Role of the parabrachial nucleus in ventilatory responses of awake rats.

Abstract

1. The parabrachial nucleus (PBN) is thought to play an important role in cardiorespiratory control. However, the circumstances under which it affects ventilation are still not known. The purpose of the present study was to investigate how the PBN modulates the ventilatory responses to hypercapnia, hypoxia or a resistive load in awake rats with chemical lesions of the PBN. 2. In three groups of rats (with lateral PBN lesion, with Kolliker-Fuse nucleus lesion and control), ventilation was measured under various conditions. 3. There was no difference in the breathing of normal room air in any of the groups. However, the lesioned groups showed a reduced ventilatory response to hyperoxic hypercapnia (inspired CO2 fractions (FIc02) of 3, 5, 8 and 10%) and to graded hypoxia (inspired 02 fractions (FI 02) of 16, 12, 10 and 8 %) compared with the control group. The control group showed a biphasic response to sustained hypoxia (FN,A at 10% for 30 min), known as 'hypoxic depression', while the lesioned groups showed moderate ventilatory exaggeration throughout hypoxia. In response to a resistive load, the lateral PBN lesion group showed no change in ventilatory compensation. 4. The PBN appeared to have a considerable influence on ventilation stimulated in various ways during wakefulness.It has been suggested that the parabrachial nucleus (PBN) is one of the main relays for the transfer of a wide array of autonomic-related information from the more caudal levels of the neuraxis to supracollicular structures (Shannon & Lindsey, 1983;Milner, Joh, Miller & Pickel, 1984;Segers, Shannon & Lindsey, 1985;Berkley & Scofield, 1990). The PBN, in turn, is known to project to several autonomic nuclei interconnecting with the higher brain, and participates in cardiovascular and/or respiratory control (Fulwiler & Saper, 1984;Ward, 1988 (Ling, Karius & Speck, 1993. These disparate findings may be partly due to the structural complexity of the PBN. In addition, considering its location and neural connections, the PBN may prove to be a respiratory modulator, particularly during wakefulness. For example, decerebration around the level of the PBN changes the hypoxic ventilatory response in rats (MartinBody, 1988 (20 000 i.u., I.M.) was administered on the first three post-operative days. During the first 2-3 days the animals were fed with wet mash, but after that they resumed normal feeding and drinking. Subsequently they were kept on a 12 h light-12 h dark schedule with food and water available ad libitum for 1 week until the final experiments, by which time no unfavourable effects of surgery, such as hypophagia or loss of body weight, were present in any group of rats. Experimental preparations Ventilation was measured using the barometric method of plethysmography as described elsewhere (Mizusawa et al. 1994). Briefly, rats were placed in a 7 1 Plexiglass chamber which was connected to a reference chamber through a pressure transducer (model MP-45, + 5 cmH2O; Validyne, Northridge, CA, USA).Respiratory frequency (f) was calculated from th...

Comparative study of the sources of neuronal projections to the site of gonadotrophin-releasing hormone perikarya and to the anteroventral periventricular nucleus in female rats

“…The parabrachial nucleus is a complex of nuclei that integrate and relay visceral and autonomic input from the caudal brainstem and spinal cord to higher brain areas. Located in the dorsal pons, it is divided by the superior cerebellar peduncle into two parts: the lateral part, which has been implicated in autonomic and behavioral responses to pain or other aversive stimuli (Mizusawa et al, 1995;Gauriau and Bernard, 2002;Jurgens, 2002), and the medial part, which has been implicated in gustatory and appetitive functions (Spector, 1995;Reilly, 1999;Bray, 2000).…”

A latent serotonin-1A receptor-gated spinal afferent pathway inhibiting breathing

“…Although the loci of our kainic acid microinjections were localized mainly to Fig. 1d), the dosage of injection (50 nl at a concentration of 1 lg/ll) was such that a major part of the LPBN (including its dorsal subdivision) located within 0.5-1.0 mm around the center of injection would have been destroyed (Mizusawa et al 1995;Song and Poon 2009a, b). Hence, the respiratory effects of LPBN lesion elicited by lumbar-intrathecal injection of 8-OH-DPAT or WAY-100635 are ascribable to the interruption of a 5-HT 1A R-gated lumbar spinoparabrachial pathway, as previously conjectured (Poon 2009).…”

Regulation of the chemosensory control of breathing by Kölliker-Fuse neurons

“…Studies using c-Fos-immunoreactive expression as a marker of neuronal activity showed intense activation of the KF region after hypoxia, hypercapnia, or stimulation of the carotid sinus nerve (3, 5, 29, 61). Studies in cats and rats showed that after bilateral lesions of the parabrachial and the Kölliker-Fuse complex, the breathing increase during hypoxia or hypercapnia was attenuated (29,38,(55)(56)(57).However, most of the experiments showing the role of the pontine regions in viscerosensory control consider the parabrachial complex as a unique brain structure involved in different physiological functions, including breathing and autonomic regulation. Therefore, the main goal of this study was to determine the involvement of the KF and the LPBN in the resting respiratory rhythm and cardiorespiratory responses elicited by chemoreceptor activation in unanesthetized rats.…”