Biology subjects

Hiroi, M.

Publications and source records attributed to Hiroi, M..

3 recordsLinked to original sources

bioRxiv2026

Hierarchical processing and polarization encoding in the cephalopod visual system

Coleoid cephalopods (octopus, cuttlefish and squid, hereafter cephalopods) have evolved a range of complex visually-guided behaviours, from dexterous hunting to skin-pattern based camouflage and communication1. They have also evolved sensitivity to the polarization of light2, an adaptation thought to help detect camouflaged or semitransparent predators and prey in low visibility underwater environments3-10. How visual information is processed by the cephalopod brain to support their behaviours remains unclear. Here, studying the bigfin reef squid Sepioteuthis lessoniana, we performed calcium imaging and electrophysiological recordings from populations of neurons in the large visual center of the cephalopod brain, the optic lobe (OL). We revealed that the retina-recipient superficial OL contains a diversity of functionally distinct cell types, spatially organized into sub-layers, processing spatio-temporal features of light intensity and possessing polarization angle specificity. More complex features, e.g. direction selectivity, are seen in deeper regions of the OL cortex, which also exhibits spontaneous waves of neural activity in the absence of visual input. Neurons in the downstream OL medulla exhibit visual receptive field sizes and spontaneous activity levels which increase with brain depth, consistent with the hierarchical processing of visual information through the medullas tree-like anatomical organization. Medulla neurons exhibit sensitivity to local decreases in the degree of linear polarization (DoLP), which they integrate additively with light intensity information. Underwater imaging in the squids habitat off the coast of Okinawa, Japan, demonstrate that polarization sensitivity confers a robust short-range boost in object-background contrast over a range of objects and environmental conditions. These findings reveal convergent principles of hierarchical visual processing shared between cephalopods and vertebrates, and highlight how cephalopods utilise their distinct adaptation of polarization sensitivity to solve universal visual challenges underwater.

neuroscience↗

bioRxiv2025

A sensory system for mating in octopus

Sensory systems for mate recognition maintain species boundaries and influence diversification. Therefore, uncovering how molecules and receptors evolve to mediate this critical function is essential to understanding biodiversity. Male octopuses use a specialized arm called the hectocotylus to identify females and navigate their internal organs to reach the oviduct and deliver sperm. Here, we discovered that the hectocotylus is a dual sensory and mating organ that uses contactdependent chemosensation of progesterone, a conserved ovarian hormone. We identify chemotactile receptors for progesterone and resolve the structural basis for their evolution from ancestral neurotransmitter receptors and subsequent expansion and tuning across cephalopods. These findings reveal principles by which sensory innovations shape reproductive behavior and suggest mechanisms for how sensory evolution contributes to the diversification of life.

cell biology↗

bioRxiv2023

Revisiting the role of cAMP in Drosophila aversive olfactory memory formation

In the olfactory aversive conditioning of Drosophila melanogaster, an odor, the conditioned stimulus (CS), is associated with electric shock, the unconditioned stimulus (US). The Rutabaga adenylyl cyclase in Kenyon cells (KCs) of the fly brain synthesizes cAMP, which is believed to serve as the coincidence detector synergistically stimulated by calcium/calmodulin evoked by the odor reception and GS released in response to the dopamine signaling elicited by electric shock. However, live imaging analyses revealed that olfactory stimulation itself prompted the activation of dopaminergic neurons and resulted in the elevation of cAMP levels in KCs that received dopamine, regardless of calcium signaling. This finding raises questions about the longstanding and fundamental comprehension of conditioning mechanisms, as the cAMP levels in conditioned stimulus-positive (CS+) KCs could not be distinguished from those in the rest of the KCs. Our findings suggest that cAMP concentrations do not function as a mnemonic engram to CS+ neurons. Rather, the collective dynamics of cAMP are capable of integratively encoding the valence ascribed to odors being perceived at a given time. Furthermore, our investigation revealed that associative conditioning induces modifications in dopamine levels in response to both CS and US, resulting in alterations in cAMP levels. The increase in cAMP exerts a deleterious effect on the acetylcholine transmission from KCs. Accordingly, we postulate that, during conditioning, cAMP depresses KCs, thereby skewing the valence of the CS+ odor towards a more aversive state for the conditioned flies, and ultimately culminating in the formation of aversive memories.

neuroscience↗