Costa, W. | bioRxiv Science

bioRxiv2025

Anti-malarial contact dependent blocking of transmission of Plasmodium vivax by Anopheles darlingi mosquito vector

Malaria, caused by protozoa of the genus Plasmodium and transmitted to humans through the bite of mosquitoes of the genus Anopheles, remains a public health problem. Long-Lasting Insecticide -treated bed Nets (LLINS) and Indoor Residual Spraying (IRS) represent the main vector control measures for malaria prevention. However, to address the concerns of mosquito resistance to pyrethroids, other malaria control strategies are being explored for effectively blocking malaria transmission by eliminating or reducing the parasite in the vector. This study evaluated the use of antimalarials through tarsal contact of female Anopheles darlingi infected with Plasmodium vivax via a Direct Membrane Feeding Assay (DMFA). Female An. darlingi were exposed tarsally using Petri dishes impregnated with antimalarials at 1 mmol/m2 for exposure times of 6 or 60 minutes. Among the antimalarials evaluated were Atovaquone (ATQ), Tafenoquine (TQ), Chloroquine (CQ), Mefloquine (MQ), Primaquine (PQ), and the compound Nanchangmycin (NCG). Atovaquone was the only antimalarial evaluated before and after DMFA at exposure times of 60 min and 6 min. The results demonstrate complete elimination of P. vivax in female An. darlingi exposed to ATQ by tarsal contact 60 min before infection. ATQ was also effective 6 min before or after infection, reducing infection prevalence. In addition, MQ also significantly reduced infection intensity, but there was no difference in infection prevalence. No significant differences were observed for the other antimalarials. Author SummaryMalaria caused by Plasmodium vivax is the most prevalent in the Amazon region, with Anopheles darlingi as its main vector. Mosquito resistance to pyrethroid insecticides, already described in African countries, also raises an alarm for areas endemic for vivax malaria. Given this scenario, strategies that involve blocking parasite transmission have proven effective. Our study involved the transmission-blocking potential of antimalarials administered via tarsal contact to An. darlingi infected with P. vivax. Tarsal exposure involves the direct contact of the mosquitoes tarsi with surfaces impregnated with antimalarials. We speculate that in a real-world setting, this approach could be translated by treating surfaces like bed nets, eaves, or resting sites with the compounds, exploiting the natural resting and host-seeking behaviors of mosquitoes that bring their tarsi into contact with these treated substrates. If the drugs/compounds penetrate the cuticle, they could impact the parasites biological cycle within the vector. Our results confirmed this potential, Atovaquone was able to eliminate or reduce P. vivax from the midguts of An. darlingi at different exposure times, demonstrating successful uptake through the tarsi. Mefloquine was also reduced parasite intensity via tarsal contact. These findings reinforce the potential of this approach as a complementary tool in malaria control.

zoology↗

bioRxiv2024

Loss of neuropeptidergic regulation of cholinergic transmission induces CaV1-mediated homeostatic compensation in muscle cells

Chemical synaptic transmission at the neuromuscular junction (NMJ) is regulated by electrical activity of the motor circuit, but may also be affected by neuromodulation. Here, we assess the role of neuropeptide signaling in the plasticity of NMJ function in Caenorhabditis elegans. We show that the CAPS (Ca2+-dependent activator protein for secretion) ortholog UNC-31, which regulates the exocytosis of dense core vesicles (DCVs), affects both pre- and post-synaptic functional properties, as well as NMJ-mediated locomotion. Despite reduced evoked acetylcholine transmission, the loss of unc-31 results in a more vigorous response to presynaptic stimulation, i.e., enhanced muscle contraction and Ca2+ transients. Based on expression profiles, we identified neuropeptides involved in both cholinergic (FLP-6, NLP-9, NLP-21 and NLP-38) and GABAergic motor neurons (FLP-15, NLP-15), that mediate normal transmission at the NMJ. In the absence of these peptides, neurons fail to upregulate their transmitter output in response to increased cAMP signaling. We also identified proprotein convertases encoded by aex-5/kpc-3 and egl-3/kpc-2 that act synergistically to generate these neuropeptides. We propose that postsynaptic homeostatic scaling, mediated by increased muscle excitability, could compensate for the reduced cholinergic transmission in mutants affected for neuropeptide signaling, thus maintaining net synaptic strength. We show that in the absence of UNC-31 muscle excitability is modulated by upregulating the expression of the muscular L-type voltage gated Ca2+ channel EGL-19 (CaV1). Collectively, our results unveil a role for neuropeptidergic regulation in synaptic plasticity, linking changes in presynaptic transmission to compensatory changes in muscle excitability.

neuroscience↗