Among the cues that a mosquito uses to find a host for blood-feeding, the smell of the host plays an important role. Previous studies have shown that host odors contain hundreds of chemical odorants, which are detected by different receptors on the peripheral sensory organs of mosquitoes. But how individual odorants are encoded by downstream neurons in the mosquito brain is not known. We developed an in vivo preparation for patch-clamp electrophysiology to record from projection neurons and local neurons in the antennal lobe of Aedes aegypti. Combining intracellular recordings with dye-fills, morphological reconstructions, and immunohistochemistry, we identify different sub-classes of antennal lobe neurons and their putative interactions. Our recordings show that an odorant can activate multiple neurons innervating different glomeruli, and that the stimulus identity and its behavioral preference are represented in the population activity of the projection neurons. Our results provide the first detailed description of olfactory neurons in the central nervous system of mosquitoes and lay a foundation for understanding the neural basis of their olfactory behaviors.

Among the cues that a mosquito uses to find a host for blood-feeding, the smell of the host plays an important role. Previous studies have shown that host odors contain hundreds of chemical odorants, which are detected by different receptors on the peripheral sensory organs of mosquitoes. But how individual odorants are encoded by downstream neurons in the mosquito brain is not known. We developed an in vivo preparation for patch-clamp electrophysiology to record from projection neurons and local neurons in the antennal lobe of Aedes aegypti. Combining intracellular recordings with dye-fills, morphological reconstructions, and immunohistochemistry, we identify different sub-classes of antennal lobe neurons and their putative interactions. Our recordings show that an odorant can activate multiple neurons innervating different glomeruli, and that the stimulus identity and its behavioral preference are represented in the population activity of the projection neurons. Our results provide a detailed description of the second-order olfactory neurons in the central nervous system of mosquitoes and lay a foundation for understanding the neural basis of their olfactory behaviors.

No abstract

Carbon dioxide (CO2) is one of the prominent sensory cues used by mosquitoes to find hosts for blood-feeding. CO2 is detected on the maxillary palps by capitate peg sensory neurons, whose axons project to the antennal lobe in the brain. Behavioral studies have shown that mosquitoes prefer non-homogenous plumes of CO2 over homogenous plumes and CO2 greatly enhances the attractiveness of lactic acid, a skin volatile. However, the neural mechanisms underlying these behavioral preferences are not known. Using in vivo intracellular recordings from projection neurons and local neurons in the antennal lobe, along with single sensillum recordings from the maxillary palps, we checked the representations of CO2 in the first two layers of the Aedes aegypti olfactory system. We found that the preference to non-homogeneous plumes of CO2 and its synergistic attraction with lactic acid are encoded in the PN population responses. Our results provide a foundation for understanding CO2-mediated host-attraction in mosquitoes.

Maxillary palps, in addition to the antennae, are major olfactory organs in mosquitoes and play an important role in the detection of human hosts. The sensory neurons of the maxillary palps reside in the capitate peg sensilla, each of which contains three neurons. In Aedes aegypti, the neuron with the largest spike amplitude in the sensillum is known to detect carbon dioxide. However, the responses of the other two neurons and the functional consequences of the grouping of these neurons within sensilla are not well understood. Here we identify odorants that activate the other two neurons. We detect a short-term plasticity in the odor-evoked local field potential of the sensillum and show that it originates in the spiking responses of the smallest-amplitude neuron, even though all three neurons contribute to the local field potential. We also detect inhibitory interactions among these neurons within the sensillum. We further show that the plasticity and the lateral interactions are functionally important as they affect the responses of the downstream projection neurons in the antennal lobe.