Semistarvation-induced hyperactivity compensates for decreased norepinephrine and dopamine turnover in the mediobasal hypothalamus of the rat

Abstract

Male Wistar rats were housed in running wheel cages and were restricted in their food intake, in order to reduce the initial body weight by 30% within 10 days. Rats increased their daily running up to distances between 7 and 11 km compared to the maximum 2.5 km in controls fed ad libitum. The hypothalamic noradrenaline (NE) turnover, as estimated by the concentration of the major metabolite MHPG, was significantly decreased in semistarved sedentary rats compared to controls. Hyperactivity resulted in marked elevation of NE turnover at all time points examined. Semistarvation-induced decreases of dopamine (DA) turnover as estimated by the concentrations of its major metabolite DOPAC, could also be compensated by hyperactivity. The circadian pattern of NE turnover parallels the pattern of running activity. MHPG levels at times of high activity were even higher than in controls fed ad libitum (p less than 0.01). The availability of the precursor tyrosine, as indicated by the ratio of plasma tyrosine to the large neutral amino acids, was significantly decreased in semistarvation (p less than 0.0001); hyperactivity caused a further decrease (p less than 0.001), indicating that tyrosine availability is not, under these conditions, a limiting factor for noradrenaline turnover. The combined influence of semistarvation and hyperactivity on central catecholamine turnover in the rat is discussed as an animal model for the effects of malnutrition and heavy exercise often observed in anorexia nervosa.

Psychological and Neuroendocrine Responses to Social Stress and to the Administration of the alpha-2-Receptor Antagonist, Yohimbine, in Highly Trained Endurance Athletes in Comparison to Untrained Healthy Controls

“…In rodents, acute motor activity was associated with an increased turnover of noradrenaline in the mediobasal hypothalamus [24], In a special strain of rats characterized by high motor activity elevated levels of extracellular NE were measured causing a down-regulation of alpha(2)-adrenergic receptors [36], Therefore, we had hypothesized that similar to the action of noradrenaline reuptake inhibitors, repeated episodes of noradrenergic stimulation could induce postsynaptic changes leading to decreased sensitivity for pharmacological or psychological inputs. However, the results of the present study do not support the assumption that exercise-induced downregulation of central noradrenergic neurotransmission mediates the anxiolytic and antidepressive effects of exercise.…”

“…Semistarvation-induced hyperactivity was associated with highly significant increases in noradrenaline turnover as estimated by the main metabolite MHPG in the mediobasal hypothalamus of rats [24]. Other studies using chronic activity wheel running confirmed increased tissue concentrations of 5-HT and NE at rest [24][25][26][27][28][29].…”

Diurnal Behavioral and Metabolic Patterns in Chronic Malnourished Rats

“…It is now well documented that undernutrition modifies the physiology of the liver (Reif et al, 1996), produces low basal metabolic rates and lower body temperature (Muralidhara & Shetty, 1990). Those physiological modifications have been interpreted as a compensatory mechanism aimed at counteracting the nutritional unbalance induced by diet composition (Brooks et al, 1990).…”

Decreased Neuroendocrine Responses to Meta-Chlorophenylpiperazine (m-CPP) but Normal Responses to Ipsapirone in Marathon Runners

“…Also, urinary and CSF MHPG was significantly higher during a day of increased motor activity in comparison with a day with usual ward activities in depressed patients (Beckmann et al 1979). Semistarvation-induced hyperactivity was associated with highly significant increases in noradrenaline turnover as estimated by the main metabolite MHPG in the mediobasal hypothalamus of rats (Broocks et al 1990). Other studies using chronic activity wheel running confirmed increased tissue concentration of 5-HT and NE at rest (Broocks et al 1990;Broocks et al 1991;Dishman 1997;Dunn et al 1996).…”

“…Semistarvation-induced hyperactivity was associated with highly significant increases in noradrenaline turnover as estimated by the main metabolite MHPG in the mediobasal hypothalamus of rats (Broocks et al 1990). Other studies using chronic activity wheel running confirmed increased tissue concentration of 5-HT and NE at rest (Broocks et al 1990;Broocks et al 1991;Dishman 1997;Dunn et al 1996). A protective effect of exercise against NE depletion in locus coeruleus cell bodies after footshock was also reported (Dishman 1997;Dunn et al 1996).…”