Elliot A. Stein

Effects of exercise training on brain opioid peptides and serum LH in female rats.

In order to investigate the effects of long-term exercise training on brain endorphin systems, and the latters possible effects on the hypothalamic-pituitary-gonadal axis, female Wistar rats were subjected to daily treadmill running. A sedentary control group was also employed. After 8 weeks of training, and just prior to sacrifice, one-half of each group received a final fatiguing bout of exercise. Thus the final four groups consisted of a trained-fatigued (TF), trained-nonfatigued (TN), control-fatigued (CF), and control-nonfatigued (CN) group. Regional brain levels of beta-endorphin (beta E), methionine enkephalin and leucine enkephalin (LE) were assayed with independent RIAs from the nucleus accumbens, cortex, caudate-putamen, septum, amygdala, anterior and posterior hypothalamus, substantia nigra and ventral tegmentum. Diestrus serum levels of luteinizing hormone (LH), follicle stimulating hormone and prolactin (PRL) were also determined. Fatiguing resulted in a decrease in serum LH levels as well as an increase in beta E content in the nucleus accumbens, and LE content in the ventral tegmentum. Finally, TF animals exhibited less LE in the amygdala than the TN rats. Taken together, these changes in brain endorphins may indicate an acute, fatigue-running modulation of the hypothalamic-pituitary-gonadal axis.

Naloxone depresses osmoregulatory drinking in rats

The effect of an opiate antagonist, naloxone, on hypertonic NaCl-induced drinking was studied in rats in a within-subject design. Naloxone reduced drinking at all dosage levels used (0.3-10.0 mg/kg) when compared to a control condition. These results extend previous findings of naloxone mediated reduction in fluid intake in water deprived and osmotically challenged animals. Naloxones effects on fluid intake seems to be independent of procedure employed, and thus quite general. Possible mechanisms were considered.

Naloxone-induced hypodipsia: A CNS mapping study

Opiate antagonists have been shown to reliably attenuate drinking behavior. Recent research points to a central site of action for this antidipsogenic effect. To pursue this issue of site specificity, naloxone, a specific opiate antagonist, was delivered into a number of discrete subcortical areas in 23 hour water-deprived rats. Water intake was measured at 5, 15, 30 and 60 minutes post drug injection. Compared to saline control injections, naloxone reliably depressed water intake, in a dose-related manner, in lateral hypothalamus, preoptic area and zona incerta. Previous research has repeatedly implicated these areas in drinking behavior. Placements which were not generally effective included lateral ventricle, nucleus accumbens, substantia nigra and cortex/corpus callosum. Latency to drink was never affected by any dose of naloxone injected into any site, suggesting an opioid influence on mechanisms involved in termination and/or maintenance rather than on initiation of drinking.

Drinking-induced alterations in reward pathways: an in vivo autoradiographic analysis

An in vivo autoradiographic technique permitted the visualization of discrete neuroanatomical changes in opiate receptor binding as a result of 23-h water deprivation and drinking. Two groups of rats (n = 5) were placed on a 23-h water deprivation schedule for 10 days. On the last day, one group was given access to water for 15 min. These groups, plus a matched ad libitum water control group (n = 5), received an injection of 0.002 mg/kg [3H]diprenorphine ([3H]Dpr) through chronically implanted jugular catheters followed by preparation for opiate receptor autoradiography. Relative cerebral blood flow was estimated non-quantitatively by the injection of 75 microCi/kg iodo-[14C]antipyrene into 3 additional groups identically treated. Results indicated that water-deprivation stress increased [3H]Dpr binding in the claustrum, lateral hypothalamus, amygdala and ventral tegmental area while decreasing binding in the medial frontal cortex, lateral septum, dorsolateral thalamus and central gray. All effects of water deprivation were reversed in animals receiving water. Observations of changes in relative blood flow were shown to have no correlation with changes in opiate receptor binding. It appears that water deprivation stress causes a reduction in opioid release in areas along the mesotelencephalic dopamine pathway which may contribute to a drive state. Water intake may then reduce or otherwise alter the drive state through the release of opioids along these pathways, contributing to the perception of reward.

Drinking behavior is modulated by CNS administration of opioids in the rat.

While opiate antagonists have been shown to reliably attenuate drinking following both central and peripheral administration, relatively few data exist on the effects of agonist agents on this behavior. To address this issue, two opiate agonists, morphine sulfate, a mu agonist, and [D-ala2, D-leu5]-enkephalin (DADLE), a semi-synthetic delta analog of a delta agonist, were administered into several CNS sites in rats. There was a dose-related, naloxone-reversible reduction of water intake following morphine injections into the lateral hypothalamus (LH) and preoptic area (POA). In addition, injections of DADLE also attenuated drinking when injected into LH and POA, but not following the ventral tegmental area or zona incerta administration. These data are discussed in view of a role for the endogenous opioid peptides in the regulation of drinking behavior.

