Jelly snakes to reduce early postoperative vomiting in children after adenotonsillectomy: The randomized controlled snakes trial

BACKGROUND

Despite the use of dual antiemetic agents, postoperative nausea and vomiting (PONV) occurs in an unacceptably large number of patients post-tonsillectomy. There has been increased interest in alternative and non-pharmacological treatments for PONV e.g., chewing gum. We investigated if chewing a large confectionary jelly snake had prophylactic antiemetic effects postoperatively in young children.

METHODS

Prospective, open-label randomised controlled trial of 240 patients, 2-16 years. Patients administered a confectionary jelly snake to chew postoperatively were compared with a control group. The primary outcome was the number of episodes of vomiting within 6 h of the operation on an intention-to-treat basis.

SECONDARY OUTCOMES

incidence of nausea, vomiting at 6 and 24 h, rescue antiemetic use, acceptability, delayed discharge.

RESULTS

233 patients were randomised to receive the confectionary snake (snake group, 118) or standard care (control group, 115). The number of vomiting episodes in 6 h was similar between groups on an intention-to-treat basis, with 39 episodes across 22 (19%) patients in the control group and 31 across 19 (16%) patients in the snake group (p = 0.666). From post anaesthetic care unit until 24 h there was no difference in doses of antiemetics or delayed discharge due to PONV. A secondary as per protocol analysis did not change this result.

CONCLUSIONS

Chewing of confectionery jelly snakes within one hour of waking following adenotonsillectomy with vapour-maintained anaesthesia and two prophylactic antiemetics did not further reduce the incidence of early vomiting.

REGISTRATION

prospective registration at the Australia and New Zealand Clinical Trials Registry (ACTRN12618000637246).

A hospital-based asynchronous ENT telehealth service for children with otitis media: Cost-minimisation and improved access

AIM

The purpose of this study is to explore the effectiveness of a hospital-based asynchronous ear, nose, and throat (ENT) telehealth service (the Ear Portal) in reducing cost and improving access for children with otitis media.

METHODS

Participants were recruited to the Ear Portal from a tertiary hospital ENT waiting list. Ear and hearing assessments were conducted during appointments by the Ear Portal research assistant, and data was stored for an asynchronous review by the Ear Portal multidisciplinary team. A cost-minimisation analysis was conducted for the Ear Portal and the standard care pathways. Waiting times to provide care for both pathways were calculated for children with semi-urgent (i.e. Category 2) and non-urgent (i.e. Category 3) referrals.

RESULTS

The running cost for the Ear Portal was $67.70 for initial appointments and $37.34 for follow-up appointments. Conversely, the running cost for the standard care pathway was $154.65 for initial appointments and $86.10 for follow-up appointments. A total of 223 appointments were required to offset the initial Ear Portal investment of $19,384.00. The median waiting time for the Ear Portal from initial contact to care plan delivery was <30 days, whereas the median waiting times for children in the standard care pathway were 291 days (interquartile range (IQR) = 117) for Category 2 and 371 days (IQR = 311) for Category 3 referrals.

CONCLUSION

Under the current circumstances, the Ear Portal service can reduce costs for the health care system by reducing marginal costs per patient in addition to providing ENT specialist care within the clinically recommended timeframes.

Predicting obstructive sleep apnoea and perioperative respiratory adverse events in children: role of upper airway collapsibility measurements

BACKGROUND

Obstructive sleep apnoea (OSA) and perioperative respiratory adverse events are significant risks for anaesthesia in children undergoing adenotonsillectomy. Upper airway collapse is a crucial feature of OSA that contributes to respiratory adverse events. A measure of upper airway collapsibility to identify undiagnosed OSA can help guide perioperative management. We investigated the utility of pharyngeal closing pressure (PCLOSE) for predicting OSA and respiratory adverse events.

METHODS

Children scheduled for elective adenotonsillectomy underwent in-laboratory polysomnography 2-12 weeks before surgery. PCLOSE measurements were obtained while the child was anaesthetised and breathing spontaneously just before surgery. Logistic regression was used to assess the predictive performance of PCLOSE for detecting OSA and perioperative respiratory adverse events after adjusting for potential covariates.

RESULTS

In 52 children (age, mean [standard deviation] 5.7 [1.8] yr; 20 [38%] females), airway collapse during PCLOSE was observed in 42 (81%). Of these, 19 of 42 (45%) patients did not have OSA, 15 (36%) had mild OSA, and eight (19%) had moderate-to-severe OSA. All 10 children with no evidence of airway collapse during the PCLOSE measurements did not have OSA. PCLOSE predicted moderate-to-severe OSA (odds ratio [OR] 1.71; 95% confidence interval [CI]: 1.2-2.8; P=0.011). All children with moderate-to-severe OSA could be identified at a PCLOSE threshold of -4.0 cm H2O (100% sensitivity), and most with no or mild OSA were ruled out (64.7% specificity; receiver operating characteristic/area under the curve=0.857). However, there was no significant association between respiratory adverse events and PCLOSE (OR 1.0; 95% CI: 0.8-1.1; P=0.641).

CONCLUSIONS

Measurement of PCLOSE after induction of anaesthesia can reliably identify moderate or severe OSA but not perioperative respiratory adverse events in children before adenotonsillectomy.

CLINICAL TRIAL REGISTRATION

ANZCTR ACTRN 12617001503314.

The utility of balloon dilation for piriform aperture stenosis - A first line surgical treatment

AIM

Describe the long-term outcomes of patients with piriform aperture stenosis managed with balloon dilation.

METHODS

Review of current literature. A retrospective case series of 6 patients with piriform aperture stenosis initially managed with balloon dilation at a tertiary paediatric hospital.

RESULTS

Six neonates diagnosed with piriform aperture were managed with balloon dilation under general anaesthesia after failing conservative treatment. Average age at first dilation was 28 days old (range 6-54). The piriform aperture was an average width of 5.15 mm, with a 4-6.5 mm range, as measured on axial CT scan. The average width at 25% of the nasal cavity, 50% and 75% was 7.7 mm, 9.3 mm and 9.98 mm respectively. Four neonates required only a single balloon dilation - two of these were stented post-operatively. The remaining two neonates required multiple balloon dilations with eventual drill-out through a sublabial approach. There was a trend of smaller piriform and nasal cavity diameters in those who required multiple procedures. The mean follow-up was 30 months.

CONCLUSION

Balloon dilation should be considered for primary operative management in neonates with piriform aperture stenosis who fail medical interventions. Balloon dilation can treat the narrowing at and beyond the piriform aperture. Patients who require more than one dilation are more likely to have a smaller piriform aperture and may need a drill-out procedure. The impact of nasal stents on outcomes is unclear.

Ear Portal: An urban-based ear, nose, and throat, and audiology referral telehealth portal to improve access to specialist ear-health services for children

INTRODUCTION

Shortage of ear, nose, and throat specialists in public hospitals can result in delays in the detection and management of otitis media. This study introduced a new hospital-based telehealth service, named the Ear Portal, and investigated its role in improving access to specialist care.

METHODS

The study included 87 children (aged 6 months to 6 years) referred to a tertiary children's hospital due to otitis media-related concerns. A specialist multidisciplinary team met fortnightly to review pre-recorded data and provide care plans.

RESULTS

The service resulted in a median waiting time of 28 days to receive a diagnosis and care plan by the multidisciplinary team, compared to a mean waiting time of 450 days for a reference group receiving standard healthcare services. Most children (90.3%) received bilateral ear diagnosis. Normal findings were found in 43.9%. However, the majority required further ear, nose, and throat with or without audiology face-to-face follow-up due to a diagnosis of middle-ear disease, unknown hearing status, or concerns not related to ears. The mean time required for clinical assessments completion by research assistants and multidisciplinary team review was 37.6 and 5.1 min per participant, respectively.

DISCUSSION

Children in the Ear Portal service received a diagnosis and care plan in a median of 28 days, which is within the clinically recommended timeframes. With sufficient clinical information, this service can provide faster access to specialist care than the standard healthcare pathway. The service can reduce the time required by the specialist to provide a diagnosis and care plan which may help increase the specialists' capacity.

Re-thinking congenital piriform aperture stenosis: Modern imaging demonstrates narrowing of the full nasal cavity length

OBJECTIVE

Measure the width of the nasal cavity in cases of piriform aperture stenosis using computerised tomography scans.

METHODS

Retrospective study performed at a paediatric tertiary referral centre in Australia. Comparison nasal cavity widths (measured on computerised tomography scans in the axial plane) at the piriform aperture, choana and points 25, 50 and 75% along the length of nasal cavity, between cases with piriform aperture stenosis and controls.

