Somatostatin-Positive Neurons in the Rostral Zona Incerta Modulate Innate Fear-Induced Defensive Response in Mice

Control of defensive behavior by the nucleus of Darkschewitsch GABAergic neurons

The nucleus of Darkschewitsch (ND), mainly composed of GABAergic neurons, is widely recognized as a component of the eye-movement controlling system. However, the functional contribution of ND GABAergic neurons (NDGABA) in animal behavior is largely unknown. Here, we show that NDGABA neurons were selectively activated by different types of fear stimuli, such as predator odor and foot shock. Optogenetic and chemogenetic manipulations revealed that NDGABA neurons mediate freezing behavior. Moreover, using circuit-based optogenetic and neuroanatomical tracing methods, we identified an excitatory pathway from the lateral periaqueductal gray (lPAG) to the ND that induces freezing by exciting ND inhibitory outputs to the motor-related gigantocellular reticular nucleus, ventral part (GiV). Together, these findings indicate the NDGABA population as a novel hub for controlling defensive response by relaying fearful information from the lPAG to GiV, a mechanism critical for understanding how the freezing behavior is encoded in the mammalian brain.

Glutamatergic Projection from the Ventral Tegmental Area to the Zona Incerta Regulates Fear Response

Innate defensive behavior is important for animal survival. The Vglut2+ neurons in the ventral tegmental area (VTA) have been demonstrated to play important roles in innate defensive behaviors, but the neural circuit mechanism is still unclear. Here, we find that VTA - zona incerta (ZI) glutamatergic projection is involved in regulating innate fear responses. Combining calcium signal recording and chemogentics, we find that VTA-Vglut2+ neurons respond to foot shock stimulus. Inhibition of VTA-Vglut2+ neurons reduces foot shock-evoked freezing, while chemogentic activation of these neurons results in an enhanced fear response. Using viral tracing and immunofluorescence, we show that VTA - Vglut2+ neurons send direct excitatory outputs to the ZI. Moreover, we find that the activity of VTAVglut2 - ZI projection is pivotal in modulating fear response. Together, our study reveals a new VTA - ZI glutamatergic circuit in mediating innate fear response and provides a potential target for treating post-traumatic stress disorder.

Low-frequency stimulation in the zona incerta attenuates seizure via driving GABAergic neuronal activity

BACKGROUND

Managing refractory epilepsy presents a significant a substantial clinical challenge. Deep brain stimulation (DBS) has emerged as a promising avenue for addressing refractory epilepsy. However, the optimal stimulation targets and effective parameters of DBS to reduce seizures remian unidentified.

OBJECTIVES

This study endeavors to scrutinize the therapeutic potential of DBS within the zona incerta (ZI) across diverse seizure models and elucidate the associated underlying mechanisms.

METHODS

We evaluated the therapeutic potential of DBS with different frequencies in the ZI on kainic acid (KA)-induced TLE model or M1-cortical seizures model, pilocarpine-induced M1-cortical seizure models, and KA-induced epilepsy model. Further, employing calcium fiber photometry combined with cell-specific ablation, we sought to clarified the causal role of ZI GABAergic neurons in mediating the therapeutic effects of DBS.

RESULTS

Our findings reveal that DBS in the ZI alleviated the severity of seizure activities in the KA-induced TLE model. Meanwhile, DBS attenuated seizure activities in KA- or pilocarpine-induced M1-cortical seizure model. In addition, DBS exerts a mitigating influence on KA induced epilepsy model. DBS in the ZI showed anti-seizure effects at low frequency spectrum, with 5 Hz exhibiting optimal efficacy. The low-frequency DBS significantly increased the calcium activities of ZI GABAergic neurons. Furthermore, selective ablation of ZI GABAergic neurons with taCasp3 blocked the anti-seizure effect of low-frequency DBS, indicating the anti-seizure effect of DBS is mediated by the activation of ZI GABAergic neurons.

CONCLUSION

Our results demonstrate that low-frequency DBS in the ZI attenuates seizure via driving GABAergic neuronal activity. This suggests that the ZI represents a potential DBS target for treating both hippocampal and cortical seizure through the activation of GABAergic neurons, thereby holding therapeutic significance for seizure treatment.

Disentangling the identity of the zona incerta: a review of the known connections and latest implications

The zona incerta (ZI) is a subthalamic region composed by loosely packed neurochemically mixed neurons, juxtaposed to the main ascending and descending bundles. The extreme neurochemical diversity that characterizes this area, together with the diffuseness of its connections with the entire neuraxis and its hard-to-reach positioning in the brain caused the ZI to keep its halo of mystery for over a century. However, in the last decades, a rich albeit fragmentary body of knowledge regarding both the incertal anatomical connections and functional implications has been built mostly based on rodent studies and its lack of cohesion makes difficult to depict an integrated, exhaustive picture regarding the ZI and its roles. This review aims to provide a unified resource that summarizes the current knowledge regarding the anatomical profile of interactions of the ZI in rodents and non-human primates and the functional significance of its connections, highlighting the aspects still unbeknown to research.

