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Intravenous saline injection as an interoceptive signal in rats.

ABSTRACT: RATIONALE:Addictive drugs are commonly delivered in the organism by means of intravenous (i.v.) injections. Since saline mimics the blood environment by basic ionic properties and pH, it is generally assumed that it should not have any physiological effects, serving as a control for the effects induced by drugs. OBJECTIVE:The aim of the study was to examine central, behavioral, and physiological effects of stress- and cue-free i.v. saline injection in freely moving rats. METHODS:We examined how a typical low-volume and slow-speed saline injections affect cortical electroencephalograpy (EEG), neck electromyography (EMG), locomotor activity as well as central and peripheral temperatures. RESULTS:Saline injection made during slow-wave synchronized activity induces rapid transient EEG desynchronization, manifesting as a drop of EEG total power, decrease in alpha activity, and increases in beta and gamma activities. Saline injection did not affect locomotor activity as well as brain and body temperatures, but induced a transient increase in neck EMG activity and a rapid brief drop in skin temperature, suggesting peripheral vasoconstriction. These responses were virtually fully absent when saline injection was made during naturally occurring desynchronized EEG activity during behavioral activity. CONCLUSIONS:Since i.v. injection is able to produce a peripheral sensory signal that is transmitted rapidly to the CNS and followed by a more prolonged effect of the injected drug on brain cells, with repeated drug administrations, the injection itself could play a role of drug-related sensory cue, thus inducing conditioned physiological responses and altering the effects of injected drugs.

SUBMITTER: Kiyatkin EA

PROVIDER: S-EPMC3377945 | biostudies-literature | 2011 Oct

REPOSITORIES: biostudies-literature

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Intravenous saline injection as an interoceptive signal in rats.

Kiyatkin Eugene A EA Lenoir Magalie M

Psychopharmacology 20110415 3

<h4>Rationale</h4>Addictive drugs are commonly delivered in the organism by means of intravenous (i.v.) injections. Since saline mimics the blood environment by basic ionic properties and pH, it is generally assumed that it should not have any physiological effects, serving as a control for the effects induced by drugs.<h4>Objective</h4>The aim of the study was to examine central, behavioral, and physiological effects of stress- and cue-free i.v. saline injection in freely moving rats.<h4>Method ...[more]

PMID: 21494787

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Project description:BackgroundRubus occidentalis, also known as black raspberry, contains several bioactive components that vary depending on the maturity of the fruit. The goal of this study was to evaluate the efficacy of immature Rubus occidentalis extract(iROE) on acid-induced hyperalgesia, investigate the mechanism involved, and compare the antihyperalgesic effect of immature and mature ROEs.MethodsIn adult male Sprague-Dawley rats, chronic muscle pain was induced via two injections of acidic saline into one gastrocnemius muscle. To evaluate the dose response, the rats were injected intraperitoneally with 0.9% saline or iROE (10, 30, 100, or 300 mg/kg) following hyperalgesia development. To evaluate the mechanism underlying iROE-induced analgesia, the rats were injected intraperitoneally with saline, yohimbine 2 mg/kg, dexmedetomidine 50 μg/kg, prazosin 1 mg/kg, atropine 5 mg/kg, mecamylamine 1 mg/kg, or naloxone 5 mg/kg 24 h after hyperalgesia development, followed by iROE 300 mg/kg administration. To compare immature versus mature ROE, the rats were injected with mature ROE 300 mg/kg and immature ROE 300 mg/kg after hyperalgesia development. For all experiments, the mechanical withdrawal threshold(MWT) was evaluated using von Frey filaments before the first acidic saline injection, 24 h after the second injection, and at various time points after drug administration. Data were analysed using multivariate analysis of variance(MANOVA) and the linear mixed-effects model(LMEM). We compared the MWT at each time point using analysis of variance with the Bonferroni correction.ResultsThe iROE 300 mg/kg injection resulted in a significant increase in MWT compared with the control, iROE 30 mg/kg, and iROE 100 mg/kg injections at ipsilateral and contralateral sites. The iROE injection together with yohimbine, mecamylamine, or naloxone significantly decreased the MWT compared with iROE alone, whereas ROE together with dexmedetomidine significantly increased the MWT. According to MANOVA, the effects of immature and mature ROEs were not significantly different; however, the LMEM presented a significant difference between the two groups.ConclusionsImmature R. occidentalis showed antihyperalgesic activity against acid-induced chronic muscle pain, which may be mediated by the α2-adrenergic, nicotinic cholinergic, and opioid receptors. The iROE displayed superior tendency regarding analgesic effect compared to mature ROE.

Dataset Information

Intravenous saline injection as an interoceptive signal in rats.

Publications

Intravenous saline injection as an interoceptive signal in rats.

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