RESULTS

In cases of piriform aperture stenosis the piriform aperture along with the nasal cavity is statistically significantly narrower than controls, measured at 25, 50 and 75% along the distance between the piriform aperture and the choana.

CONCLUSION

This modern imaging review has illustrated the need for a change in the treatment paradigm for neonates with this condition, suggesting the need for further investigation of techniques that treat narrowing beyond the aperture.

A quality improvement study: Optimizing pneumococcal vaccination rates in children with cochlear implants

Children with cochlear implants are at increased risk of invasive pneumococcal disease, with national and international guidelines recommending additional pneumococcal vaccines for these children. This study aimed to examine the pneumococcal immunization status and rate of invasive pneumococcal disease in children with cochlear implants at a tertiary paediatric hospital over a 12-year period. Additionally, the impacts of vaccination reminders and a dedicated immunization clinic on pneumococcal vaccination rates were assessed. This quality improvement study included 200 children who had received a cochlear implant through the Children's Hearing Implant Program at a tertiary paediatric hospital servicing the state of Western Australia. The majority of children (88%) were not up to date with additionally recommended pneumococcal vaccinations. Over the 12-year study period, 2% of children developed invasive pneumococcal disease associated with cochlear implant infections. Generic and personalized electronic immunization reminders improved pneumococcal vaccine up-take in this paediatric cochlear implant setting from 12% (19/153) at baseline to 49% (75/153, p < 0.0001) post implementation. The value of a nurse-led dedicated immunization clinic was also demonstrated with all children (42/42, 100%) up to date with Prevenar13 and the majority (34/42, 81%) up to date with Pneumovax23 post initiation of this referral pathway. These data support the expansion of this model to other medically-at-risk paediatric groups that have been highlighted consistently to be under-vaccinated.

Early detection of hearing loss for infants in Western Australia: Comparison to international benchmarks

AIM

To assess the degree to which timely audiological assessment of congenital hearing loss is achieved at our institution - Perth Children's Hospital, Western Australia, and to review cases which breached this timeframe in order to address barriers to timely assessment. The benchmark used to determine timely assessment is that set out by The Joint Committee on Infant Hearing (JCIH) in which diagnostic audiological testing occurs by three months of age for those who do not pass newborn hearing screening.

METHODS

A retrospective chart review of infants who underwent diagnostic auditory assessment at Perth Children's Hospital between 2016-2019. A total of 151 children were identified as meeting the inclusion criteria and their medical files were reviewed. Time to first dABR was the time point for whether testing was achieved within the 3 month timeframe.

RESULTS

Of the 151 children who underwent dABR assessments, 1 was identified as having breached the 90 day time limit (tested on day 91) for which no valid reason for delay could be identified. The timely delivery of dABR assessments in 99.3% of cases within this cohort compares favourably with the literature.

CONCLUSIONS

Conclusion Timely diagnostic audiological assessment is achievable for children with congenital hearing loss. The reasons for patients breaching this timeframe are explored in the paper along with factors which may help avoid delays.

A novel approach in managing challenging tracheoesophageal fistulae

OBJECTIVE

To analyze the outcomes of an open anterior cervical approach and tospecifically describe a novel extended tracheotomy incision ("Key-hole technique") torepair H-type and other challenging tracheoesophageal fistulae (TOF) at a singletertiary pediatric center.

METHOD

A retrospective chart analysis of pediatric patients (0-18 years old) who had undergone repair of TOF's between January 2006 and March 2020 were reviewed. A case series of patients who had undergone open cervical utilizing three different techniques were included. Patient demographics, surgical management and post-operative surgical outcomes including complications were evaluated.

RESULTS

During the study period, 117 pediatric patients were diagnosed and anaged with TOFs with or without oesophageal atresia. Within this group, 12 patients (10%) had anterior open cervical repair of congenital or persisting TOFs (6 males and 6 females). Eight cases (7%) had congenital Type E (known as H-type), two had type D, one type B and one type C TOF. Median gestational age was 37 weeks (range 28-41 weeks), age of presentation ranged from 1 day old to 3 years old with 67% being diagnosed within the first month of life. At the time of definitive surgery all patients had a bronchoscopy and oesophagoscopy to confirm the diagnosis, identify the level of the fistula and place a catheter through the fistula. This cases series of open anterior cervical repair of TOFs comprised of seven (58%) patients who had primary extraluminal tracheal approach, four (33%) with extended tracheotomy incision ('Key-hole' technique) and one (9%) patient with slide tracheoplasty for recurrent type C TOF in the presence of subglottic stenosis. Eleven of the twelve patients had successful open anterior cervical repair of TOF. One patient who had primary open anterior cervical repair with the 'Key-hole' technique had recurrence managed successfully with slide tracheoplasty. There were no cases of recurrent laryngeal nerve injury.

CONCLUSION

This series demonstrates that open anterior cervical approach to correct TOFs is an effective and safe method in the majority of cases of congenital and acquired fistulae where there is no oesophageal atresia or the atresia is corrected (in the case of recurrent or second fistulae). We also present the outcomes of a novel surgical "Keyhole" technique to manage TOF fistulas via an extended-tracheotomy incision. We also found that slide tracheoplasty is an effective salvage operation in the case of complex recurrent fistulae.

Pediatric Microlaryngoscopy and Bronchoscopy in the COVID-19 Era

Importance

As an aerosol-generating procedure, traditional pediatric microlaryngoscopy and bronchoscopy techniques must be adapted in order to reduce the risk of transmission of severe acute respiratory syndrome coronavirus 2.

Objective

To describe a modified technique for pediatric microlaryngoscopy and bronchoscopy for use in the COVID-19 era and present a case series of patients for whom the technique has been used.

Design, Setting, and Participants

Observational case series of pediatric patients undergoing emergency or urgent airway procedures performed at a tertiary pediatric otolaryngology department in Australia. Procedures were completed between March 23 and April 9, 2020, with a median (range) follow-up of 24.5 (11-28) days.

Exposures

Modified technique for microlaryngoscopy and bronchoscopy, minimizing aerosolization of respiratory tract secretions.

Main Outcomes and Measures

The main outcome was the feasibility of technique, which was measured by ability to perform microlaryngoscopy and bronchoscopy with comparable success to the usual technique (ie, adequate examination of the patient for diagnostic procedures and ability to perform interventional procedures).

Results

The technique was used successfully in 8 patients (median [range] age, 160 days [27 days to 2 years 6 months]); 5 patients were male, and 3 were female. Intervention was performed on 6 patients; 2 balloon dilations for subglottic stenosis, 2 injections of hyaluronic acid for type 1 clefts, and 2 cold-steel supraglottoplasties. No adverse events occurred.

Conclusions and Relevance

In this case series, feasibility of a modified technique for pediatric microlaryngoscopy and bronchoscopy was demonstrated. By reconsidering the surgical approach in light of specific COVID-19 infection risks, this technique may be associated with reduced spread of aerosolized respiratory secretions perioperatively and intraoperatively, but the technique and patient outcomes require further study.

Aspects of the assessment and management of pharyngoesophageal dysphagia

Swallowing complaints are common and may have significant consequences for nutrition and pulmonary health. Etiology varies and different aspects of the deglutitive system may be affected. A thorough assessment from the oral cavity to the stomach will provide physiologic information that enables specific targeted management plans to be devised. Although the swallow trajectory bridges anatomic areas, there has previously been a tendency to compartmentalize assessment and treatment by arbitrary anatomic boundaries. It is now clear that this approach fails to appreciate the complexity of swallow mechanics and that systems (oral, pharyngeal, esophageal, and pulmonary) are intertwined and codependent. Swallowing specialists from different backgrounds and with complementary skill sets form a multidisciplinary team that can provide insight and address multiple areas of management. With the advent of new tools for instrumental evaluation, such as manometry, targeted rehabilitative strategies can be informed by physiology, increased in precision and breadth, and assessed quantitatively. Surgical approaches have evolved toward endoscopic techniques, and food technology is expanding options in dietary management. The multidisciplinary team is core to managing this varied and often neglected patient population. This review is for clinicians treating swallowing disorders and will explore the selected aspects of the assessment and management of pharyngoesophageal swallowing disorders.

Ten years of paediatric airway foreign bodies in Western Australia

BACKGROUND

Whenever a paediatric airway foreign body (PAFB) is suspected, decisions may be difficult without a clearly defined or accepted treatment algorithm. History and examination are commonly non-diagnostic and the risks associated with either watchful waiting or proceeding to MLB are significant. This paper reviews a 10 year cohort of suspected PAFBs for the predictive utility of history, examination and investigations and subsequent positive findings at MLB.

