Optogenetic Inhibition of Medial Prefrontal Cortex-Pontine Nuclei Projections During the Stimulus-free Trace Interval Impairs Temporal Associative Motor Learning.

The medial prefrontal cortex (mPFC) is closely involved in many higher-order cognitive functions, including learning to associate temporally discontiguous events (called temporal associative learning). However, direct evidence for the role of mPFC and the neural pathway underlying modulation of temporal associative motor learning is sparse. Here, we show that optogenetic inhibition of the mPFC or its axon terminals at the pontine nuclei (PN) during trace intervals or whole trial period significantly impaired the trace eyeblink conditioning (TEC), but had no significant effects on TEC during the conditioned stimulus or intertrial interval period. Our results suggest that activities associated with the mPFC-PN projection during trace intervals is crucial for trace associative motor learning. This finding is of great importance in understanding the mechanisms and the relevant neural pathways underlying mPFC modulation of temporal associative motor learning.

Medial Prefrontal Cortex-Pontine Nuclei Projections Modulate Suboptimal Cue-Induced Associative Motor Learning.

Diverse and powerful mechanisms have evolved to enable organisms to modulate learning and memory under a variety of survival conditions. Cumulative evidence has shown that the prefrontal cortex (PFC) is closely involved in many higher-order cognitive functions. However, when and how the medial PFC (mPFC) modulates associative motor learning remains largely unknown. Here, we show that delay eyeblink conditioning (DEC) with the weak conditioned stimulus (wCS) but not the strong CS (sCS) elicited a significant increase in the levels of c-Fos expression in caudal mPFC. Both optogenetic inhibition and activation of the bilateral caudal mPFC, or its axon terminals at the pontine nucleus (PN) contralateral to the training eye, significantly impaired the acquisition, recent and remote retrieval of DEC with the wCS but not the sCS. However, direct optogenetic activation of the contralateral PN had no significant effect on the acquisition, recent and remote retrieval of DEC. These results are of great importance in understanding the elusive role of the mPFC and its projection to PN in subserving the associative motor learning under suboptimal learning cue.

Prepulse inhibition and acoustic startle response in young healthy Chinese.

Prepulse inhibition (PPI) and habituation of the acoustic startle response (ASR) are considered to be effective neurobiological measures of sensorimotor gating and information processing. The deficit of PPI and habituation of ASR has been proposed to be candidate endophenotypes of schizophrenia spectrum disorders. However, there has been little information on PPI and ASR measures in Chinese. The present study aimed to provide more information about the characteristics of PPI and ASR in young healthy Chinese and investigate their sensitivity to experimental parameters and characteristics of population. In this study, we examined the PPI and habituation of ASR in 41 young healthy adults (21 males and 20 females), using an acoustic startle stimulus of 115 dB and a prepulse of 75 dB at a lead interval (LI) of 60 ms and 120 ms, respectively. The behavioral performance demonstrated that the PPI and habituation of ASR in all the young participants were robust. The significant difference was not observed in PPI and habituation between male and female. The block effect on PPI was significant; PPI reduces with increasing training. Latency facilitation was observed under prepulse conditions, with a significant effect of LI. Compared to previous studies in Caucasians, Chinese in this study shows a higher habituation and PPI. In conclusion, this research provides more data of behavioral characteristics of PPI and ASR in young healthy Chinese. Chinese in this study shows a higher habituation and PPI than Caucasians in previous studies.

Prefrontal control of cerebellum-dependent associative motor learning.

Behavioral studies have demonstrated that both medial prefrontal cortex (mPFC) and cerebellum play critical roles in trace eyeblink conditioning. However, little is known regarding the mechanism by which the two brain regions interact. By use of electrical stimulation of the caudal mPFC as a conditioned stimulus, we show evidence that persistent outputs from the mPFC to cerebellum are necessary and sufficient for the acquisition and expression of a trace conditioned response (CR)-like response. Specifically, the persistent outputs of caudal mPFC are relayed to the cerebellum via the rostral part of lateral pontine nuclei. Moreover, interfering with persistent activity by blockade of the muscarinic Ach receptor in the caudal mPFC impairs the expression of learned trace CRs. These results suggest an important way for the caudal mPFC to interact with the cerebellum during associative motor learning.

