Effects of ethyl alcohol on central neurons.-

NMDA receptor function within the anterior piriform cortex and lateral hypothalamus in rats on the control of intake of amino acid-deficient diets

Animals decrease intake of an indispensable amino acid (AA)-deficient or devoid diet, due in part to decreased dietary limiting AA (DLAA) concentrations within the anterior piriform cortex (APC), and to a recognition process that occurs as early as 20 min following exposure to AA deficiencies. Glutamate levels within the APC change in response to AA deficiencies. The APC projects to the lateral hypothalamus (LH), where glutamate acts to stimulate food intake. We hypothesize that the APC, through glutamatergic projections to the LH, inhibits the LH, which signals to reject the AA-deficient or devoid diet, and trigger aversions to the AA-deficient or devoid diet via an ascending pathway to the APC. We examined the effects of (1) bilateral APC and LH blockade of glutamate's NMDA receptors with the antagonist, D-AP5, (2) APC blockade of AMPA receptors with the antagonist, NBQX, to block glutamate transmission from the APC, and (3) direct injection of the agonist, NMDA, into the LH on intake of the AA-deficient, devoid, or corrected diet. Administration of D-AP5 into the APC increased intake of AA-deficient diet by 6 h, but D-AP5 in the LH decreased AA-devoid diet preferentially over AA corrected intake sooner. NBQX in the APC increased AA-deficient diet intake, also at 6 h. NMDA injection into the LH-stimulated intake of the AA corrected diet by 3 h, but did not affect AA-devoid diet intake. Thus, the glutamate receptors in the APC and LH are involved in the feeding responses to AA-deficient diet, albeit with regional differences. We suggest that glutamate mediates the anorectic responses to AA-deficient diets through recognition of AA-devoid diet with the glutamatergic output cells of the APC sending glutamate-based signals for changes in food intake within the LH and through learned avoidance of AA-deficient diet within the APC, as indicated through the more immediate and prolonged periods of activation within the LH and APC, respectively.

Evidence for the ability of hippocampal neurons to develop acute tolerance to ethanol in behaving rats

BACKGROUND

The cellular mechanisms underlying acute tolerance to alcohol are unclear. This study aimed to determine whether hippocampal neurons have the ability to develop acute tolerance to alcohol in behaving rats.

METHODS

Intrahippocampal microdialysis was performed in freely behaving rats, and the firing of single neurons in the dialysis area was recorded. The control microdialysis fluid, artificial cerebrospinal fluid (ACSF), was replaced with 1 M ethanol in ACSF for a 30 min period. One hour later, the ethanol perfusion was repeated. To test the functional integrity of the microdialysis probe in situ, each microdialysis session was completed with recording the effect of a 10-20 min perfusion of 500 microM N-methyl-D-aspartate (NMDA). The extracellular concentration profile of ethanol during intrahippocampal microdialysis with 1 M ethanol was estimated in a separate study in anesthetized rats. The ethanol content was measured in tissue slices surrounding the probe with gas chromatography (GC), and the generated data were analyzed with a mathematical model for microdialysis to estimate the concentration of ethanol at the recording site.

RESULTS

The predominant effect of the first intrahippocampal microdialysis with ethanol was a decrease in firing rate in both pyramidal cells and interneurons. In contrast, such firing rate decrease did not develop during the second ethanol perfusion. Subsequent NMDA perfusion still induced robust changes in the electrical activity of the neurons. The estimated extracellular ethanol concentration at the recording site was 45-70 mM.

CONCLUSION

This study revealed that hippocampal neurons have the ability to develop acute tolerance to a single exposure of clinically relevant concentrations of ethanol in behaving rats, without influences from the rest of the body.

Bicuculline sensitive depressor response to ethanol infusion into the lateral hypothalamus

Decreased GABA function in the hypothalamus increases mean arterial pressure (MAP) and heart rate (HR). Since ethanol acts on GABA-A receptors, blocking GABA-A receptors can prevent a decrease of MAP and HR by ethanol in the lateral hypothalamus (LH). Ethanol at 5-30 mM, with or without 25 ng/microl bicuculline, was infused into the LH, and the activity of the site was validated with 100 nmoles of serotonin. Male rats were anesthetized with pentobarbital, and the femoral artery was catheterized to measure MAP and HR. Microinfusion was performed with a 28-gauge cannula placed into the LH. Serotonin increased MAP and HR within 15 sec. Ethanol decreased the MAP by -21.15 +/- 3.92 mmHg and HR by -53.61 +/- 14.95 BPM, at 15 min, which recovered by 15 min after the infusion was terminated. These maximum decreases were produced by 20 mM ethanol giving a U-shaped dose response. The aCSF vehicle had no effect. Bicuculline prevented ethanol-induced changes and had no effect when administered alone. Both serotonin and ethanol have direct effects on LH neurons with cardiovascular function. Ethanol produces this effect through GABA-A receptors.

