ABSTRACT
Low doses of ethanol increase responding for brain stimulation. Recently, other intoxicating effects of ethanol have been reversed by the imidazobenzodiazepine, Ro 15-4513. Possibly, Ro 15-4513 blockade also acts on reward-enhancing properties of ethanol. Rats trained to alternately shuttle between nose poke and lever operanda for rewarding stimulation to the medial forebrain bundle, were tested following intragastric intubations of ethanol (18%, 1.35 g/kg), Ro 15-4513 (3 mg/kg in 18% ethanol), or vehicle. Ro 15-4513 reversed ethanol-enhanced effects on reinforced responses. Because Ro 15-4513 did not completely block instrumental responding for brain stimulation, we conclude its effects on ethanol were not acting on the same reward substrate as the current and consummatory response.
Subject(s)
Azides/pharmacology , Benzodiazepines/pharmacology , Brain/drug effects , Conditioning, Operant/drug effects , Ethanol/antagonists & inhibitors , Reward , Animals , Brain/physiology , Dopamine Agents/pharmacology , Male , Psychomotor Performance/drug effects , Rats , Rats, Inbred Strains , Reinforcement, Psychology , Stimulation, ChemicalABSTRACT
The present experiments examined the effects of cyclic dosing with methylmercury (MeHg) on some psychological functions in pigeons. A delayed sequence discrimination task involving order competency and a feeding task involving perceptual motor skill were tested in pigeons dosed with 2.0 mg/kg, 0.5 mg/kg, or no MeHg (the control group) during cycles of brief daily MeHg exposure and extended behavioral testing. Performance in the sequence discrimination and the feeding task was affected after a cumulative dose of only 20 mg/kg in the 2.0 mg/kg group. Sequence discrimination recovered within three months after dosing when MeHg was stopped, but feeding skill did not recover over the remainder of the experiment (about 4 1/2 months later). A cumulative dose of 86 mg/kg in the 0.5 mg/kg group had no observable effect on either task.
Subject(s)
Discrimination Learning/drug effects , Methylmercury Compounds/toxicity , Psychomotor Performance/drug effects , Visual Perception/drug effects , Animals , Behavior, Animal/drug effects , Brain/drug effects , Brain/metabolism , Columbidae , Dose-Response Relationship, Drug , Feeding Behavior/drug effects , Male , Methylmercury Compounds/metabolism , Optic Lobe, Nonmammalian/drug effects , Optic Lobe, Nonmammalian/pathology , Time FactorsABSTRACT
Moderate doses of naloxone (1, 5, 10 mg/kg) did not reduce response rate measured by the initiation of intracranial self-stimulation bursts to the medial forebrain bundle or central gray, at several current intensities (30, 60, or 90 microA). Raising current intensity rates and duration of lever pressing at both sites. Naloxone produced a dose dependent reduction in self-selected current duration at both sites averaged over intensity. However, naloxone completely blocked the effect of intensity only at the gray site. In contrast to research showing effects of only high naloxone doses (e.g., 40 mg/kg) on self-stimulation at opiate-rich and opiate-poor receptor sites, this study indicates that endogenous opiates and opiate receptor mechanisms interact with aversive properties to modify central gray self-stimulation.
Subject(s)
Brain/physiology , Naloxone/pharmacology , Self Stimulation/drug effects , Animals , Brain/anatomy & histology , Electric Stimulation , Male , Medial Forebrain Bundle/physiology , Periaqueductal Gray/physiology , Rats , Rats, Inbred Strains , Time FactorsABSTRACT
Lawful relationships established between lever-pressing and parameters of brian stimulation reward (BSR) were examined for several tasks. Task-contingent BSR was given to the same rats at identical sites using identical stimulation parameters. Lengthening stimulation duration from 100 to 300 msec increased lever-press rates. Subsequent lengthening from 400 to 800 msec decreased lever-press rates. Wheel-turning rates increased linearly with lengthening duration. The form of the response-duration function depended on current for lever-pressing but not for wheel-turning. As duration lengthened, time between responses increased systematically for the lever and was invariant for the wheel. Stimulation of the substantia nigra, posterior medial forebrain bundle, and anterior hypothalamus produced similar relations. To further examine the generality of these findings, licking and barrier-jumping were tested. Licking decreased monotonically as stimulation duration lengthened. Barrier-jumping increased from 100 to 500 msec and subsequently remained stable despite lengthening duration to 900 msec. In all tasks examined BSR was rewarding, but the form of the response-duration function depended on task characteristics. Since identical sites were stimulated, task differences cannot be attributed to neurochemical substrates. Results provide evidence for behavioral constraints on BSR.
Subject(s)
Behavior, Animal/physiology , Brain/physiology , Conditioning, Operant/physiology , Self Stimulation/physiology , Animals , Electric Stimulation/methods , Female , Hypothalamus, Anterior/physiology , Hypothalamus, Posterior/physiology , Male , Medial Forebrain Bundle/physiology , Motor Activity/physiology , Motor Skills/physiology , Rats , Rats, Inbred Strains , Reinforcement, Psychology , Substantia Nigra/physiologyABSTRACT
Numerous studies in the rat indicate that catecholamines (CA) mediate rewarding properties of self-administered electrical stimulation to the brain. One such property is the learning of new response-reinforcement relationships. In the present experiment, amphetamine which potentiates CA at the synapse produces stereotypical responding but does not interfere with the learning of new response-reinforcement relationships. Apomorphine, which mimics dopamine (DA) at DA receptors, also produces stereotypy and interferes with learning. The results suggest that DA released by stimulation mediates the stereotyped responding seen in intracranial self-stimulation (ICS) but norepinephrine mediates reward of newly learned responses.
