TRPV1-lineage somatosensory fibers communicate with taste neurons in the mouse parabrachial nucleus

Trigeminal neurons supply somatosensation to craniofacial tissues. In mouse brain, ascending projections from medullary trigeminal neurons arrive at taste neurons in the autonomic parabrachial nucleus, suggesting taste neurons participate in somatosensory processing. However, the genetic cell types that support this convergence were undefined. Using Cre-directed optogenetics and in vivo neurophysiology in anesthetized mice of both sexes, here we studied whether TRPV1-lineage nociceptive and thermosensory fibers are primary neurons that drive trigeminal circuits reaching parabrachial taste cells. We monitored spiking activity in individual parabrachial neurons during photoexcitation of the terminals of TRPV1-lineage fibers that arrived at the dorsal spinal trigeminal nucleus pars caudalis, which relays orofacial somatosensory messages to the parabrachial area. Parabrachial neural responses to oral delivery of taste, chemesthetic, and thermal stimuli were also recorded. We found that optical excitation of TRPV1-lineage fibers frequently stimulated traditionally defined taste neurons in lateral parabrachial nuclei. The tuning of neurons across diverse tastes associated with their sensitivity to excitation of TRPV1-lineage fibers, which only sparingly engaged neurons oriented to preferred tastes like sucrose. Moreover, neurons that responded to photostimulation of TRPV1-lineage afferents showed strong responses to temperature including noxious heat, which predominantly excited parabrachial bitter taste cells. Multivariate analyses revealed the parabrachial confluence of TRPV1-lineage signals with taste captured sensory valence information shared across aversive gustatory, nociceptive, and thermal stimuli. Our results reveal that trigeminal fibers with defined roles in thermosensation and pain communicate with parabrachial taste neurons. This multisensory convergence supports dependencies between gustatory and somatosensory hedonic representations in the brain.

A Purkinje cell to parabrachial nucleus pathway enables broad cerebellar influence over the forebrain and emotional valence

In addition to its well-known contributions to motor control and motor learning, the cerebellum is involved in language, emotional regulation, anxiety, and affect1-4. We found that suppressing the firing of cerebellar Purkinje cells (PCs) rapidly excites forebrain areas that could contribute to such functions, including the amygdala, basal forebrain, and septum, but that the classic cerebellar outputs, the deep cerebellar nuclei (DCN), do not project to these regions. Here we show that parabrachial nuclei (PBN) neurons that receive direct PC input, project to and influence all of these forebrain regions and many others. Furthermore, the function of this pathway is distinct from the canonical pathway: suppressing PC to PBN activity is aversive, whereas suppressing the PC to DCN pathway is rewarding. Therefore, the PBN pathway allows the cerebellum to influence the entire spectrum of valence, modulate the activity of forebrain regions known to regulate diverse nonmotor behaviors, and may be the substrate for many nonmotor disorders related to cerebellar dysfunction.

Ultra-Low Frequency Transcutaneous Electrical Nerve Stimulation on Pain Modulation in a Rat Model with Myogenous Temporomandibular Dysfunction

Masticatory myofascial pain (MMP) is one of the most common causes of chronic orofacial pain in patients with temporomandibular disorders. To explore the antinociceptive effects of ultra-low frequency transcutaneous electrical nerve stimulation (ULF-TENS) on alterations of pain-related biochemicals, electrophysiology and jaw-opening movement in an animal model with MMP, a total of 40 rats were randomly and equally assigned to four groups; i.e., animals with MMP receiving either ULF-TENS or sham treatment, as well as those with sham-MMP receiving either ULF-TENS or sham treatment. MMP was induced by electrically stimulated repetitive tetanic contraction of masticatory muscle for 14 days. ULF-TENS was then performed at myofascial trigger points of masticatory muscles for seven days. Measurable outcomes included maximum jaw-opening distance, prevalence of endplate noise (EPN), and immunohistochemistry for substance P (SP) and μ-opiate receptors (MOR) in parabrachial nucleus and c-Fos in rostral ventromedial medulla. There were significant improvements in maximum jaw-opening distance and EPN prevalence after ULF-TENS in animals with MMP. ULF-TENS also significantly reduced SP overexpression, increased MOR expression in parabrachial nucleus, and increased c-Fos expression in rostral ventromedial medulla. ULF-TENS may represent a novel and applicable therapeutic approach for improvement of orofacial pain induced by MMP.

Vestibular CCK neurons drive motion-induced malaise

ABSTRACTPassive motion can induce kinetosis (motion sickness, MS) in susceptible individuals. MS is an evolutionary conserved mechanism caused by mismatches between motion-related sensory information and past visual and motion memory, triggering a malaise accompanied by hypolocomotion, hypothermia, hypophagia and aversion to novel foods presented coincidentally. Vestibular nuclei (VN) are critical for the processing of movement input, and motion-induced activation of VN neurons recapitulates MS-related signs. However, the genetic identity of VN neurons mediating MS-related autonomic and aversive responses remains unknown. Here, we identify a glutamatergic vestibular circuitry necessary to elicit MS-related behavioral responses, defining a central role of cholecystokinin (CCK)- expressing glutamatergic VN neurons in vestibular-induced malaise. Moreover, we show that CCK VN inputs onto the parabrachial nucleus activate Calca-expressing neurons and are sufficient to establish hypothermia and aversion to novel food. Together, we provide novel insight into the neurobiological regulation of MS, unravelling key genetically defined neural substrates for kinetosis.

Calcitonin gene related peptide α is dispensable for many danger-related motivational responses

Calcitonin gene related peptide (CGRP) expressing neurons in the parabrachial nucleus have been shown to encode danger. Through projections to the amygdala and other forebrain structures, they regulate food intake and trigger adaptive behaviors in response to threats like inflammation, intoxication, tumors and pain. Despite the fact that this danger-encoding neuronal population has been defined based on its CGRP expression, it is not clear if CGRP is critical for its function. It is also not clear if CGRP in other neuronal structures is involved in danger-encoding. To examine the role of CGRP in danger-related motivational responses, we used male and female mice lacking αCGRP, which is the main form of CGRP in the brain. These mice had no, or only very weak, CGRP expression. Despite this, they did not behave differently compared to wildtype mice when they were tested for a battery of danger-related responses known to be mediated by CGRP neurons in the parabrachial nucleus. Mice lacking αCGRP and wildtype mice showed similar inflammation-induced anorexia, conditioned taste aversion, aversion to thermal pain and pain-induced escape behavior, although it should be pointed out that the study was not powered to detect any possible differences that were minor or sex-specific. Collectively, our findings suggest that αCGRP is not necessary for many threat-related responses, including some that are known to be mediated by CGRP neurons in the parabrachial nucleus.