The pontine respiratory group, particularly the Kölliker-Fuse nucleus, mediates phases of the hypoxic ventilatory response in unanesthetized goats

Blockade of dorsolateral pontine 5HT1A receptors destabilizes the respiratory rhythm in C57BL6/J wild-type mice

The neurotransmitter serotonin (5HT) acting via 5HT1a receptors (5HT1aR) is a potent determinant of respiratory rhythm variability. Here, we address the 5HT1aR-dependent control of respiratory rhythm variability in C57BL6/J mice. Using the in situ perfused preparation, we compared the effects of systemic versus focal blockade of 5HT1aRs. Blocking 5HT1aRs in the Kölliker-Fuse nucleus (KFn) increased the occurrence of spontaneous apneas and accounted for the systemic effects of 5HT1aR antagonists. Further, 5HT1aRs of the KFn stabilized the respiratory rhythm's response to arterial chemoreflex perturbations; reducing the recovering time, e.g., the latency to return to the baseline pattern. Together, these results suggest that the KFn regulates both intrinsic and sensory determinants of respiratory rhythm variability.

Dichlorvos exposure to the Kölliker-fuse nuclei is sufficient but not necessary for OP induced apnea

Patients exposed to organophosphate (OP) compounds demonstrate a central apnea. The Kölliker-fuse nuclei (KF) are cholinergic nuclei in the brainstem involved in central respiratory control. We hypothesize that exposure of the KF is both necessary and sufficient for OP induced central apnea. We performed an animal study of acute OP exposure. Anesthetized and spontaneously breathing Wistar rats (n=24) were exposed to a lethal dose of dichlorvos using three experimental models. Experiment 1 (n=8) involved systemic OP poisoning using subcutaneous (SQ) 2,2-dichlorovinyl dimethyl phosphate (dichlorvos) at 100mg/kg or 3× LD50. Experiment 2 (n=8) involved isolated poisoning of the KF using stereotactic microinjections of dichlorvos (625μg in 50μl) into the KF. Experiment 3 (n=8) involved systemic OP poisoning with isolated protection of the KF using SQ dichlorvos (100mg/kg) and stereotactic microinjections of organophosphatase A (OpdA), an enzyme that degrades dichlorvos. Respiratory and cardiovascular parameters were recorded continuously. Animals were followed post exposure for 1h or until death. There was no difference in respiratory depression between animals with SQ dichlorvos and those with dichlorvos microinjected into the KF. Despite differences in amount of dichlorvos (100mg/kg vs. 1.8mg/kg) and method of exposure (SQ vs. CNS microinjection), 10min following dichlorvos both groups (SQ vs. microinjection respectively) demonstrated a similar percent decrease in respiratory rate (51.5 vs. 72.2), minute ventilation (49.2 vs. 68.8) and volume of expired gas (17.5 vs. 0.0). Animals with OpdA exposure to the KF during systemic OP exposure demonstrated less respiratory depression, compared to SQ dichlorvos alone (p<0.04). No animals with SQ dichlorvos survived past 25min post exposure, compared to 50% of animals with OpdA exposure to the KF. In conclusion, exposure of the KF is sufficient but not necessary for OP induced apnea. Protection of the KF during systemic OP exposure mitigates OP induced apnea.

Anatomical characterization of a rabbit cerebellar eyeblink premotor pathway using pseudorabies and identification of a local modulatory network in anterior interpositus

Rabbit eyeblink conditioning is a well characterized model of associative learning. To identify specific neurons that are part of the eyeblink premotor pathway, a retrograde transsynaptic tracer (pseudorabies virus) was injected into the orbicularis oculi muscle. Four time points (3, 4, 4.5, and 5 d) were selected to identify sequential segments of the pathway and a map of labeled structures was generated. At 3 d, labeled first-order motor neurons were found in dorsolateral facial nucleus ipsilaterally. At 4 d, second-order premotor neurons were found in reticular nuclei, and sensory trigeminal, auditory, vestibular, and motor structures, including contralateral red nucleus. At 4.5 d, labeled third-order premotor neurons were found in the pons, midbrain, and cerebellum, including dorsolateral anterior interpositus nucleus and rostral fastigial nucleus. At 5 d, labeling revealed higher-order premotor structures. Labeled fourth-order Purkinje cells were found in ipsilateral cerebellar cortex in cerebellar lobule HVI and in lobule I. The former has been implicated in eyeblink conditioning and the latter in vestibular control. Labeled neurons in anterior interpositus were studied, using neurotransmitter immunoreactivity to classify individual cell types and delineate their interconnectivity. Labeled third-order premotor neurons were immunoreactive for glutamate and corresponded to large excitatory projection neurons. Labeled fourth-order premotor interneurons were immunoreactive for GABA (30%), glycine (18%), or both GABA and glycine (52%) and form a functional network within anterior interpositus involved in modulation of motor commands. These results identify a complete eyeblink premotor pathway, deep cerebellar interconnectivity, and specific neurons responsible for the generation of eyeblink responses.

Anatomic changes in multiple brainstem nuclei after incremental, near-complete neurotoxic destruction of the pre-Bötzinger Complex in adult goats

Abrupt, bilateral destruction of the pre-Bötzinger Complex (preBötC) leads to terminal apnea in unanesthetized goats and rats. In contrast, respiratory rhythm and pattern and arterial blood gases in goats during wakefulness and sleep are normal after incremental (over a month) destruction of > 90% of the preBötC. Here, we tested the hypothesis that the difference in effects between abrupt and incremental destruction of the preBötC are a result of time-dependent plasticity, which manifests as anatomic changes at sites within the respiratory network. Accordingly, we report data from histological analyses comparing the brainstems of control goats, and goats that had undergone bilateral, incremental, ibotenic acid (IA)-induced preBötC lesioning. A major focus was on the parafacial respiratory group/retrotrapezoid nucleus (pFRG/RTN) and the pontine respiratory group (PRG), which are sites thought to contribute to respiratory rhythmogenesis. We also studied the facial (FN), rostral nucleus ambiguus (NA), medullary raphé (MRN), hypoglossal (HN), and the dorsal motor vagal (DMV) nuclei. Neuronal counts, count region area (mm²), and neuronal densities were calculated using computer-assisted analyses and/or manual microscopy to compare control and preBötC-lesioned animals. We found that within the ventral and lateral medulla 2mm rostral to the caudal pole of the FN (presumed pFRG/RTN), there were 25% and 65% more (P < 0.001) neurons, respectively, in preBötC-lesioned compared to control goats. Lesioned goats also showed 14% and 13% more (P < 0.001) neurons in the HN and medial parabrachialis nucleus, but 46%, 28%, 7%, and 17% fewer (P < 0.001) neurons in the FN, NA, DMV, and Kölliker-Fuse nuclei, respectively. In the remaining sites analyzed, there were no differences between groups. We conclude that anatomic changes at multiple sites within the respiratory network may contribute to the time-dependent plasticity in breathing following incremental and near-complete destruction of the preBötC.