Kazuyoshi Otake

Axonal projections of pulmonary slowly adapting receptor relay neurons in the rat.

We elucidated efferent projections of second‐order relay neurons (P‐cells) activated by afferents originating from slowly adapting pulmonary receptors (SARs) to determine the central pathway of the SAR‐evoked reflexes. Special attention was paid to visualizing the P‐cell projections within the nucleus tractus solitarii (NTS), which may correspond to the inhibitory pathway from P‐cells to second‐order relay neurons (RAR‐cells) of rapidly adapting pulmonary receptors. P‐cells were recorded from the NTS in Nembutal‐anesthetized, paralyzed, and artificially ventilated rats. First, we used electrophysiological methods of antidromic mapping and showed that the majority of the P‐cells examined projected their axons to the caudal NTS and to the dorsolateral pons corresponding to the parabrachial complex. Second, a mixture of HRP and Neurobiotin was injected intracellularly or juxtramembranously into P‐cells. (1) Stained P‐cells (n = 7) were located laterally to the solitary tract and had dendrites extending characteristically along the lateral border of the solitary tract. (2) All P‐cells had stem axons projecting to the ipsilateral medulla. Of these, the axons from five P‐cells projected to the nucleus ambiguus and its vicinity with distributing boutons. Some of these axons further ascended in the ventrolateral medulla, and distributed boutons in the areas ventral or ventrolateral to the nucleus ambiguus. (3) All the P‐cells had axonal branches with boutons in the NTS area. In particular, axons from three P‐cells projected bilaterally to the medial NTS caudal to the obex, i.e., to the area of RAR‐cells. These results show anatomic substrates for the connections implicated in the P‐cell inhibition of RAR‐cells as well as the SAR‐induced respiratory reflexes. J. Comp. Neurol. 446:81–94, 2002.

Sites of origin of corticotropin-releasing factor-like immunoreactive projection fibers to the paraventricular thalamic nucleus in the rat.

Neurons containing the peptide corticotropin-releasing factor (CRF) are thought to play a pivotal role in orchestrating autonomic and behavioral responses to stress. CRF afferents to the thalamus are almost entirely concentrated in the midline nuclei, especially in the paraventricular thalamic nucleus. In chloral hydrate-anesthetized male Wistar rats, we sought to determine the sites of origin of the CRF projection fibers to the thalamus, employing a combination of retrograde neuronal tracing and immunocytochemistry for CRF. Prethalamic neurons showing CRF immunoreactivity were detected in the continuum formed by the central nucleus of amygdala and the bed nucleus of the stria terminalis. Additional sources of the CRF fibers to the thalamus were also detected in the parabrachial nuclei and ventrolateral medulla.

Vestibular afferents to the dorsal vagal complex: substrate for vestibular-autonomic interactions in the rat.

Vestibular afferents to the nucleus tractus solitarii (NTS) were identified for the first time in the male Sprague-Dawley rat. Cells of vestibular origin were labeled by deposits of cholera toxin B (CT-B) centered on the general viscerosensory division of NTS and dorsal motor nucleus (DMX). Vestibular-visceral afferents derive from neurons concentrated at caudal levels of medial and inferior vestibular nuclei as observed in other species. Vestibular afferent processes were labeled in the NTS and DMX by anterograde transport of the tracer, biotinylated dextran-amine from injection deposits confined to the inferior and/or medial vestibular nuclei. Vestibular axons terminate in the NTS, predominantly at intermediate levels of the dorsal vagal complex. Projections overlapped sites in NTS that receive terminal input from first-order alimentary and cardiorespiratory afferents. The somato-visceral reflex circuit corroborates recent evidence in the rat of increases in functional activity in the vestibular nuclear complex and NTS in response to changes in gravito-inertial force [Kaufman, G.D., Anderson, J.H. and Beitz, A.J., J. Neurosci., 12 (1992) 4489-4500]. Vestibular input to the NTS and DMX may assist in compensating for the effects imposed by movements and gravity on breathing, alimentary reflex function and the systemic circulation.