Midlatency auditory-evoked potentials in the rat: effects of interventions that modulate arousal

The vertex-recorded P13 midlatency auditory-evoked potential in the rat shows the same characteristics as the P1 potential in the human, namely, sleep-state dependence, rapid habituation and blockade by the cholinergic antagonist scopolamine. The P13 potential appears to be generated, at least in part, by projections of the pedunculopontine nucleus, the cholinergic arm of the reticular activating system. On the other hand, the auditory cortex-recorded P7 potential appears to be of primary cortical origin. Simultaneous recordings from the vertex and the auditory cortex showed that (1) the P13 potential was suppressed by administration of the anesthetics ketamine, pentobarbital or halothane in a dose-dependent manner, but the P7 potential was not; (2) the P13 potential was suppressed by intragastric injections of ethanol in a dose-dependent manner, but the P7 potential was not; (3) the amplitude of the P13 potential was negatively correlated with blood ethanol levels; (4) both the P13 and P7 potentials were still present following injections of the neuromuscular blocker pancuronium bromide; and (5) both the P13 and P7 potentials were decreased by diffuse brain injury induced by a weight-drop device in a weight-dependent manner. These findings suggest that the P13 potential is more sensitive than the P7 potential to changes in arousal and that the P13 and P7 potentials are not of myogenic but of neural origin.

Neurochemical changes after imbalanced diets suggest a brain circuit mediating anorectic responses to amino acid deficiency in rats

Amino acid-imbalanced (IMB) diets induce an acute amino acid deficiency and hypophagic responses in most animals. The neural circuits underlying these responses are unknown. To ascertain potential neural circuits involved in the recognition of IMB, we measured the concentrations of norepinephrine, dopamine, serotonin, their metabolites and 20 amino acids in 14 rat brain areas in three studies. Rats were prefed a basal diet with L-amino acids as the protein source for at least 1 wk. For the experiments, either threonine or isoleucine IMB diet was offered for 2.5 or 3.5 h. Brains were taken before (using a mildly IMB diet) or after (using moderately or severely IMB diet) food intake was significantly (P < 0.05) depressed. Brain areas were dissected and analyzed for monoamines, metabolites and amino acids. Only in the anterior piriform cortex (APC), a brain area that may contain the amino acid chemosensor, was the limiting amino acid lower in IMB groups than in controls across all of the experiments. Before the onset of the anorectic response to the IMB diets, monoaminergic activity was affected in areas that have recognized monosynaptic connections with the APC. We propose a circuit for the neural responses in the initial recognition of acute amino acid deprivation that begins with activation of the APC and includes areas in the hindbrain and hypothalamus. After a significant hypophagic response, serotonergic indicators were altered in areas of the taste pathway and the limbic system. These results suggest that different circuits mediate the initial recognition and secondary conditioned responses to IMB diets.

Ethanol affects hypothalamic neurons projecting to the hippocampus and inhibits dentate granule cell LTP

In previous studies we demonstrated that ethanol inhibition of hippocampal granule cell long-term potentiation (LTP) is mediated by angiotensin II (AII), and the inhibition can be blocked by losartan, a specific AII receptor antagonist. The purpose of the present study was to demonstrate that this low-dose ethanol inhibition of dentate granule cell LTP induction is mediated by lateral hypothalamic (LH) afferents that project to the granule cells. In urethane anesthetized rats, we compared the effects of ethanol infusion, 6.0 microliter/30 min, by means of an open-ended push-pull type cannula, in both the LH and the dentate gyrus, on dentate granule cell LTP. Results demonstrate a dose-dependent inhibition of LTP induction when the LH is perfused that can be blocked by losartan, 10 mg/kg i.p.. Four doses of ethanol were used: 5, 10, 20, and 30 mM. There was no effect when the dentate gyrus was infused with 30 mM ethanol and normal granule cell LTP was observed. Also, these results demonstrate for the first time a low-dose ethanol effect on a physiological function, LTP in a specific neural pathway, directly related to the anterograde amnesia produced by ethanol on short-term memory. Therefore, these data support our hypothesis that ethanol inhibition of LTP induction at the medial perforant path-granule cell synapse can be attributed to a presynaptic release of AII and cannot be explained in terms of a direct postsynaptic effect on the granule cells.

Lateral hypothalamic stimulation inhibits dentate granule cell LTP: direct connections

We discovered that angiotensin II (Ang II) applied directly to the dentate gyrus inhibited LTP induction in medial perforant path-dentate granule cell synapses and that the inhibition can be blocked by losartan, an Ang II AT1 receptor specific antagonist. In the first part of this study we found that electrical stimulation of the lateral hypothalamus (LH) inhibits LTP in these synapses and the inhibition can be blocked by pretreating the animals with losartan, indicating that LH angiotensin-containing neurons project to the dentate gyrus. Results of the second part of the study demonstrate clearly that some angiotensin-containing LH neurons project directly to dentate granule cells. LH neurons were identified by retrograde tracers applied to the granule cell layer. Double-labeled neurons containing angiotensin and HRP were sparsely distributed and both fusiform and multipolar LH neurons appeared in a small cluster lateral and ventral to the fornix at the level of the paraventricular nucleus. Large numbers of angiotensin staining neurons were observed in the hypothalamus. Results support our hypothesis that some angiotensin containing LH neurons project directly to the dentate gyrus.