Prelimbic cortex-nucleus accumbens core projection positively regulates itch and itch-related aversion.

Itch is one of the most common clinical symptoms in patients with diseases of the skin, liver, or kidney, and it strongly triggers aversive emotion and scratching behavior. Previous studies have confirmed the role of the prelimbic cortex (Prl) and the nucleus accumbens core (NAcC), which are reward and motivation regulatory centers, in the regulation of itch. However, it is currently unclear whether the Prl-NAcC projection, an important pathway connecting these two brain regions, is involved in the regulation of itch and its associated negative emotions. In this study, rat models of acute neck and cheek itch were established by subcutaneous injection of 5-HT, compound 48/80, or chloroquine. Immunofluorescence experiments determined that the number of c-Fos-immunopositive neurons in the Prl increased during acute itch. Chemogenetic inhibition of Prl glutamatergic neurons or Prl-NAcC glutamatergic projections can inhibit both histaminergic and nonhistaminergic itch-scratching behaviors and rectify the itch-related conditioned place aversion (CPA) behavior associated with nonhistaminergic itch. The Prl-NAcC projection may play an important role in the positive regulation of itch-scratching behavior by mediating the negative emotions related to itch.

The Anterior Insula and its Projection to the Prelimbic Cortex are Involved in the Regulation of 5-HT-Induced Itch.

Itch is an unpleasant sensation that urges people and animals to scratch. Neuroimaging studies on itch have yielded extensive correlations with diverse cortical and subcortical regions, including the insular lobe. However, the role and functional specificity of the insular cortex (IC) and its subdivisions in itch mediation remains unclear. Here, we demonstrated by immunohistochemistry and fiber photometry tests, that neurons in both the anterior insular cortex (AIC) and the posterior insular cortex (PIC) are activated during acute itch processes. Pharmacogenetic experiments revealed that nonselective inhibition of global AIC neurons, or selective inhibition of the activity of glutaminergic neurons in the AIC, reduced the scratching behaviors induced by intradermal injection of 5-hydroxytryptamine (5-HT), but not those induced by compound 48/80. However, both nonselective inhibition of global PIC neurons and selective inhibition of glutaminergic neurons in the PIC failed to affect the itching-scratching behaviors induced by either 5-HT or compound 48/80. In addition, pharmacogenetic inhibition of AIC glutaminergic neurons effectively blocked itch-associated conditioned place aversion behavior, and inhibition of AIC glutaminergic neurons projecting to the prelimbic cortex significantly suppressed 5-HT-evoked scratching. These findings provide preliminary evidence that the AIC is involved, at least partially via aversive emotion mediation, in the regulation of 5-HT-, but not compound 48/80-induced itch.

Corticostriatal Neurons in the Anterior Auditory Field Regulate Frequency Discrimination Behavior.

The anterior auditory field (AAF) is a core region of the auditory cortex and plays a vital role in discrimination tasks. However, the role of the AAF corticostriatal neurons in frequency discrimination remains unclear. Here, we used c-Fos staining, fiber photometry recording, and pharmacogenetic manipulation to investigate the function of the AAF corticostriatal neurons in a frequency discrimination task. c-Fos staining and fiber photometry recording revealed that the activity of AAF pyramidal neurons was significantly elevated during the frequency discrimination task. Pharmacogenetic inhibition of AAF pyramidal neurons significantly impaired frequency discrimination. In addition, histological results revealed that AAF pyramidal neurons send strong projections to the striatum. Moreover, pharmacogenetic suppression of the striatal projections from pyramidal neurons in the AAF significantly disrupted the frequency discrimination. Collectively, our findings show that AAF pyramidal neurons, particularly the AAF-striatum projections, play a crucial role in frequency discrimination behavior.

The prelimbic cortex regulates itch processing by controlling attentional bias.

