Thermoregulatory pathway underlying the pyrogenic effects of prostaglandin E2 in the lateral parabrachial nucleus of male rats.

It has been shown that prostaglandin (PG) E2 synthesized in the lateral parabrachial nucleus (LPBN) is involved in lipopolysaccharide-induced fever. But the neural mechanisms of how intra-LPBN PGE2 induces fever remain unclear. In this study, we investigated whether the LPBN-preoptic area (POA) pathway, the thermoafferent pathway for feed-forward thermoregulatory responses, mediates fever induced by intra-LPBN PGE2 in male rats. The core temperature (Tcore) was monitored using a temperature radiotelemetry transponder implanted in rat abdomen. We showed that microinjection of PGE2 (0.28 nmol) into the LPBN significantly enhanced the density of c-Fos-positive neurons in the median preoptic area (MnPO). The chemical lesioning of MnPO with ibotenate or selective genetic lesioning or inhibition of the LPBN-MnPO pathway significantly attenuated fever induced by intra-LPBN injection of PGE2. We demonstrated that EP3 receptor was a pivotal receptor for PGE2-induced fever, since microinjection of EP3 receptor agonist sulprostone (0.2 nmol) or EP3 receptor antagonist L-798106 (2 nmol) into the LPBN mimicked or weakened the pyrogenic action of LPBN PGE2, respectively, but this was not the case for EP4 and EP1 receptors. Whole-cell recording from acute LPBN slices revealed that the majority of MnPO-projecting neurons originating from the external lateral (el) and dorsal (d) LPBN were excited and inhibited, respectively, by PGE2 perfusion, initiating heat-gain and heat-loss mechanisms. The amplitude but not the frequency of spontaneous and miniature glutamatergic excitatory postsynaptic currents (sEPSCs and mEPSCs) in MnPO-projecting LPBel neurons increased after perfusion with PGE2; whereas the frequency and amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) and the A-type potassium (IA) current density did not change. In MnPO-projecting LPBd neurons, neither sEPSCs nor sIPSCs responded to PGE2; however, the IA current density was significantly increased by PGE2 perfusion. These electrophysiological responses and the thermoeffector reactions to intra-LPBN PGE2 injection, including increased brown adipose tissue thermogenesis, shivering, and decreased heat dissipation, were all abolished by L-798106, and mimicked by sulprostone. These results suggest that the pyrogenic effects of intra-LPBN PGE2 are mediated by both the inhibition of the LPBd-POA pathway through the EP3 receptor-mediated activation of IA currents and the activation of the LPBel-POA pathway through the selective enhancement of glutamatergic synaptic transmission via EP3 receptors.

A parabrachial-hypothalamic parallel circuit governs cold defense in mice.

Thermal homeostasis is vital for mammals and is controlled by brain neurocircuits. Yet, the neural pathways responsible for cold defense regulation are still unclear. Here, we found that a pathway from the lateral parabrachial nucleus (LPB) to the dorsomedial hypothalamus (DMH), which runs parallel to the canonical LPB to preoptic area (POA) pathway, is also crucial for cold defense. Together, these pathways make an equivalent and cumulative contribution, forming a parallel circuit. Specifically, activation of the LPB → DMH pathway induced strong cold-defense responses, including increases in thermogenesis of brown adipose tissue (BAT), muscle shivering, heart rate, and locomotion. Further, we identified somatostatin neurons in the LPB that target DMH to promote BAT thermogenesis. Therefore, we reveal a parallel circuit governing cold defense in mice, which enables resilience to hypothermia and provides a scalable and robust network in heat production, reshaping our understanding of neural circuit regulation of homeostatic behaviors.

Hypothalamic warm-sensitive neurons require TRPC4 channel for detecting internal warmth and regulating body temperature in mice.

