Quantitative and qualitative sex difference in habenula-induced inhibition of midbrain dopamine neurons in the rat

Sex-specific habenular dysconnectivity in patients with late-life depression

There are significant sex differences in the prevalence, symptom presentation, treatment response and brain abnormalities of patients with late-life depression (LLD). The functional connectivity of the habenula has been associated with depressive symptoms and cognitive impairments in patients with LLD. However, sex differences in habenular functional connectivity patterns among LLD patients remain unclear. One hundred and fourteen patients with LLD and 75 healthy controls (HCs) were included in the present study. Resting-state functional magnetic resonance imaging was used to analyse the static and dynamic functional connectivity (sFC and dFC) of the habenula. There were significant interactions between diagnosis (LLD vs. HCs) and sex for the dFC of the left habenula with the left insula, precentral gyrus, angular gyrus, and middle frontal gyrus and for the right habenula with the right middle temporal gyrus. Pairwise comparisons revealed a trend of HC males > HC females and LLD males < HC males for the connections between the left habenula and the left precentral gyrus, angular gyrus and middle frontal gyrus. Conversely, a trend of HC males < HC females and LLD males > HC males was found for the connections between the right habenula and right middle temporal pole. Furthermore, there was a significant interaction for the sFC of the right habenula with the right fusiform gyrus, with trends of HC males > HC females, LLD males < HC males, and LLD females > HC females. Regression analysis revealed that left habenular-left insular dFC was associated with long-delay memory in females and working memory in males; right habenular-right middle temporal pole dFC was associated with information processing speed in females. Sex moderated the relationships between cognitive function (global cognition, delay-recalled memory and working memory) and dFC between the left habenula and left insula. In conclusions, this study revealed sex-specific alterations in the functional connectivity patterns of the habenula in LLD patients, and these alterations were associated with various cognitive functions in a sex-specific manner. These findings provide a neurobiological basis for understanding sex differences in LLD patients.

Blockade of mGluR1 and mGluR5 in the lateral habenula produces the opposite effects in the regulation of depressive-like behaviors in the hemiparkinsonian rats

Depression is one of the most common non-motor symptoms in Parkinson's disease (PD) and the hyperactivity of the lateral habenula (LHb) may contribute to depression. The present study was performed to investigate the effects and mechanisms of group I metabotropic glutamate receptors (mGluRs) in the LHb on PD-related depressive-like behaviors. Unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc) were used to establish the PD rat model. The group I mGluRs agonist and antagonists for mGluR1 and mGluR5 were microinjected into the LHb to observe their effects on PD-related depressive-like behaviors, electrical activities of the LHb, release of monoamines in the medial prefrontal cortex (mPFC) in sham and the lesioned rats. Lesions of the SNc induced depressive-like behaviors and hyperactivity of LHb neurons. Activation of group I mGluRs by 3,5-DHPG induced or enhanced depressive-like behaviors, increased the firing rate of the LHb neurons, and decreased dopamine (DA) and serotonin (5-HT) levels in the mPFC in the two groups of rats. Blockade of mGluR1 by YM298198 also produced similar effects with 3,5-DHPG, however, blockade of mGluR5 by MTEP produced opposite effects. Western blotting data showed that lesions of the SNc in rats down-regulated the expression of mGluR1 and mGluR5 in the LHb. These results suggest that mGluR1 and mGluR5 in the LHb induce opposite effects on depressive-like behaviors, which may attribute to the changed firing rate of LHb neurons by the presynaptic and postsynaptic mechanisms, and the changes in the monoamine levels.