OBJECTIVES

STUDY DESIGN: The medical records of 127 children who underwent MLB for suspected PAFB between 2007 and 2016 were examined. The data was retrospectively reviewed for epidemiological details, history, examination, radiological findings and MLB outcomes.

RESULTS

Sensitivity for PAFB on MLB with all three; history, examination and imaging (x-ray) positive for PAFB was 87.7%. Of the patients who were both symptom and sign positive (n = 96), chest x-ray findings did not significantly alter the chance of finding a PAFB. Chest x-ray had a low specificity (17%) in symptom and sign positive patients. Conversely, sensitivity of chest x-ray was high (88%), for symptom and sign positive patients.

CONCLUSIONS

For a child with both signs and symptoms, xray is unlikely to assist in decision making around suspected PAFB. When only sign or symptom is present, positive imaging may significantly increase the chance that PAFB is the cause.For patients with a low suspicion of PAFB, consideration of a CT can be a helpful means of excluding a PAFB and avoiding an unnecessary general anaesthetic in this potentially high-risk group.A greater level of public awareness is needed with regards to appropriate food types for children and the importance of eating seated and supervised in order to reduce the risk of PAFB.

Batten disease: features to facilitate early diagnosis

AIMS

To ascertain the clinical and electrophysiological features in patients with juvenile neuronal ceroid lipofuscinosis (jNCL/Batten disease) and to identify those features that facilitate early diagnosis.

METHODS

Nine patients with jNCL were identified retrospectively and their case notes reviewed. All had undergone an extensive clinical examination, including electrophysiology. Blood and molecular genetic testing confirmed the diagnosis.

RESULTS

Age at onset ranged from 4-8 years. At presentation, two of nine patients had normal fundi; only two of nine patients had a bull's eye maculopathy. The electroretinogram (ERG) findings in this series included undetectable rod specific ERGs, an electronegative maximal response, reduced and delayed cone flicker ERGs, reduction in the b:a ratio in the photopic single flash ERG, and an undetectable pattern ERG. Vacuolated lymphocytes on peripheral blood film testing were present in eight of nine patients. Five of eight patients were homozygous for the 1.02 kb deletion on the CLN3 gene on molecular genetic testing; two of eight patients were heterozygous for that deletion.

CONCLUSION

jNCL should be considered in children of 10 years and under presenting with visual loss and fundal changes ranging from normal through to pigmentary/atrophic changes or a bull's eye maculopathy. Electrophysiology may suggest jNCL. Although currently untreatable, early diagnosis is important to institute appropriate counselling and support.

Expression of AMPA receptor subunit flip/flop splice variants in the rat auditory brainstem and inferior colliculus

The expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunit mRNAs and their flip/flop splice variants was evaluated in the rat auditory brainstem and inferior colliculus employing in situ hybridization with radiolabeled oligonucleotide probes. A differential expression of AMPA receptor subunits in auditory nuclei was observed. In general, neurons in all nuclei of the auditory brainstem express high levels of GluR-C flop and GluR-D flop mRNA, but low to very low levels of GluR-A and GluR-B mRNA. The strongest GluR-C and -D flop expression is found in the ventral and medial part of the anteroventral cochlear nucleus, the posteroventral cochlear nucleus, and the medial and the lateral superior olive. These nuclei are part of the binaural auditory pathway which is important for sound localization in space. In contrast, neurons in the central nucleus of the inferior colliculus express high levels of GluR-B flip but only low levels of the other AMPA receptor subunits. From our data, we conclude that neurons of nuclei involved in binaural processing exhibit a specific "auditory AMPA receptor" which consists primarily of GluR-C flop and -D flop and often lacks GluR-B subunits; this indicates fast kinetics and high Ca(2+) permeability of AMPA receptor currents. In contrast, neurons in the central nucleus of the inferior colliculus contain large amounts of GluR-B flip subunits resulting in Ca(2+) impermeable AMPA receptors with slow kinetics.

Glycine, glycine receptor subunit and glycine transporters in the rat parabrachial and Kölliker-Fuse nuclei

In the present study, we investigated the expression and distribution of key molecules in the parabrachial (PB) and Kölliker-Fuse nuclei (KF) that determine glycinergic signal transduction. By means of immunocytochemistry, we analyzed the amino acid glycine (Gly), the glycine transporters 1 and 2 (GlyT1, GlyT2), and the ligand binding glycine receptor-subunit alpha 1 (GlyR alpha 1). Gly-immunoreactivity (-ir) was mainly found in varicose fibers and presumed terminal boutons; Gly-ir cell bodies were only occasionally seen. Immunoreactivity for GlyT2 was located in axons while GlyT1-staining was diffuse in the neuropil. Immunolabeling for GlyR alpha 1 occurred mostly as granular staining diffusely distributed throughout the neuropil. Only in the superior lateral PB, the lateral crescent of the PB, and caudally in the KF did GlyR alpha 1-ir outline cell bodies and primary and higher-order dendrites. Furthermore, our data demonstrate a distinct codistribution of immunoreactivities for Gly, GlyT2. and GlyR alpha 1 in a specific set of PB nuclei and in the KF. Strong staining was consistently seen in the internal lateral PB, the ventral lateral PB, the lateral crescent, the medial PB adjacent to the superior cerebellar peduncle, and the rostral two-thirds of the KF. Moderate to weak immunostaining was present in the superior, central, and dorsal lateral PB, the external medial PB, the medioventral part of the medial PB, and caudally in the KF. In contrast, remaining nuclei such as the external lateral PB and the waist area were essentially devoid of Gly-ir profiles, GlyT2-ir, and GlyR alpha 1-ir. Immunoreactivity for GlyT1 was evenly distributed throughout all nuclei of the medial and lateral PB, including the external lateral PB and the waist area, while the KF was only weakly stained. Our data provide evidence that glycinergic mechanisms might play a role for neural processing in most nuclei of the PB and in the KF. Only the external lateral PB and the waist area are apparently not subject to glycinergic inhibition.

Expression of N-methyl-D-aspartate receptor subunits in the rat parabrachial and Kölliker-Fuse nuclei and in selected pontomedullary brainstem nuclei

In the present study, we investigated the expression of N-methyl-D-aspartate (NMDA) receptor subunits in the parabrachial/Kölliker-Fuse complex (PB/KF), the intertrigeminal region, the ventrolateral pons, the nucleus of the solitary tract, the ventrolateral medulla with the ambiguus nucleus, and the caudal spinal trigeminal nucleus, which are presumably involved in mediating the autonomic responses to nasotrigeminal stimulation (diving response). Our immunocytochemical data demonstrate that the majority of neurons in the respective nuclei stain for the NR1 subunit, which is a mandatory component of all NMDA receptors. NR1 immunoreactivity was found mainly on neuronal cell bodies and primary dendrites. The ubiquitous expression of the NR1 subunit was confirmed by in situ hybridization, revealing a strong NR1 mRNA signal over neurons in all nuclei investigated. Among the NR2A-D subunits, the strongest expression was observed for the NR2D transcript, both in the PB/KF and in the brainstem. For the PB/KF, we found in addition a moderate expression of NR2A mRNA in the internal lateral PB and of NR2B mRNA in the external lateral PB. The remaining PB nuclei and the KF were essentially devoid of NR2A-C transcripts. For the nucleus of the solitary tract and in the spinal trigeminal nucleus, we found, in addition to the strong NR2D mRNA signal, moderate expression of the NR2A-C transcripts. In the ventrolateral medulla, a moderate signal was seen for NR2C transcript, whereas signals for the NR2A and -B subunits were negligible. Our data suggest that, in PB/KF and pontomedullary brainstem nuclei involved in mediating the diving response, glutamatergic neurotransmission is apparently mediated through a specific type of NMDA receptor channels, consisting essentially of NR1 and NR2D subunits.

In situ hybridization analysis of flip/flop splice variants of AMPA-type glutamate receptor subunits in the rat parabrachial and Kölliker-Fuse nuclei

The aim of the present study was to analyze the occurrence and distribution of flip/flop splice variants of AMPA-type glutamate receptors (GluRA-D) in the rat parabrachial and Kölliker-Fuse nuclei (PB/KF). We performed in situ hybridization experiments on sections through different rostro-caudal levels of the PB/KF and analyzed the subunit expression semiquantitatively by means of grain counts for each probe in eight PB nuclei and in the KF. Our experiments revealed that the splice variants of the AMPA receptor subunit mRNAs are expressed differentially in the distinct nuclei of the PB/KF. The flip splice variants were predominantly expressed (GluRB-D flip) while the flop splice variants (GluRA flop and C flop) were expressed considerably weaker. Within the PB/KF, several nuclei expressed transcripts of GluRB flip (superior, central, dorsal, external, and ventral lateral PB, waist area, medial PB, KF) and GluRC flip (internal, superior, central, dorsal, external, and ventral lateral PB, waist area, KF). GluRB transcripts were not found in neurons of the internal lateral PB and in only 50% of the neurons in the KF. A more restricted expression in the PB/KF was observed for the GluRD flip (internal lateral PB), GluRA flop (medial PB, KF) and GluRC flop mRNA (superior lateral PB, KF). The present data demonstrate that the nuclei of the PB/KF show a differential expression of AMPA receptor subunits. This suggests that the anatomically and functionally distinct nuclei might make use of AMPA-type glutamate receptors with different physiological properties and ion selectivities.

