Hyperthermia sensitizes rats to cocaine's proconvulsive effects and unmasks EEG evidence of kindling after chronic cocaine

Radio telemetry devices to monitor breathing in non-sedated animals

Radio telemetry equipment has significantly improved over the last 10-15 years and is increasingly being used in research for monitoring a variety of physiological parameters in non-sedated animals. The aim of this review is to provide an update on the current state of development of radio telemetry for recording respiration. Our literature review found only rare reports of respiratory studies via radio telemetry. Much of this article will hence report our experience with our custom-built radio telemetry devices designed for recording respiratory signals, together with numerous other physiological signals in lambs. Our current radio telemetry system allows to record 24 simultaneous signals 24h/day for several days. To our knowledge, this is the highest number of physiological signals, which can be recorded wirelessly. Our devices have been invaluable for studying respiration in our ovine models of preterm birth, reflux laryngitis, postnatal exposure to cigarette smoke, respiratory syncytial virus infection and nasal ventilation, all of which are relevant to neonatal respiratory problems.

Evaluation and applications of radiotelemetry in small laboratory animals

Radiotelemetry is the "state of the art" for monitoring physiological functions in awake and freely moving laboratory animals, while minimizing stress artifacts. For researchers, especially those in the fields of pharmacology and toxicology, the technique provides a valuable tool for defining the physiological and pathophysiological consequences derived from advances molecular, cellular, and tissue biology and in predicting the effectiveness and safety of new compounds in humans. There is ample evidence that radiotelemetry systems for measuring physiological functions has been sufficiently validated. Today, the technology is an important tool for collection of a growing number of physiological parameters, for contributing to animal welfare (reduction and refinement alternatives), and for reducing overall animal research costs.

Adaptation to repeated cocaine administration in rats

Quantitative electroencephalogram (EEG) studies in cocaine-dependent human patients show deficits in slow-wave brain activity, reflected in diminished EEG power in the delta and theta frequency bands. In the present study, electrophysiological measures were monitored in 10 nonanesthetized, adult male Sprague-Dawley rats via bipolar, epidural electrodes implanted over the somatosensory cortex. Control electrocorticograms (ECoG) were recorded twice within a two-week interval to establish a baseline. Rats were subsequently injected daily with cocaine HCl at 15 mg/kg, i.p., for two weeks. The ECoG was recorded during a 1-h session one day after the last injection. Total concentrations of dopamine (DA) and its metabolites were assayed in caudate nucleus (CN) and frontal cortex (FC) using HPLC/EC. Compared with controls, marked increases in DA concentrations were observed in both regions. The DA turnover decreased significantly. The power spectra, obtained by use of a fast Fourier transformation, revealed a significant decrease in slow-wave delta frequency bands following repeated exposure to cocaine. These data are consistent with reported findings in humans that repeated exposures to cocaine result in a decrease in slow-wave brain activity. Further studies are necessary to establish whether regional alterations in blood flow and metabolic activity may underlie such observations.

Investigation of the sleep electrocorticogram of the common marmoset (Callithrix jacchus) using radiotelemetry

OBJECTIVE

To evaluate the use of a totally implantable radiotelemetry system for recording the sleep electrocorticogram (ECoG) of a small new world primate, the common marmoset (Callithrix jacchus) without restraint during data collection.

METHODS

Under anaesthesia a telemetry transmitter, which allowed the recording of a single ECoG channel, was implanted intraperitoneally. This system allowed ECoG data to be recorded overnight from animals living in pairs within their habitual laboratory environment over a period of 12 months. Data were subsequently scored using modified Rechtschaffen and Kales criteria (A manual of standardized terminology, techniques and scoring system for sleep stages of human subjects. Los Angeles, UCLA Brain Information Service/Brain Research Institute, 1968) into stages of waking, light sleep, deep sleep and probable rapid eye movement sleep (pREM). Concurrent video recording was used to assist in the categorising of pREM.

RESULTS

Results showed that, as in man, the marmoset exhibits sleep cycles with stages alternating between non-REM (deep sleep and light sleep) and pREM sleep throughout the night. In common with other non-human primates the duration of each of the sleep stages was relatively short and punctuated with frequent waking.

CONCLUSIONS

These data suggest that sleep in marmosets housed under laboratory conditions (a) can be recorded without restraint and (b) has potential to be used as a model for human sleep.