Neuronal Properties in the Lateral Habenula and Adult-Newborn Interactions in Virgin Female and Male Mice

The behavioral interactions between adults and newborns are decisive for the fitness and the survival of offspring across the animal kingdom. In laboratory mice, while virgin females display caregiving behaviors, virgin males are rather neglectful or aggressive toward pups. Despite the importance of these behavioral variations, the underlying neural mechanisms remain poorly understood. Brain regions encoding these behaviors may exhibit sex-dependent functional differences at the baseline. Additionally, these structures might undergo sex-specific plasticity after adults interact with the offspring. Emerging evidence suggests sex-based differences in input connectivity, genetics, and receptor expression of the epithalamic lateral habenula (LHb). Moreover, LHb neuronal activity is instrumental for adult-newborn interactions. However, whether LHb neuronal function varies between sexes and/or undergoes adaptations following interactions with pups has not been fully investigated. In this study, we used in vivo and ex vivo single-cell electrophysiology to examine the basal LHb neuronal activity of virgin female and male mice. In a second set of experiments, we exposed mice to pups and recapitulated sex-based divergent behaviors. Recordings in acute slices showed no alterations in LHb firing properties, regardless of sex or pup exposure. These findings suggest that, although the LHb participates in adult behaviors toward pups, this is not mediated by sex-dependent functional differences or adaptations in the neuronal firing properties. Thus, this study provides new insights into the neural basis of sex-specific adult-newborn behaviors and the role of the LHb in these processes.

The lateral habenula integrates age and experience to promote social transitions in developing rats

Early caregiving adversity (ECA) is associated with social behavior deficits and later development of psychopathology. However, the infant neural substrates of ECA are poorly understood. The lateral habenula (LHb), a highly conserved brain region with consistent links to adult psychopathology, is understudied in development, when the brain is most vulnerable to environmental impacts. Here, we describe the structural and functional ontogeny of the LHb and its behavioral role in infant and juvenile rat pups. We show that the LHb promotes a developmental transition in social approach behavior under threat as typically reared infants mature. By contrast, we show that ECA disrupts habenular ontogeny, including volume, protein expression, firing properties, and corticohabenular connectivity. Furthermore, inhibiting a specific corticohabenular projection rescues infant social approach deficits following ECA. Together, these results identify immediate biomarkers of ECA in the LHb and highlight this region as a site of early social processing and behavior control.

Substantia Nigra Dopamine Neuronal Responses to Habenular Stimulation and Foot Shock Are Altered by Lesions of the Rostromedial Tegmental Nucleus

Dopamine (DA) neurons of the substantia nigra (SN) and ventral tegmental area generally respond to aversive stimuli or the absence of expected rewards with transient inhibition of firing rates, which can be recapitulated with activation of the lateral habenula (LHb) and eliminated by lesioning the intermediating rostromedial tegmental nucleus (RMTg). However, a minority of DA neurons respond to aversive stimuli, such as foot shock, with a transient increase in firing rate, an outcome that rarely occurs with LHb stimulation. The degree to which individual neurons respond to these two stimulation modalities with the same response phenotype and the role of the RMTg is not known. Here, we record responses from single SN DA neurons to alternating activation of the LHb and foot shock in male rats. Lesions of the RMTg resulted in a shift away from inhibition to no response during both foot shock and LHb stimulation. Furthermore, lesions unmasked an excitatory response during LHb stimulation. The response correspondence within the same neuron between the two activation sources was no different from chance in sham controls, suggesting that external inputs rather than intrinsic DA neuronal properties are more important to response outcome. These findings contribute to a literature that shows a complex neurocircuitry underlies the regulation of DA activity and, by extension, behaviors related to learning, anhedonia, and cognition.

The lateral habenula: A hub for value-guided behavior

The habenula is an evolutionarily highly conserved diencephalic brain region divided into two major parts, medial and lateral. Over the past two decades, studies of the lateral habenula (LHb), in particular, have identified key functions in value-guided behavior in health and disease. In this review, we focus on recent insights into LHb connectivity and its functional relevance for different types of aversive and appetitive value-guided behavior. First, we give an overview of the anatomical organization of the LHb and its main cellular composition. Next, we elaborate on how distinct LHb neuronal subpopulations encode aversive and appetitive stimuli and on their involvement in more complex decision-making processes. Finally, we scrutinize the afferent and efferent connections of the LHb and discuss their functional implications for LHb-dependent behavior. A deepened understanding of distinct LHb circuit components will substantially contribute to our knowledge of value-guided behavior.