Precise monitoring of internal temperature is vital for thermal homeostasis in mammals. For decades, warm-sensitive neurons (WSNs) within the preoptic area (POA) were thought to sense internal warmth, using this information as feedback to regulate body temperature (Tcore). However, the cellular and molecular mechanisms by which WSNs measure temperature remain largely undefined. Via a pilot genetic screen, we found that silencing the TRPC4 channel in mice substantially attenuated hypothermia induced by light-mediated heating of the POA. Loss-of-function studies of TRPC4 confirmed its role in warm sensing in GABAergic WSNs, causing additional defects in basal temperature setting, warm defense, and fever responses. Furthermore, TRPC4 antagonists and agonists bidirectionally regulated Tcore. Thus, our data indicate that TRPC4 is essential for sensing internal warmth and that TRPC4-expressing GABAergic WSNs function as a novel cellular sensor for preventing Tcore from exceeding set-point temperatures. TRPC4 may represent a potential therapeutic target for managing Tcore.

Cooling-activated dorsomedial hypothalamic BDNF neurons control cold defense in mice.

BDNF and its expressing neurons in the brain critically control feeding and energy expenditure (EE) in both rodents and humans. However, whether BDNF neurons would function in thermoregulation during temperature challenges is unclear. Here, we show that BDNF neurons in the dorsomedial hypothalamus (DMHBDNF ) of mice are activated by afferent cooling signals. These cooling-activated BDNF neurons are mainly GABAergic. Activation of DMHBDNF neurons or the GABAergic subpopulations is sufficient to increase body temperature, EE, and physical activity. Conversely, blocking DMHBDNF neurons substantially impairs cold defense and reduces energy expenditure, physical activity, and UCP1 expression in BAT, which eventually results in bodyweight gain and glucose/insulin intolerance. Therefore, we identify a subset of DMHBDNF neurons as a novel type of cooling-activated neurons to promote cold defense. Thus, we reveal a critical role of BDNF circuitry in thermoregulation, which deepens our understanding of BDNF in controlling energy homeostasis and obesity.

Parabrachial neuron types categorically encode thermoregulation variables during heat defense.

Heat defense is crucial for survival and fitness. Transmission of thermosensory signals into hypothalamic thermoregulation centers represents a key layer of regulation in heat defense. Yet, how these signals are transmitted into the hypothalamus remains poorly understood. Here, we reveal that lateral parabrachial nucleus (LPB) glutamatergic prodynorphin and cholecystokinin neuron populations are progressively recruited to defend elevated body temperature. These two nonoverlapping neuron types form circuits with downstream preoptic hypothalamic neurons to inhibit the thermogenesis of brown adipose tissues (BATs) and activate tail vasodilation, respectively. Both circuits are activated by warmth and can limit fever development. The prodynorphin circuit is further required for regulating energy expenditure and body weight homeostasis. Thus, these findings establish that the genetic and functional specificity of heat defense neurons occurs as early as in the LPB and uncover categorical neuron types for encoding two heat defense variables, inhibition of BAT thermogenesis and activation of vasodilation.

A Brain Signaling Framework for Stress-Induced Depression and Ketamine Treatment Elucidated by Phosphoproteomics.

Depression is a common affective disorder characterized by significant and persistent low mood. Ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist, is reported to have a rapid and durable antidepressant effect, but the mechanisms are unclear. Protein phosphorylation is a post-translational modification that plays a crucial role in cell signaling. Thus, we present a phosphoproteomics approach to investigate the mechanisms underlying stress-induced depression and the rapid antidepressant effect of ketamine in mice. We analyzed the phosphoprotein changes induced by chronic unpredictable mild stress (CUMS) and ketamine treatment in two known mood control centers, the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAc). We initially obtained >8,000 phosphorylation sites. Quantitation revealed 3,988 sites from the mPFC and 3,196 sites from the NAc. Further analysis revealed that changes in synaptic transmission-related signaling are a common feature. Notably, CUMS-induced changes were reversed by ketamine treatment, as shown by the analysis of commonly altered sites. Ketamine also induced specific changes, such as alterations in synapse organization, synaptic transmission, and enzyme binding. Collectively, our findings establish a signaling framework for stress-induced depression and the rapid antidepressant effect of ketamine.

