos are more mechanically rigid, requiring full opening of the vulva for efficient release (Li et al. 2013). We propose that changes in the internal hydrostatic pressure that accompany food consumption and embryo production activate mechanoreceptors that facilitate the onset of defecation and egg-laying behaviors. As animals age, they continue to eat and grow larger, but their defecation frequency decreases (Bolanowski et al. 1981). Egg laying frequency also increases with age for as long as animals have sufficient sperm for oocyte fertilization (McCarter et al. 1999). This increase in egg laying in older adults reflects both an increase in the number of eggs expelled with each vulval opening and longer active behavior states.​ We propose that the timing of expulsive behaviors including defecation and egg laying is regulated by sensory mechanisms that detect changes in internal pressure and/or stretch to maintain homeostasis. Feedback of successful egg laying might also signal to the germ line to ensure the continued production of oocytes for fertilization.