Recognition and neural plasticity responding to deficient nutrient intake scanned by a functional MRI in the brain of rats with L-lysine deficiency

Each L-amino acid (AA) in plasma and brain remains unchanged while normal diet is available. Once L-lysine (Lys) deficient diet was offered to rats, Lys in plasma and brain declined, and anorexia occurred. When solutions of AAs were offered, they selected the Lys solution, and their food intake and growth normalized. The single neuron activity in the lateral hypothalamic area of these rats suggested that neural plasticity occurred, specifically responding to Lys, both by iontophoretic application and during ingestion of AA. The recognition site for deficient nutrient intake in the brain of rats with Lys deficiency was identified by non-invasive magnetic resonance imaging (MRI 4.7 tesla, 40 cm bore in diameter) developed to monitor changes in cerebral blood flow and oxygenation in rat brain. Wistar strain young male rats fed with Lys deficient diet for 4 days, were adapted to be settled in the center of the bore. When they received a Lys injection intraperitoneally (0.2 M, 10 mL/kg), a signal intensity decrease in the medial and lateral hypothalamus appeared 30 minutes later in T2 weighted images, reflecting increased oxygenation which lasted for 30 minutes, and then gradually recovered. These changes never occurred in any other areas of the brain of rats with Lys deficiency, i.e., the thalamus, the cortex, the hippocampus, etc. There were no changes in the signal intensity with control injection of saline. In addition, oxygen consumption in the brain of rats without Lys deficiency was not altered by intraperitoneal Lys injection. The present results suggest that in essential AA deficiency, the medial and lateral hypothalamus may play important roles in recognition responses to particular deficient nutrients in order to maintain homeostasis.

Role of angiotensin II and AT1 receptors in hippocampal LTP

Results of a previous study showed that angiotensin II (AII) inhibited the induction of long-term potentiation (LTP) in hippocampal granule cells in response to dorsomedial perforant path stimulation in urethane-anesthetized rats. The results of present experiments demonstrate a dose-dependent inhibition of LTP induction under the same conditions due to ethanol (EtOH) administered by stomach tube and diazepam (DZ) injected IP. The inhibition of LTP induction by EtOH and DZ can be blocked by saralasin (SAR) applied directly to the dorsal hippocampus and by lorsartan (DuP 753) administered IP. Lorsartan or a metabolite crosses the blood-brain barrier because it also blocks the inhibition of LTP induction due to AII administration directly into the dorsal hippocampus. Lorsartan is a competitive antagonist of the AT1 subtype AII receptor. Therefore, the AII and the EtOH and DZ inhibition of LTP induction are mediated by the AII subtype receptor AT1. AIII and the AT2 antagonist PD123319 did not produce any significant effects. These in vivo effects can be reproduced in brain slices and therefore cannot be attributed to other factors, such as the urethane. In addition, electrical stimulation of the lateral hypothalamus (LH) inhibits LTP induction, and the inhibition can be blocked by SAR. These data on LH stimulation indicate that LH AII-containing neurons send axons into the hippocampus that inhibit the induction of LTP. These results not only provide new information on a neurotransmitter involved in the amnesic effects of benzodiazepines and ethanol-induced memory blackouts, but also testable hypotheses concerning recent observations that angiotensin converting enzyme (ACE) inhibitors elevate mood and improve certain cognitive processes in the elderly.

Ethanol dependence and withdrawal selectively alter localized cerebral glucose utilization

The 2-deoxyglucose technique was used to determine local cerebral glucose utilization (LCGU) in over 50 brain regions of rats physically dependent upon ethanol and compared to those of acutely intoxicated and those undergoing an overt ethanol-withdrawal syndrome. Dependent-intoxicated rats (average blood ethanol concentration 64 mM) had decreased LCGU in 13/54 regions, including those associated with the limbic system, cerebellum, and motor system. The ethanol withdrawal syndrome was associated with 17/50 gray regions showing an increase, including regions involved with motor function, auditory system, and mammillary bodies-anterior thalamus-cingulate cortex pathway. The most pronounced differences between these groups occurred in regions associated with motor function, cerebellar function, anterior thalamus, and median raphe. Comparisons between dependent-intoxicated and acutely intoxicated rats (average blood ethanol concentration 66 mM) revealed that acute intoxication was associated with a relatively greater reduction in LCGU in regions involved with sensory-related functions, mammillary bodies, and median raphe. With the development of dependence, adaptation occurred in these regions except for inferior colliculus and median raphe. Dependence was also associated with a relative decrease in LCGU in white matter, limbic system, and extrapyramidal motor system.

Recent Advances in Pharmacological Research on Alcohol

Alcohol dependence is a major public health problem. Studies have shown that a person dependent on alcohol often coabuses other substances, such as cocaine. Cocaine is a powerful stimulant whereas ethanol is generally considered to be a depressant, with some stimulating properties. The subjective effects of these two substances in a dependent individual may often appear to be more similar than they are different. Animals also self-administer both substances. Basically, although both substances have anesthetic properties and both act to functionally increase catecholaminergic function, especially that of dopamine, there are some differences in their actions. Both alcohol and cocaine have various effects on several neurotransmitters and systems, which ultimately interact to produce the feeling of well-being avidly sought by many individuals today. This drive often eventually produces a dependence which has associated social and medical consequences. It seems likely that the neurochemical changes that ensue following abuse of these substances underlie the phenomena of dependence, tolerance, and subsequent withdrawal. The apparent similarities and differences between these two substances will be reviewed in this chapter.

