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J Yeomans

Publications and source records attributed to J Yeomans.

10 recordsLinked to original sources
PubMed2001

M5 muscarinic receptors are needed for slow activation of dopamine neurons and for rewarding brain stimulation.

Mesopontine cholinergic neurons (Ch5 and Ch6 cell groups) activate the cerebral cortex via thalamic projections, and activate locomotion and reward via dopamine neurons in the substantia nigra and ventral tegmental area (VTA). Nicotinic receptors in VTA activate dopamine neurons quickly, and are needed for the stimulant and rewarding effects of nicotine in rats. Muscarinic receptors in VTA activate dopamine neurons slowly, and are needed for the rewarding effects of hypothalamic stimulation, but do not increase locomotion. Antisense oligonucleotides targetting M5 mRNA, when infused into the VTA, inhibited M5 receptor binding and rewarding hypothalamic stimulation. Mutant mice with truncated M5 muscarinic receptor genes drank more water than wild-type controls. Spontaneous locomotion and locomotor responses to amphetamine and scopolamine were unchanged. Electrical stimulation near Ch6 induced dopamine release in the nucleus accumbens in two phases, an early phase (0-2 min after stimulation) dependent on nicotinic and gluatamatergic receptors in VTA, and a late phase (8-50 min after stimulation) dependent on muscarinic receptors in VTA. The late phase was lost in M5 mutant mice, while the early phase was unchanged. M5 muscarinic receptors bind slowly to muscarinic ligands, and appear to mediate slow secretions.

Acetylcholine↗
PubMed1997

Both nicotinic and muscarinic receptors in ventral tegmental area contribute to brain-stimulation reward.

Cholinergic neurons of the pedunculopontine tegmental nucleus (Ch5) and laterodorsal tegmental nucleus (Ch6) monosynaptically activate dopamine neurons of the substantia nigra and ventral tegmental area (VTA) via nicotinic and muscarinic receptors. The nicotinic receptors near the VTA have been proposed to be important for nicotine self-administration in rats and for tobacco smoking in humans. Nicotinic and muscarinic blockers were microinjected into the VTA of rats trained to lever-press for lateral hypothalamic stimulation via an ipsilateral electrode. The competitive nicotinic blocker dihydro-beta-erythroidine (DH beta E; 5-60 micrograms) shifted rate-frequency curves to the right by a mean of 6-27% in a dose-related manner; the noncompetitive nicotinic blocker mecamylamine (10-300 micrograms) produced similar shifts of 7-21%. Atropine (30 micrograms) shifted the curves to the right by a mean of 82% in three of the sites tested with DH beta E. All blockers decreased maximum bar-pressing rates significantly in some sites when the shifts were large. Therefore, nicotinic receptors in the VTA make small contributions to the maintained rewarding effect of brain-stimulation reward in rats, but muscarinic receptors in the VTA appear to be more important.

Animals↗
PubMed1995

Electrically evoked behaviors: axons and synapses mapped with collision tests.

The properties of many axon bundles mediating electrically evoked responses have been described using double-pulse methods in behaving animals. The directly stimulated axons whose activation leads to the behavior are defined by their refractory periods, conduction velocities and trajectories in those studies. In this review, new collision effects (asymmetric collision) are described that locate synapses mediating turning and startle responses. The direction, time and reliability of transmission are determined by the direction, time and strength of the asymmetry. In systems mediating turning, five axon bundles have been localized with symmetric collision effects and evidence for two synapses has been provided with asymmetric collision effects. In systems mediating startle responses, three fast, reliable synapses have been located with asymmetric collision. Asymmetric collision effects between a loud acoustic stimulus and a single electrical pulse in hindbrain sites define the timing and location of the acoustic volley that produces acoustic startle. Therefore, when synapses are strong, circuit diagrams can be constructed by use of collision tests in behaving animals.

Animals↗
PubMed1994

Further characterization of the executive memory impairment following frontal lobe lesions.

In this article we describe a 41-year-old man who, following an operation to repair a ruptured anterior communicating artery aneurysm, manifested the "hallmark" features of a dysexecutive memory impairment. Of particular note was the patient's apparently normal level of recognition memory but impaired recall on tasks matched for difficulty in control subjects. However, further testing revealed that the patient's recognition memory was not normal under all circumstances. Implications of these data for the interpretation and further investigation of the dysexecutive deficit are discussed.

Adult↗
PubMed1986

Current-distance relations of axons mediating circling elicited by midbrain stimulation.

Stimulation of mediocaudal midbrain in rats produces ipsiversive circling due to the stimulation of longitudinal axons. The refractory periods of these axons were measured by delivering trains of conditioning and testing pulses via a single electrode at various conditioning-testing (C-T) intervals. As C-T interval increased from 0.3 to 2.0 ms, the frequency required to produce a constant amount of circling halved. The current-distance relations of these axons were measured by placing two electrodes lateral to one another, and delivering conditioning pulses via one electrode and testing pulses via the second electrode. The required frequency decreased less at C-T intervals in the refractory period range using two electrodes rather than using a single electrode. This partial refractoriness suggests that only part of the axons were stimulated by both electrodes. The refractoriness increased as current increased or as interelectrode distance decreased. The overlap in the fields of stimulation at each current was calculated from the refractoriness observed in single and double electrode experiments. The results suggest that the axons mediating circling have a wide range of thresholds rather than a single threshold. The current required to activate an axon is roughly equal to K X r2, were K is a constant and r is the radial distance from electrode to axon. K must range from 400 to at least 3000 microA/mm2, to account for the circling data. For axons mediating medial forebrain bundle self-stimulation3, K must range from 1000 to at least 6400 microA/mm2. Estimation of the K distribution allows calculation of the effects of electrode size, placement and current on the recruitment of axons with different thresholds.

Animals↗
PubMed1985

Behaviorally measured refractory periods are lengthened by reducing electrode tip exposure or raising current.

Small tip exposures and high currents allow the stimulation of high-threshold axons. These studies were conducted to measure the effects of current and tip surface area on stimulation parameters required to produce a constant rate of self-stimulation of lateral hypothalamic sites, or of circling when stimulating medial brain stem sites. Thresholds for circling decreased when tip surface area was decreased to 0.01 mm2. Refractory period curves for both circling and self-stimulation were shifted to slightly longer intrapair intervals when tip surface area was decreased or current was increased. This suggests that long refractory period axons make larger contributions when current density is increased. Chronaxies were not lengthened by small tip exposures but were reduced when electrodes were placed far lateral to the circling substrate.

Animals↗
PubMed1980

Behavioral methods for inferring anatomical linkage between rewarding brain stimulation sites.

Rats lever pressed for concurrent electrical stimulation of the lateral hypothalamus and ventral tegmentum. The pulse-pair stimulation technique was used, with the first pulse of each pair applied to one electrode and the second to the other electrode; the intrapair interval was varied. The effectiveness of stimulation, measured behaviorally, increased abruptly (within .4 msec) as the intrapair interval was increased in the range from 1.0 to 2.0 msec. These results, which do not resemble single-electrode refractory period results, are interpreted as evidence of collision in the directly stimulated, reward-related neurons linking the two sites. We conclude that self-stimulation of the medial forebrain bundle involves the direct activation of long-axon, longitudinal pathways. Estimates of the conduction velocity in the fibers subserving the collision-like effects are consistent with the properties of small myelinated axons but not central monoaminergic fibers.

Animals↗