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Biomedical subjects

N White

Publications and source records attributed to N White.

At least 145 records · Page 8Linked to original sources
PubMed1979

Impaired hypothalamic control of prolactin secretion in massive obesity.

Intravenous insulin tolerance tests and thyrotropin-releasing hormone (T.R.H.) stimulation tests were performed in nine massively obese women and six lean female controls and the prolactin, growth hormone, and cortisol responses were measured. A combined pituitary function test (insulin, T.R.H., and gonadotropin-releasing hormone) was performed in eleven other massively obese women. In the obese women to whom insulin was given separately there was no prolactin release, and growth hormone and cortisol responses were impaired. T.R.H. stimulation produced a prolactin response which was subnormal. These changes were not apparent in the obese women in whom a combined pituitary function test was performed. The results suggest an alteration of hypothalamic function in massive obesity.

Adolescent↗
PubMed1979

Performance effects with repeated-response measures during pimozide-produced dopamine receptor blockade.

Rats were trained to lever-press for either food reward or brain-stimulation reward on a continuous reinforcement schedule. Following training each animal was extinguished (i.e. tested with the reward omitted) under the influence of pimozide (0.25 mg/Kg or 0.5 mg/Kg). Pimozide produced a dose-dependent reduction in the mean number of responses to extinction made by rats in ecach group. In a second experiment, pimozide produced a similar dose-dependent decrease in the performance of a naturally occurring behavior (nose-poking) that had never been associated with reward. These data suggest that dopamine receptor blockade can produce a perofrmance deficit in situations which require repetitive responses, and that this deficit is unrelated to the presence or absence of reward.

Animals↗
PubMed1979

Age-dependent changes in the inactivation of thyrotrophin-releasing hormone by different areas of rat brain.

Age-dependent changes in the inactivation of thyrotrophin-releasing hormone (TRH) were investigated in two subcellular fractions prepared from hypothalamus, thalamus, cortex and cerebellum of male rats. It was found that, in both supernatant and particulate fractions from the four brain areas, enzyme activity increased to a peak at 10-25 days of age and then decreased gradually until adult levels were reached. The changes in TRH degradation observed may be related to alterations in hypothalamic TRH content with age and to maturation of the tripeptide's putative neurotransmitter/neuromodulator function.

Age Factors↗
PubMed1978

Effects of catecholamine manipulations on three different self-stimulation behaviors.

Rats with self-stimulation electrodes in the medial part of lateral hypothalamus (LH) or in the lateral part of LH were trained to bar press, to run in a continuous, square-shaped runway, and to move their tails from side to side while otherwise restrained, all using LH stimulation on an FI 2 sec schedule as the reinforcement. At low doses of pimozide (a dopaminergic blocker) or of FLA-57 (a dopamine beta-hydroxylase inhibitor) different effects on rates of responding were observed on each of the three tasks at the two electrode placements, indicating that the rate reductions were not the results of specific performance effects of the drugs. The patterns of rate changes suggested that the effects of LH stimulation on behavior in the runway were primarily, but not exclusively mediated by a dopaminergic system; that the effects of LH stimulation on tail movement were primarily, but not exclusively mediated by a noradrenergic system; and that the effect of LH stimulation on bar pressing was mediated by both, or either of these substrates. These results suggest that the reinforcement of behavior by LH stimulation is flexibly mediated by at least two different neural systems.

Animals↗
PubMed1978

Effects of catecholamine manipulations on three different self-stimulation behaviors.

Rats with self-stimulation electrodes in the medial part of lateral hypothalamus (LH) or in the lateral part of LH were trained to bar press, to run in a continuous, square-shaped runway, and to move their tails from side to side while otherwise restrained, all using LH stimulation on an FI 2 sec schedule as the reinforcement. At low doses of pimozide (a dopaminergic blocker) or of FLA-57 (a dopamine beta-hydroxylase inhibitor) different effects on rates of responding were observed on each of the 3 tasks at the 2 electrode placements, indicating that the rate reductions were not the results of specific performance effects of the drugs. The patterns of rate changes suggested that the effects of LH stimulation on behavior in the runway were primarily, but not exclusively mediated by a dopaminergic system; that the effects of LH stimulation on tail movement were primarily, but not exclusively mediated by a noradrenergic system; and that the effect of LH stimulation on bar pressing was mediated by both, or either of these substrates. These results suggest that the reinforcement of behavior by LH stimulation is flexibly mediated by at least 2 different neural systems.