Pontine cholinergic mechanisms enhance trigeminally evoked respiratory suppression in the anesthetized rat

In the present study, we investigated in anesthetized rats the influences of the pontine rapid-eye-movement (REM) sleep center on trigeminally induced respiratory responses. We evoked the nasotrigeminal reflex by electrical stimulation of the ethmoidal nerve (EN5) and analyzed the EN5-evoked respiratory suppression before and after injections into the pontine reticular nuclei of the cholinergic agonist carbachol. After injections of 80-100 nl of carbachol (20 mM), we observed a decrease in respiratory rate, respiratory minute volume, and blood pressure but an increase in tidal volume. In those cases in which carbachol injections alone caused these REM sleep-like autonomic responses, we also observed that the EN5-evoked respiratory suppression was significantly potentiated. Unfortunately, carbachol injections failed to depress genioglossus electromyogram (EMG) effectively, because the EMG activity was already strongly depressed by the anesthetic alpha-chloralose. We assume that pontine carbachol injections in our anesthetized rats cause autonomic effects that largely resemble REM sleep-like respiratory and vascular responses. We therefore conclude that the observed potentiation of EN5-evoked respiratory suppression after carbachol might be due to REM sleep-associated neuronal mechanisms. We speculate that activation of sensory trigeminal afferents during REM sleep might contribute to pathological REM sleep-associated respiratory failures.

Distribution of metabotropic glutamate receptors in the parabrachial and Kölliker-Fuse nuclei of the rat

In the present study, we analysed the distribution and cellular localization of metabotropic glutamate receptors (1alpha, 2/3, 5) in parabrachial and Kölliker-Fuse nuclei using subtype-specific antisera. Immunolabelling revealed that different nuclei express different sets of metabotropic glutamate receptors. Metabotropic glutamate receptor la immunoreactivity was found in the Kölliker-Fuse nucleus and in several parabrachial nuclei, including the waist area, lateral crescent, medial, external medial and ventral lateral nuclei. The external lateral and internal lateral parabrachial nuclei were devoid of metabotropic glutamate receptor 1alpha immunoreactivity. Metabotropic glutamate receptor 5 immunoreactivity was observed in the Kölliker-Fuse and in the medial parabrachial nuclei, while in the remaining nuclei the staining was very weak. Again, the external lateral nucleus was devoid of metabotropic glutamate receptor 5 immunoreactivity. The metabotropic glutamate receptor 2/3 antisera stained all lateral parabrachial nuclei as well as the Kölliker-Fuse nucleus, while staining in the medial parabrachial nucleus was weak. Metabotropic glutamate receptor 1alpha immunoreactivity was observed on presumed dendritic profiles, while metabotropic glutamate receptor 5 immunoreactivity was found predominantly on neuronal cell bodies. Metabotropic glutamate receptor 2/3 immunoreactivity was present as a fine, punctate immunostaining in the neuropil. Our data suggest that glutamate release in the parabrachial and Kölliker-Fuse nuclei might induce a variety of second messenger cascades, as indicated by the presence or absence of certain types of metabotropic glutamate receptors.

NMDA receptor subunit NR1-immunoreactivity in the rat pons and brainstem and colocalization with Fos induced by nasal stimulation

In the present study, we examined the distribution of neurons in the parabrachial nucleus (PB), the Kölliker-Fuse nucleus (KF), the spinal trigeminal nucleus caudalis (Sp5C), the nucleus of the solitary tract (NTS) and the ventrolateral medulla (VLM), which are activated by evoking the nasotrigeminal reflex and which exhibit immunoreactivity for the N-methyl-D-aspartate (NMDA) receptor subunit NR1. By stimulating the nasal mucosa with saline, we induced the expression of the immediate early gene c-fos and combined the immunocytochemical detection of the Fos protein with the detection of the NR1 subunit. Cell counts revealed that nasal stimulation, compared to anesthesia controls, resulted in highly significant increases (p < or = 0.001) of Fos-immunoreactive (-ir) neurons in the midlevel KF, the external lateral PB, and the Sp5C. In the central lateral PB, the rostral ventrolateral medulla including the Bötzinger/pre-Bötzinger complex, and in the ventrolateral and commissural NTS the increases were only moderately significant (p < or = 0.05). With respect to the numbers of NR1-/Fos-ir double-labeled neurons, significant increases were only observed in a subset of these pontomedullary nuclei. Increases were highly significant in the Sp5C (p < or = 0.001) and the midlevel KF (p < or = 0.01) and moderately significant (p < or = 0.05) in the external lateral PB, Bötzinger/pre-Bötzinger complex, and ventrolateral NTS. The present study revealed that nasotrigeminally activated neurons in mandatory and potential relay sites of the nasotrigeminal reflex circuit express the NR1 subunit. This finding strongly suggests that NMDA-type glutamate receptors are involved in the mediation of the nasotrigeminally evoked cardiovascular and respiratory responses.

GABA, GABA transporters, GABA(A) receptor subunits, and GAD mRNAs in the rat parabrachial and Kölliker-Fuse nuclei

In the present study, we investigated the key molecules that determine gamma-aminobutyric acid (GABA)ergic signal transduction in the parabrachial/Kölliker-Fuse complex (PB/KF) by means of immunocytochemistry and in situ hybridization. Our data demonstrate a dense plexus of GABA-immunoreactive (-ir) varicosities throughout the nuclei of the PB and the KF. The number of neurons expressing GAD65 or GAD67 mRNA was fairly low in the PB, whereas caudally in the KF an accumulation of GAD-expressing neurons was observed. The GABA transporter-3 (GAT-3) was detected in all parts of the PB/KF, whereas immunolabeling for GAT1 was not observed. All nuclei of the PB and the KF exhibited immunoreactivity for the gamma2-, alpha2-, and alpha3-subunits of the GABA(A) receptor. Gamma2-ir was strong and similar in all PB/KF nuclei. In contrast, alpha2-labeling was particularly intense in the superior lateral PB, and alpha3-labeling was most prominent in the external lateral and external medial PB, compared with the remaining nuclei. With respect to the subcellular localization, we found gamma2-ir in cell bodies and higher order dendrites, whereas alpha2- and alpha3-ir was predominantly found in cell bodies. Immunolabeling for the beta2/3- and the alpha1-subunit was seen in cell bodies and presumed dendritic profiles. The staining intensity was strongest in the dorsal lateral PB. Most importantly, the external lateral PB and the waist area were totally devoid of beta2/3- and alpha1-ir. Our data suggest that neural processing in the PB/KF is under a strong GABAergic inhibition that is apparently mediated by different types of GABA(A) receptors in functionally different pathways through the PB/KF.

NMDA and GABAA receptors in the rat Kolliker-Fuse area control cardiorespiratory responses evoked by trigeminal ethmoidal nerve stimulation

1. Electrical stimulation (10 s) of the ethmoidal nerve (EN5) evokes the nasotrigeminal reflex responses, including apnoea, bradycardia and rise in arterial blood pressure. In the present study, we examined the involvement of N-methyl-D-aspartate (NMDA), AMPA/kainate, (gamma-aminobutyric acidA (GABAA) and glycine receptors in the Kolliker-Fuse (KF) nucleus in the mediation of the nasotrigeminal reflex responses. 2. Unilateral injections (n = 6) of 50-100 nl of the NMDA receptor antagonist AP5 into the KF area led to a significant blockade of the EN5-evoked respiratory depression and bradycardia. Injections placed into the midlevel of the KF area were most effective (80-90 % blockade). The rise in arterial blood pressure remained unaffected. 3. Unilateral injections (n = 6) of the AMPA/kainate receptor antagonist CNQX into the KF area failed to block EN5-evoked autonomic responses significantly. 4. Unilateral injections (n = 5) of the GABAA receptor antagonist bicuculline enhanced the EN5-evoked respiratory depression and bradycardia. The effect persisted for up to 30 s after stimulation. Bicuculline injections into the midlevel of the KF area were most effective. The increase in arterial blood pressure remained unaffected. 5. Unilateral injections (n = 5) of the glycine receptor antagonist strychnine into the KF area did not produce any significant effects on EN5-evoked autonomic responses. 6. Our results suggest that the KF area represents a mandatory relay for the nasotrigeminally induced apnoea and bradycardia which are predominantly mediated by NMDA receptors in the KF. Furthermore, it appears that KF neurons are under a potent GABAergic inhibitory control. The EN5-evoked rise in arterial blood pressure was not altered by any of the drugs and, therefore, appears not to be mediated via the KF.

