Functional properties of habenular neurons are determined by developmental stage and sequential neurogenesis

Abstract

Neural development is not just a linear expansion of the brain. Instead, the structure and function of developing brain circuits undergo drastic alterations that have a direct impact on the animals' expanding behavioural repertoire. Here we investigated the developmental changes in the habenula, a brain region that mediates behavioural flexibility during learning, social interactions and aversive experiences. We showed that developing habenular circuits exhibit multiple alterations, which increase the structural and functional diversity of cell types, inputs and functional modules within habenula. As the neural architecture of habenula develops, it sequentially transforms into a multi-sensory brain region that can process visual and olfactory information. Moreover, we also observed that already at early developmental stages, the habenula exhibits spatio-temporally structured spontaneous neural activity that shows prominent alterations and refinement with age. Interestingly, these alterations in spontaneous activity are accompanied by sequential neurogenesis and integration of distinct neural clusters across development. Finally, by combining an in vivo neuronal birthdating method with functional imaging, we revealed that clusters of habenular neurons with distinct functional properties are born sequentially at distinct developmental time windows. Our results highlight a strong link between the function of habenular neurons and their precise birthdate during development, which supports the idea that sequential neurogenesis leads to an expansion of neural clusters that correspond to distinct functional modules in the brain.

The Zebrafish Dorsolateral Habenula Is Required for Updating Learned Behaviors

“…Our multi-day CPA training protocol revealed that 4-week-old zebrafish can recall CPA memories even after 24 h. Adult zebrafish were shown to recall memories encoded by telencephalic neural activity ( Aoki et al., 2013 ), homologous to the mammalian cortex ( Mueller and Wullimann, 2009 ), resembling the memory engrams described in mammals ( Liu et al., 2012 ; Ramirez et al., 2014 ; Kitamura et al., 2017 ). Our results showed a long-term memory recall in juvenile zebrafish with small and relatively translucent brains that are amenable for functional brain imaging ( Jetti et al., 2014 ; Fore et al., 2019 ; Vendrell-Llopis and Yaksi, 2015 ), at single neuron resolution. Future studies will be necessary to further investigate the neural basis of memory at different timescales and to understand how brain regions that are involved in short-term and long-term learning interact with each other to generate memory engrams.…”

“…To investigate the ontogeny of CPA learning, we focus on the first 4 weeks of development, during which zebrafish (i.e., nacre mutants with reduced pigmentation) ( Lister et al., 1999 ) are relatively translucent and amenable for functional imaging of dorsal brain regions ( Jetti et al., 2014 ; Fore et al., 2019 ; Vendrell-Llopis and Yaksi, 2015 ). During these first 4 weeks, we observed that the size of zebrafish increased significantly from the larval to juvenile stage ( Figure S1 B).…”

“…Similar to adult zebrafish ( Agetsuma et al., 2010 ), narp:Gal4 is expressed in dlHb neurons of juvenile zebrafish ( Figures S5 A–S5F; Video S1 ). More lateral narp:Gal4 expression in adults is due to sequential habenular neurogenesis across development ( Fore et al., 2019 ). Next, we compared dlHb-ablated juvenile zebrafish with the control group in multi-day CPA training.…”

The zebrafish dorsolateral habenula is required for updating learned behaviors

“…In juvenile zebrafish, narp:Gal4 is expressed exclusively in dHb neurons, and it is comparable to adult zebrafish [23] ( Figure S5 A-F). Slightly more lateral location of narp:Gal4 expressing dHb neurons in adults is due to sequential habenular neurogenesis across development [29]. Next, we compared dHb ablated juvenile zebrafish with the control group in a multiday training protocol.…”

Stimulus-specific behavioral responses of zebrafish to a large range of odors exhibit individual variability

“…Odors are powerful drivers of a wide range of behavioral responses in fish, such as reproduction, foraging, and defensive behaviors [1][2][3]. The neural pathways underlying these stereotyped behaviors have been the focus of extensive research and are well described [4][5][6][7][8][9][10][11][12][13][14][15]. In the sea lampreys, a neural pathway comprising the olfactory bulb, posterior tuberculum, and mesencephalic locomotor region converts olfactory inputs into locomotor outputs by activating conserved brainstem pre-motor neurons (the reticulospinal neurons) [16][17][18][19], which in turn control the spinal cord locomotor centers [4].…”