β-endorphin and sprint training

Abstract Male, Wistar rats were sprint trained using a high intensity, interval type, treadmill running protocol. Sprint training produced a significant decrease in plasma β-endorphin levels. Conversely, animals who performed a high intensity acute run displayed significant increases in the concentration of plasma β-endorphin which may be stress-related. Neither training nor acute running had any significant effect on the β-endorphin levels of the pituitrary, cortex, posterior or anterior hypothalamus.

Effect of intravenous heroin and naloxone on regional cerebral blood flow in the conscious rat

Regional cerebral blood flow (RCBF) was measured with the [14C]iodoantipyrine technique and quantitative autoradiography in awake, restrained rats shortly after intravenous injection of heroin, naloxone or naloxone before heroin. The RCBF observed in these animals was compared to those obtained in similarly treated, saline-injected rats. In an identically treated series of animals, no significant change in arterial blood gases, pH or bicarbonate was seen following any of the drug treatments at the equivalent time RCBF was determined. Blood flow increased an average 36% in 37 of the 40 areas measured 1 min after heroin injection. Significant increases were found in 21 areas including visual and piriform cortex, basal ganglia, diencephalon, limbic system, midbrain tegmentum, superior colliculus, periaqueductal gray, internal capsule and fornix. These elevations in blood flow were reversed in rats receiving heroin following naloxone pretreatment. RCBF decreased in 35 areas (mean = -12%) 4 min after naloxone injection; a 40% decrease in blood flow to entorhinal cortex was significant. These results suggest that opiate receptor stimulation by heroin increases functional activity within selected brain areas, and this effect is not limited to regions with dense populations of opiate receptors.

Effects of intracranial self-stimulation on brain opioid peptides

The neurochemical system(s) underlying brain stimulation reward (ICSS) has been investigated for many years. The catecholamine hypothesis is currently most accepted with predominant emphasis on the role of dopamine. The present report examines the role of three opioid peptides--Methionine and Leucine Enkephalin (ME and LE) and beta-Endorphin (beta-E) in this behavior. Peptide levels from pituitary, hypothalamus and whole brain were determined by independent RIAs and analyzed according to treatment: low, moderate and high ICSS responders, sham controls, animals receiving nonspecific stimulation, and naloxone--with and without ICSS. Not only did naloxone reduce ICSS from high responders by 74%, it also was able to reduce peptide levels--most notably for ME and beta E in most regions. Additionally, the effects of ICSS on endorphin levels was found to be related to the rate category of responding. Since endorphins are known to interact with dopamine systems, it is therefore considered likely that the endogenous opioid peptides play an important role in ICSS either directly or indirectly via their influence on catecholamine systems.

Brain stimulation of the ventral tegmental area attenuates footshock escape: an in vivo autoradiographic analysis of opiate receptors.

An in vivo autoradiographic technique was employed to visualize discrete neuroanatomical changes in opiate receptor binding as a result of aversive footshock (FS) and rewarding electrical brain stimulation (ICS). Footshock-induced escape responding was shown to be attenuated by the simultaneous presentation of non-contingent ICS. Rats were divided into 4 groups (n = 6) receiving ICS, FS, ICS + FS or neither stimulus in an escape paradigm. During the final behavioral test session, rats were injected with 0.002 mg/kg [3H]diprenorphine ( [3H]Dpr) and subsequently prepared for autoradiography. Results indicated two groups of brain areas distinguishable by their treatment-induced changes in [3H]Dpr binding. One group of areas included the nucleus accumbens, claustrum, claustrocortex, perirhinal cortex and ventral tegmental area. These structures showed increased binding due to both FS and ICS. The other group consisted of the diagonal band of Broca, bed nucleus of the stria terminalis, lateral hypothalamus-medial forebrain bundle and amygdala. In these regions, an increase in binding ipsilateral to the electrode was observed in animals receiving ICS with no apparent effect of FS. These results demonstrate that non-contingent ICS may not be strictly aversive and suggest an anatomic, opioid-sensitive basis for both a rewarding and aversive component of this stimulus. It appears, further, that ICS can inhibit the release of endogenous opioid peptides in areas along the mesotelencephalic dopamine pathways, possibly to regulate the activity of neurons conveying reward information. Finally, the observed changes in opiate receptor binding may indicate a mechanism for ICS to produce both drive and reward.

Bilateral cannula system for intracranial chemical microinjection in small animals

An easily constructed and inexpensive bilateral cannula assembly for microinjection of chemicals into neural tissue in small animals is described. It reduces problems sometimes encountered with commercially available units, making it useful in both research and teaching laboratory settings. Suggestions for implant procedures and modifications for use in unique applications are suggested.