Chronic cocaine treatment induces dysregulation in the circadian pattern of rats' feeding behavior

The effects of protracted cocaine administration (15 mg/kg i.p., twice a day for 9 days) on the circadian pattern of feeding behavior was studied in individually housed male Sprague-Dawley rats, maintained under a 12:12 light:dark cycle. Water and food were available ad libitum and food intake was measured twice a day before, during and after withdrawal of cocaine (or saline) treatment. Neither total 24-h food intake, nor body mass at the end of the experiment, was significantly different between cocaine-treated and control animals. However, cocaine administration affected the temporal distribution of food consumption. During the dark (activity) phase, rats receiving cocaine injections consumed significantly less food than control animals, and this effect persisted for up to 3 days of cocaine withdrawal. During the light (rest) phase, cocaine administration promoted food consumption and a significantly higher food intake was also observed during the first five cocaine withdrawal days. Continuous monitoring of locomotor activity did not reveal significant changes in the circadian pattern of activity between the two experimental groups during different treatment periods, except for an acute increase in locomotion within an hour after daytime cocaine injection. The results of this study demonstrate that sub-chronic cocaine administration alters the circadian pattern of rats' feeding behavior.

Concurrent monitoring of EEG and performance in the common marmoset: a methodological approach

A model has been developed in a nonhuman primate, the common marmoset (Callithrix jacchus), which should enable the study of long term effects of compounds with potentially psychoactive properties. The technique facilitates concurrent monitoring of both behavioral and electrophysiological parameters while animals remain in their home cages. Subjects were trained to perform tests from a neuropsychological test battery (The Cambridge Neuropsychological Test Automated Battery, CANTAB) in which they learned to discriminate between pairs of stimuli presented on a touch sensitive computer screen. Single channel cortical electroencephalography (EEG) by radiotelemetry was simultaneously recorded while behavioral testing took place.

Physiological and subjective effects of acute cocaine withdrawal (crash) in rats

The physiological and subjective effects of high acute doses of cocaine and the subsequent homeostatic acute withdrawal syndrome were measured in rats. Radiotelemetry recordings of body temperature and activity were monitored in rats for 48 h after 32 mg/kg cocaine (COC) and saline (SAL) were administered by both intraperitoneal and subcutaneous (s.c.) routes. COC initially produced hypothermia and hyperactivity, followed by a prolonged hyperthermic and hypoactive rebound that seemed to peak around 12 h after injections. The s.c. route of administration produced the greatest rebound effect. Eight additional rats were monitored for EEG activity by telemetry for 48 h after SC administration of SAL or 32 mg/kg COC. COC produced an initial decrease in alpha and beta wavelength bands, with a trend toward increases in alpha and beta power demonstrated from the 10th through 14th h after injections. Using a three-choice haloperidol (HDL), saline, and COC drug discrimination task, we demonstrated a COC-like subjective state produced during the 10th through 12th h after a 32-mg/kg s.c. COC injection with no HDL-like responding engendered during any tested period of the acute or rebound effects of COC. These data provide evidence for an acute COC withdrawal syndrome (crash) in rats occurring 10-14 h after a high-dose COC treatment.

Prenatal exposure to phenobarbital and quantifiable alterations in the electroencephalogram of adult rat offspring

OBJECTIVE

Our purpose was to measure central nervous system insult from prenatal phenobarbital by quantified electroencephalographic evaluation of mature rat offspring.

STUDY DESIGN

Twenty-four adult female rats were given phenobarbital as 0, 20, 40, or 60 mg/kg/day subcutaneously between 9 and 10 AM for 28 days before breeding and throughout gestation. The electroencephalograms of 90-day-old offspring were sampled over 24 hours and converted to the power spectra.

RESULTS

Female offspring exposed prenatally to 20 mg and males exposed prenatally to 40 mg displayed an increase in delta and a decrease in alpha and middle-beta waveform activities. Females exposed prenatally to 40 mg and males exposed prenatally to 60 mg displayed decreases in delta, theta, alpha, and middle-beta activities.

CONCLUSIONS

Prenatal phenobarbital exposure produced dose- and sex-dependent changes in the electroencephalogram of mature offspring consistent with a generalized deficit in the neuronal synchronization mechanisms that are critical for normal sleep and learning.