Itch is a complex and unpleasant sensory experience. Recent studies have begun to investigate the neural mechanisms underlying the modulation of sensory and emotional components of itch in the brain. However, the key brain regions and neural mechanism involved in modulating the attentional processing of itch remain elusive. Here, we showed that the prelimbic cortex (PrL) is associated with itch processing and that the manipulation of itch-responsive neurons in the PrL significantly disrupted itch-induced scratching. Interestingly, we found that increasing attentional bias toward a distracting stimulus could disturb itch processing. We also demonstrated the existence of a population of attention-related neurons in the PrL that drive attentional bias to regulate itch processing. Importantly, itch-responsive neurons and attention-related neurons significantly overlapped in the PrL and were mutually interchangeable in the regulation of itch processing at the cellular activity level. Our results revealed that the PrL regulates itch processing by controlling attentional bias.

A brain-tumor neural circuit controls breast cancer progression in mice.

Tumor burden, considered a common chronic stressor, can cause widespread anxiety. Evidence suggests that cancer-induced anxiety can promote tumor progression, but the underlying neural mechanism remains unclear. Here, we used neuroscience and cancer tools to investigate how the brain contributes to tumor progression via nerve-tumor crosstalk in a mouse model of breast cancer. We show that tumor-bearing mice exhibited significant anxiety-like behaviors and that corticotropin-releasing hormone (CRH) neurons in the central medial amygdala (CeM) were activated. Moreover, we detected newly formed sympathetic nerves in tumors, which established a polysynaptic connection to the brain. Pharmacogenetic or optogenetic inhibition of CeMCRH neurons and the CeMCRH→lateral paragigantocellular nucleus (LPGi) circuit significantly alleviated anxiety-like behaviors and slowed tumor growth. Conversely, artificial activation of CeMCRH neurons and the CeMCRH→LPGi circuit increased anxiety and tumor growth. Importantly, we found alprazolam, an antianxiety drug, to be a promising agent for slowing tumor progression. Furthermore, we show that manipulation of the CeMCRH→LPGi circuit directly regulated the activity of the intratumoral sympathetic nerves and peripheral nerve-derived norepinephrine, which affected tumor progression by modulating antitumor immunity. Together, these findings reveal a brain-tumor neural circuit that contributes to breast cancer progression and provide therapeutic insights for breast cancer.

Reevaluating the role of the medial prefrontal cortex in delay eyeblink conditioning.

It has been proposed that the medial prefrontal cortex (mPFC) is not necessary for delay eyeblink conditioning (DEC). Here, we investigated the involvement of the mPFC in DEC with a soft or loud tone as the conditioned stimulus (CS) by using electrolytic lesions or muscimol inactivation of guinea pig mPFC. Interestingly, when a soft tone was used as a CS, electrolytic lesions of the mPFC significantly retarded acquisition of the conditioned response (CR), and muscimol infusions into mPFC distinctly inhibited the acquisition and expression of CR, but had no significant effect on consolidation of well-learned CR. In contrast, both electrolytic lesions and muscimol inactivation of mPFC produced no significant deficits in the CR when a loud tone was used as the CS, or in the unconditioned response (UR) when a soft or loud tone was used as the CS. These results demonstrate that the mPFC is essential for the DEC with the soft tone CS but not for the DEC with the loud tone CS.

Classical eyeblink conditioning using electrical stimulation of caudal mPFC as conditioned stimulus is dependent on cerebellar interpositus nucleus in guinea pigs.

