A developmental approach to diversifying neuroscience through effective mentorship practices: perspectives on cross-identity mentorship and a critical call to action.

Many early-career neuroscientists with diverse identities may not have mentors who are more advanced in the neuroscience pipeline and have a congruent identity due to historic biases, laws, and policies impacting access to education. Cross-identity mentoring relationships pose challenges and power imbalances that impact the retention of diverse early career neuroscientists, but also hold the potential for a mutually enriching and collaborative relationship that fosters the mentee\u27s success. Additionally, the barriers faced by diverse mentees and their mentorship needs may evolve with career progression and require developmental considerations. This article provides perspectives on factors that impact cross-identity mentorship from individuals participating in Diversifying the Community of Neuroscience (CNS)-a longitudinal, National Institute of Neurological Disorders and Stroke (NINDS) R25 neuroscience mentorship program developed to increase diversity in the neurosciences. Participants in Diversifying CNS were comprised of 14 graduate students, postdoctoral fellows, and early career faculty who completed an online qualitative survey on cross-identity mentorship practices that impact their experience in neuroscience fields. Qualitative survey data were analyzed using inductive thematic analysis and resulted in four themes across career levels: (1) approach to mentorship and interpersonal dynamics, (2) allyship and management of power imbalance, (3) academic sponsorship, and (4) institutional barriers impacting navigation of academia. These themes, along with identified mentorship needs by developmental stage, provide insights mentors can use to better support the success of their mentees with diverse intersectional identities. As highlighted in our discussion, a mentor\u27s awareness of systemic barriers along with active allyship are foundational for their role

Central Neural Circuitry of Food and Water Seeking in Drosophila melanogaster

The role of homeostatic hormones in the control of ingestive behaviors is well established, however the understanding of how cortical and subcortical reward systems (like the dopaminergic reward pathways) integrate with hormonal signals and other brain regions to regulate motivational seeking is incomplete. To better understand the neuronal circuitry underlying the neurobiology of obesity and motivation, it is essential to address the pre-ingestive phase of motivated homeostatic seeking behavior, when individuals are actively seeking reward.To understand the fundamental neural processes underlying basic behaviors, like food, water, and drug seeking, it is critical to evaluate the potential interactions between common and diverse neural substrates known to mediate complex behaviors, like food and drug addiction. In the first part of this dissertation (chapter 1) I review distinct and overlapping neural motifs underlying motivated food and drug-related behaviors in Drosophila melanogaster to better understand the circuit logic underlying motivational survival behavior hierarchies (hunger, thirst, fear avoidance, sleep, copulation).In the second part of this dissertation (chapter 2), I provide evidence that dopaminergic wiring within the fly brain is necessary and sufficient to promote food-seeking behavior in a satiation-state dependent manner. Here, we use sophisticated genetic tools to reversibly activate and inactivate neuronal ensembles and have categorized the function of discrete dopaminergic clusters of neurons. I demonstrate their ability to promote or inhibit pre-ingestive food seeking behaviors by using a novel food seeking assay. More importantly, we show that expression of the D1 receptor, DopR, is necessary in the mushroom bodies to promote food seeking in starved animals.In the final part of this dissertation (chapter 3) I show that a persistent state of thirst is evoked by the precise activation of six central brain neurons in adult Drosophila. In a neuronal activation screen, we identified a subset of GABA and AstA-expressing neurons that evoke robust thirst-related behaviors, including water seeking and intake; we named these neurons Janu, the Estonian for thirsty. These central brain neurons function downstream of sensory input and internal osmotic sensors to drive seeking to either open or inaccessible water. Importantly, activation of Janu neurons overrides food seeking in water replete but hungry flies. We also identified neuropeptide F receptor (NPFR)-expressing neurons that appear to function as a water seeking homeostat. Neurons expressing NPFR, the invertebrate homolog of the NPY receptor, also promote insatiable hunger and voracious feeding. Like Janu neurons but independent of them, activation of NPFR neurons overrides food seeking in water replete but hungry flies. Thus, neural circuit elements that regulate hunger and thirst are tightly integrated. These studies provide an entry point for mapping the fundamental homeostatic thirst neurons and the hierarchical wiring of neural circuits that encode opposing motivational states

Central Neural Circuitry of Food and Water Seeking in Drosophila melanogaster

The role of homeostatic hormones in the control of ingestive behaviors is well established, however the understanding of how cortical and subcortical reward systems (like the dopaminergic reward pathways) integrate with hormonal signals and other brain regions to regulate motivational seeking is incomplete. To better understand the neuronal circuitry underlying the neurobiology of obesity and motivation, it is essential to address the pre-ingestive phase of motivated homeostatic seeking behavior, when individuals are actively seeking reward.To understand the fundamental neural processes underlying basic behaviors, like food, water, and drug seeking, it is critical to evaluate the potential interactions between common and diverse neural substrates known to mediate complex behaviors, like food and drug addiction. In the first part of this dissertation (chapter 1) I review distinct and overlapping neural motifs underlying motivated food and drug-related behaviors in Drosophila melanogaster to better understand the circuit logic underlying motivational survival behavior hierarchies (hunger, thirst, fear avoidance, sleep, copulation).In the second part of this dissertation (chapter 2), I provide evidence that dopaminergic wiring within the fly brain is necessary and sufficient to promote food-seeking behavior in a satiation-state dependent manner. Here, we use sophisticated genetic tools to reversibly activate and inactivate neuronal ensembles and have categorized the function of discrete dopaminergic clusters of neurons. I demonstrate their ability to promote or inhibit pre-ingestive food seeking behaviors by using a novel food seeking assay. More importantly, we show that expression of the D1 receptor, DopR, is necessary in the mushroom bodies to promote food seeking in starved animals.In the final part of this dissertation (chapter 3) I show that a persistent state of thirst is evoked by the precise activation of six central brain neurons in adult Drosophila. In a neuronal activation screen, we identified a subset of GABA and AstA-expressing neurons that evoke robust thirst-related behaviors, including water seeking and intake; we named these neurons Janu, the Estonian for thirsty. These central brain neurons function downstream of sensory input and internal osmotic sensors to drive seeking to either open or inaccessible water. Importantly, activation of Janu neurons overrides food seeking in water replete but hungry flies. We also identified neuropeptide F receptor (NPFR)-expressing neurons that appear to function as a water seeking homeostat. Neurons expressing NPFR, the invertebrate homolog of the NPY receptor, also promote insatiable hunger and voracious feeding. Like Janu neurons but independent of them, activation of NPFR neurons overrides food seeking in water replete but hungry flies. Thus, neural circuit elements that regulate hunger and thirst are tightly integrated. These studies provide an entry point for mapping the fundamental homeostatic thirst neurons and the hierarchical wiring of neural circuits that encode opposing motivational states

