Dorsolateral septum GLP-1R neurons regulate feeding via lateral hypothalamic projections.

OBJECTIVE: Although glucagon-like peptide 1 (GLP-1) is known to regulate feeding, the central mechanisms contributing to this function remain enigmatic. Here, we aim to test the role of neurons expressing GLP-1 receptors (GLP-1R) in the dorsolateral septum (dLS; dLSGLP-1R) that project to the lateral hypothalamic area (LHA) on food intake and determine the relationship with feeding regulation. METHODS: Using chemogenetic manipulations, we assessed how activation or inhibition of dLSGLP-1R neurons affected food intake in Glp1r-ires-Cre mice. Then, we used channelrhodopsin-assisted circuit mapping, chemogenetics, and electrophysiological recordings to identify and assess the role of the pathway from dLSGLP-1R →LHA projections in regulating food intake. RESULTS: Chemogenetic inhibition of dLSGLP-1R neurons increases food intake. LHA is a major downstream target of dLSGLP-1R neurons. The dLSGLP-1R→LHA projections are GABAergic, and chemogenetic inhibition of this pathway also promotes food intake. While chemogenetic activation of dLSGLP-1R→LHA projections modestly decreases food intake, optogenetic stimulation of the dLSGLP-1R→LHA projection terminals in the LHA rapidly suppresses feeding behavior. Finally, we demonstrate that the GLP-1R agonist, Exendin 4 enhances dLSGLP-1R →LHA GABA release. CONCLUSIONS: Together, these results demonstrate that dLS-GLP-1R neurons and the inhibitory pathway to LHA can regulate feeding behavior, which might serve as a potential therapeutic target for the treatment of eating disorders or obesity.

State-dependent central synaptic regulation by GLP-1 is essential for energy homeostasis.

Central nervous system (CNS) control of metabolism plays a pivotal role in maintaining energy homeostasis. Glucagon-like peptide-1 (GLP-1, encoded by Gcg), secreted by a distinct population of neurons located within the nucleus tractus solitarius (NTS), suppresses feeding through projections to multiple brain targets1-3. Although GLP-1 analogs are proven clinically effective in treating type 2 diabetes and obesity4, the mechanisms of GLP-1 action within the brain remain unclear. Here, we investigate the involvement of GLP-1 receptor (GLP-1R) mediated signaling in a descending circuit formed by GLP-1R neurons in the paraventricular hypothalamic nucleus (PVNGLP-1R) that project to dorsal vagal complex (DVC) neurons of the brain stem in mice. PVNGLP- 1R→DVC synapses release glutamate that is augmented by GLP-1 via a presynaptic mechanism. Chemogenetic activation of PVNGLP-1R→DVC neurons suppresses feeding. The PVNGLP-1R→DVC synaptic transmission is dynamically regulated by energy states. In a state of energy deficit, synaptic strength is weaker but is more profoundly augmented by GLP-1R signaling compared to an energy-replete state. In an obese state, the dynamic synaptic strength changes in the PVNGLP-1R→DVC descending circuit are disrupted. Blocking PVNGLP-1R→DVC synaptic release or ablation of GLP-1R in the presynaptic compartment increases food intake and causes obesity, elevated blood glucose, and impaired insulin sensitivity. These findings suggest that the state-dependent synaptic plasticity in this PVNGLP-1R→DVC descending circuit mediated by GLP-1R signaling is an essential regulator of energy homeostasis.

Dorsolateral septum GLP-1R neurons regulate feeding via lateral hypothalamic projections.