The medical nucleus of the solitary tract mediates the trigeminally evoked pressor response

The present study examined whether the nucleus of the solitary tract (NTS) plays a role in mediating the trigeminally evoked pressor response which occurs after noxious perturbation of the nasal mucosa or electrical stimulation of the ethmoidal nerve (EN5). We recorded arterial blood pressure responses to EN5 stimulations before and after injections of the calcium channel blocker CoCl2 into the NTS. Unilateral and bilateral injections of CoCl2 into the medial NTS resulted in significant blockade (p < 0.05 and p < 0.01, respectively) of the EN5-evoked pressor responses. Recovery of the pressor responses was observed 15-25 min after the CoCl2 injections. CoCl2 injections into the caudal commissural NTS remained largely ineffective with respect to blocking the EN5-evoked pressor responses. These findings strongly suggest that the medial NTS is a crucial link for the trigeminally induced pressor response.

Effects of anesthetics on Fos protein expression in autonomic brain nuclei related to cardiovascular regulation

We tested the influence of urethane, chloral hydrate and a mixture of ketamine/xylazine on Fos protein expression in autonomic brain regions related to blood pressure. We conclude that ketamine/xylazine is a suitable anesthetic to be used in studies looking at c-fos expression in neural circuits serving cardiovascular regulation.

Fos expression in the rat parabrachial and Kölliker-Fuse nuclei after electrical stimulation of the trigeminal ethmoidal nerve and water stimulation of the nasal mucosa

The present study examined the location of neurons in the lateral parabrachial nucleus (PBL), Kölliker-Fuse nucleus (KF), nucleus of the solitary tract (NTS), spinal trigeminal nucleus (Sp5C) and upper cervical cord possibly involved in the transmission of autonomic responses (apnea, bradycardia and rise in arterial blood pressure) elicited by nasotrigeminal stimulation in the rat. To identify these neurons we employed immunocytochemical detection of the transcription factor Fos. To induce the expression of Fos protein, two kinds of stimuli and experimental controls were performed in chloralose/urethane-anesthetized animals: (i) electrical stimulation of the trigeminal ethmoidal nerve (EN5) and, as sham controls, dissection of the EN5 without electrical stimulation, (ii) stimulation of the nasal mucosa with water and, as control experiments, no stimulation. Both forms of stimulation lead to a consistent pattern of Fos-positive neurons in the PBL and KF. Differences could be observed rostrally in the PBL and KF, where significantly higher numbers of Fos-positive neurons were present after EN5 versus water stimulation. The EN5-stimulated group had a significantly higher number of Fos-immunoreactive neurons in the KF than the sham controls, especially in the midlevel region. In the PBL significant differences in the numbers of activated cells could be observed between EN5-stimulated versus sham controls. In the water-stimulated rats compared with the anesthesia controls, a significantly higher number of Fos-immunoreactive neurons was always observed at all rostrocaudal levels in the KF and in the midlevel PBL. Electrical EN5 stimulation induced Fos expression in the Sp5C at the level of the area postrema and caudally in the upper cervical cord. In contrast, after water stimulation Fos-positive neurons were exclusively found in the Sp5C. In addition, all forms of stimuli and controls induced strong expression of Fos in the medial and commissural NTS. Linear correlations were found between the numbers of Fos-immunoreactive neurons in the Sp5C versus the KF and the NTS versus the PBL. The activated neurons may belong to two functionally discrete pathways: the nasotrigeminal reflex circuit, which is activated by nasal sensory afferents running through the EN5 via the Sp5C to the KF, and a pathway activated most likely by baro- and chemoreceptor afferents running through the NTS to the PBL. Our results indicate that the PB/KF plays a pivotal role in the mediation and maintenance of the autonomic responses induced by the nasotrigeminal reflex.

Afferent and efferent connections of the ventrolateral tegmental area in the rat

The present study examined the organization of afferent and efferent connections of the rat ventrolateral tegmental area (VLTg) by employing the retrograde and anterograde axonal transport of Fluorogold and Phaseolus vulgaris-leucoagglutinin, respectively. Our interest was focused on whether the anatomical connections of the VLTg would provide evidence as to the involvement of this reticular area in audiomotor behavior. Our retrograde experiments revealed that minor inputs to the VLTg arise in various telencephalic structures, including the cerebral cortex. Stronger projections originate in the lateral preoptic area, the zona incerta, the nucleus of the posterior commissure and some other thalamic areas, the lateral substantia nigra, the deep layers of the superior colliculus, the dorsal and lateral central gray, the deep mesencephalic nucleus, the paralemniscal zone, the intercollicular nucleus, the external cortex of the inferior colliculus, the oral and caudal pontine reticular nucleus, the deep cerebellar nuclei, the gigantocellular and lateral paragigantocellular reticular nuclei, the prepositus hypoglossal nucleus, the spinal trigeminal nuclei, and the intermediate layers of the spinal cord. Most importantly, we disclosed strong auditory afferents arising in the dorsal and ventral cochlear nuclei and in the cochlear root nucleus. The efferent projections of the VLTg were found to be less widespread. Telencephalic structures do not receive any input from the VLTg. Moderate projections were seen to diencephalic reticular areas, the zona incerta, the nucleus of the posterior commissure, and to various other thalamic areas. The major VLTg projections terminate in the deep layers of the superior colliculus, the deep mesencephalic nucleus, the intercollicular nucleus and external cortex of the inferior colliculus, the oral and caudal pontine reticular nucleus, the gigantocellular and lateral paragigantocellular reticular nuclei, and in the medial column of the facial nucleus. From our data, we conclude that the VLTg might play a role in sensorimotor behavior.

Spinal afferents to functionally distinct periaqueductal gray columns in the rat: an anterograde and retrograde tracing study

The segmental and laminar organization of spinal projections to the functionally distinct ventrolateral (vlPAG) and lateral periaqueductal gray (lPAG) columns was examined by using retrograde and anterograde tracing techniques. It was found 1) that spinal input to both vlPAG and lPAG columns arose predominantly from neurons in the upper cervical (C1-4) and sacral spinal cord; 2) that there was a topographical separation of vl-PAG projecting and lPAG-projecting neurons within the upper cervical spinal cord; but 3) that below spinal segment C4, vlPAG-projecting and lPAG-projecting spinal neurons were similarly distributed, predominantly within contralateral lamina I, the nucleus of the dorsolateral fasciculus (the lateral spinal nucleus) and the lateral (reticular) part of lamina V. Consistent with the retrograde results, the greatest density of anterograde label, within both the vlPAG and lPAG, was found after tracer injections made either in the superficial or deep dorsal horn of the upper cervical spinal cord. Tracer injections made within the thoraco-lumbar spinal cord revealed that the vlPAG column received a convergent input from both the superficial and deep dorsal horn. However, thoraco-lumbar input to the lPAG was found to arise uniquely from the superficial dorsal horn; whereas the deep dorsal horn was found to innervate the "juxta-aqueductal" PAG region rather than projecting to the lPAG. These findings suggest that similar to spino-parabrachial projections, spinal projections to the lPAG (and juxta-aqueductal PAG) are topographically organised, with distinct subgroups of spinal neurons projecting to specific lPAG or juxta-aqueductal PAG subregions. In contrast, the vlPAG receives a convergent spinal input which arises from the superficial and deep dorsal horn of cervical, thoracic, lumbar, and sacral spinal segments.

The Kölliker-Fuse nucleus mediates the trigeminally induced apnoea in the rat

The present study examined whether the Kölliker-Fuse nucleus (KF) plays a role in mediating the trigeminally induced apnoea which occurs after noxious perturbation of the nasal mucosa. We stimulated the ethmoidal nerve (EN5) electrically and recorded respiratory responses before and after injections of the calcium channel blocker CoCl2 into the KF. Unilateral EN5 stimulations resulted in an apnoea or in a reduction of respiratory frequency and tidal volume. EN5 stimulations immediately after ipsilateral CoCl2 injections into the caudal KF caused only minor respiratory suppression, indicating a blockade of synaptic transmission. Recovery of the respiratory responses was observed 15-120 min after the CoCl2 injection. Our data strongly suggest that the caudal KF is an obligatory relay site for trigeminally induced apnoea.

