Effects of optogenetic stimulation of basal forebrain parvalbumin neurons on Alzheimer's disease pathology.

Neuronal activity can modify Alzheimer's disease pathology. Overexcitation of neurons can facilitate disease progression whereas the induction of cortical gamma oscillations can reduce amyloid load and improve cognitive functions in mouse models. Although previous studies have induced cortical gamma oscillations by either optogenetic activation of cortical parvalbumin-positive (PV+) neurons or sensory stimuli, it is still unclear whether other approaches to induce gamma oscillations can also be beneficial. Here we show that optogenetic activation of PV+ neurons in the basal forebrain (BF) increases amyloid burden, rather than reducing it. We applied 40 Hz optical stimulation in the BF by expressing channelrhodopsin-2 (ChR2) in PV+ neurons of 5xFAD mice. After 1-h induction of cortical gamma oscillations over three days, we observed the increase in the concentration of amyloid-ß42 in the frontal cortical region, but not amyloid-ß40. Amyloid plaques were accumulated more in the medial prefrontal cortex and the septal nuclei, both of which are targets of BF PV+ neurons. These results suggest that beneficial effects of cortical gamma oscillations on Alzheimer's disease pathology can depend on the induction mechanisms of cortical gamma oscillations.

Biased M1-muscarinic-receptor-mutant mice inform the design of next-generation drugs.

Cholinesterase inhibitors, the current frontline symptomatic treatment for Alzheimer's disease (AD), are associated with low efficacy and adverse effects. M1 muscarinic acetylcholine receptors (M1 mAChRs) represent a potential alternate therapeutic target; however, drug discovery programs focused on this G protein-coupled receptor (GPCR) have failed, largely due to cholinergic adverse responses. Employing novel chemogenetic and phosphorylation-deficient, G protein-biased, mouse models, paired with a toolbox of probe molecules, we establish previously unappreciated pharmacologically targetable M1 mAChR neurological processes, including anxiety-like behaviors and hyper-locomotion. By mapping the upstream signaling pathways regulating these responses, we determine the importance of receptor phosphorylation-dependent signaling in driving clinically relevant outcomes and in controlling adverse effects including 'epileptic-like' seizures. We conclude that M1 mAChR ligands that promote receptor phosphorylation-dependent signaling would protect against cholinergic adverse effects in addition to driving beneficial responses such as learning and memory and anxiolytic behavior relevant for the treatment of AD.

Gap-induced inhibition of the post-auricular muscle response in humans and guinea pigs.

A common method for measuring changes in temporal processing sensitivity in both humans and animals makes use of GaP-induced Inhibition of the Acoustic Startle (GPIAS). It is also the basis of a common method for detecting tinnitus in rodents. However, the link to tinnitus has not been properly established because GPIAS has not yet been used to objectively demonstrate tinnitus in humans. In guinea pigs, the Preyer (ear flick) myogenic reflex is an established method for measuring the acoustic startle for the GPIAS test, while in humans, it is the eye-blink reflex. Yet, humans have a vestigial remnant of the Preyer reflex, which can be detected by measuring skin surface potentials associated with the Post-Auricular Muscle Response (PAMR). A similar electrical potential can be measured in guinea pigs and we aimed to show that the PAMR could be used to demonstrate GPIAS in both species. In guinea pigs, we compare the GPIAS measured using the pinna movement of the Preyer reflex and the electrical potential of the PAMR to demonstrate that the two are at least equivalent. In humans, we establish for the first time that the PAMR provides a reliable way of measuring GPIAS that is a pure acoustic alternative to the multimodal eye-blink reflex. Further exploratory tests showed that while eye gaze position influenced the size of the PAMR response, it did not change the degree of GPIAS. Our findings confirm that the PAMR is a sensitive method for measuring GPIAS and suggest that it may allow direct comparison of temporal processing between humans and animals and may provide a basis for an objective test of tinnitus.

Gap-induced reductions of evoked potentials in the auditory cortex: A possible objective marker for the presence of tinnitus in animals.

Animal models of tinnitus are essential for determining the underlying mechanisms and testing pharmacotherapies. However, there is doubt over the validity of current behavioural methods for detecting tinnitus. Here, we applied a stimulus paradigm widely used in a behavioural test (gap-induced inhibition of the acoustic startle reflex GPIAS) whilst recording from the auditory cortex, and showed neural response changes that mirror those found in the behavioural tests. We implanted guinea pigs (GPs) with electrocorticographic (ECoG) arrays and recorded baseline auditory cortical responses to a startling stimulus. When a gap was inserted in otherwise continuous background noise prior to the startling stimulus, there was a clear reduction in the subsequent evoked response (termed gap-induced reductions in evoked potentials; GIREP), suggestive of a neural analogue of the GPIAS test. We then unilaterally exposed guinea pigs to narrowband noise (left ear; 8-10 kHz; 1 h) at one of two different sound levels - either 105 dB SPL or 120 dB SPL - and recorded the same responses seven-to-ten weeks following the noise exposure. Significant deficits in GIREP were observed for all areas of the auditory cortex (AC) in the 120 dB-exposed GPs, but not in the 105 dB-exposed GPs. These deficits could not simply be accounted for by changes in response amplitudes. Furthermore, in the contralateral (right) caudal AC we observed a significant increase in evoked potential amplitudes across narrowband background frequencies in both 105 dB and 120 dB-exposed GPs. Taken in the context of the large body of literature that has used the behavioural test as a demonstration of the presence of tinnitus, these results are suggestive of objective neural correlates of the presence of noise-induced tinnitus and hyperacusis.