Amino acid and NaCl appetite, and LHA neuron responses of lysine-deficient rat

Rats' preferences for amino acids and NaCl in their drinking behavior were noted when they were fed either a control diet of gluten plus 20% purified egg protein, or (same rats, different time) a lysine-deficient diet. In control, the order of the rats' preferences was arginine greater than saline greater than monosodium L-glutamate (MSG, umami) greater than glycine greater than water greater than threonine greater than histidine greater than lysine. When fed a lysine-deficient diet the order of preference was lysine greater than saline greater than MSG greater than glycine greater than threonine greater than water greater than arginine greater than histidine. To relate neural activity with preference for amino acids and NaCl, activity of lateral hypothalamic (LHA) neurons was recorded during ingestion of MSG, lysine, arginine, glycine, saline, glucose, or water by the control and lysine-deprived condition, following a different cue tone. When the diet was lysine deficient, some neurons responded specifically to lysine ingestion. More neurons responded nondifferentially during licking in control, and responded to lysine, but fewer to other amino acid ingestion during lysine deficiency. Responses to cue tone were associated with those during licking. The present results suggest that preference for deficient amino acids might be mediated in the LHA.

Acute effect of ethanol on the pattern of behavioural specialization of neurons in the limbic cortex of the freely moving rabbit

Single-unit activity was studied in the limbic cortex of eight freely moving rabbits in order to find out what kind of changes in the organization of unit activity correlate with behavioural disturbances following an acute administration of ethanol (1 g kg-1). The rabbits were taught to acquire food by pressing pedals in the experimental cage. Unit activity was recorded during this behaviour in a control experiment and the alcohol experiment took place the next day. The number of behavioural mistakes significantly increased in the alcohol experiments. The pattern of behavioural specialization of the units also differed between the control and alcohol experiments. In the control experiments 55% of units did not show any constant activations in relation to the behavioural phases (non-involved units), 28% of the units were constantly activated in relation to one or more behavioural phases learned in the cage (e.g. use of pedals; L units) and 17% of units showed activations in relation to the behaviour learned before the teaching of food acquisition (e.g. movements in general; M units). In the alcohol experiments the number of active units decreased by one-third compared with that found in the control experiments. The relative number of non-involved units did not change, whereas the relation between L and M units was reversed (11% L units and 34% M units). This was the result of a decrease in the number of active L units, mainly in the upper layers of the cortex. The results indicate that ethanol has a selective depressing effect on cortical neurons with different behavioural specialization, which could explain the behavioural disturbances observed in the alcohol experiments.

Oral self-administration of ethanol and not experimenter-administered ethanol facilitates rewarding electrical brain stimulation

The effects of ethanol on brain-stimulation reward (BSR) were investigated in rats orally self-administering ethanol. Electrodes were stereotaxically implanted in the medial forebrain bundle (MFB) of male F-344 rats. A rate free threshold procedure was used. Animals demonstrated significant threshold-lowering effects after considerable ethanol self-administration experience. To elucidate the significance of the contingent nature of the route of administration in the threshold-lowering effects of ethanol on BSR, a comparison of animals self-administering ethanol to yoked animals receiving it passively through a gastric cannula was made. Significant threshold-lowering effects were only found in the animals self-administering ethanol and not those receiving it noncontingently. Thus, to the extent that brain-stimulation reward is a model of drug-induced euphoria, these results suggest that the reinforcing effects of ethanol are dependent to a greater degree on an interaction between experimental, environmental and pharmacological factors, than other abused drugs.

Effects of ethanol on expiratory neuronal activities in decerebrated cats

The effects of ethanol on two types of bulbar expiratory neurones, post-inspiratory (early expiratory) and expiratory (late expiratory) neurones, were studied in decerebrated, paralyzed and artificially ventilated cats. Intravenous injection of ethanol (300 mg/kg) depressed the efferent activity in the phrenic and recurrent laryngeal nerves which displayed the augmenting discharge during inspiration and the decrementing discharge during the early stage of expiration (stage I expiration). It reduced the duration of expiration, with a preferential effect on stage I expiration. Out of 22 medullary respiratory neurones consisting of 14 post-inspiratory and 8 expiratory neurones, 12 neurones were depolarized by ethanol and 10 neurones were hyperpolarized. In both cases, the respiratory fluctuations of membrane potential diminished and synaptic noises decreased. Input resistances of these neurones remained unchanged. Ethanol depressed the spike activity during stage I expiration of the post-inspiratory neurones. In expiratory neurones, a suppression of firing was greater in stage I expiration than in later stages of expiration. The present results demonstrate that ethanol reduces the expiratory period mainly through the depression of the post-inspiratory neuronal activity in the bulbar respiratory control mechanism.