Analysis of projections from the cochlear nucleus to the lateral paragigantocellular reticular nucleus in the rat

Golgi-staining, retrograde and anterograde tract-tracing, and a two-color immunoperoxidase technique have been employed, at the light- and electron-microscopic levels, to analyze the auditory projections from the cochlear nucleus (CN) to the lateral paragigantocellular reticular nucleus (LPGi) in the rat. We have found that the auditory input originates predominantly in the posteroventral and cochlear root nuclei. The auditory axons terminate in the cell-poor, ventral portion of the LPGi, which is strongly invaded by beaded dendritic profiles, originating from parent cell bodies located in the dorsal half of the LPGi. Ultrastructural analysis has revealed that the anterogradely labeled auditory axons form functional synapses preferentially with dendritic shafts. These axo-dendritic contacts are apparently excitatory in nature. By means of a sequential two-color immunoperoxidase staining method, we have further characterized potential postsynaptic neurons in the LPGi. Black-stained auditory fibers intermingle with brown-stained serotonergic or adrenergic neurons. Varicose auditory axons are often closely apposed to immunoreactive dendritic profiles of serotonergic and adrenergic neurons, indicating the presence of possible synaptic contacts of auditory terminal fibers with these transmitter-classified cells. The monosynaptic auditory in- put from the CN may modulate the activity of B3 sero-tonergic and C1 adrenergic cells in the LPGi and may thus induce adaptive changes in response to acoustic stimuli.

Distribution of alpha 2-adrenergic binding sites in the parabrachial complex of the rat

The present study describes the distribution of alpha 2-adrenoceptors in the parabrachial and Kölliker-Fuse nucleus of the rat by employing the tritium-labeled alpha 2-receptor antagonist rauwolscine ([3H]-RAUW) as a ligand. The [3H]-RAUW binding was densitometrically quantified in five nuclei of the parabrachial (PB) complex in serial coronal sections. We found that cytoarchitectonically and anatomically distinct nuclei of the PB complex exhibit different numbers of [3H]-RAUW-binding sites. The largest number of binding sites was observed over the external lateral PB and caudally over the waist area of the PB. Lower numbers of binding sites were found in the remaining lateral PB nuclei, followed by the medial PB and the Kölliker-Fuse nucleus. In addition we disclosed that the internal lateral PB contains a very low number of binding sites while the external medial PB is marked by dense [3H]-RAUW binding. Also, the affinities of the binding sites differed between the PB areas. High affinities were observed in the external lateral PB, the remaining lateral PB nuclei and in the waist area of the PB, while the medial PB and the Kölliker-Fuse nucleus exhibited only low affinities for the ligand. Furthermore, saturation curves demonstrated non-linear profiles, indicating the presence of more than one population of binding sites in the PB nuclei for the radioligand. Our data demonstrate that the PB exhibits a distinct distribution of alpha 2-adrenergic binding sites. These correlate well with the cytoarchitectonically defined nuclei of the PB complex and with the pattern of ascending axons from the medial nucleus of the solitary tract and the area postrema terminating in the PB. Since a large number of these projection neurons utilize adrenaline or noradrenaline as their transmitters, we conclude that solitary-parabrachial neurotransmission to the forebrain is, at least in part, mediated via alpha 2-adrenoceptors.

Morphology and dendritic domains of neurons in the lateral parabrachial nucleus of the rat

The present study provides a description of the dendritic morphology and the dendritic domains of neurons in the lateral parabrachial nucleus (PB) of the rat. The cells were intracellularly stained in vitro with Lucifer yellow. A subpopulation of these cells was characterized beforehand as neurons projecting to the amygdaloid complex by retrograde transport with rhodamine beads. With respect to their dendritic arborization, different types of "spatially" organized PB neurons were discriminated. One major cell type in the external lateral PB (PBel) is characterized by long, elongated dendritic trees that are preferentially oriented parallel to the superior cerebellar peduncle. The majority of their dendrites appears to respect subnuclear boundaries, yet their distal dendrites often exceed the limits of the PBel to encroach upon adjacent subnuclei located dorsally and ventrolaterally to the PBel. Another prominent cell type in the PBel has fairly small and locally restricted dendritic trees that are also elongated, running with their main axis from ventrolateral to dorsomedial. The dendrites of the majority of these neurons apparently stay within the confines of the PBel. A distinct group of neurons is found in the ventral portion of the PBel. The majority of their dendrites is mediolaterally oriented and not confined to the PBel subnucleus. In addition, we found a smaller number of neurons scattered within the lateral PB whose dendrites do not show a preferential orientation but travel across subnuclear boundaries into several different PB subnuclei. Our data show that the dendrites of a large proportion of neurons in the lateral PB either stay within the confines of a particular subnucleus or slightly extend across subnuclear limits. In any case, they appear to match with terminal territories of afferent axons and, thus, maintain the functional specificity of inputs by their relay through the PB. In contrast, PB neurons that extend their dendrites across subnuclear boundaries or known terminal territories are likely to receive inputs of different qualities from a variety of sources and therefore transmit a more general, integrated signal to the forebrain.

Topographic organization of spinal and trigeminal somatosensory pathways to the rat parabrachial and Kölliker-Fuse nuclei

We examined the organization of somatosensory projections to the parabrachial (PB) and Kölliker-Fuse (KF) nuclei by employing the retrograde and anterograde axonal transport of Fluorogold and Phaseolus vulgaris-leucoagglutinin (PHA-L), respectively. Small PHA-L injections were made into different parts of the spinal trigeminal complex, including the paratrigeminal nucleus, and into different segments and laminae of the spinal dorsal horn. The subnuclear distribution of axonal labeling in the PB and KF was mapped with a camera lucida. Our results show that the somatosensory input to the PB and KF is highly organized. Neurons in the spinal trigeminal nuclei project predominantly to the KF and to the ventral portion of the external lateral PB. Neurons in the paratrigeminal nucleus project to the ventral lateral PB, the external medial PB, and to caudal aspects of the medial PB. These findings were supported by retrograde tracing experiments with Fluorogold. Spinal cord neurons located in the superficial dorsal horn (laminae I-II) of upper cervical segments project specifically to the ventral portion of the external lateral PB and, although more sparsely, to various other lateral PB nuclei. In contrast, neurons in the superficial dorsal horn of thoracic and lumbar spinal segments project mainly to the dorsal lateral and the central lateral PB. Finally, neurons in the lateral reticulated area and the lateral spinal nucleus of all spinal segments project almost exclusively to the internal lateral PB, whereas neurons in the respective nuclei of upper cervical segments also project to the KF. From our data we conclude that the somatosensory projections to the PB and KF are topographically organized. It is assumed that these pathways, which run from trigeminal and spinal neurons through the PB and KF to various forebrain, medullary, and spinal nuclei, form functionally different neural circuits that are involved in somatoautonomic processing.

Substance P and other putative transmitters modulate the activity of reticular pontine neurons: an electrophysiological and immunohistochemical study

In this study we investigated the effects of possible modulatory transmitters on acoustically responsive neurons of the caudal pontine reticular nucleus (PnC). From previous work in our laboratory it has been suggested that the acoustically responsive giant neurons of this nucleus are the sensorimotor interface mediating the acoustic startle response. Furthermore they are the site of some of the modulatory influence impinging on this response. Besides a possibly glutamatergic excitation from the amygdala a cholinergic input from the midbrain has been described which may use substance P as cotransmitter. Therefore we used electrophysiological and histochemical methods to study this possible modulatory influence in the caudal pontine reticular nucleus. In the first part of this study we recorded extracellularly from single units in the PnC in vivo and studied the effects of iontophoretically applied transmitters. Substance P elicited a long lasting excitation. This excitatory effect of SP was potentiated by acetyl-beta-methylcholine (AMCh, an acetylcholine agonist), whereas single application of AMCh showed no uniform response. Glutamate elicited a potent brief excitation, while application of GABA showed a potent brief inhibition of PnC neurons. In the second part of this study we employed immunoperoxidase staining for substance P, which revealed a fairly dense network of substance P-immunoreactive (SP-ir) fibers in the lateral and ventral aspects of the PnC. Combining retrograde tracing and immunocytochemistry for substance P, we demonstrated that the SP-ir axons in the PnC originate mainly in the laterodorsal tegmental nucleus. We therefore conclude that activation of the laterodorsal tegmental nucleus may facilitate the acoustic startle response by a long lasting excitation of neurons in the caudal pontine reticular nucleus.

