The habenula is a paired nucleus residing in the dorsal thalamus. It consists of medial and lateral subnuclei (MHb, LHb), which connect to distinct targets in the ventral midbrain. Lesion studies of the entire habenula in animals have implicated this area in diverse functions, including circadian rhythms and sleep, stress responses, intracranial self-stimulation reward, and the behavioral effects of nicotine and other drugs of abuse. In humans, a few preliminary clinical studies have linked habenula reward pathways to possible mechanisms of depression, but the function of this nucleus remains largely unclear. Recent work has shown that some LHb neurons inhibit dopamine (DA) signaling in the ventral tegmental area (VTA), and thus mediate a negative reward signal. In contrast, the MHb projects almost exclusively to the interpeduncular nucleus (IP), adjacent to the VTA, which projects in turn to the raphe and dorsal tegmental areas. The MHb has dorsal (dMHb) and ventral (vMHb) subnuclei, which make specific connections to the lateral and medial IP, respectively. Prior studies have not distinguished the roles of these subnuclei, yet there is littl reason to believe they have the same function. Our new optogenetic data show that, in contrast to the LHb, stimulation of the dMHb generates a positive reward signal, and we hypothesize that this is mediated via a MHb-IP pathway to the brainstem. Here we will use Cre-drivers specific for the dMHb and vMHb, combined with transgenic mice that allow inducible expression of the optogenetic proteins Channelrhodopsin and Halorhodopsin, to activate and silence MHb neurons in order to examine the functional link from the MHb to GABA neurons in the IP. Genetically targeted approaches will also be used to examine the IP connection to 5HT neurons in the raphe, using neuroanatomical, electrophysiological, and behavioral readouts.
Aim 1. We will use Cre-mediated transgenic, viral, and conventional tract-tracing to determine the anatomical connectivity of pathways from the habenula, via the IP, to hindbrain centers mediating reward and fear responses. We will assign neurotransmitter phenotypes to the neurons in these pathways to determine whether they transmit excitatory or inhibitory signals.
Aim 2. We will test the physiological connections between the MHb-IP and the IP-raphe in brain slice preparations, using optogenetic activation of specific presynaptic neurons combined with intracellular recording of postsynaptic neurons, and identification of the recorded neurons with transgenic markers.
Aim 3. We will use optogenetics to activate and silence the dMHb and vMHb in behavioral models of reward and depression, including open field locomotion, intracranial self-stimulation, real-time place preference/aversion, conditioned place preference/aversion, and learned helplessness. At the conclusion of these experiments we will better understand the specific habenula components and their downstream pathways, and the potential role of the habenula in mood disorders.

Public Health Relevance

Neurotransmitter systems in the brainstem, particularly dopamine and serotonin, play roles in mood and anxiety disorders and in drug addiction. In this proposal we will study a brain region called the habenula, which provides input to the dopamine and serotonin systems from higher brain centers. Although recent work has shown a role for the habenula in behavioral responses to reward stimuli, little is known about the output circuits of the habenula, and in this project we will study these circuits in mice using new methods for manipulating the activity of genetically defined neurons with light.

Agency
National Institute of Health (NIH)
Institute
National Institute on Drug Abuse (NIDA)
Type
Research Project (R01)
Project #
5R01DA035838-03
Application #
9059062
Study Section
Neurobiology of Motivated Behavior Study Section (NMB)
Program Officer
Sorensen, Roger
Project Start
2014-05-01
Project End
2019-04-30
Budget Start
2016-05-01
Budget End
2017-04-30
Support Year
3
Fiscal Year
2016
Total Cost
Indirect Cost
Name
Seattle Children's Hospital
Department
Type
DUNS #
048682157
City
Seattle
State
WA
Country
United States
Zip Code
98101
Morton, Glenn; Nasirova, Nailyam; Sparks, Daniel W et al. (2018) Chrna5-expressing neurons in the interpeduncular nucleus mediate aversion primed by prior stimulation or nicotine exposure. J Neurosci :
Hsu, Yun-Wei A; Gile, Jennifer J; Perez, Jazmine G et al. (2017) The Dorsal Medial Habenula Minimally Impacts Circadian Regulation of Locomotor Activity and Sleep. J Biol Rhythms 32:444-455
Quina, Lely A; Harris, Julie; Zeng, Hongkui et al. (2017) Specific connections of the interpeduncular subnuclei reveal distinct components of the habenulopeduncular pathway. J Comp Neurol 525:2632-2656
Hsu, Yun-Wei A; Morton, Glenn; Guy, Elizabeth G et al. (2016) Dorsal Medial Habenula Regulation of Mood-Related Behaviors and Primary Reinforcement by Tachykinin-Expressing Habenula Neurons. eNeuro 3:
Quina, Lely A; Tempest, Lynne; Ng, Lydia et al. (2015) Efferent pathways of the mouse lateral habenula. J Comp Neurol 523:32-60
Hsu, Yun-Wei A; Wang, Si D; Wang, Shirong et al. (2014) Role of the dorsal medial habenula in the regulation of voluntary activity, motor function, hedonic state, and primary reinforcement. J Neurosci 34:11366-84