Raphe neurons and barbiturate induced rhythmic activity in the subthalamic nucleus and ventral tegmental area

Multisecond oscillations in the subthalamic nucleus: effects of apomorphine and dopamine cell lesion

Clinical and preclinical data indicate that the subthalamic nucleus (STN) plays a critical role in mediating the hyper- and hypoactive behavioral states associated with increases and decreases in dopamine receptor stimulation in the basal ganglia. The present study investigates effects of dopamine receptor stimulation on slow multisecond oscillations in firing rates in STN neurons. Extracellular, single-unit recordings were performed in locally anesthetized and immobilized rats which were either intact or had received unilateral 6-OHDA lesions of the medial forebrain bundle. The majority (64%) of spike trains recorded from STN neurons exhibited periodic oscillations in firing rate within the range of 2-60 sec, with an average period of 24 sec. The distribution of these baseline periodicities was not altered by unilateral 6-OHDA lesion, but periods were significantly shortened by systemic administration of the D1/D2 agonist apomorphine. This effect was observed in a greater proportion of neurons recorded from 6-OHDA-lesioned rats as compared to intact rats, was notably diminished in rats systemically anesthetized with chloral hydrate, and did not correlate with drug-induced changes in firing rate. These oscillations are similar to slow periodicities in firing rate recently reported in other basal ganglia nuclei. The possibility that these periodic oscillations in firing rate play a significant role in basal ganglia function was supported by the observation that the time of onset of apomorphine induced alterations in amplitude and periodicity of slow oscillations in STN spike trains is coincident with the onset of behavioral effects of this drug in 6-OHDA-lesioned animals. Synapse 38:38-50, 2000. Published 2000 Wiley-Liss, Inc.

Brainstem mechanisms underlying variations in the occurrence of experimentally elicited rhythmic oral movements in the rat

Mechanical stimulation of the oral cavity of the decerebrate rat induces rhythmic oral movements in some animals but not in others. Reasons for this difference were sought using electrical stimulation of the lip to elicit a variety of responses which were capable of accurate quantification. Neither the digastric reflex threshold, size of suprathreshold response nor the ability to generate rhythmic activity within the brainstem differed in the two groups. Depression of the digastric reflex by an electrical stimulus applied 30-150 ms previously was, however, significantly greater in those animals not showing rhythmic oral movements. It is suggested that the two groups differed in their ability to produce rhythmic oral movements because of differences in the level of stimulus related inhibition rather than any tonic effects on trigeminal neuronal activity.