Cholinergic neurons in the pedunculopontine tegmental nucleus are involved in the mediation of prepulse inhibition of the acoustic startle response in the rat

The amplitude of the acoustic startle response (ASR) is markedly reduced when the startle eliciting pulse is preceded by a weak, non-startling stimulus at an appropriate lead time, usually about 100 ms. This phenomenon is termed prepulse inhibition (PPI) and has received considerable attention in recent years as a model of sensorimotor gating. We report here on experiments which were undertaken in order to investigate some of the neural mechanisms of PPI. We focused on the characterization of the cholinergic innervation of the pontine reticular nucleus, caudal part (PnC), an obligatory relay station in the primary startle pathway. The combination of retrograde tracing with choline acetyltransferase-immunocytochemistry revealed a cholinergic projection from the pedunculopontine tegmental nucleus (PPTg) and laterodorsal tegmental nucleus (LDTg) to the PnC. Extracellular recording from single PnC units, combined with microiontophoretic application of the acetylcholine (ACh) agonists acetyl-beta-methylcholine (AMCH) and carbachol revealed that ACh inhibits the majority of acoustically responsive PnC neurons. Neurotoxic lesions of the cholinergic neurons of the PPTg significantly reduced PPI without affecting the ASR amplitude in the absence of prepulses. No effect on long-term habituation of the ASR was observed. The present data indicate that the pathway mediating PPI impinges upon the primary acoustic startle circuit through an inhibitory cholinergic projection from the PPTg to the PnC.

Topography of descending projections from the inferior colliculus to auditory brainstem nuclei in the rat

We examined the organization of descending projections from the inferior colliculus (IC) to auditory brainstem nuclei and to pontine and reticular nuclei in the rat by employing the anterograde axonal tracer Phaseolus vulgaris-leucoagglutinin (PHA-L). Small PHA-L injections into cytologically defined subnuclei of the IC revealed that each subnucleus has a unique pattern of efferent projections. The central nucleus of the IC projects in a topographic order to the dorsal nucleus of the lateral lemniscus (DLL), the rostral periolivary nucleus (RPO), the ventral nucleus of the trapezoid body (VNTB), and the dorsal cochlear nucleus (DCN). It is assumed that this topography represents a cochleotopic arrangement. The external cortex of the IC projects to the nucleus sagulum (Sag), the RPO, the VNTB, and the DCN. Minor projections were found to pontine and reticular nuclei. Efferent fibers from the dorsal cortex of the IC terminate mainly in the Sag, while other nuclei of the auditory and extra-auditory brainstem receive only minor projections. The intercollicular zone sends a moderate number of fibers to the DLL and very few, if any, to the remaining auditory brainstem nuclei. In contrast, fairly strong projections from the intercollicular zone to the reticular formation were found. The present data demonstrate that the four subnuclei of the IC have a differential pattern of descending projections to nuclei in the pontine and medullary brainstem. These parallel colliculofugal pathways, assumed to belong to functionally separate circuits, may modulate auditory processing at different levels of the auditory neuraxis.

Evidence for projections from medullary nuclei onto serotonergic and dopaminergic neurons in the midbrain dorsal raphe nucleus of the rat

The anterograde tracer Phaseolus vulgaris-leucoagglutinin was injected into the medial nucleus of the solitary tract and into the rostral dorsomedial medulla. A sequential two-color immunoperoxidase staining was accomplished in order to demonstrate the co-distribution of presumed terminal axons with chemically distinct neurons in the dorsal raphe nucleus of the midbrain central gray, i.e., B7 serotonergic and A10dc dopaminergic neurons. Black-stained efferent fibers from the medial nucleus of the solitary tract and the rostral dorsomedial medulla intermingled with brown-stained serotonergic (5-hydroxytryptamine-immunoreactive) or dopaminergic (tyrosine hydroxylase-immunoreactive) neurons. Light microscopy revealed that the black-stained efferent axons exhibited numerous en passant and terminal varicosities that were often found in close apposition to brown-stained serotonergic and dopaminergic somata, and to proximal and distal dendrites and dendritic processes. The close association of immunoreactive elements suggests the presence of axo-somatic and axo-dendritic synaptic contacts of medullary fibers with serotonergic and dopaminergic neurons in the dorsal raphe nucleus. These projections could be involved in the modulation of dorsal raphe neurons, depending on the autonomic status of an animal.

Organization of medullary adrenergic and noradrenergic projections to the periaqueductal gray matter in the rat

The periaqueductal or midbrain central gray matter (CG) in the rat contains a dense network of adrenergic and noradrenergic fibers. We examined the origin of this innervation by using retrograde and anterograde axonal tracers combined with immunohistochemistry for the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT). Following injections of the fluorescent tracers Fast Blue or Fluorogold into the CG, double-labeled neurons in the medulla were identified mainly in the noradrenergic A1 group in the caudal ventrolateral medulla (VLM) and A2 group in the medial part of the nucleus of the solitary tract (NTS); and in the adrenergic C1 group in the rostral ventrolateral medulla and C3 group in the rostral dorsomedial medulla. Injections of Phaseolus vulgaris-leucoagglutinin (PHA-L) into these cell groups resulted in a distinct pattern of axonal labeling in various subdivisions of the CG. Anterogradely labeled fibers originating in the medial NTS were predominantly found in the lateral portion of the dorsal raphe nucleus and in the adjacent part of the lateroventral CG (CGlv). Following PHA-L injections into the C3 region the anterogradely labeled fibers were diffusely distributed in the CGlv and the dorsal raphe nucleus at caudal levels, but rostrally tended to be located laterally in the CGlv. In contrast, ascending fibers from the caudal and rostral VLM terminated in the rostral dorsal part of the CGlv and in the dorsal nucleus of the CG, whereas ventral parts of the CG, including the dorsal raphe nucleus, contained few afferent fibers. Double-label studies with antisera against DBH and PNMT confirmed that noradrenergic neurons in the A1 and A2 groups and adrenergic neurons in the C1 and C3 groups contributed to these innervation patterns in the CGlv. Noradrenergic and adrenergic projections from the medulla to the CG may play an important role in a variety of autonomic, sensory and behavioral processes.

Auditory projections from the cochlear nucleus to pontine and mesencephalic reticular nuclei in the rat

We investigated projections from the cochlear nucleus in the rat using the anterograde tracer Phaseolus vulgaris-leucoagglutinin. We focused on nuclei in the brainstem which are not considered to be part of the classical auditory pathway. In addition to labeling in auditory nuclei, we found presumed terminal fibers in 4 pontine and mesencephalic areas: (1) the pontine nucleus (PN), which receives bilateral projections from the antero- and posteroventral cochlear nuclei; (2) the ventrolateral tegmental nucleus (VLTg), which receives a contralateral projection from the rostral portion of the anteroventral cochlear nucleus; (3) the caudal pontine reticular nucleus (PnC), which receives bilateral input originating predominantly in the dorsal cochlear nucleus; and (4) the lateral paragigantocellular nucleus (LPGi), which receives projections from all subdivisions of the cochlear nuclei. In the VLTg and PnC, anterogradely labeled varicose axons were often found in close apposition to the primary dendrites and somata of large reticular neurons. Injections of the retrograde fluorescent tracer Fluoro-Gold into the VLTg demonstrated that the neurons of origin are mainly located contralaterally in the rostral anteroventral cochlear nucleus and in the cochlear root nucleus. The relevance of these auditory projections for short-latency audio-motor behaviors and acoustically elicited autonomic responses is discussed.

Distribution and origin of noradrenergic and serotonergic fibers in the cochlear nucleus and inferior colliculus of the rat

We examined the monoaminergic innervation of the rat cochlear nucleus (CN) and the inferior colliculus (IC) by using retrograde transport of the fluorescent dye Fluoro-Gold combined with immunohistochemistry. We used antisera against the catecholamine synthesizing enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT), and one against the transmitter serotonin (5-HT). Each substance revealed a distinct pattern of immunoreactive staining in the CN and the IC. In the CN, DBH-immunoreactive (-ir) fibers were present in all subnuclei. The molecular layer of the dorsal CN and the granular layer of the ventral CN, however, were largely devoid of DBH-ir fibers. In contrast, 5-HT-ir fibers were abundant in the molecular layer and the granular cell layer of the CN. In the dorsal CN and the postero- and anteroventral CN, however, this innervation was less dense and evenly distributed across subnuclei. In the IC, the DBH-ir fibers were slightly more numerous in layer 2 of the dorsal cortex than in other subnuclei, while the layer 1 of both the dorsal and the external cortex contained only a few fibers. In contrast, the 5-HT-ir fibers formed a dense network in both the dorsal and external cortices of the IC, while they were less abundant in the remaining subnuclei. PNMT-ir fibers were not found in any of the auditory brainstem nuclei. Following Fluoro-Gold injections into the CN or IC, retrogradely labeled DBH-ir neurons were found in the A6 noradrenergic cell group (locus coeruleus). The CN received additional projections from the A5 noradrenergic cell group, as well as sparse projections from the A4 and A7 cell groups. The serotonergic innervation of the CN and IC originated largely in the B7 serotonergic cell group (dorsal raphe nucleus). Serotonergic neurons in other groups of the raphe nuclei were only occasionally labeled. Our data indicate that both noradrenaline and serotonin may play a role in central auditory processing. Their differential distribution in the IC and CN subnuclei suggests that these transmitter systems might influence different functional circuits.

