Brainstem Respiratory Nuclei Research Articles

Developmental study of cytochrome oxidase activity in the brain stem respiratory nuclei of postnatal rats.

We utilized cytochrome oxidase (CO) as a marker of neuronal functional activity to examine metabolic changes in brain stem respiratory nuclei of rats from newborn to 21 day of age. The pre-Bötzinger complex (PBC), upper airway motoneurons of nucleus ambiguus (NA(UAM)), ventrolateral nucleus of solitary tract (NTS(VL)), and medial and lateral parabrachial nuclei (PB(M) and PB(L), respectively) were examined at postnatal days (P) 0, 1, 2, 3, 4, 5, 7, 14, and 21. CO histochemistry was performed, and the intensity of CO reaction product was quantitatively analyzed by optical densitometry. In addition, CO histochemistry was combined with neurokinin-1 receptor (NK1R) immunogold-silver staining to doubly label neurons of PBC in P14 animals. The results showed that levels of CO activity generally increased with age in all of the nuclei examined. However, a significant decrease was found in NA(UAM) at P3 (P < 0.01), and a distinct plateau of CO activity was noted at P3 in PBC and at P3 and P4 in NTS(VL), PB(M), and PB(L). Of the neurons examined in PBC, 83% were doubly labeled with CO and NK1R. Of these, CO activity was high in 33.9%, moderate in 27.3%, and light in 38.8% of neurons, suggesting different energy demands in these metabolic groups that may be related to their physiological or synaptic properties. The transient decrease or plateau in CO activity at P3 and P4 implies a period of synaptic adjustment or reorganization during development, when there may be decreased excitatory synaptic drive or increased inhibitory synaptic drive, or both, in these brain stem respiratory nuclei. The adjustment, in turn, may render the system less responsive to respiratory insults. This may bear some relevance to our understanding of pathological events during postnatal development, such as occurs in sudden infant death syndrome.

Development of the rat phrenic nucleus and its connections with brainstem respiratory nuclei.

The development of phrenic motoneurons and descending bulbospinal projections to the cervical spinal cord have been examined in prenatal and early postnatal rats with the aid of the carbocyanine dyes DiI and DiA. Phrenic motoneurons could be identified by retrograde labelling as early as E13, while aggregation of phrenic motoneurons into a column and the formation of dendritic bundles became apparent from E16. The initial phrenic motoneuron dendritic bundles were oriented in the dorsolateral and ventromedial directions, while ventrolaterally directed bundles entering the marginal zone appeared by E16, and rostrocaudal bundles were clearly visible by E21. The column of phrenic motoneurons extended rostrocaudally from C2 to C6 at E13 and E14, but this became confined to the C3-5 segments by E21. Two-way tracing of connections between putative brainstem respiratory centres and cervical spinal cord with the carbocyanine dyes, DiI and DiA, indicated that brainstem bulbospinal neurons in the position of the adult ventral respiratory group (VRG) and medial parabrachial (MPB) nuclei appeared to project to the cervical cord white matter as early as E15 and may contribute axons to the grey matter of the cervical cord as early as E17 These findings are consistent with electrophysiological studies of respiratory function development in the fetal rat, which found relatively regular rhythmic phrenic discharge by E20 to 21. In summary, our findings indicate that the structural differentiation of phrenic motoneurons is well-advanced prior to birth and that the descending pathways involved in the control of respiratory function are in place several days before birth.

Scanning electron microscopy of the floor of the fourth ventricle in rats subjected to graded impact injury to the sensorimotor cortex.

Respiratory dysfunction including apnea frequently follows head injury in humans. The purpose of this study was to identify any structural alterations in the region of brainstem respiratory nuclei that might account for immediate postinjury respiratory abnormalities in anesthetized experimental animals. Using scanning electron microscopy, the authors examined the floor of the fourth ventricle in injured rats after a piston strike to the sensorimotor cortex that depressed the dura 1, 2, or 4 mm. The rats were killed within minutes of injury. Cortical impact depths measuring either 1 or 2 mm (eight rats) produced no respiratory abnormalities, and the structural integrity of the ependymal lining of the ventricular floor in these animals was not compromised. Thirteen rats were subjected to impact to a 4-mm depth and 10 of these exhibited immediate temporary or permanent apnea. The medullae of nine of these rats were studied using scanning electron microscopy, and the fourth ventricular floors of all nine rats showed tears. Four rats that exhibited immediate, permanent apnea had tears in the caudal fourth ventricle floor near the obex, whereas five rats with no or only transient apnea had tears located more anteriorly, near the aqueduct or laterally. Changes in cerebrospinal fluid flow or pressure dynamics may have caused these tears. Light microscopy, focused near the area postrema, revealed a shearing defect through the ependyma of the fourth ventricular floor into the subjacent neuropil with a disruption of axonal pathways. Respiratory neuronal network components lying within 2 mm of the area postrema may well have been disrupted by the caudal tears producing permanent apnea. A similar phenomenon could account for the transient or permanent postinjury apnea seen in humans with severe head injury.