Cholecystokinin and substance P immunoreactive projections to the paraventricular thalamic nucleus in the rat

Cholecystokinin (CCK) and substance P (SP) are thought to play an important role in a variety of stress responses. Both CCK- and SP-positive fibers innervating the thalamus are found principally in the midline nuclei, including the paraventricular thalamic nucleus (PVT), which has strong reciprocal connections with the medial prefrontal cortex. In the present study, we determined the source of the CCK- and SP-immunoreactive fibers to the PVT, employing combination of retrograde neuronal tracing and immunohistochemistry in the rat. The PVT-projecting neurons showing CCK immunoreactivity were detected in the dorsomedial nucleus of the hypothalamus, and ventral mesencephalic periaqueductal gray, including the Edinger-Westphal nucleus and the dorsal raphe nucleus. Sources of SP afferents to the PVT were detected in the Edinger-Westphal nucleus, the mesopontine tegmentum and the medullary raphe nucleus. CCK- and SP-immunoreactive fibers may exert modulatory influence on the prefrontal cortical activity via the PVT and regulate behavioral components of stress-adaptation responses.

Excitation and inhibition of medullary inspiratory neurons by two types of burst inspiratory neurons in the cat

In Nembutal-anesthetized and artificially ventilated cats, we studied the connectivity of burst inspiratory (I) neurons in the Bötzinger complex and the ventral respiratory group (VRG) with spike-triggered averaging methods. Burst I neurons exhibited tonic (I-TON) or decrementing (I-DEC) firing patterns. Spikes of I-TON neurons induced monosynaptic EPSPs in intracellularly recorded I neurons of both the VRG and the dorsal respiratory group (DRG). Spikes of I-DEC neurons induced monosynaptic inhibitory postsynaptic potentials (IPSPs) in both VRG and DRG I neurons.

Axonal projections from Bötzinger expiratory neurons to contralateral ventral and dorsal respiratory groups in the cat.

SummaryWe studied projection patterns of the augmenting expiratory neurons of the Bötzinger complex (BÖT) in the contralateral brainstem. Three experimental approaches were used: 1) electrophysiological analysis using antidromic microstimulation, and morphological analyses using 2) intraaxonal injection of HRP, and 3) application of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). Taken together, the three methods revealed morphological details of the axonal arborizations of the expiratory neurons in the BÖT and the ventral respiratory group (VRG). The majority of augmenting expiratory neurons of the BÖT had axonal collaterals in the contralateral brainstem. The stem axons to the contralateral side crossed the midline almost at the level of the cell somata. They descended dorsomedial to the ventral spinocerebellar tract and gave off collateral branches directed dorsomedially. Terminal boutons were distributed abundantly in the caudal part of the BÖT and in the more caudally situated VRG. Axon collaterals sometimes ran to the dorsal respiratory group (DRG) and distributed terminal boutons there. Together with the fact of extensive ipsilateral arborizations shown previously, the present results indicate that the augmenting expiratory neurons of the BÖT have wide bilateral influence on the BÖT, VRG, DRG, and spinal cord.

