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[Model representation of rat motor behavior during electric self stimulation of the brain. II. Concretization of function shape. Comparison with experiment].

In this chapter the function of activity of the motor behavior in selfstimulation situation and function of the stimulation of the brain are determined. Solutions of the equation give the relation between the motor behavior and parameters of stimulation. The solutions agree with many experimental data in selfstimulation situation in the Skinner's box.

Animals↗

Lesions and inactivation implicate dorsolateral hindbrain in MFB self-stimulation.

Two experiments explored the role of the motor nucleus of the trigeminal nerve (Mo5) and surrounding area in the rewarding effects of medial forebrain bundle (MFB) stimulation. In the first, eight rats received serial bilateral lesions of the target region. The reward value of MFB stimulation was assessed at 200, 400, and 800 microA using the rate-frequency curve shift paradigm. In five rats, no lesions affecting the motor nucleus or its surrounding area affected the frequency required to maintain half-maximal response rate at any current. One rat with a relatively ventrally placed lesion showed substantial enhancement of stimulation reward value at two currents, while two rats with lesions affecting the area around the descending fibers of the superior cerebellar peduncle (scp) showed substantial increases in required frequency. In the second experiment, six rats received uni- and bilateral injections of lidocaine to temporarily inactivate the target area. Two rats with injections centered near the descending fibers of the scp showed substantial increases in required frequency, as great as 0.30 log(10) units. Two rats with injections slightly rostral to these showed little change in required frequency. Two rats with injections in the ventral cerebellum, just lateral to the fastigial nucleus, showed increases in required frequency, particularly following injections contralateral to the MFB stimulation site. These data are interpreted to imply a role for the area around the lateral pole of the scp, perhaps including axons arising from the cerebellum, in MFB stimulation reward.

Anesthetics, Local↗

Effects of naltrexone on nucleus accumbens, lateral hypothalamic and ventral tegmental self-stimulation rate-frequency functions.

Rats trained to lever-press for electrical stimulation of the nucleus accumbens, lateral hypothalamus, or ventral tegmental area, were tested with a range of stimulation frequencies to assess the effects of naltrexone (2.5, 5.0, 10.0, 20.0 mg/kg, i.p.) during sessions beginning 15 or 45 min after injection. Naltrexone, when effective, shifted the rate-frequency functions to the right; the magnitude of the effect depended on site of stimulation and on the delay after injection. The greatest effect was observed with stimulation of the nucleus accumbens and the least with stimulation of the ventral tegmental area. There was a greater attenuation of responding during the late test sessions than during the early ones. The time course of naltrexone's effect on brain stimulation reward was determined for the highest dose by measuring a rat's rate of responding over a 3 h period in sessions with immediate access (5-min delay) or delayed access (45-min delay) to stimulation. The greatest decreases in responding were observed 45, 65, and 85 min after injection and the delay in access made little difference. The fact that the drug was more effective 45 min after injection explains some of the inconsistencies in the literature; the fact that its effectiveness was independent of early exposure to stimulation would suggest pharmacological rather than experiential factors as the explanation of the delayed effectiveness.

Animals↗