AIM: To determine whether electrical stimulation of caudal medial prefrontal cortex (mPFC) as conditioned stimulus (CS) paired with airpuff unconditioned stimulus (US) was sufficient for establishing eyeblink conditioning in guinea pigs, and whether it was dependent on cerebellar interpositus nucleus. METHODS: Thirty adult guinea pigs were divided into 3 conditioned groups, and trained on the delay eyeblink conditioning, short-trace eyeblink conditioning, and long-trace eyeblink conditioning paradigms, respectively, in which electrical stimulation of the right caudal mPFC was used as CS and paired with corneal airpuff US. A pseudo conditioned group of another 10 adult guinea pigs was given unpaired caudal mPFC electrical stimulation and the US. Muscimol (1 µg in 1 µL saline) and saline (1 µL) were infused into the cerebellar interpositus nucleus of the animals through the infusion cannula on d 11 and 12, respectively. RESULTS: The 3 eyeblink conditioning paradigms have been successfully established in guinea pigs. The animals acquired the delay and short-trace conditioned responses more rapidly than long-trace conditioned responses. Muscimol infusion into the cerebellar interpositus nucleus markedly impaired the expression of the 3 eyeblink conditioned responses. CONCLUSION: Electrical stimulation of caudal mPFC is effective CS for establishing eyeblink conditioning in guinea pigs, and it is dependent on the cerebellar interpositus nucleus.

Case report: Remedial surgical treatment of aorto-duodenal fistula with infected aneurysm after endovascular aortic repair.

Aorto-duodenal fistula (ADF) is a rare cause of upper gastrointestinal bleeding, but it is associated with high mortality. It usually occurs in patients with prior aortic surgery or who have undergone aortic graft placement. Abdominal aortic aneurysm (AAA) might be a cause of primary ADF, which could develop into sudden shock. Because ADF is difficult to diagnose, surgery to correct it has a poor outcome. We here report the successful treatment of an ADF complicated with infected AAA after endovascular repair of a ruptured aneurysm of the iliac artery.

Infralimbic cortex-medial striatum projections modulate the itch processing.

Itch is an unpleasant sensation that induces the desire to scratch. Except for a sketchy map focusing on neural mechanisms underlying itch processing being drawn at the peripheral and spinal level over the past decades, the brain mechanisms remain poorly understood. Several previous studies indicated that anterior cingulate cortex (ACC) and prelimbic cortex (PrL), two subregions of the medial prefrontal cortex (mPFC) play an important role in regulating itch processing. However, the knowledge about whether infralimbic cortex (IL), another subregion of mPFC, is involved in modulating itch processing remains unclear. Here, we showed that the activity of IL excitatory pyramidal neurons was significantly elevated during itch-related scratching, and pharmacogenetic inhibition of IL pyramidal neurons significantly impaired itch-related scratching. Moreover, IL-medial striatum (MS) projections were verified as a critical neural pathway for modulating itch processing. Therefore, the present study firstly presents the regulatory function of IL pyramidal neurons during itch processing and also reveals that IL-MS projections are involved in modulating the itch processing.

Itch-specific neurons in the ventrolateral orbital cortex selectively modulate the itch processing.

Itch is a cutaneous sensation that is critical in driving scratching behavior. The long-standing question of whether there are specific neurons for itch modulation inside the brain remains unanswered. Here, we report a subpopulation of itch-specific neurons in the ventrolateral orbital cortex (VLO) that is distinct from the pain-related neurons. Using a Tet-Off cellular labeling system, we showed that local inhibition or activation of these itch-specific neurons in the VLO significantly suppressed or enhanced itch-induced scratching, respectively, whereas the intervention did not significantly affect pain. Conversely, suppression or activation of pain-specific neurons in the VLO significantly affected pain but not itch. Moreover, fiber photometry and immunofluorescence verified that these itch- and pain-specific neurons are distinct in their functional activity and histological location. In addition, the downstream targets of itch- and pain-specific neurons were different. Together, the present study uncovers an important subpopulation of neurons in the VLO that specifically modulates itch processing.

Specific stimulation of PV+ neurons at early stage ameliorates prefrontal ischemia-induced spatial working memory impairment.

