R.D. Myers

Injection of solutions into cerebral tissue: Relation between volume and diffusion

Abstract The relationship between the extent of diffusion of a solution and the volume injected has been investigated for cerebral tissue in anesthetized rats. Each of four dyes of unequal molecular weights was injected in a volume of either 0.5, 1.0, 2.0, 3.0 or 4.0 μl into the thalamus or hypothalamus, using stereotaxic procedures. The brain was rapidly frozen in situ 10–25 min after the intracerebral injection, and the area of dye penetration determined by sectioning of fresh or partially fixed tissue. The diffusion of the dye into the tissue surrounding the site of injection bore a direct relationship to the volume given, although there was some variation in spread between the dyes. Because of the unusual magnitude of diffusion, it was suggested, for injections into the brain of the rat, that a volume no larger than 0.5 μl (average spread —1.04 mm) be given if localization of the action of a drug is attempted. Volumes as large as 2.0 μl (average spread— 2.4 mm) could be used for intracerebral injections in a larger animal such as the cat or monkey if an entire area within a diencephalic structure is to be chemically stimulated.

Feeding and temperature responses in the unrestrained rat after injections of cholinergic and aminergic substances into the cerebral ventricles

Abstract Cholinergic, aminergic and related compounds produce dose-dependent eating, hyper- and hypothermia when given by the intraventricular route in the satiated, normothermic rat. In 335 experiments with 45 rats, acetylcholine and eserine evoked hyperthermia but no eating or drinking. The indole amine, serotonin and its precursor, 5-hydroxytryptophan, caused hypothermia but had little effect on ingestive behavior. The catecholamines, dopamine, norepinephrine and epinephrine selectively elicited dose-dependent eating, but no drinking; these amines also produced intense hyperthermia. L-dopa, a precursor of catecholamines, in equivalent doses caused the same responses although with a diminished magnitude and longer latency. The beta -adrenergic agonist, isoproterenol, evoked hyperthermia but no feeding, and hence alpha and beta adrenergic functions in the central nervous system may be distinguished. Although aminergic substances administered intraventricularly evoke eating and temperature changes, cholinergic compounds given by this route produce only changes in temperature.

Antagonism by naltrexone of voluntary alcohol selection in the chronically drinking macaque monkey

An opiate receptor antagonist can reduce excessive alcohol drinking in the rat previously given intracerebroventricular (ICV) infusions of a tetrahydroisoquinoline. Recently, it was found that cerebrospinal fluid (CSF) obtained from volunteers or human patients and subsequently injected ICV in macaque monkeys markedly alters the voluntary consumption of ethyl alcohol in certain of these primates. The purpose of the present study was to determine whether an opioid antagonist would affect the pattern of alcohol intake in selected monkeys which drank excessive amounts of alcohol. Initially, the preferred concentration of alcohol was determined individually for each monkey which consistently drank from 3.0-6.0 g/kg alcohol per day. Subsequently, the single concentration, which ranged from 5-15%, was offered together with water during three consecutive periods as follows: (1) 4-day control baseline period; (2) a 3-day interval during which a saline control vehicle or 0.6 or 1.2 mg/kg naltrexone was administered subcutaneously at 0900 and 1700 hours; and (3) a final 4-day post-injection period during which the alcohol-water preference test was continued. The results showed that both doses of naltrexone significantly attenuated voluntary alcohol drinking up to 60% of the baseline intake during the 3 days of its administration. In two monkeys, alcohol drinking continued to be suppressed up to 50% of basal intake during all or a part of the 4-day post-naltrexone interval. These findings suggest that an opiate receptor mechanism in the brain could be partially involved in the action of the chemical constituents of the humans CSF which serve to induce an abnormally high intake of alcohol in the infra-human primate.

Genetic differences in ethanol drinking of the rat following injection of 6-OHDA, 5,6-DHT or 5,7-DHT into the cerebral ventricles ☆ ☆☆

The preference characteristics for ethanol of four different strains of rats were determined in a two-choice situation by offering water and ethanol in a concentration which was increased from 3 to 30% over a 12-day test sequence. Using stereotaxic procedures, 50 mug 5,6-dihydroxytryptamine (5,6-DHT), 200 mug 6-hydroxydopamine (6-OHDA) or 100 mug 5,7-dihydroxytryptamine (5,7-DHT) were then injected acutely into the lateral cerebral ventricle in a 20 mul volume. Rats of the Sprague-Dawley strain increased their ethanol preference following the lesioning of the serotonergic system by 5,6-DHT, whereas similar destruction of catecholaminergic neurons by 6-OHDA markedly suppressed ethanol intake; Long-Evans rats displayed a similar trend in ethanol drinking patterns. However, animals of the Holtzman strain manifested the increased drinking after 5,6-DHT, but showed no suppression of drinking following 6-OHDA. The preference of rats of the Wistar strain was unaffected by 5,6-DHT but attenuated by 6-OHDA. 5,7-DHT had little or no effect on ethanol consumption in any of these strains. These findings thus suggest that genetic factors are an important determinant in an animals response to a drug that affects 5-HT or NE systems in the brain, particularly when ethanol selection is investigated.