Efferent projections of the infralimbic cortex of the rat

On the basis of stimulation studies, it has been proposed that the infralimbic cortex (ILC), Brodmann area 25, may serve as an autonomic motor cortex. To explore this hypothesis, we have combined anterograde tracing with Phaseolus vulgaris leucoagglutinin (PHA-L) and retrograde tracing with wheat germ aggutinin conjugated to horseradish peroxidase (WGA-HRP) to determine the efferent projections from the ILC. Axons exit the ILC in one of three efferent pathways. The dorsal pathway ascends through layers III and V to innervate the prelimbic and anterior cingulate cortices. The lateral pathway courses through the nucleus accumbens to innervate the insular cortex, the perirhinal cortex, and parts of the piriform cortex. In addition, some fibers from the lateral pathway enter the corticospinal tract. The ventral pathway is by far the largest and innervates the thalamus (including the paraventricular nucleus of the thalamus, the border zone between the paraventricular and medial dorsal nuclei, and the paratenial, reuniens, ventromedial, parafasicular, and subparafasicular nuclei), the hypothalamus (including the lateral hypothalamic and medial preoptic areas, and the suprachiasmatic, dorsomedial, and supramammillary nuclei), the amygdala (including the central, medial, and basomedial nuclei, and the periamygdaloid cortex) and the bed nucleus of the stria terminalis. The ventral efferent pathway also provides descending projections to autonomic cell groups of the brainstem and spinal cord including the periaqueductal gray matter, the parabrachial nucleus, the nucleus of the solitary tract, the dorsal motor vagal nucleus, the nucleus ambiguus, and the ventrolateral medulla, as well as lamina I and the intermediolateral column of the spinal cord. The ILC has extensive projections to central autonomic nuclei that may subserve a role in modulating visceral responses to emotional stimuli, such as stress.

Topography of projections from the auditory cortex to the inferior colliculus in the rat

We examined the organization of descending projections from auditory and adjacent cortical areas to the inferior colliculus (IC) in the rat by using the retrograde and anterograde transport of wheat germ agglutinin-horseradish peroxidase. Small tracer injections were placed into cytologically defined subnuclei of the IC. On the basis of the resulting pattern of retrogradely labeled neurons in the cortex, different cortical areas and fields were defined. Two secondary areas located ventrocaudally (Te2) and ventrally (Te3) to the primary auditory area (Te1) were delineated. The primary auditory area was subdivided into a posterior (Te1.p), a medial (Te1.m), and an anterior (Te1.a) auditory field. In addition, we outlined an area located rostrally to the auditory areas comprising a part of the secondary somatosensory cortex, as well as a dorsal belt surrounding dorsally the auditory areas. The following basic patterns of corticocollicular projections are revealed: 1) layers 2 and 3 of the dorsal cortex of the IC (DC2, DC3) are differentially innervated by the primary auditory fields (Te1.p and Te1.a project bilaterally to DC2, while Te1.m projects bilaterally and in topographical order to DC3); cells in Te1.m, arranged in caudal to rostral sequence, project to corresponding loci in DC3 arranged from dorsolateral to ventromedial; 2) the fibrocellular capsule of the IC, comprising layer 1 of the dorsal and external cortex of the IC, receives input from the secondary auditory area Te2; 3) layers 2 and 3 of the external cortex of the IC are only weakly innervated by the primary and secondary auditory cortex; 4) the intercollicular zone receives its major input from the secondary auditory area Te3, the secondary somatosensory cortex, and the dorsal belt; and 5) finally, the central nucleus of the IC receives no input from the temporal cortex at all. Our results demonstrate that the corticocollicular projections are highly organized. These pathways may modulate auditory processing in different functional circuits of the inferior colliculus.

Organization of cortical, basal forebrain, and hypothalamic afferents to the parabrachial nucleus in the rat

In a previous study (Herbert et al., J. Comp. Neurol. [1990];293:540-580), we demonstrated that the ascending afferent projections from the medulla to the parabrachial nucleus (PB) mark out functionally specific terminal domains within the PB. In this study, we examine the organization of the forebrain afferents to the PB. The PB was found to receive afferents from the infralimbic, the lateral prefrontal, and the insular cortical areas; the dorsomedial, the ventromedial, the median preoptic, and the paraventricular hypothalamic nuclei; the dorsal, the retrochiasmatic, and the lateral hypothalamic areas; the central nucleus of the amygdala; the substantia innominata; and the bed nucleus of the stria terminalis. In general, forebrain areas tend to innervate the same PB subnuclei from which they receive their input. Three major patterns of afferent termination were noted in the PB; these corresponded to the three primary sources of forebrain input to the PB: the cerebral cortex, the hypothalamus, and the basal forebrain. Hypothalamic afferents innervate predominantly rostral portions of the PB, particularly the central lateral and dorsal lateral subnuclei. The basal forebrain projection to the PB ends densely in the external lateral and waist subnuclei. Cortical afferents terminate most heavily in the caudal half of the PB, particularly in the ventral lateral and medial subnuclei. In addition, considerable topography organization was found within the individual projections. For example, tuberal lateral hypothalamic neurons project heavily to the central lateral subnucleus and lightly to the waist area; in contrast, caudal lateral hypothalamic neurons send a moderately heavy projection to both the central lateral and waist subnuclei. Our results show that the forebrain afferents of the PB are topographically organized. These topographical differences may provide a substrate for the diversity of visceral functions associated with the PB.

Connections of the parabrachial nucleus with the nucleus of the solitary tract and the medullary reticular formation in the rat

We examined the subnuclear organization of projections to the parabrachial nucleus (PB) from the nucleus of the solitary tract (NTS), area postrema, and medullary reticular formation in the rat by using the anterograde and retrograde transport of wheat germ agglutinin-horseradish peroxidase conjugate and anterograde tracing with Phaseolus vulgaris-leucoagglutinin. Different functional regions of the NTS/area postrema complex and medullary reticular formation were found to innervate largely nonoverlapping zones in the PB. The general visceral part of the NTS, including the medial, parvicellular, intermediate, and commissural NTS subnuclei and the core of the area postrema, projects to restricted terminal zones in the inner portion of the external lateral PB, the central and dorsal lateral PB subnuclei, and the "waist" area. The dorsomedial NTS subnucleus and the rim of the area postrema specifically innervate the outer portion of the external lateral PB subnucleus. In addition, the medial NTS innervates the caudal lateral part of the external medial PB subnucleus. The respiratory part of the NTS, comprising the ventrolateral, intermediate, and caudal commissural subnuclei, is reciprocally connected with the Kölliker-Fuse nucleus, and with the far lateral parts of the dorsal and central lateral PB subnuclei. There is also a patchy projection to the caudal lateral part of the external medial PB subnucleus from the ventrolateral NTS. The rostral, gustatory part of the NTS projects mainly to the caudal medial parts of the PB complex, including the "waist" area, as well as more rostrally to parts of the medial, external medial, ventral, and central lateral PB subnuclei. The connections of different portions of the medullary reticular formation with the PB complex reflect the same patterns of organization, but are reciprocal. The periambiguus region is reciprocally connected with the same PB subnuclei as the ventrolateral NTS; the rostral ventrolateral reticular nucleus with the same PB subnuclei as both the ventrolateral (respiratory) and medial (general visceral) NTS; and the parvicellular reticular area, adjacent to the rostral NTS, with parts of the central and ventral lateral and the medial PB subnuclei that also receive rostral (gustatory) NTS input. In addition, the rostral ventrolateral reticular nucleus and the parvicellular reticular formation have more extensive connections with parts of the rostral PB and the subjacent reticular formation that receive little if any NTS input. The PB contains a series of topographically complex terminal domains reflecting the functional organization of its afferent sources in the NTS and medullary reticular formation.