Shared neurocircuitry underlying feeding and drugs of abuse in Drosophila

The neural circuitry and molecules that control the rewarding properties of food and drugs of abuse appear to partially overlap in the mammalian brain. This has raised questions about the extent of the overlap and the precise role of specific circuit elements in reward and in other behaviors associated with feeding regulation and drug responses. The much simpler brain of invertebrates including the fruit fly Drosophila, offers an opportunity to make high-resolution maps of the circuits and molecules that govern behavior. Recent progress in Drosophila has revealed not only some common substrates for the actions of drugs of abuse and for the regulation of feeding, but also a remarkable level of conservation with vertebrates for key neuromodulatory transmitters. We speculate that Drosophila may serve as a model for distinguishing the neural mechanisms underlying normal and pathological motivational states that will be applicable to mammals

Satiation state-dependent dopaminergic control of foraging in Drosophila.

Hunger evokes stereotypic behaviors that favor the discovery of nutrients. The neural pathways that coordinate internal and external cues to motivate foraging behaviors are only partly known. Drosophila that are food deprived increase locomotor activity, are more efficient in locating a discrete source of nutrition, and are willing to overcome adversity to obtain food. We developed a simple open field assay that allows flies to freely perform multiple steps of the foraging sequence, and we show that two distinct dopaminergic neural circuits regulate measures of foraging behaviors. One group, the PAM neurons, functions in food deprived flies while the other functions in well fed flies, and both promote foraging. These satiation state-dependent circuits converge on dopamine D1 receptor-expressing Kenyon cells of the mushroom body, where neural activity promotes foraging independent of satiation state. These findings provide evidence for active foraging in well-fed flies that is separable from hunger-driven foraging

Satiation state-dependent dopaminergic control of foraging in Drosophila.

Hunger evokes stereotypic behaviors that favor the discovery of nutrients. The neural pathways that coordinate internal and external cues to motivate foraging behaviors are only partly known. Drosophila that are food deprived increase locomotor activity, are more efficient in locating a discrete source of nutrition, and are willing to overcome adversity to obtain food. We developed a simple open field assay that allows flies to freely perform multiple steps of the foraging sequence, and we show that two distinct dopaminergic neural circuits regulate measures of foraging behaviors. One group, the PAM neurons, functions in food deprived flies while the other functions in well fed flies, and both promote foraging. These satiation state-dependent circuits converge on dopamine D1 receptor-expressing Kenyon cells of the mushroom body, where neural activity promotes foraging independent of satiation state. These findings provide evidence for active foraging in well-fed flies that is separable from hunger-driven foraging

Hypothalamic neurons that mirror aggression

Social interactions require awareness and understanding of the behavior of others. Mirror neurons, cells representing an action by self and others, have been proposed to be integral to the cognitive substrates that enable such awareness and understanding. Mirror neurons of the primate neocortex represent skilled motor tasks, but it is unclear if they are critical for the actions they embody, enable social behaviors, or exist in non-cortical regions. We demonstrate that the activity of individual VMHvlPR neurons in the mouse hypothalamus represents aggression performed by self and others. We used a genetically encoded mirror-TRAP strategy to functionally interrogate these aggression-mirroring neurons. We find that their activity is essential for fighting and that forced activation of these cells triggers aggressive displays by mice, even toward their mirror image. Together, we have discovered a mirroring center in an evolutionarily ancient region that provides a subcortical cognitive substrate essential for a social behavior

Internode length is reduced during myelination and remyelination by neurofilament medium phosphorylation in motor axons

The distance between nodes of Ranvier, referred to as internode length, positively correlates with axon diameter, and is optimized during development to ensure maximal neuronal conduction velocity. Following myelin loss, internode length is reestablished through remyelination. However, remyelination results in short internode lengths and reduced conduction rates. We analyzed the potential role of neurofilament phosphorylation in regulating internode length during remyelination and myelination. Following ethidium bromide induced demyelination, levels of neurofilament medium (NF-M) and heavy (NF-H) phosphorylation were unaffected. Preventing NF-M lysine-serine-proline (KSP) repeat phosphorylation increased internode length by 30% after remyelination. To further analyze the role of NF-M phosphorylation in regulating internode length, gene replacement was used to produce mice in which all KSP serine residues were replaced with glutamate to mimic constitutive phosphorylation. Mimicking constitutive KSP phosphorylation reduced internode length by 16% during myelination and motor nerve conduction velocity by ~27% without altering sensory nerve structure or function. Our results suggest that NF-M KSP phosphorylation is part of a cooperative mechanism between axons and Schwann cells that together determine internode length, and suggest motor and sensory axons utilize different mechanisms to establish internode length