Drinking of high concentrations of ethanol versus palatable fluids in alcohol-preferring (P) rats: valid animal model of alcoholism

A genetically based animal model of alcoholism has been characterized in Wistar-derived rats in terms of their preference (P rats) or lack of preference (NP rats) for 10% ethanol over water. The present experiments were designed to determine: 1) whether a 10% solution of ethanol is the optimal concentration for differentiation of these lines; 2) what concentrations of ethanol are maximally preferred by P and NP rats; and 3) whether highly palatable fluids presented simultaneously with each rats preferred solution of ethanol would alter the patterns of drinking by either the P or NP or both lines of rats. A three-bottle procedure was used to establish preference for ethanol in the presence of water as well as highly palatable solutions. The results showed that, when concentrations ranging from 3-30% were presented over a 12-day test interval, the mean absolute intake of ethanol of the P rats was 6.7 g/kg per day, with a maximum intake of 10.9 g/kg per day at the 25% concentration. These levels of intake were significantly higher than the 4.3 g/kg per day consumed during the presentation of the commonly used constant concentration of 10%. Similarly, the mean absolute intake of ethanol by the NP rats was also elevated significantly at concentrations of 15-30% (2.0 g/kg per day) above that consumed at the 10% concentration (0.4 g/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Isoquinolines, beta-carbolines and alcohol drinking: involvement of opioid and dopaminergic mechanisms

Two classes of amine-aldehyde adducts, the tetrahydroisoquinoline (TIQ) and beta-carboline (THBC) compounds, have been implicated in the mechanism in the brain underlying the addictive drinking of alcohol. One part of this review focuses on the large amount of evidence unequivocally demonstrating not only the corporeal synthesis of the TIQs and THBCs but their sequestration in brain tissue as well. Experimental studies published recently have revealed that exposure to alcohol enhances markedly the endogenous formation of condensation products. Apart from their multiple neuropharmacological actions, certain adducts when delivered directly into the brain of either the rat or monkey, to circumvent the brains blood-barrier system, can evoke an intense and dose-dependent increase in the voluntary drinking of solutions of alcohol even in noxious concentrations. That the abnormal intake of alcohol is related functionally to opioid receptors in the brain is likely on the basis of several dinstinct lines of evidence which include: the attenuation of alcohol drinking by opioid receptor antagoists; binding of a TIQ to opiate receptors in the brain; and marked differences in enkephalin values in animals genetically predisposed to the ingestion of alcohol. Finally, it is proposed that the dopaminergic reward pathways which traverse the meso-limbic-forebrain systems of the brain more than likely constitute an integrative anatomical substrate for the adduct-opioid cascade of neuronal events which promote and sustain the aberrant drinking of alcohol.

Dopamine and thermoregulation: An evaluation with special reference to dopaminergic pathways

The complex role of dopamine (DA) in the diencephalic mechanisms involved in the control of body temperature is reviewed and evaluated. In the context of the monoamine theory of thermoregulation, catecholaminergic synapses in the anterior hypothalamic pre-optic area, are proposed mediate the pathways in the brain-stem which subserve heat dissipation. Within this theoretical framework, hypothalamic DA is considered to underlie a portion of the functional component of the heat loss system. This deduction is based on pharmacological studies in which both the catecholamine and receptor antagonists have been infused directly into the hypothalamus. In view of the action of DA applied to the substantia nigra and other subcortical structures, the unique anatomical circuitry of the central dopaminergic projections has also been analyzed in terms of specific connections within critical morphological regions related to thermal functions. In particular, the nigro-striatal pathway could be involved in the mediation of one or more of the different aspects of the thermoregulatory system integrating both autonomic and behavioral responses. Finally, an anatomical schema which portrays the suggested mechanisms of DA activity is presented.

In vivo acetaldehyde in the brain of the rat treated with ethanol

Abstract Ethanol, 4.5 g/kg, was administered intragastrically to rats to determine if acetaldehyde could be detected in brain interstitial fluid. Samples from both blood and brain were collected at half-hour intervals. Brain interstitial fluid samples were collected from both the caudate nucleus and the thalamushypothalamus region using the push-pull perfusion technique. The ethanol and acetaldehyde concentrations in these samples were determined by a head space gas Chromatographie technique. Blood ethanol levels typically ranged from 200 to 400 mg/100ml, while acetaldehyde levels ranged from 15 to 40 μM in blood and 5 to 20 μM in brain fluid. When disulfiram was given to the rats 20 hr prior to ethanol administration, blood acetaldehyde increased to 70–280 μM and brain interstitial fluid acetaldehyde increased to between 25 and 120 μM. Whole brain acetaldehyde levels were also measured after an ethanol dose was given. No acetaldehyde could be detected in whole brain unless the animal had first been treated with disulfiram. These data demonstrate that acetaldehyde does enter the brain, coming into direct contact with the brain cells bathed in the interstitial fluid. The acetaldehyde concentration in the interstitial fluid is higher than that in the brain cells, probably due to its rapid oxidation in the cells catalyzed by aldehyde dehydrogenase.

Body temperature: possible ionic mechanism in the hypothalamus controlling the set point.

The body temperature of many mammals is set at or around 37�C. The mechanism for this set point appears to depend on a constant and inherent balance between sodium and calcium ions within the posterior hypothalamus. When this region is perfused in unanesthetized cats, an extracellular excess or a normal physiological concentration of sodium ions evokes a rise in body temperature if calcium is not in the perfusate. At the same site, an excess or normal concentration of calcium ions causes the temperature to fall when sodium is absent.

A procedure for eliminating position habit in preference-aversion tests for ethanol and other fluids

A method is described for eliminating the position habit which often arises in experiments designed to determine preference-aversion thresholds for water and a test fluid such as ethanol. A three bottle (i.e., three position) paradigm is employed, but only water and a test fluid are offered to the animal. The third bottle is empty but is rotated every day in a predetermined sequence along with the other two bottles. In preference determinations for different concentrations of ethanol, stable fluid intake functions are obtained.