Biology subjects

Parekh, R.

Publications and source records attributed to Parekh, R..

7 recordsLinked to original sources

bioRxiv2025

Postembryonic Development and Morphology of the Reproductive System in the Acoel Hofstenia atroviridis

Reconstructing ancestral reproductive systems is essential for understanding the evolution of bilaterian body plans, yet the origin and development of reproductive organs remain poorly characterized. Here, we investigate postembryonic sexual development in the xenacoelomorph Hofstenia atroviridis, a basal acoel species, to gain insight into early bilaterian reproductive evolution. Individuals were reared from eggs to adulthood, and the ontogeny of reproductive organs was examined using histology and immunohistochemistry with muscle and neural markers. H. atroviridis is a protandrous simultaneous hermaphrodite, with sexual maturity correlated with body size rather than age. The male copulatory system comprises a seminal vesicle, granular vesicle, penis with a penile bulb, and a single copulatory stylet, accompanied by regionally specialized musculature and innervation. In contrast, the female reproductive system consists of paired, asaccate ovaries containing large, follicle cell-bound oocytes and lacks a discrete gonopore or copulatory organ. Fertilization occurs via traumatic insemination, and eggs are likely released through the mouth. Despite the organisms overall morphological simplicity, the male reproductive system exhibits pronounced structural differentiation. These findings suggest that sexual selection acting on a hermaphroditic ancestor may have contributed to the early diversification of bilaterian copulatory organs and establish H. atroviridis as a useful model for studying the evolutionary origins of animal reproductive systems.

evolutionary biology↗

bioRxiv2024

Comparative connectomics of the descending and ascending neurons of the Drosophila nervous system: stereotypy and sexual dimorphism

In most complex nervous systems there is a clear anatomical separation between the nerve cord, which contains most of the final motor outputs necessary for behaviour, and the brain. In insects, the neck connective is both a physical and information bottleneck connecting the brain and the ventral nerve cord (VNC, spinal cord analogue) and comprises diverse populations of descending (DN), ascending (AN) and sensory ascending neurons, which are crucial for sensorimotor signalling and control. Integrating three separate EM datasets, we now provide a complete connectomic description of the ascending and descending neurons of the female nervous system of Drosophila and compare them with neurons of the male nerve cord. Proofread neuronal reconstructions have been matched across hemispheres, datasets and sexes. Crucially, we have also matched 51% of DN cell types to light level data defining specific driver lines as well as classifying all ascending populations. We use these results to reveal the general architecture, tracts, neuropil innervation and connectivity of neck connective neurons. We observe connected chains of descending and ascending neurons spanning the neck, which may subserve motor sequences. We provide a complete description of sexually dimorphic DN and AN populations, with detailed analysis of circuits implicated in sex-related behaviours, including female ovipositor extrusion (DNp13), male courtship (DNa12/aSP22) and song production (AN hemilineage 08B). Our work represents the first EM-level circuit analyses spanning the entire central nervous system of an adult animal.

neuroscience↗

bioRxiv2023

A comprehensive neuroanatomical survey of the Drosophila Lobula Plate Tangential Neurons with predictions for their optic flow sensitivity

Flying insects exhibit remarkable navigational abilities controlled by their compact nervous systems. Optic flow, the pattern of changes in the visual scene induced by locomotion, is a crucial sensory cue for robust self-motion estimation, especially during rapid flight. Neurons that respond to specific, large-field optic flow patterns have been studied for decades, primarily in large flies, such as houseflies, blowflies, and hover flies. The best-known optic-flow sensitive neurons are the large tangential cells of the dipteran lobula plate, whose visual-motion responses, and to a lesser extent, their morphology, have been explored using single-neuron neurophysiology. Most of these studies have focused on the large, Horizontal and Vertical System neurons, yet the lobula plate houses a much larger set of optic-flow sensitive neurons, many of which have been challenging to unambiguously identify or to reliably target for functional studies. Here we report the comprehensive reconstruction and identification of the Lobula Plate Tangential Neurons in an Electron Microscopy (EM) volume of a whole Drosophila brain. This catalog of 58 LPT neurons (per brain hemisphere) contains many neurons that are described here for the first time and provides a basis for systematic investigation of the circuitry linking self-motion to locomotion control. Leveraging computational anatomy methods, we estimated the visual motion receptive fields of these neurons and compared their tuning to the visual consequence of body rotations and translational movements. We also matched these neurons, in most cases on a one-for-one basis, to stochastically labeled cells in genetic driver lines, to the mirror-symmetric neurons in the same EM brain volume, and to neurons in an additional EM data set. Using cell matches across data sets, we analyzed the integration of optic flow patterns by neurons downstream of the LPTs and find that most central brain neurons establish sharper selectivity for global optic flow patterns than their input neurons. Furthermore, we found that self-motion information extracted from optic flow is processed in distinct regions of the central brain, pointing to diverse foci for the generation of visual behaviors.

