Intracranial self-stimulation and the rapid decline of frustrative nonreward

Animals deprived of reward for a task previously rewarded behave differently, depending on whether the reward is food or positive brain stimulation. Unlike the relatively stable frustration effects obtained with conventional reward, frustration produced by withholding brain stimulation dissipates rapidly with time.     

Intracranial self-stimulation and wakefulness: effect of manipulating ambient brain catecholamines

Rats were given disulfiram, an inhibitor of norepinephrine biosynthesis, to see if norepinephrine is a transmitter for motivation in electrical stimulation of the brain. Animals given the drug paused in bar pressing, appearing asleep or sedated; if replaced on the bar, they always resumed pressing at normal rates. The decrease in bar pressing may result from a direct or indirect effect of the drug on wakefulness rather than on reward.     

Histamine: effect on self-stimulation

When injected discretely into the lateral hypothalamus of rats, histamine inhibited electrical self-stimulation at the injection site without affecting self-stimulation in the contralateral lateral hypothalamus. This effect was blocked by prior treatment with antihistaminics. Histidine, the amino acid precursor of histamine, produced a similar effect after a delay of 6 to 10 minutes.     

Circadian rhythm of brain self-stimulation behavior

Under constant conditions of light, sound, temperature, and humidity, rats exhibited circadian rhythmicity in rate of bar-pressing with hypothalamic and septal reinforcing brain stimulation. Variations in reinforcer magnitude aflected absolute levels of operant response emission but not the frequency of the circadian rhythm. In long sessions, the time of peak responding deviated systematically from a strict 24-hour period. Such data show marked similarity to free-running rhythms of motor activity.     

Slowing of heart rate after septal self-stimulation in rats

Heart rate, recorded continuously from rats trained to press a bar for intracranial electrical stimulation of their septal areas, fell consistently after brain stimulation. Interpretation of the rewarding effect of septal stimulation had previously been limited by the absence of any data on the autonomic effects of the stimulation. The results of this study suggest that the rewarding effect may possibly be produced by a parasympathetic (quieting) reaction of the autonomic nervous system to septal stimulation.     

Relation between REM sleep and intracranial self-stimulation

Depriving rats of rapid eye movement (REM) sleep was shown to lower their thresholds and raise their response rates for rewarding brain stimulation. Conversely, allowing rats to self-stimulate while they were being deprived of this sleep form reduced the amount of REM rebound during recovery from deprivation. These results demonstrate a reciprocal relation between rewarding brain stimulation and REM sleep.     

Estrous cycle in the rat: effects on self-stimulation behavior

The performance of female rats, in pressing a bar for electrical stimulation of the hypothalamus, changes during the estrous cycle. Highest barpressing rates accompany the appearance of vaginal cornification. This increase is not an artifact of increased spontaneous activity at estrus, although the factors underlying these changes in activity may also mediate the changes in self-stimulation behavior.     

Metabolic mapping of the brain during rewarding self-stimulation

Local rates of cerebral glucose utilization were measured in rats by the quantitative 2-deoxy-D-[14C]glucose autoradiographic method during electrical stimulation of the ventral tegmental area. Rats trained in intracranial self-stimulation showed a pattern of changes in forebrain metabolic activity distinctly different from the pattern seen in rats stimulated by the experimenter. These findings provide information about the distribution of local cerebral activity specific to reinforced instrumental behavior.     

Intracranial mobility in the coelacanth

Analysis of the jaw mech anism of the coelacanth Latimeria shows' that the action of the intracranial artic ulation and the associated subcephalic muscles (a system unique to the Cros sopterygii) is important in increasing the angle of ihe gape and the power of the bite. Maximum rotation at the in tracranial joint is approximately 15 de grees.     

Lateral hypothalamus: food current intensity in maintaining self-stimulation of hunger

Rats displaying stimulus-bound eating will press bars for currents slightly above eating threshold only when food is near the bar. At higher currents self-stimulation is maintained without food. Such currents may spread to activate consummatory feedback appropriate to the drive elicited; or, for more intensely stimulated drive mechanisms, wider ranges of sensory feedback may be reinforcing.     

Facilitation of brain self-stimulation by central administration of norepinephrine

Rats with electrodes implanted in the medial forebrain bundle stimulated their own brains at sharply reduced rates after systemic administration of disulfiram or intraventricular administration of diethyldithiocarbamate. Both drugs inhibit dopamine-beta-hydroxylase, the enzyme responsible for the final step in the biosynthesis of norepinephrine. The suppressed behavior was reinstated by intraventricular injections of 1-norepinephrine, but not by injection of its biologically inactive isomer, d-norepinephrine. Intraventricular administration of dopamine and serotonin did not restore self-stimulation. The rewarding effect of medial forebrain bundle stimulation may depend on the availability of norepinephrine as a transmitter, but not on dopamine or serotonin.     

Heart rate: differential effects of hypothalamic and septal self-stimulation

Heart rate in rats was recorded during self-stimulation with electrodes permanently implanted in both the hypothalamus and the septal region. Acceleration was observed during stimulation of the hypothalamus, and deceleration during stimulation of the septal region. In both areas self-stimulation reduced variability in heart rate.     

Vagotomy: effect on electrically elicited eating and self-stimulation in the lateral hypothalamus

A subdiaphragmatic vagotomy markedly inhibits eating and self-stimulation produced in rats by lateral hypothalamic stimulation. The stomach is known to be affected by hypothalamic stimulation via the vagus, and afferents from the stomach can influence the hypothalamus via the same nerve. Consequently, this result suggests that eating and self-stimulation may be partly controlled by hypothalamic influences on the stomach which, in turn, affects hypothalamic sensitivity.     

Temporal summation and refractoriness in hypothalamic reward neurons as measured by self-stimulation behavior

A neurophysiological technique of double-pulse stimulation has been applied to freely moving rats with chronic indwelling electrodes in the hypothalamic reward area. Self-stimulation thresholds, measured as a function of the interpulse interval, generated curves with time constants characteristic of refractory periods and temporal synaptic summation. The results indicate a way of studying central neuronal processes for which the overt behavior of the animal is the dependent variable.     

Strontium-90 in man

The world-wide average strontium-90 content of man was about 0.12 micromicrocurie per gram of calcium (1/10,000 of the maximum permissible concentration) in the fall of 1955. A few values as high as 10 times the average have been obtained. This value is in accord with the predicted value based on fallout measurements and fractionation through the soilplant-milk-human chain. With the present burden of strontium-90, this average level should rise to 1 to 2 micromicrocuries of strontium-90 per gram of calcium by 1970.     

A behavioral measure of homosynaptic and heterosynaptic temporal summation in the self-stimulation system of rats

Bilateral stimulation of the medial forebrain bundle with pulses of varying interpulse intervals elicited a pattern of self-stimulation behavior in the rat indicative of temporal synaptic summation: the shorter the interval the greater the response. In contrast, the effectiveness of unilateral stimulation at very short intervals was limited by neuronal refractory periods. The results support the notion that there is convergence of the medial forebrain bundle self-stimulation system from the two sides of the brain and suggest ways of studying the degree of convergence. They also suggest a technique for behaviorally comparing heterosynaptic and homosynaptic mechanisms of summation.