Objective: Although glucagon-like peptide 1 (GLP-1) is known to regulate feeding, the central mechanisms contributing to this function remain enigmatic. Here, we aim to test the role of neurons expressing GLP-1 receptors (GLP-1R) in the dorsolateral septum (dLS; dLS GLP-1R ) and their downstream projections on food intake and determine the relationship with feeding regulation. Methods: Using chemogenetic manipulations, we assessed how activation or inhibition of dLS GLP-1R neurons affected food intake in Glp1r-ires-Cre mice. Then, we used channelrhodopsin-assisted circuit mapping, chemogenetics, and electrophysiological recordings to identify and assess the role of the pathway from dLS GLP-1R neurons to the lateral hypothalamic area (LHA) in regulating food intake. Results: Chemogenetic inhibition of dLS GLP-1R neurons increases food intake. LHA is a major downstream target of dLS GLP-1R neurons. The dLS GLP-1R →LHA projections are GABAergic, and chemogenetic inhibition of this pathway also promotes food intake. While chemogenetic activation of dLS GLP-1R →LHA projections modestly decreases food intake, optogenetic stimulation of the dLS GLP-1R →LHA projection terminals in the LHA rapidly suppressed feeding behavior. Finally, we demonstrate that the GLP-1R agonist, Exendin 4 enhances dLS GLP-1R →LHA GABA release. Conclusions: Together, these results demonstrate that dLS-GLP-1R neurons and the inhibitory pathway to LHA can regulate feeding behavior, which might serve as a potential therapeutic target for the treatment of eating disorders or obesity. Highlights: Chemogenetic inhibition of dLS GLP-1R neurons boosts food intake in mice dLS GLP-1R neuron activation does not alter feeding, likely by collateral inhibition dLS GLP-1R neurons project to LHA and release GABA Activation of dLS GLP-1R →LHA axonal terminals suppresses food intake GLP-1R agonism enhances dLS GLP-1R →LHA GABA release via a presynaptic mechanism.

Metabolic and behavioral alterations associated with viral vector-mediated toxicity in the paraventricular hypothalamic nucleus.

OBJECTIVE: Combining adeno-associated virus (AAV)-mediated expression of Cre recombinase with genetically modified floxed animals is a powerful approach for assaying the functional role of genes in regulating behavior and metabolism. Extensive research in diverse cell types and tissues using AAV-Cre has shown it can save time and avoid developmental compensation as compared to using Cre driver mouse line crossings. We initially sought to study the impact of ablation of corticotropin-releasing hormone (CRH) in the paraventricular hypothalamic nucleus (PVN) using intracranial AAV-Cre injection in adult animals. METHODS: In this study, we stereotactically injected AAV8-hSyn-Cre or a control AAV8-hSyn-GFP both Crh-floxed and wild-type mouse PVN to assess behavioral and metabolic impacts. We then used immunohistochemical markers to systematically evaluate the density of hypothalamic peptidergic neurons and glial cells. RESULTS: We found that delivery of one specific preparation of AAV8-hSyn-Cre in the PVN led to the development of obesity, hyperphagia, and anxiety-like behaviors. This effect occurred independent of sex and in both floxed and wild-type mice. We subsequently found that AAV8-hSyn-Cre led to neuronal cell death and gliosis at the site of viral vector injections. These behavioral and metabolic deficits were dependent on injection into the PVN. An alternatively sourced AAV-Cre did not reproduce the same results. CONCLUSIONS: Our findings reveal that delivery of a specific batch of AAV-Cre could lead to cellular toxicity and lesions in the PVN that cause robust metabolic and behavioral impacts. These alterations can complicate the interpretation of Cre-mediated gene knockout and highlight the need for rigorous controls.

Metabolic and behavioral alterations associated with viral vector-mediated toxicity in the paraventricular hypothalamic nucleus.

Objective: Combining adeno-associated virus (AAV)-mediated expression of Cre recombinase with genetically modified floxed animals is a powerful approach for assaying the functional role of genes in regulating behavior and metabolism. Extensive research in diverse cell types and tissues using AAV-Cre has shown it can save time and avoid developmental compensation as compared to using Cre driver mouse line crossings. We initially sought to study the impact of ablation of corticotropin-releasing hormone (CRH) in the paraventricular hypothalamic nucleus (PVN) using intracranial AAV-Cre injection in adult animals. Methods: In this study, we stereotactically injected AAV8-hSyn-Cre or a control AAV8-hSyn-GFP both Crh-floxed and wild-type mouse PVN to assess behavioral and metabolic impacts. We then used immunohistochemical markers to systematically evaluate the density of hypothalamic peptidergic neurons and glial cells. Results: We found that delivery of one specific preparation of AAV8-hSyn-Cre in the PVN led to the development of obesity, hyperphagia, and anxiety-like behaviors. This effect occurred independent of sex and in both floxed and wild-type mice. We subsequently found that AAV8-hSyn-Cre led to neuronal cell death and gliosis at the site of viral vector injections. These behavioral and metabolic deficits were dependent on injection into the PVN. An alternatively sourced AAV-Cre did not reproduce the same results. Conclusions: Our findings reveal that delivery of a specific batch of AAV-Cre could lead to cellular toxicity and lesions in the PVN that cause robust metabolic and behavioral impacts. These alterations can complicate the interpretation of Cre-mediated gene knockout and highlight the need for rigorous controls.