Abstract
In a completely crossed, double blind designed study, six rats received intraventricular injections of 0.1, 1.0 and 10 micrograms of alpha-MSH and a placebo. The rats were tested for response to painful thermal stimuli with the tail-flick test. All of the doses of alpha-MSH produced hyperalgesia during the first 20 min of testing. Only the 1.0 microgram dose of alpha-MSH produced hyperalgesia throughout the 80 min course of the experiment. This study, coupled with previous reports that MSH/ACTH fragments may attenuate morphine-induced analgesia, suggest that MSH can have opposite actions from those of the endorphins. It is possible that alpha-MSH and related peptides may be endogenous anti-opiates.
Highlights
It is possible that a-melanoeyte stimulating hormone (MSH) and related peptides may be endogenous anti-opiates
Among the most direct evidence of a modulating relationship between these peptides is the attenuation of opioid-induced analgesia by MSH/ACTH compounds [14]
Since major behavioral differences have been related to small changes in thestructure of MSH/ACTH fragments [21], the current study was designed to investigate the hyperalgesic influence of a-MSH
Summary
Histological confirmation of placement of the cannulae indicated that six rats reliably received intraventricular administration of the peptide, Surgery. At least a week before testing, ventricular cannulae were implanted into the left ventricle of the rats. The cannulae were secured with dental acrylic and stainless steel hooks. SANDMAN AND KASTIN a microsyringe was extended 1 mm below the cannulae for injections of the a-MSH. Histological verification of the cannulae placement was done by observation of marker dyes injected into the ventricle before sacrifice. Response to thermal stimulation was measured with the tail-flick test of D'Amour and Smith [8]. The apparatus consisted of an adjustable heat source directed to the rat's tail. The timer and the heat were terminated when the tail was withdrawn from the source of heat. The latency of response, to tenths of a second, provided a measure of pain sensitivity
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