A prospective audit of pain profiles following general and urological surgery in children.

BACKGROUND: Postoperative pain is frequently undertreated in children both in hospital and at home following discharge. Pain has both short- and long-term consequences for children, their families, and the healthcare system. A greater understanding of procedure-specific postoperative pain trajectories is required to improve pain management. AIM: To determine the duration and severity of acute postoperative pain experienced by children undergoing 8 different general and urological procedures (primary outcomes). Behavioral disturbance rates, nausea and vomiting scores, and parental satisfaction were also examined during the follow-up period (secondary outcomes). METHOD: Families of children (0-18 years) undergoing common general and urological procedures were invited to enroll in the study. Children's pain scores, measured using a parental proxy 0-10 numerical rating scale, were collected by telephone interview until pain was resolved. Analgesia prescribed and given, behavioral disturbance, nausea and vomiting scores, the method of medication education communication, and parental satisfaction were also measured. RESULTS: Of 360 patients recruited, 326 complete datasets were available. Patients underwent laparoscopic appendicectomy (57), open appendicectomy (19), circumcision (50), cystoscopy (52), hypospadias repair (22), inguinal hernia repair (51), orchidopexy (51), or umbilical hernia repair (24). Postoperative pain peaked on the day of or the day after surgery in all groups, and decreased over time. Pain lasted a median duration of 5 postoperative days following open appendicectomy, and 0-2 postoperative days for other procedures. Behavioral disturbance rates closely followed pain scores. Analgesia administration at home varied widely between and within groups. CONCLUSION: Pain management was inadequate in most of the groups studied, particularly after appendicectomy or umbilical hernia repair, with most children experiencing at least moderate pain on the day of and day after surgery. There was a need for a standardized management, with increased dual analgesia prescribing, to ensure that children receive adequate postoperative analgesia in hospital and at home.

Pain after discharge following head and neck surgery in children.

BACKGROUND: It is well established that children experience significant pain for a considerable period following adenotonsillectomy. Less is known, however, about pain following other common head and neck operations. AIM: The aim of this study was to describe the severity and duration of postoperative pain experienced by children undergoing elective head and neck procedures (primary outcomes). Behavioral disturbance, nausea and vomiting, parental satisfaction, and medical reattendance rates were also measured (secondary outcomes). METHOD: Parents of children (0-18 years) undergoing common head and neck operations were invited to participate. Pain scores on the day of surgery and each day post discharge were collected via multiple telephone interviews. Data collected included pain levels, analgesia prescribed and given, behavioral disturbance rates, and nausea and vomiting scores. Follow-up was continued until pain resolved. RESULTS: Two hundred and fifty-one patients were analyzed (50 adenoidectomy, 51 adenotonsillectomy, 19 myringoplasty, 52 myringotomy, 43 strabismus, and 36 tongue tie divisions). On the day of surgery myringoplasty, strabismus surgery, and adenotonsillectomy patients on average had moderate pain, whereas adenoidectomy, tongue tie, and myringotomy patients had mild pain. Adenotonsillectomy patients continued to have moderate pain for several days with pain lasting on average 9 days. From day 1 postoperatively mild pain was experienced in the other surgical groups with the average duration of pain varying from 1 to 3 days depending on the surgery performed. Frequency of behavioral issues closely followed pain scores for each group. Analgesic prescribing and regimes at home varied widely, both within and between the different surgical groups. Rates of nausea and vomiting following discharge were low in all groups. The overall unplanned medical reattendance rate was 16%. CONCLUSION: Adenotonsillectomy patients represent the biggest challenge in postoperative pain management of the head and neck surgeries evaluated. The low rates of pain, nausea, and vomiting reported in the days following surgery for the other procedures suggests that children can be cared for at home with simple analgesia. Discharge information and analgesia prescribing on discharge should be tailored to the operation performed.

Anesthetic techniques to facilitate lung lavage for pulmonary alveolar proteinosis in children-new airway techniques and a review of the literature.

Pediatric patients with pulmonary alveolar proteinosis require whole lung lavage to clear the accumulation of lipoproteinaceous material within the alveoli, to maintain respiratory function. Anesthesia for this presents a challenge due to preexisting respiratory failure, and the small diameter and length of the pediatric airway, which is often unable to accommodate existing one-lung isolation and ventilation equipment. Novel techniques to facilitate lung lavage on seven occasions are described and placed in the context of the existing literature to date.