A nigroincertal projection mediates aversion and enhances coping responses to potential threat

Recent studies have shown that the non-DA neurons in the ventral tegmental area (VTA) and substantia nigra (SN) not only modulate motivational behaviors but also regulate defensive behaviors. While zona incerta (ZI) is a threat-responsive substrate and receives innervations from the ventral midbrain, the function of the ventral midbrain-to-ZI connection remains poorly defined. Here, we demonstrate that the ZI receives heterogenous innervations from the ventral midbrain. By utilizing a retrograde AAV preferentially labeling non-DA neurons in the ventral midbrain, we found that ZI-projecting non-DA cells in the ventral midbrain are activated by restraint stress. We focused on the SN and found that SN-to-ZI GABAergic input is engaged by a predatory odor. Sustained pan-neuronal SN-to-ZI activation results in aversion and enhances defensive behaviors, likely through a disinhibition mechanism to recruit downstream brain regions that regulate defensive behaviors. Collectively, our results reveal a novel role of nigroincertal projection in mediating negative valence and regulating defensive behaviors.

Advances in neural circuits of innate fear defense behavior

Fear, a negative emotion triggered by dangerous stimuli, can lead to psychiatric disorders such as phobias, anxiety disorders, and depression. Investigating the neural circuitry underlying congenital fear can offer insights into the pathophysiological mechanisms of related psychiatric conditions. Research on innate fear primarily centers on the response mechanisms to various sensory signals, including olfactory, visual and auditory stimuli. Different types of fear signal inputs are regulated by distinct neural circuits. The neural circuits of the main and accessory olfactory systems receive and process olfactory stimuli, mediating defensive responses like freezing. Escape behaviors elicited by visual stimuli are primarily regulated through the superior colliculus and hypothalamic projection circuits. Auditory stimuli-induced responses, including escape, are mainly mediated through auditory cortex projection circuits. In this article, we review the research progress on neural circuits of innate fear defensive behaviors in animals. We further discuss the different sensory systems, especially the projection circuits of olfactory, visual and auditory systems, to provide references for the mechanistic study of related mental disorders.

Providing or receiving alloparental care promote partner preference and alter central oxytocin and dopamine systems in adult mandarin voles

Juveniles of cooperative breeding species usually remain in the natal area and provide care to younger siblings, a behavior considered one form of alloparenting in the natural condition. Previous studies have demonstrated the effects of providing or receiving alloparental care on adult behaviors, including anxiety-like behavior, social interaction, and parental behavior, but little is known about the influences on species-typical bonding behaviors, such as pair-bond formation. In this study, we explored this concept using socially monogamous mandarin voles (Lasiopodomys mandarinus). As the oxytocin (OT) and dopamine systems are involved in alloparental and pair-bonding behaviors, we also examined the levels of central OT and tyrosine hydroxylase (TH), as well as OT receptor (OTR) and dopamine D1-type and D2-type receptors (D1R and D2R) mRNA expression in the nucleus accumbens (NAcc) and amygdala to investigate the underlying mechanisms. Our results show that mandarin voles providing alloparental care to younger siblings displayed facilitation of partner preference formation, lower levels of OT expression in the paraventricular nucleus of the hypothalamus (PVN) and lateral hypothalamus (LH), and increased OTR and D2R mRNA expression in the NAcc compared to controls. Individuals receiving alloparental care also demonstrated facilitation of partner preference formation in adult voles. Additionally, alloparental care enhanced OT expression in the PVN, anterior medial preoptic nucleus (MPOAa), medial amygdala (MeA), and TH expression in the ventral tegmental area (VTA) and zona incerta (ZI). Furthermore, males displayed decreased D1R mRNA expression in the NAcc, whereas females showed slightly increased D2R expression in the amygdala. These results demonstrate that providing or received alloparental care can promote partner preference formation in monogamous species and that these changes are associated with altered OT and dopamine levels and their receptors in specific brain regions.

A parabrachial to hypothalamic pathway mediates defensive behavior

Defensive behaviors are critical for animal's survival. Both the paraventricular nucleus of the hypothalamus (PVN) and the parabrachial nucleus (PBN) have been shown to be involved in defensive behaviors. However, whether there are direct connections between them to mediate defensive behaviors remains unclear. Here, by retrograde and anterograde tracing, we uncover that cholecystokinin (CCK)-expressing neurons in the lateral PBN (LPB^CCK) directly project to the PVN. By in vivo fiber photometry recording, we find that LPB^CCK neurons actively respond to various threat stimuli. Selective photoactivation of LPB^CCK neurons promotes aversion and defensive behaviors. Conversely, photoinhibition of LPB^CCK neurons attenuates rat or looming stimuli-induced flight responses. Optogenetic activation of LPB^CCK axon terminals within the PVN or PVN glutamatergic neurons promotes defensive behaviors. Whereas chemogenetic and pharmacological inhibition of local PVN neurons prevent LPB^CCK-PVN pathway activation-driven flight responses. These data suggest that LPB^CCK neurons recruit downstream PVN neurons to actively engage in flight responses. Our study identifies a previously unrecognized role for the LPB^CCK-PVN pathway in controlling defensive behaviors.