Orexinergic fibers are in contact with Kölliker-Fuse nucleus neurons projecting to the respiration-related nuclei in the medulla oblongata and spinal cord of the rat.

The neural pathways underlying the respiratory variation dependent on vigilance states remain unsettled. In the present study, we examined the orexinergic innervation of Kölliker-Fuse nucleus (KFN) neurons sending their axons to the rostral ventral respiratory group (rVRG) and phrenic nucleus (PhN) as well as to the hypoglossal nucleus (HGN) by using a combined retrograde tracing and immunohistochemistry. After injection of cholera toxin B subunit (CTb) into the KFN, CTb-labeled neurons that are also immunoreactive for orexin (ORX) were found prominently in the perifornical and medial regions and additionally in the lateral region of the hypothalamic ORX field. After injection of fluorogold (FG) into the rVRG, PhN or HGN, we found an overlapping distribution of ORX-immunoreactive axon terminals and FG-labeled neurons in the KFN. Within the neuropil of the KFN, asymmetrical synaptic contacts were made between these terminals and neurons. We further demonstrated that many neurons labeled with FG injected into the rVRG, PhN, or HGN are immunoreactive for ORX receptor 2. Present data suggest that rVRG-, PhN- and HGN-projecting KFN neurons may be under the excitatory influence of the ORXergic neurons for the state-dependent regulation of respiration.

[Distribution of GABAergic neurons in pneumotaxic center nuclei in the early postnatal period in norm and in prenatal deficiency of serotoninergic system in rats].

The aim of this study was to determine the distribution of GABAergic neurons in pneumotaxic center structures (parabrachial complex medial subnucleus and Kölliker-Fuse nucleus) in norm and in deficiency of serotoninergic system during the prenatal period of development in Wistar rats. Reduction of endogenous serotonin levels in fetal rats was achieved by tryptophan hydroxylase inhibition with para-chlorophenylalanine (PCPA), which was administered to female rats on Day 16 of gestation. Material was obtained from the area of the pons from experimental and control (intact) rat pups at early postnatal (Days 5, 10 and 12) and juvenile (Day 20) periods. At each time point, 5-6 animals were studied from both experimental and control groups. To demonstrate GABAergic neurons, antibodies against glutamate decarboxylase (GAD-67), the enzyme involved in its synthesis, were used. The results have shown that Kölliker-Fuse nucleus contained a population of GABAergic neurons at early postnatal period, the size of which was preserved until juvenile age. In parabrachial complex medial subnucleus during the early postnatal period, a small number of GABAergic neurons was detected, which was somewhat increased by juvenile age. Serotonin deficiency in pneumotaxic center structures lead to a reduction of the numbers of GABAergic neurons, GABAergic synapses and their clusters. A reduction of serotonin levels during the prenatal period may cause the disturbances in the inhibitory afferent signaling of the pneumotaxic center nuclei and lead to the changes of local inhibitory GABAergic networks in its nuclei, resulting in the disturbances of the inhibitory processes in the center structures.