Whole-brain connections of glutamatergic neurons in the mouse lateral habenula in both sexes

BACKGROUND

The lateral habenula (LHb) is an epithalamus nucleus that is evolutionarily conserved and involved in various physiological functions, such as encoding value signals, integrating emotional information, and regulating related behaviors. The cells in the LHb are predominantly glutamatergic and have heterogeneous functions in response to different stimuli. The circuitry connections of the LHb glutamatergic neurons play a crucial role in integrating a wide range of events. However, the circuitry connections of LHb glutamatergic neurons in both sexes have not been thoroughly investigated.

METHODS

In this study, we injected Cre-dependent retrograde trace virus and anterograde synaptophysin-labeling virus into the LHb of adult male and female Vglut2-ires-Cre mice, respectively. We then quantitatively analyzed the input and output of the LHb glutamatergic connections in both the ipsilateral and contralateral whole brain.

RESULTS

Our findings showed that the inputs to LHbvGlut2 neurons come from more than 30 brain subregions, including the cortex, striatum, pallidum, thalamus, hypothalamus, midbrain, pons, medulla, and cerebellum with no significant differences between males and females. The outputs of LHbvGlut2 neurons targeted eight large brain regions, primarily focusing on the midbrain and pons nuclei, with distinct features in presynaptic bouton across different brain subregions. While correlation and cluster analysis revealed differences in input and collateral projection features, the input-output connection pattern of LHbvGlut2 neurons in both sexes was highly similar.

CONCLUSIONS

This study provides a systematic and comprehensive analysis of the input and output connections of LHbvGlut2 neurons in male and female mice, shedding light on the anatomical architecture of these specific cell types in the mouse LHb. This structural understanding can help guide further investigations into the complex functions of the LHb.

Neuronal Excitability in the Medial Habenula and Ventral Tegmental Area Is Differentially Modulated by Nicotine Dosage and Menthol in a Sex-Specific Manner

The medial habenula (MHb) has been identified as the limiting factor for nicotine intake and facilitating nicotine withdrawal. However, few studies have assessed MHb neuronal excitability in response to nicotine, and, currently, a gap in knowledge is present for finding behavioral correlates to neuronal excitability in the region. Moreover, no study to date has evaluated sex or nicotine dosage as factors of excitability in the MHb. Here, we utilized an e-vape self-administration (EVSA) model to determine differences between sexes with different nicotine dosages ± menthol. Following this paradigm, we employed patch-clamp electrophysiology to assess key metrics of MHb neuronal excitability in relation to behavioral endpoints. We observed female mice self-administered significantly more than males, regardless of dosage. We also observed a direct correlation between self-administration behavior and MHb excitability with low-dose nicotine + menthol in males. Conversely, a high dose of nicotine ± menthol yields an inverse correlation between excitability and self-administration behavior in males only. In addition, intrinsic excitability in the ventral tegmental area (VTA) does not track with the amount of nicotine self-administered. Rather, they correlate to the active/inactive discrimination of mice. Using fast-scan cyclic voltammetry, we also observed that dopamine release dynamics are linked to reinforcement-related behavior in males and motivation-related behaviors in females. These results point to a sex-specific difference in the activity of the MHb and VTA leading to distinct differences in self-administration behavior. His could lend evidence to clinical observations of smoking and nicotine-use behavior differing between males and females.

The lateral habenula integrates age and experience to promote social transitions in developing rats

Social behavior deficits are an early-emerging marker of psychopathology and are linked with early caregiving quality. However, the infant neural substrates linking early care to social development are poorly understood. Here, we focused on the infant lateral habenula (LHb), a highly-conserved brain region at the nexus between forebrain and monoaminergic circuits. Despite its consistent links to adult psychopathology, this brain region has been understudied in development when the brain is most vulnerable to environmental impacts. In a task combining social and threat cues, suppressing LHb principal neurons had opposing effects in infants versus juveniles, suggesting the LHb promotes a developmental switch in social approach behavior under threat. We observed that early caregiving adversity (ECA) disrupts typical growth curves of LHb baseline structure and function, including volume, firing patterns, neuromodulatory receptor expression, and functional connectivity with cortical regions. Further, we observed that suppressing cortical projections to the LHb rescued social approach deficits following ECA, identifying this microcircuit as a substrate for disrupted social behavior. Together, these results identify immediate biomarkers of ECA in the LHb and highlight this region as a site of early social processing and behavior control.