Zhao, R. J. | Search bioRxiv

bioRxiv2024

Temporal Dynamics of Nucleus Accumbens Neurons in Male Mice During Reward Seeking

The nucleus accumbens (NAc) regulates reward-motivated behavior, but the temporal dynamics of NAc neurons that enable "free-willed" animals to obtain rewards remain elusive. Here, we recorded Ca2+ activity from individual NAc neurons when mice performed self-paced lever-presses for sucrose. NAc neurons exhibited three temporally-sequenced clusters, defined by times at which they exhibited increased Ca2+ activity: approximately 0, -2.5 or -5 sec relative to the lever-pressing. Dopamine D1 receptor (D1)-expressing neurons and D2-neurons formed the majority of the -5-sec versus -2.5-sec clusters, respectively, while both neuronal subtypes were represented in the 0-sec cluster. We found that pre-press activity patterns of D1- or D2-neurons could predict subsequent lever-presses. Inhibiting D1-neurons at -5 sec or D2-neurons at -2.5 sec, but not at other timepoints, reduced sucrose-motivated lever-pressing. We propose that the time-specific activity of D1- and D2-neurons mediate key temporal features of the NAc through which reward motivation initiates reward-seeking behavior.

neuroscience↗

bioRxiv2024

Body reconstruction and size estimation of plesiosaurs

Body size, especially body mass, is the key to understanding many biological properties. The scaling approaches and volumetric-density (VD) approaches are often employed to estimate the body masses of extinct amniotes. Precise skeletal reconstruction represents a pivotal step in all VD approaches, while the ribcage serves as one of the key determinants of thoracic shape and volume. Although being extensively investigated in physiological studies, the ribcage restoration remains poorly discussed during skeletal reconstruction. This study proposes one possible programme of skeletal reconstruction of extinct amniotes in 2D environments, focusing on the restoration of ribcage cross-sections. One recent VD approach, the cross-sectional method (CSM), was utilized to integrate the restored cross-sections into volume, therefore the workflow proposed here serves as a supplementary guideline of the application of the CSM in paleontology. Following this programme, a uniform set of reconstruction criteria was proposed for plesiosaurs, a clade of Mesozoic marine reptiles. Twenty-four plesiosaur models were created, then multiple regression models (Ordinary Least Squares, OLS; and Phylogenetically Generalized Least Squares, PGLS) based on them were employed to investigate the performance of various skeletal elements as size proxy. Despite the high disparity of their body plans, the trunk length and dimensions of dorsal vertebrae were found to be the most robost proxy for volume in plesiosaurs. The hybrid approach applied in this study, which incorporates VD estimates created under the same criteria as scaling samples, mitigates previous critiques focusing on inconsistent standards and inadequate taxonomic coverage. It allows fast and convenient body volume estimation for numerus individuals, even when only fragmentary fossil materials are available. The volumetric formulae for plesiosaurs can accommodate the size diversity of most taxa, except for some extremely giant pliosaurs, the largest of which might reach or exceed 20 metric tons in body mass. To demonstrate the utility of the formulae provided in this study, the body volumes of 113 plesiosaur taxa was estimated, and the branch-specific rates of size evolution computed from the data were mapped onto a plesiosaur phylogeny for visualization.

paleontology↗

bioRxiv2023

Estimating body volumes and surface areas of animalsfrom cross-sections

Body mass and surface area are among the most important biological properties, but such information are lacking for some extant organisms and all extinct species. Numerous methods have been developed for body size estimation for this reason. There are two main categories of mass-estimating methods: volumetric-density approaches and extant-scaling approaches. In this paper, a new 2D volumetric-density approach named cross-sectional method is presented. Cross-sectional method integrates biological cross-sections to obtain volume and surface area accurately. Unlike all previous 2D methods, cross-sectional method processes true cross-sectional profiles directly rather than approximating. Cross-sectional method also has the advantage over others that it can deal with objects with gradually changing cross-sections. It generates very accurate results, with errors always lower than 2% in all cases tested.

paleontology↗