Intravenous saline injection as an interoceptive signal in rats
Psychopharmacology. 2011-04-15; 217(3): 387-396
DOI: 10.1007/s00213-011-2294-4
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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.
DOI: 10.1007/s00213-011-2294-4
PMCID: PMC3377945
PMID: 21494787 [Indexed for MEDLINE]