Assessment of dynorphin-A depletion in the anorexia of Walker-256 tumor bearing rats

Naloxone-induced anorexia increases neuropeptide Y concentrations in the dorsomedial hypothalamus: evidence for neuropeptide Y-opioid interactions in the control of food intake

We measured neuropeptide Y (NPY) concentration in microdissected hypothalamic nuclei, by radioimmunoassay, and NPY mRNA in the hypothalamus in rats treated systemically with the nonspecific opioid antagonist, naloxone, to produce mild anorexia. Twenty rats were treated with daily SC injections of naloxone (7.5 mg/kg); 20 were treated with vehicle alone. Naloxone produced a 7% reduction in food intake (p < 0.01) and a reduction in weight gain (p < 0.002). Neuropeptide Y concentrations were increased specifically in the dorsomedial nucleus of the hypothalamus (DMN) in rats treated with naloxone (6.8 +/- 0.7 fmol/micrograms protein vs. 3.1 +/- 1.0 fmol/micrograms protein, p < 0.05, n = 10 per group). Total hypothalamic NPY mRNA was unchanged. Neuropeptide Y-opioid interactions may be important in the control of food intake.

Feeding elicited by cholinergic and adrenergic hypothalamic stimulation of anorectic tumor-bearing rats

Injection of norepinephrine into the hypothalamus of methylcholanthrene sarcoma-bearing rats elicited a normal feeding response both prior to and following the development of anorexia. Feeding elicited by cholinergic stimulation of the hypothalamus of tumor-bearing rats with carbachol was normal prior to the onset of anorexia, but decreased in magnitude as the anorexia became more severe. These data indicate that noradrenergic feeding mechanisms in the hypothalamus of tumor-bearing rats are functioning normally during anorexia. However, cholinergic feeding mechanisms in the hypothalamus of tumor-bearing rats appear to be depressed to the same degree as ad lib intake, possibly through adaptation or depletion of endorphin systems that mediate stress-induced feeding.

Nocturnal depletion of hypothalamic dynorphin in anorexic Walker-256 tumor-bearing rats

Rats implanted with the Walker-256 (W-256) tumor exhibit marked anorexia that is most apparent at night. In this model, the hypothalamic kappa opioid system was examined for deficits that might contribute to this tumor-induced anorexia. In anorexic tumor-bearing rats (TBR), nocturnal levels of ir-DYN-8 were significantly reduced in the hypothalamus, but ir-DYN-17 levels were not. Accumulation of 3H-etorphine or 3H-ethylketocyclazocine, a putative ligand for the kappa receptor subtype, was not increased in the hypothalamus of the TBR, as might have been expected if there were less endogenous dynorphin to occupy the opioid receptors in this region. In vitro binding assays with 3H-ethylketocyclazocine indicated that dynorphin depletion in the TBR was not sufficient to increase the numbers of kappa opioid receptors in the hypothalamus. Also, the sensitivity of kappa opioid receptors involved in feeding was not altered in the TBR as indicated by an intact feeding response to ketocyclazocine. In summary, the marginal deficits of hypothalamic dynorphin in W-256 tumor-bearing rats that coincide with the phase of tumor-induced anorexia may contribute to the reduction in food intake.

Endogenous opiates: 1985

This paper is the eighth installment of our annual review of research involving the endogenous opiate peptides. It is restricted to the non-analgesic and behavioral studies of the opiate peptides published in 1985. The specific topics this year include stress, tolerance and dependence, eating, drinking and alcohol consumption, gastrointestinal and renal activity, mental illness, learning and memory, cardiovascular responses, respiration and thermoregulation, seizures and neurological disorders, activity, and some other selected topics.