Dopaminergic neurons: simultaneous measurements of dopamine release and single-unit activity during stimulation of the medial forebrain bundle
ABSTRACT Simulataneous electrical and chemical recordings have been made of dopamine neuronal activity in the rat brain during electrical stimulation of the medial forebrain bundle. Tungsten recording electrodes were placed at the level of the substantia nigra and carbon-fiber, Nafion-coated, voltammetric electrodes were placed in the neostratum. Dopamine units, verified by histology to be in the zona compacta of the substantia nigra, were identified by previously established electrophysiological criteria. Dopamine release was detected by fast-scan cyclic voltammetry, a technique which allows dopamine to be determined in vivo on a sub-second time scale. The majority of dopamine cells examined (7 out of 10) were antidromically activated by 60 Hz stimulation of the medial forebrain bundle. The same stimulus also elicits dopamine overflow in the caudate nucleus. Following stimulation, dopamine concentrations in the extracellular fluid of the neostriatum rapidly declined to prestimulus levels. In addition, impulse flow in dopaminergic neurons was inhibited for 20s following stimulation. These measurements represent the first direct observation from a neuronal tract of simultaneous unit activity and chemical release of a neurotransmitter in real time.
Article: Priming of locomotor initiation by electrical stimulation in the hypothalamus and preoptic region in the anesthetized rat.[show abstract] [hide abstract]
ABSTRACT: Electrical stimulation at a locomotor site can prime (i.e., shorten the latency to initiate) stepping elicited by subsequent stimulation of the same or a different site. We tested for the priming effect in representative sites along the medial forebrain bundle, and determined if its magnitude showed regional differences. Rats (n = 20) were anesthetized with Nembutal and held in a stereotaxic apparatus over a wheel. Stepping was detected by accelerometers attached to the hindlimbs. Priming and test trains of stimulation (0.5-ms cathodal pulses, 50 Hz, 25-75 microA, 7-9-s train duration) separated by 20 s were delivered every 90 s. When the priming and test stimulations were applied to the same site, the priming effects were similar along the entire extent of the medial forebrain bundle. When the priming and test sites were different, the priming effect depended on their relative positions. Anterior stimulation primed posterior sites at magnitude comparable to those produced by stimulating the same posterior site. Posterior stimulation primed anterior sites at a level half of that produced by stimulation of the same anterior site. This pattern was found for priming and test sites that were ipsilateral and contralateral. Priming is a general and robust phenomenon with properties that may be useful for studying locomotor initiation pathways.Physiology & Behavior 05/1995; 57(4):641-8. · 2.87 Impact Factor