Ethanol withdrawal alters apomorphine-induced motility

Acute administration of ethanol is accompanied by alterations in dopamine turnover and release, and chronic ethanol exposure is associated with changes in biochemical measures of dopamine receptor function. This paper presents data examining the effects of chronic ethanol exposure on behavioral responses to the dopamine receptor agonist apomorphine. Measurements of behavior were obtained through the use of an electronic motility monitor which permitted the quantification of movements in terms of their characteristic frequency components. Results are presented which indicate that apomorphine-induced movements with modal frequencies of 2 Hz and of 8-9 Hz are significantly increased during the 12 to 24 hr following ethanol withdrawal, suggesting an increase in the functional responsiveness of central dopaminergic systems.

Acute ethanol administration selectively alters localized cerebral glucose metabolism

The effects of acute ethanol administration on glucose utilization in the CNS of rat were studied using the 2-deoxyglucose technique. Cerebral glucose utilization was determined for 53 brain regions at peak and descending blood ethanol concentrations averaging 14, 26 and 66 mM. Decreased glucose utilization was the predominant finding and was observed in 20% of the regions evaluated, with median raphe, vestibular nucleus, cerebellar vermis, and various structures associated with the auditory system showing the greatest reductions. The only structures that showed increased glucose utilization were the dentate region of the hippocampus and the superior olive, and this was only apparent at a blood ethanol concentration of 14 mM.

Effect of ethanol on motor performance and hippocampal population spikes in some standard and selectively outbred rat strains

Ethanol sensitivity of Wistar and Long-Evans rats was compared in vivo and in vitro. Ethanol was more effective in reducing motor performance in Long-Evans than in Wistar rats, as determined by the tilting plane test. In addition, ethanol produced a greater reduction in the population spikes recorded from hippocampal slices (in vitro) of Long-Evans rats compared to Wistar rats. When rats from the Wistar, Long-Evans, and Sprague-Dawley strains were crossbred and then selectively outbred for high (ANT) and low (AT) sensitivity to ethanol-induced impairment of motor performance, no differences were observed in the ethanol sensitivity of the hippocampal population spike between these two strains. These data suggest that differences in ethanol sensitivity may exist among standard laboratory rodent strains. Selective outbreeding may reduce or eliminate the differences in ethanol sensitivity of brain regions or neurons other than those directly involved in producing the selected behavior. Therefore, it may be incorrect to assume a general difference in ethanol sensitivity when these traits are not coselected during outbreeding, thus indicating different neuronal pools in terms of sensitivity to ethanol.

Effects of acute ethanol administration on neocortical inhibition

The hypothesis that acutely administered ethanol could interfere with neocortical recurrent inhibition (RI) was supported. The large surface negative wave in response to antidromic stimulation of the cerebral peduncle represents a summation of inhibitory postsynaptic potentials, a measure of RI. In acute experiments on adult rats, blood alcohol levels of less than about 120 mg/100 ml slightly facilitated the surface negative wave. Higher blood alcohol levels always blocked the surface negative response. Stimulation of the somatosensory thalamic relay nuclei produced a cortical response on which ethanol had a moderate blocking effect. Conditioning-test procedures revealed that cerebral peduncle stimulation strongly blocked the thalamocortical (test) response, especially after ethanol, but thalamic stimulation (conditioning) had no effect upon the surface negative wave. This demonstrates a differential effect on the two cortical processes. Cortical RI seems to be especially sensitive to blood alcohol level, but the function of cortical RI is complex. By way of acting on RI, ethanol likely affects control of sensory input and cortical sensory organization as well as selectivity and magnitude of motor discharge.

Effects of chronic ethanol treatment on neocortex

Neocortical inhibition and neuronal morphology were studied in rats following chronic ethanol treatment (CET). In terminal acute experiments, spontaneous neuronal discharges in pair-fed and naive rats were inhibited by epicortical stimulation, a procedure known to produce postsynaptic inhibition. Few units in CET rats were inhibited by such stimulation. Cortical recurrent inhibition, indicated by a surface-negative potential in response to antidromic stimulation of the cerebral peduncle, was little affected by a challenge dose of ethanol, compared with the response in pair-fed animals. Recurrent inhibition involves inhibitory interneurons. CET apparently made inhibitory interneurons and inhibitory postsynaptic receptors less responsive to ethanol. Apical dendritic spines on some portions of pyramidal neurons increased in number with CET. This could reflect a compensatory growth in neurons not damaged by CET. The overall observations are consistent with ethanol affecting one or more specific systems of cortical motor control as opposed to its presumed general disinhibitory effect.

