Respiratory alkalosis provokes spike-wave discharges in seizure-prone rats

Hyperventilation reliably provokes seizures in patients diagnosed with absence epilepsy. Despite this predictable patient response, the mechanisms that enable hyperventilation to powerfully activate absence seizure-generating circuits remain entirely unknown. By utilizing gas exchange manipulations and optogenetics in the WAG/Rij rat, an established rodent model of absence epilepsy, we demonstrate that absence seizures are highly sensitive to arterial carbon dioxide, suggesting that seizure-generating circuits are sensitive to pH. Moreover, hyperventilation consistently activated neurons within the intralaminar nuclei of the thalamus, a structure implicated in seizure generation. We show that intralaminar thalamus also contains pH-sensitive neurons. Collectively, these observations suggest that hyperventilation activates pH-sensitive neurons of the intralaminar nuclei to provoke absence seizures.

Respiratory modulation of pre- and postganglionic lumbar vasomotor sympathetic neurons in the rat

The respiratory contribution to the activity of lumbar vasomotor pre- and postganglionic neurons was compared with previously reported respiratory patterns in the activity of neurons in the rostral ventrolateral medulla (RVLM-SE). Two patterns of respiratory modulation were observed characterized by (1) a depression of activity during inspiration and a postinspiratory peak (n = 19), and (2) a peak of activity during inspiration (n = 3). These patterns were similar to those previously reported in RVLM-SE neurons. The latency from the phrenic burst to the onset of respiratory modulation was consistent with the conduction time from the RVLM to the sympathetic chain. This suggests that respiratory modulation observed in lumbar sympathetic activity originates, in part, in RVLM-SE neurons.

Neurobiology of brain stem cardiopulmonary control mechanisms

A function shared by both respiratory and cardiovascular systems is the delivery of metabolic substrate (e.g., oxygen) and removal of metabolic waste products (e.g., carbon dioxide) from tissue.

Regional differences in the sensitivity of cholinergic neurons to dopaminergic drugs and quipazine in the rat striatum

Marked differences were found in the activity of choline acetylase (ChAc) in various discrete areas of the rat striatum. The richest cholinergic innervation was observed in the centrolateral part of the structure. A similar distribution was obtained by measuring acetycholine (ACh) levels in punches taken from frozen frontal serial slices. As revealed by the analysis of the topographical distributions of ChAc activity, ACh, 5-HT and DA, the regional cholinergic innervation differed markedly from that of aminergic terminals. Changes in ACh levels induced by drugs could be estimated in microdiscs of tissues punched from frozen slices. Apomorphine and haloperidol, which increased and decreased ACh levels respectively, induced similar effects in the various striatal areas examined. By contrast quipazine, a drug acting on 5-HT uptake and release and on serotoninergic receptors, selectively increased ACh levels in some areas of the striatum but not in others. The regional changes in ACh levels induced by quipazine were satisfactorily correlated with the regional distribution of 5-HT but not with that of DA. These results suggest that a limited population of striatal cholinergic neurons is under the inhibitory control of serotoninergic neurons. They also indicate that some striatal cholinergic neurons influenced by dopaminergic neurons are not controlled by serotoninergic neurons.