Prefrontal ischemia can cause impairments in learning and memory, executive functions and cognitive flexibility. However, the related cellular mechanisms at the early stage are still elusive. The present study used ischemic stroke in medial prefrontal cortex and systemically investigated the electrophysiological changes of the parvalbumin (PV+) interneurons 12 h post ischemia. We found that Ih and the related voltage sags in PV+ interneurons are downregulated post ischemia, which correlates with hyperpolarization of the membrane potentials and increased input resistance in these interneurons. Consistent with the suppression of Ih, postischemic PV+ interneurons exhibited a reduction in excitability and exerted a less inhibitory control over the neighboring pyramidal excitatory neurons. Moreover, we found that specifically chemogenetic activation of PV+ neurons at early stage ameliorated prefrontal ischemia-induced spatial working memory dysfunction in T-maze without effects on the locomotor coordination and balance. In contrast, suppression of PV+ neurons by blockade of Ih leaded to further aggravate the damage of spatial memory. These findings indicate that dysfunctional Ih in the PV+ neuron postischemia induces the imbalance of excitation and inhibition, which might represent a novel mechanism underlying the prefrontal ischemia-induced cognitive impairment.

Differential roles of prelimbic and anterior cingulate cortical region in the modulation of histaminergic and non-histaminergic itch.

Itch is an unpleasant sensation that evokes a desire to scratch. Itch processing in the peripheral and spinal cord has been studied extensively, but the mechanism of itch in the central nervous system is still unclear. Anterior cingulate cortex (ACC) and prelimbic cortex (Prl), two subregions of the prefrontal cortex closely related to emotion and motivation, have been reported to be activated during itching in a series of functional imaging studies. However, the exact role of Prl and the differences between ACC and Prl in itch modulation remains unknown. To directly test the differential roles of ACC and Prl in itch processing, we chemogeneticlly inhibited the caudal ACC and Prl, respectively. We found that inhibition of caudal ACC reduced histaminergic but not non-histaminergic itch-induced scratching behaviors. In contrast, inhibition of Prl reduced both histaminergic and non-histaminergic itch-induced scratching behaviors. Our study provided direct evidence of Prl involvement in itch modulation and revealed the differential roles of caudal ACC and Prl in regulating histaminergic and non-histaminergic itch.

Optogenetic Neuronal Stimulation Promotes Functional Recovery After Spinal Cord Injury.

Although spinal cord injury (SCI) is the main cause of disability worldwide, there is still no definite and effective treatment method for this condition. Our previous clinical trials confirmed that the increased excitability of the motor cortex was related to the functional prognosis of patients with SCI. However, it remains unclear which cell types in the motor cortex lead to the later functional recovery. Herein, we applied optogenetic technology to selectively activate glutamate neurons in the primary motor cortex and explore whether activation of glutamate neurons in the primary motor cortex can promote functional recovery after SCI in rats and the preliminary neural mechanisms involved. Our results showed that the activation of glutamate neurons in the motor cortex could significantly improve the motor function scores in rats, effectively shorten the incubation period of motor evoked potentials and increase motor potentials' amplitude. In addition, hematoxylin-eosin staining and nerve fiber staining at the injured site showed that accurate activation of the primary motor cortex could effectively promote tissue recovery and neurofilament growth (GAP-43, NF) at the injured site of the spinal cord, while the content of some growth-related proteins (BDNF, NGF) at the injured site increased. These results suggested that selective activation of glutamate neurons in the primary motor cortex can promote functional recovery after SCI and may be of great significance for understanding the neural cell mechanism underlying functional recovery induced by motor cortex stimulation.

Intestinal epithelial chemokine (C-C motif) ligand 7 overexpression protects against high fat diet-induced obesity and hepatic steatosis in mice.