Ethanol tolerance of cerebellar purkinje neurons from selectively outbred mouse lines: in vivo and in vitro electrophysiological investigations

The electrophysiological activity of cerebellar Purkinje neurons was characterized in long sleep (LS: ethanol sensitive) and short sleep (SS: ethanol insensitive) mice made tolerant to ethanol. After 1 to 4 weeks of feeding on a liquid ethanol diet, mice of both lines were less sensitive to the sedative and ataxic effects of parenteral ethanol than were controls. In addition, cerebellar Purkinje cells in ethanol-fed LS and SS mice were less responsive than the controls to the depressant effects of ethanol applied via bath perfusion in vitro and via local pressure ejection application in vivo. Tolerance to the electrophysiological effects of ethanol were already apparent after 7 to 9 days on the ethanol diet, and the degree of tolerance did not increase significantly in either mouse line fed ethanol for an additional 1-3 weeks. Finally, the differences in ethanol sensitivities of naive mice (LS greater than SS) were maintained following the development of tolerance. We conclude that tolerance to both the cellular and behavioral depressant effects of ethanol can be observed after chronic feeding with ethanol in LS and SS mice, and that there are no significant differences in the degree of tolerance developed by these mice. In addition, our data suggest that the inherited differences in ethanol sensitivity between LS and SS mice, and the changes in ethanol sensitivity which occur in these mice with chronic exposure to this depressant agent, are mediated by different mechanisms.

Ethanol effects on striatal neuron activity

Cellular effects of ethanol were investigated in the rat neostriatum with local perfusion and extracellular, single unit recording techniques. Neuronal activity was modulated specifically as a function of ethanol concentration over a wide test range. At extremely low doses (10(-9) and 10(-8) M), the neuronal responses to drug perfusion were exclusively excitatory. However, at the highest doses examined (10(-8) and 10(-4) M), the results were reversed. In the midrange, a number of apparently ineffective tests were obtained, along with bimodal (excitation followed by depression) responses. The unequivocal responsiveness to ethanol at very low concentrations raises the possibility of a physiological role for the endogenous substance.

Neonatal cerebellectomy alters ethanol-induced sleep time of short sleep but not long sleep mice

The effects of neonatal cerebellectomy on ethanol-induced sleep times in long sleep (LS) and short sleep (SS) mice were investigated. Cerebellectomy did not alter the ethanol sensitivity of LS animals for loss of righting reflex. In contrast, SS mice became more sensitive to alcohol after cerebellectomy. Even so, large differences were still observed between the alcohol-induced sleep times of cerebellectomized LS and SS mice. The data indicate that, while the cerebellum must have a prominant influence on alcohol sleep time in SS animals, this brain structure is not solely responsible for the observed differences in righting reflex sensitivity to ethanol in these two mouse lines. We postulate the existence of noncerebellar central neurons with differential sensitivities to the depressant effects of ethanol in LS and SS mice.

Differential sensitivity of cerebellar purkinje neurons to ethanol in selectively outbred lines of mice: maintenance in vitro independent of synaptic transmission

The effects of ethanol on spontaneous firing of cerebellar Purkinje neurons were examined in outbred lines of mice (short-sleep, SS; and long-sleep, LS) which exhibit differential behavioral sensitivity to ethanol. In order to determine whether the differences in Purkinje cell ethanol sensitivity which are observed in situ reflect differences in intrinsic properties of Purkinje neurons, we developed an isolated in vitro preparation of mouse cerebellum. Even when synaptic transmission was largely inhibited by elevating Mg2+ and decreasing Ca2+ concentrations, Purkinje cells demonstrated stable long-term firing rates quite similar to those observed in vivo. Purkinje cells responded to superfusion of ethanol with both increases and decreases in firing rate. Inhibition of rate was more commonly observed, and was the only response which was demonstrably dose-dependent. The differential sensitivity to ethanol which we have previously reported in vivo was maintained even under under these conditions, with the LS mice being approximately 5 times more sensitive to the depressant effects of ethanol. In addition, it was shown that ethanol, at the concentrations used in these experiments, decreased the amplitude and increased the duration of single action potentials. Thus, taken together, these results suggest that the differential sensitivity of outbred lines to the soporific effects of ethanol are paralleled by differences in the sensitivity of Purkinje neurons in vitro to superfusion with ethanol. Because these differences can be observed even when synaptic transmission is largely suppressed, it would appear that these differences are intrinsic to the purkinje neurons themselves.

Cerebellar role in the differential ethanol sensitivity of long sleep and short sleep mice

Two lines of mice have been selectively bred for differential sleep time responses to ethanol. Long sleep (LS) mice sleep over an order of magnitude longer than short sleep (SS) mice. We have found that these behavioral sensitivities are also reflected in the responsiveness of cerebellar Purkinje neurons in those two mouse lines in situ and in intraocular cerebellar brain grafts. The differential sensitivity of Purkinje cells to the depressant effects of ethanol appears to be an intrinsic property of the cerebellum and shows a high genetic correlation with the hypnotic effects of this drug as measured by sleep time. Sleep time studies of neonatally cerebellectomized LS and SS mice indicate that the cerebellum is not the primary determinant of the sensitivity of these mice to the soporific effects of ethanol. The sleep time of SS, but not LS mice, was altered by cerebellectomy suggesting that the cerebellum has different influences on the ethanol-induced loss of righting reflex in these two mouse lines.