neuroscience↗

bioRxiv2020

A connectome of the Drosophila central complex reveals network motifs suitable for flexible navigation and context-dependent action selection

Flexible behaviors over long timescales are thought to engage recurrent neural networks in deep brain regions, which are experimentally challenging to study. In insects, recurrent circuit dynamics in a brain region called the central complex (CX) enable directed locomotion, sleep, and context- and experience-dependent spatial navigation. We describe the first complete electron-microscopy-based connectome of the Drosophila CX, including all its neurons and circuits at synaptic resolution. We identified new CX neuron types, novel sensory and motor pathways, and network motifs that likely enable the CX to extract the flys head-direction, maintain it with attractor dynamics, and combine it with other sensorimotor information to perform vector-based navigational computations. We also identified numerous pathways that may facilitate the selection of CX-driven behavioral patterns by context and internal state. The CX connectome provides a comprehensive blueprint necessary for a detailed understanding of network dynamics underlying sleep, flexible navigation, and state-dependent action selection.

neuroscience↗

bioRxiv2020

The connectome of the adult Drosophila mushroom body: implications for function

Making inferences about the computations performed by neuronal circuits from synapse-level connectivity maps is an emerging opportunity in neuroscience. The mushroom body (MB) is well positioned for developing and testing such an approach due to its conserved neuronal architecture, recently completed dense connectome, and extensive prior experimental studies of its roles in learning, memory and activity regulation. Here we identify new components of the MB circuit in Drosophila, including extensive visual input and MB output neurons (MBONs) with direct connections to descending neurons. We find unexpected structure in sensory inputs, in the transfer of information about different sensory modalities to MBONs, and in the modulation of that transfer by dopaminergic neurons (DANs). We provide insights into the circuitry used to integrate MB outputs, connectivity between the MB and the central complex and inputs to DANs, including feedback from MBONs. Our results provide a foundation for further theoretical and experimental work.

neuroscience↗

bioRxiv2020

Neural circuit mechanisms of sexual receptivity in Drosophila females

Choosing a mate is one of the most consequential decisions a female will make during her lifetime. This is particularly true for species in which females either mate repeatedly with the same partner or mate infrequently but use the sperm from a single copulation to fertilize eggs over an extended period of time. Drosophila melanogaster uses the latter strategy. Here, we characterize the neural circuitry that implements mating decisions in the female brain. A female fly signals her mating choice by opening her vaginal plates to allow a courting male to copulate1,2. Vaginal plate opening (VPO) occurs in response to the male courtship song and is dependent upon the female's mating status. We sought to understand how these exteroceptive (song) and interoceptive (mating status) inputs are integrated to control VPO. We show that VPO is triggered by a pair of female-specific descending neurons, the vpoDNs. The vpoDNs receive excitatory input from vpoEN auditory neurons, which are tuned to specific features of the melanogaster song. The song responses of vpoDNs, but not vpoENs, are attenuated upon mating, accounting for the reduced receptivity of mated females. This modulation is mediated by pC1 neurons, which encode the females mating status3,4 and also provide excitatory input to vpoDNs. The vpoDNs thus directly integrate the external and internal signals to control the mating decisions of Drosophila females.

neuroscience↗

bioRxiv2020

Neuronal circuitry underlying female aggression in Drosophila

Aggressive social interactions are used to compete for limited resources and are regulated by complex sensory cues and the organisms internal state. While both sexes exhibit aggression, its neuronal underpinnings are understudied in females. Here, we describe a set of connected neurons in the adult Drosophila melanogaster central brain that drive female aggression. We identified a population of sexually dimorphic aIPg neurons whose optogenetic activation increased, and genetic inactivation reduced, female aggression. Analysis of GAL4 lines identified in an unbiased screen for increased female chasing behavior revealed the involvement of another sexually dimorphic neuron, pC1d, and implicated pC1d and aIPg neurons as core nodes regulating female aggression. pC1d activation increased female aggression and electron microscopy (EM) connectomic analysis demonstrated that aIPg neurons and pC1d have strong reciprocal connections. Our work reveals important regulatory components of the neuronal circuitry that underlies female aggressive social interactions and provides tools for their manipulation.

neuroscience↗