Morphology of pulmonary rapidly adapting receptor relay neurons in the rat

The term rapidly adapting pulmonary stretch receptor (RAR) refers to one of the major pulmonary sensory receptors that responds to inflation and deflation of the lungs as well as to irritant stimuli with rapidly adapting irregular discharges. The functional role and central pathways are largely unknown. The aim of this study was to elucidate morphological characteristics of second‐order neurons (RAR cells) activated by vagal afferent fibers originating from RARs. A mixture of horseradish peroxidase (HRP) and Neurobiotin was injected intracellularly into physiologically identified RAR cells in Nembutal‐anesthetized, immobilized, and artificially ventilated Wister rats. Direct visualization of individual RAR cells (n = 12), including their somata, dendritic arborizations, and fine axonal branches with terminal boutons, was possible for the first time. Their somata were located in the commissural or medial subdivision of the nucleus of the solitary tract, caudal to the level of the area postrema. The RAR cells had, in addition to dendrites extending into the NTS area, one or two long dendrites extending laterally and/or ventrolaterally into the medullary reticular formation. The stem axons issuing from the RAR cells first coursed ventrolaterally toward the reticular formation in the vicinity of the ambiguus nucleus and then bifurcated into ascending and descending axons: three RAR cells possessed only ascending axons. Some of the ascending axons could be traced as far as the level of the facial nucleus and some of the descending axons beyond the spinomedullary junction. These ascending and/or descending axons gave off extensive axon collaterals distributing boutons within and in the vicinity of the ambiguus nucleus. These results, showing an anatomical substrate for the network implicated in RAR‐evoked reflexes, provide useful clues for study of the RAR system. J. Comp. Neurol. 430:458–470, 2001.

Projections from the commissural subnucleus of the solitary tract onto catecholamine cell groups of the ventrolateral medulla

Efferent projections of the commissural subnucleus of the solitary tract (COM) to the ventrolateral medulla were studied in the cat using anterograde labeling with biocytin combined with dopamine beta-hydroxylase immunohistochemistry. COM neurons were observed to send their axons densely to the areas of distribution of respiration-related neurons in the ventrolateral medulla, e.g. ventral respiratory group, Bötzinger complex. Axon terminals from COM neurons were further found in the areas of distribution of catecholamine neurons (C1 and A1 cell groups), that were distributed in the close vicinity of the reported respiration-related areas in the ventrolateral medulla. Putative synaptic contacts of axon terminals from COM neurons with catecholamine neurons were often observed in the C1 area.

Possible pathways through which neurons of the shell of the nucleus accumbens influence the outflow of the core of the nucleus accumbens.

The nucleus accumbens (Acb), a major sector of the ventral striatum, is considered to be an integral part of the striatal complex. The Acb has been shown to be composed of two subdivisions, core and shell, which are distinguishable in several aspects, suggesting that these two subdivisions play different functional roles. The aim of this study was to identify pathways of the efferents of the shell of the Acb to influence the outflow of the core of the Acb. Potential disynaptic projections of the shell to the core of the Acb were investigated in chloral hydrate-anesthetized male Sprague-Dawley rats. Following ipsilateral injections of biotinylated dextran amine (BDA) into the shell of the Acb and cholera toxin B subunit (CT-B) into the core, strong overlapping distributions of BDA-labeled terminals and CT-B-labeled neuronal cell somata were found in the medial part of the ventral tegmental area, medial part of the lateral hypothalamic area, and dorsolateral part of the basolateral amygdaloid nucleus. The significance of multiple sites of relay between the efferents of the shell and the afferents of the core of the Acb at different levels of the neuraxis may be related to the functional specificity of each relay site.

Distribution of Ca2+/calmodulin-dependent protein kinase α in the rat central nervous system: an immunohistochemical study

Abstract Ca2+/calmodulin-dependent protein kinase IV (CaM-kinase IV) is activated by Cam-kinase IV kinase. We provided a rabbit antiserum against 20 amino acid residues at the carboxyl-terminal end of CaM-kinase IV kinase, and examined regional and intracellular distribution of CaM-kinase IV kinase immunohistochemically in the central nervous system of the rat by light and electron microscopy. The immunoreactivity was found in cellular nuclei of virtually all neurons. However, the immunoreactivity was weak in the nuclei of the granule cells in the cerebellar cortex, although the nuclei of the granule cells were reported to contain high CaM-kinase IV activity. Thus, it was suggested that other types of CaM-kinase IV kinase might exist in the cerebellum, and the present CaM-kinase IV kinase was named as CaM-kinase kinase α.