Animals↗
PubMed1978

Effect of pimozide on the improvement in learning produced by self-stimulation and by water reinforcement.

When rats self-stimulate immediately after the training trial of an appetitive task their performance on a retention test is improved the next day. In the present study, this improvement was blocked by pretraining injections of pimozide, a dopaminergic blocker. In a second experiment, injections of pimozide retarded learning on the same task when the learning was reinforced by drinking water, but had no effect on learning which occurred in the absence of a reinforcer. The data made the hypotheses that the animal's behavior was a result of an action of primozide on sensory or motor mechanisms, or that the drug produced state-dependent effects, highly unlikely. We concluded that neural systems involving dopamine mediate an effect of reinforcing events on behavior.

Animals↗
PubMed1977

Effects of lesions of various medial forebrain bundle components on lateral hypothalamic self-stimulation.

Unilateral lesions of various medial forebrain bundle components were assessed for their effects on lateral hypothalamic self-stimulation. Damage of areas containig nigrostriatal dopaminergic or ascending noradrenergic neurons had negligible effects on bar pressing, tail moving and alley running for hypothalamic stimulation. Lesions which appeared to destroy most or all of the catecholaminergic fibers in the posterior medial forebrain bundle virtually eliminated reinforced bar pressing and tail moving, but only partially suppressed alley running. The results suggest that brain stimulation reinforcement of the bar press and tail movement tasks depends upon the integrity of neural tissue in the area of the catecholaminergic pathways of the medial forebrain bundle, but not upon specific dopaminergic or noradrenergic systems. The data further suggest that the reinforcement of alley running is at least partially mediated by different neural tissue (possibly non-catecholaminergic) at the level of the posterior medial forebrain bundle lesions.

Animals↗
PubMed1977

Circulating immune complexes after repeated halothane anaesthesia.

A patient developed hepatitis after receiving three halothane anaesthetics in 22 days. Twenty-four hours after the onset of jaundice she developed an acute serum sickness syndrome with polyarthralgia, proteinuria, and transient impairment of renal function. Serum concentrations of complement components C1q, C4, and C3 were substantially reduced, and immune complexes capable of activating the complement system via the classical pathway were present in the serum and synovial fluid. A metabolite of halothane was associated with these complexes. Fourteen months after exposure to halothane her lymphocytes were stimulated in vitro by this metabolite. The conditions under which stimulation occurred were unusual--namely, a 7S fraction of the serum, presumably IgG, was necessary. Our results provide strong evidence that halothane may be immunogenic and that its immunogenicity is dependent on the non-covalent binding of one of its metabolites to plasma proteins.

Anesthesia↗
PubMed1977

The reinforcing action of morphine and its paradoxical side effect.

Rats were trained to run down a runway for food in the goal box, and were then tested with one trial per day for 5 days. After running in the runway and eating in the goal box each rat was injected with a drug and returned to the empty goal box for 50 min. Over the 5 trials, rats that received morphine sulphate increased their running speed approximately 400% while the amount of food they ate in the goal box decreased to about 70% of baseline values. The running speed of rats that received lithium chloride decreased to about 30%, while the amount of food they ate decreased to less than 10% of baseline. These two variables did not change for rats that received saline injections. The large increases in running speed observed in the rats that received morphine injections were attributed to an interaction (but not simple summation) between the positive reinforcing effects of morphine and food. The accompanying paradoxical decrease in amount eaten was discussed in terms of the complex pharmacological properties of morphine and it was suggested that morphine may have a reinforcing effect on behavior that is independent of its affective properties.

Animals↗
PubMed1976

Strength-duration analysis of the organization of reinforcement pathways in the medial forebrain bundle of rats.

Strength-duration curves were determined for electrical self-stimulation of the brain in rats implanted with lateral hypothalamic electrodes. The rats self-stimulated in different behavioral situations which required them to make different responses, and the parameters of the strength-duration curves determined in each situation were compared. The comparisons suggested that two distinct groups of neurons were involved in the mediation of brain stimulation reinforcement of the bar pressing response, and that one of these groups was primarily involved in mediating the reinforcement of an alley running response, while the other group primarily mediated the reinforcement of a responses suggested that the nature of the response a rat is response a rat is required to perform determines the exact combination of neurons from the two groups which participate in mediating the brain stimulation reinforcement of the task. The possible functional significance of these two neuron groups was discussed.

Animals↗