BACKGROUND: We previously found that the intestinal epithelial chemokine (C-C motif) ligand 7 (CCL7) plays an important role in the development of toxin-induced acute liver damage. The detailed effects of intestinal epithelial CCL7 on chronic diseases; however, are still unclear. Here, we aimed to investigate the impact of intestinal epithelial CCL7 overexpression on high-fat diet (HFD)-induced obesity and steatohepatitis in mice. METHODS: Intestinal epithelial CCL7 overexpression (CCL7) mice and their wild-type (WT) littermates were fed with normal chow or HFD for 16 weeks to induce obesity and non-alcoholic fatty liver disease. Body weight gain, as well as adipose tissue index were assessed. Liver injury was monitored by histological analysis and real time polymerase chain reaction. Gut microbial composition was analyzed by 16S rRNA gene sequencing. RESULTS: We found that the CCL7 mice on a HFD had markedly decreased weight gain (8.9 vs. 17.0 g, P < 0.05) and a lower adipose tissue index that include mesenteric fat (1.0% vs. 1.76%, P < 0.05), gonadal fat (2.1% vs. 6.1%, P < 0.05), subcutaneous fat (1.0% vs. 2.8%, P < 0.05) compared to WT animals. HFD-induced glucose intolerance and insulin resistance were also significantly improved in CCL7 mice compared to WT. Furthermore, HFD-fed CCL7 mice displayed less hepatic lipid accumulation and lower expression of inflammatory factors than WT mice. 16S rRNA gene sequencing demonstrated that CCL7 overexpression in intestinal epithelial cells improved HFD-induced gut microbial dysbiosis. CONCLUSIONS: Our study revealed that CCL7 overexpression in the intestinal epithelium protects mice against the progression of diet-induced obesity, hepatic steatosis, and enteric dysbiosis.

Chemogenetic activation of glutamatergic neurons in the motor cortex promotes functional recovery after ischemic stroke in rats.

Ischemic stroke is a major cause of disability and mortality worldwide, while no unequivocally efficacious drug is currently available to treat post-stroke functional impairments. Animal and clinical investigations suggest that the motor cortex stimulation constitutes a particularly promising approach for promoting function recovery after stroke. However, the cell types and mechanisms involved in stimulation-induced recovery are not well understood. Here, we used chemogenetic technique to selectively activate glutamatergic neurons in the primary motor cortex and investigated whether activation of glutamatergic neurons in the primary motor cortex can promote functional recovery after ischemic stroke in rats. The results showed that chemogenetic activation of the motor cortex glutamatergic neurons significantly decreased the neurological deficit scores, as well as significantly increased the grip test scores and the hanging time. Moreover, the glutamatergic neuronal activation also significantly decreased the escape latencies, increased the swimming speed, target quadrant time, and numbers of crossing platform position in the Morris water maze test. These results demonstrate that selective activation of the glutamatergic neurons in primary motor cortex is sufficient to promote functional recovery after ischemic stroke, and may be of importance in understanding the neural cellular mechanisms underlying the motor cortex stimulation-induced functional recovery.

Reevaluating the ability of cerebellum in associative motor learning.

It has been well established that the cerebellum and its associated circuitry constitute the essential neuronal system for both delay and trace classical eyeblink conditioning (DEC and TEC). However, whether the cerebellum is sufficient to independently modulate the DEC, and TEC with a shorter trace interval remained controversial. Here, we used direct optogenetic stimulation of mossy fibers in the middle cerebellar peduncle (MCP) as a conditioned stimulus (CS) replacement for the peripheral CS (eg, a tone CS or a light CS) paired with a periorbital shock unconditioned stimulus (US) to examine the ability of the cerebellum to learn the DEC and the TEC with various trace intervals. Moreover, neural inputs to the pontine nucleus (PN) were pharmacological blocked to limit the associative motor learning inside the cerebellum. We show that all rats quickly acquired the DEC, indicating that direct optogenetic stimulation of mossy fibers in the left MCP is a very effective and sufficient CS to establish DEC and to limit the motor learning process inside the cerebellum. However, only five out of seven rats acquired the TEC with a 150-ms trace interval, three out of nine rats acquired the TEC with a 350-ms trace interval, and none of the rats acquired the TEC with a 500-ms trace interval. Moreover, pharmacological blocking glutamatergic and GABAergic inputs to the PN from the extra-cerebellar and cerebellar regions has no significant effect on the DEC and TEC learning with the optogenetic CS. These results indicate that the cerebellum has the ability to independently support both the simple DEC, and the TEC with a trace interval of 150 or 350 ms, but not the TEC with a trace interval of 500 ms. The present results are of great importance in our understanding of the mechanisms and ability of the cerebellum in associative motor learning and memory.