Effects of ethanol on thermoregulation

Clinical reports of accidental hypothermia in alcohol intoxicated individuals exposed to low ambient temperature ( Paton , 1983) have generally been borne out by experimental studies in healthy volunteers. Small doses of ethanol, given to human subjects at normal ambient temperature (Ta), have very little effect on body temperature but a combination of large dose, low Ta and vasodilatation provoked by strenuous exercise, causes a sharp fall in rectal temperature. In experimental animals, the use of relatively larger doses of alcohol and more extreme temperatures, both above and below the thermoneutral zone, has shown that the effect of ethanol is essentially poikilothermic, i.e. an impairment of adaptation to both heat and cold. This effect has been studied in greater detail, in relation to each of the basic thermoregulatory processes. Though small doses of alcohol may increase the metabolic rate under some circumstances, the most common effect at low Ta is inhibition of shivering and therefore reduction of thermogenesis. At the same time it tends to cause increased heat loss by cutaneous vasodilatation. This makes for a greater feeling of comfort in the cold exposed subjects but increases in rate of fall of core temperature. The combination of decreased thermogenesis and increased heat loss, despite falling body temperature, is suggestive of a lowering of the set-point of the thermoregulatory control mechanisms. Consistent with this is a slight increase in ventilatory heat loss after low doses of ethanol but larger doses cause respiratory depression, so that heat loss through the lungs is minor. However, at high Ta ethanol caused hyperthermia in experimental animals and shows enhanced lethality, so that impairment of thermoregulatory effector mechanisms seems to be at least as important as change in set-point. Studies of the effects of ethanol on electrophysiological activity of single neurons in the pre-optic area and anterior hypothalamus (POAH), biochemical activities of neuronal membranes, hypothalamic blood flow, conventional neurotransmitters, amino acid putative neurotransmitters, neuropeptides, prostaglandins and inorganic ions have all failed so far to yield a clear comprehensive picture of the mechanisms by which ethanol affects thermoregulation. In each case, contradictory evidence has been obtained concerning the consequences of ethanol administration, whether by oral, intraperitoneal, intravenous, intracerebroventricular, or direct local (POAH) route.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for genetic correlation of hypnotic effects and cerebellar Purkinje neuron depression in response to ethanol in mice

In the present study, we compared phenotypic differences in behavioral and neurophysiological responses to acute ethanol administration among eight inbred strains of mice. Genetic variation for behavioral sedation, as measured by loss of the righting reflex (sleep time) after a hypnotic dose of ethanol, was shown to be present among the inbred strain population. In addition, a large genetic component of variation in the depressant action of ethanol on the spontaneous discharge of cerebellar Purkinje neurons was found. Results from an analysis of covariance of the behavioral and electrophysiological phenotypes, measured on each mouse among the inbred strains, provided strong evidence for a high genetic correlation between sleep time and inhibition of cerebellar Purkinje neuron discharge in response to acute ethanol administration. Taken together with our previously reported data on ethanol-induced electrophysiological changes in selectively bred lines, the results described here strongly support the hypothesis that the cerebellar Purkinje neuron is one important locus for the acute soporific effects of alcohol.

Actions of drugs of abuse on brain reward systems: a reconsideration with specific attention to alcohol

Research in the areas of intracranial self-stimulation and drug self-administration has provided a substantial data base that has contributed to our understanding of brain reward mechanisms. In a recent article, Wise [83] argued that dopamine is the catecholamine critically involved in the central mediation of reward. The present paper attempts to examine the available data with particular reference to alcohol, but also with reference to opiates, and argues that the reinforcing effects of at least these drugs are primarily and directly mediated by noradrenergic rather than dopaminergic systems in the brain. It also argues, in direct contrast to Wise, that in the context of these drugs, dopamine seems to play a minor if not negligible role.

Vagal unitary responses to intestinal amino acid infusions in the anesthetized cat: a putative signal for protein induced satiety

Single unitary discharges in the nodose ganglia were recorded extracellularly in chloralose anesthetized cats while amino acid solutions were being perfused through the small intestine via implanted cannulae. Test infusions consisted of either amino acid mixtures (12 amino acids; 120 mM in all) or individual amino acids (50 mM each) dissolved in Krebs Henseleit buffer. Units which were activated by amino acid infusions were also tested with 10% glucose infusions performed in the same way. Control infusions consisted of either buffer alone or a physiological saline solution isotonic to the test solution. All perfusions were performed at 38 degrees C, pH 7.4 by means of a syringe over a 10 second period. Out of 1250 vagal units activated by electrical vagal stimulation, 92 units showed an increased firing rate in response to amino acid intestinal perfusions. Of these, only 1/7 were also responsive to glucose perfusions. Osmotic, thermal or mechanical stimuli associated with infusions did not modify vagal responses to the amino acids. Among vagal units responding only to amino acid but not to glucose infusion, some were activated in a specific manner, depending on the specific amino acid infused intraduodenally. These neurons illustrated a very strict specificity regarding the nature of chemical stimuli. The very short latency, mean of 9 sec +/- 0.7 (SE) of these vagal neurons to amino acid infusions unequivocally indicates that chemoreceptors are located at the preabsorptive level. The corresponding fibers were non-myelinated (conduction velocities: 0.8/1.4 m/sec.) and were of the C type. The functional characteristics of these vagal amino acid receptors are discussed in terms of the role of intestinal signals in short term protein satiety.