A hypothalamic circuit that controls body temperature.

The homeostatic control of body temperature is essential for survival in mammals and is known to be regulated in part by temperature-sensitive neurons in the hypothalamus. However, the specific neural pathways and corresponding neural populations have not been fully elucidated. To identify these pathways, we used cFos staining to identify neurons that are activated by a thermal challenge and found induced expression in subsets of neurons within the ventral part of the lateral preoptic nucleus (vLPO) and the dorsal part of the dorsomedial hypothalamus (DMD). Activation of GABAergic neurons in the vLPO using optogenetics reduced body temperature, along with a decrease in physical activity. Optogenetic inhibition of these neurons resulted in fever-level hyperthermia. These GABAergic neurons project from the vLPO to the DMD and optogenetic stimulation of the nerve terminals in the DMD also reduced body temperature and activity. Electrophysiological recording revealed that the vLPO GABAergic neurons suppressed neural activity in DMD neurons, and fiber photometry of calcium transients revealed that DMD neurons were activated by cold. Accordingly, activation of DMD neurons using designer receptors exclusively activated by designer drugs (DREADDs) or optogenetics increased body temperature with a strong increase in energy expenditure and activity. Finally, optogenetic inhibition of DMD neurons triggered hypothermia, similar to stimulation of the GABAergic neurons in the vLPO. Thus, vLPO GABAergic neurons suppressed the thermogenic effect of DMD neurons. In aggregate, our data identify vLPO→DMD neural pathways that reduce core temperature in response to a thermal challenge, and we show that outputs from the DMD can induce activity-induced thermogenesis.

Intraruminal administration of Megasphaera elsdenii modulated rumen fermentation profile in mid-lactation dairy cows.

This study evaluated the effects of intraruminal administration of Megasphaera elsdenii on ruminal fermentation patterns, the profile of plasma metabolites, and milk yield and composition of mid-lactation dairy cows. Eight primiparous, ruminally cannulated Holstein cows were arranged in a paired 2×2 crossover design. Cows were randomly assigned to one of two treatments: 1) intraruminal inoculation of 35 ml suspension per day of M. elsdenii ATCC 25940 (MEGA), containing 108 cfu/ml of bacteria, dissolved in 35 ml of saline (0·15 m), or 2) carrier alone (35 ml saline; CTR). Both postprandial and preprandial rumen volatile fatty acids (VFA) and plasma metabolite measurements were analysed. Postprandial VFA patterns were affected the most, with butyrate (P<0·01) and valerate (P<0·01) proportions increasing, and acetate (P<0·01), isobutyrate (P=0·05) and isovalerate (P<0·01) decreasing in MEGA cows. Preprandial data measured at various days showed that MEGA dosage tended to increase the molar proportion of propionate (P=0·09) and lower the acetate to propionate ratio (P=0·07) in the rumen fluid. There was no effect of treatment on rumen pH and on the concentration of lactate in the rumen as well as on selected preprandial plasma metabolites. Postprandial plasma concentrations of cholesterol tended to increase (P=0·07) in MEGA cows compared with CTR. Concentrations of non-esterified fatty acids (NEFA) in the plasma were lower in MEGA cows after the morning feeding (P<0·01). Sampling hour also affected plasma NEFA in this study. Plasma ß-hydroxybutyrate (BHBA) were not affected by the treatment (P>0·05); however, after the morning feeding BHBA concentration was increased in both groups of cows. Dry matter intake and milk yield and composition were not affected by treatment. In conclusion, results indicate that M. elsdenii has the potential to modulate the rumen fermentation profile in mid-lactation Holstein cows, but these effects were only slightly reflected in changes in plasma metabolites and milk composition.