Experimental Missile Wounding of the Brain

If a missile penetrates a cerebral hemisphere and does not severely disrupt the brain or transit a vital brain structure, it is hypothesized that the indirect effect of ordinary pressure waves set up by the interaction of missile and tissue and that impinge on brain stem respiratory nuclei determines life or death. The likelihood of fatal apnea is a direct function of missile energy of deposit within the brain. With brain wounding, a reduction in CO may also occur, but missile energy required to produce a significant CO decrease is in excess of that required to produce respiratory problems. Unless the individual managed to survive a period of apnea or respiratory resuscitation occurred, the effects of apnea would overshadow any CO decreases. Although transmitted ordinary pressure waves might interfere with the reticular activating system within the brain stem and produce persistent coma, specific long-lasting neurologic defects from a missile wound usually result from direct missile damage to the cerebral cortex or cortical projections. In designing treatments for missile wounds of the brain, two distinct entities must be kept in mind: the brain stem and the cerebral cortex. To decrease the immediate mortality from brain wounding, prompt treatment has to be devised to aid dysfunctional respiratory nuclei and possibly cardiac control nuclei. To decrease long-term neurologic morbidity, drug therapy has to be instituted to help injured cerebral cortical neurons for days to weeks after wounding. Totally different strategies and drugs may be needed to treat the brain stem as opposed to the cerebral cortex.

Neuropeptide Y-like immunoreactivity in the brain stem respiratory nuclei of the cat

The distribution of fibres and cell bodies containing neuropeptide Y-like immunoreactivity in respiratory nuclei of the brain stem was studied using an indirect immunoperoxidase technique. In order to visualize immunoreactive perikarya, intraventricular or intratissue injections of colchicine were carried out. The richest cluster of immunoreactive perikarya was localized in the Bötzinger complex, whereas in the nuclei ambiguus, retroambiguus, parabrachialis medialis and Kölliker-Fuse area, a moderate density of cell bodies was observed. The ventrolateral subnucleus of the nucleus tractus solitarii had the lowest number of immunoreactive neurons. Neuropeptide Y-like immunoreactive fibres were abundant in the Kölliker-Fuse area, and scarce in the nuclei ambiguus, parabrachialis medialis and Kölliker-Fuse area. A moderate network of immunoreactive fibres was observed in the nuclei retroambiguus and the ventrolateral subnucleus of the nucleus tractus solitarii. The presence of neuropeptide Y-like immunoreactive areas suggests a role for this peptide in the control of respiratory mechanisms. Alternatively such a cluster of cell bodies and fibre networks might be also related with neighbouring cardiovascular control areas.

Immunocytochemical study of angiotensin-II fibres and cell bodies in the brainstem respiratory areas of the cat

The distribution of fibres and cell bodies containing angiotensin-II in brainstem respiratory nuclei was studied using an indirect immunoperoxidase technique. In order to visualize immunoreactive perikarya, intracerebral injections of colchicine were carried out. The richest cluster of immunoreactive perikarya was localized in the Bo¨tzinger complex and Ko¨lliker-Fuse areas, whereas in the nucleus ambiguus and nucleus retroambiguus a moderate density of cell bodies was observed. The nucleus tractus solitarius (ventrolateral portion) and the nucleus parabrachialis medialis had the lowest number of immunoreactive neurons. Angiotensin-II containing fibres were abundant in the nucleus parabrachialis medialis, Bo¨tzinger complex and Ko¨lliker-Fuse area, and scarce in the nuclei tractus solitarrius (ventrolateral part), ambiguus and retroambiguus. Moreover, in the dorsal motor nucleus of the vagus a dense network of immunoreactive fibres and a large number of cell bodies were observed. The presence of angiotensin-II in respiratory areas suggests a role for this octapeptide in controlling respiration.

Connections of brainstem respiratory nuclei studied by the retrograde horseradish peroxidase axon transport method

Intrabulbar connections of respiratory nuclei and the medullary reticular formation and also descending pathways from these structures in the spinal cord were studied by the retrograde horseradish peroxidase axonal transport method in cats. Neurons of the nucleus ambiguus and nucleus retroambigualis (ventral respiratory group) and of the ventrolateral part of the nucleus of the tractus solitarius (dorsal respiratory group) were shown to form direct two-way connections with each other and with the medial region of the medulla. Neurons of the pneumotaxic center send uncrossed axons to the nucleus ambiguus and to the medial medullary reticular formation. Neurons of the contralateral homonymous nucleus and neurons of the nucleus of the tractus solitarius are sources of projections of the locus coeruleus. A well developed system of direct connections was found between neurons of respiratory nuclei of the two halves of the brain. The possible role of these nuclear formations in genesis of the respiratory rhythm and regulation of the respiratory and other motor functions of the reticular formation is discussed.