Ethanol-induced depressions in cerebellar and hippocampal neurons of mice selectively bred for differences in ethanol sensitivity: an electrophysiological study

The recently discovered profound differential sensitivity of cerebellar Purkinje (P) cells in long-sleep (LS) verus short-sleep (SS) mice to the depressant effects of locally applied ethanol was extended in this study. First, the sensitivity of Purkinje neurons from HS mice (an outbred stock of mice from which the LS and SS lines were derived), was found to be almost exactly intermediate between the values for the long-sleep and short-sleep animals. Second, no differential sensitivity in long-sleep versus short-sleep hippocampal pyramidal neurons was observed. This was true using both spontaneous and evoked activity. Third, no differential sensitivity of P cells was seen in long- versus short-sleep mice with local application of halothane. Taken together with previous reports, these data strongly suggest that whatever genetically determined central nervous alterations result in the differential soporific effects of ethanol in the two (LS and SS) mouse lines, such alterations are brain region- and depressant drug-specific rather than generalized.

Electrophysiological correlates of ethanol-induced sedation in differentially sensitive lines of mice

Acute electrophysiological effects of ethanol were studied in two lines of mice that differ markedly in their response to the soporific effects of systemic alcohol administration. Cerebellar Purkinje neurons from the genetic line that had long sleep times were one to two orders of magnitude more sensitive to the depressant effects of locally administered ethanol than those from the line that had short sleep times. The data suggest that there are genetically determined specificities in the acute effects of ethanol on central neurons and that such specificities might be used to determine which regions of the cerebellum participate in differences in behavioral responses to this substance.

Selective effect of ethanol on the vestibular nucleus neurons in the cat

Effects of intravenous administration of ethanol on the neuronal activities of the lateral vestibular nucleus (LVN) and spinal trigeminal nucleus (STN) were investigated in cats. The LVN neurons were classified into three groups according to the latency of the first spike elicited by orthodromic vestibular nerve stimulation and antidromic vestibulospinal tract stimulation: monosynaptic, polysynaptic I and polysynaptic II neurons. Ethanol of 0.2--1.6 g/kg dose-dependently suppressed the orthodromic spike generation of the monosynaptic and polysynaptic II neurons without affecting their latency and antidromic spike generation of the former neuron. The mean spike numbers of the monosynaptic and polysynaptic II neurons were significantly decreased with ethanol over 0.4 g/kg. The polysynaptic I neuron, however, remained unaffected by the drug up to 0.8 g/kg. Similarly, the spike generation of the STN relay neuron and interneuron elicited by trigeminal nerve stimulation remained unaltered with ethanol given in doses up to 0.8 g/kg. These results indicate that small doses of ethanol more selectively interfere with synaptic transmission in the LVN monosynaptic and polysynaptic II neurons than transmission in the STN relay neurons and interneurons.

Biphasic action of ethanol on single units of the dorsal hippocampus and the relationship to the cortical EEG

The effects of four doses of ethanol (100, 200, 400, 800 mg/kg) administered IV, on the spontaneous firing rate of single units in the dorsal hippocampal regin of the rat were studied. At the lower doses, a mixture of excitatory and inhibitory effects occurring in that order was seen, reflecting a biphasic action of ethanol at the level of the single neuron. As the dose increased, the excitation disappeared and successively greater degrees of response inhibition prevailed. The pattern of the fronto-cortical EEG changed from predominantly low amplitude fast activity with a few episodes of high amplitude slow activity at low doses, to more sustained episodes of slow activity at high doses. The time-response curve showed that the peak of maximum inhibition seen at the highest dose occurred with a longer latency than the peak of maximum excitation seen at the lower doses. Finally, the changes in unit firing appeared to follow four general patterns and to be correlated with the mode of fronto-cortical EEG activity.

Effects of various periods of food deprivation on serotonin turnover in the lateral hypothalamus

Preliminary results indicated enhanced serotonin turnover in the lateral hypothalamus of 24 hr food deprived rats as compared to non-deprived rats. In the present study, the periods of food deprivation were extended in ordered that the effects of 0. 24, 48 and 72 hr of food deprivation on serotonin turnover could be measured. One hr following an infusion of 3H-5-hydroxytryptamine the lateral hypothalamus was perfused with physiological bacteriostatic saline for 40 min. Samples of perfusate, which corresponds to 75--90 min post-infusion, were analyzed by thin layer chromatography for estimation of 3H-labelled precursor and metabolites. The results indicate that serotonin turnover is enhanced as a function of hours of food deprivation.

Differential effects of low doses of ethanol on the impulse activity in various regions of the limbic system

This study was a follow-up to our earlier data which indicated that the hippocampus was one of the brain areas in which ethanol had a preferential action. Rabbits were chronically implanted with electrodes in 9 brain areas associated with the hippocampus. The EEG and multiple-unit activity were recorded simultaneously in each area before and for 15 min after i.p. injection of ethanol at dosages of 0, 150, 300, or 600 mg/kg, given in random order. Subjective evaluation of EEG tracings from all brain areas did not disclose any regional differences. The incidence of hippocampal theta rhythm was depressed transiently at the 2 lower doses and was increased in some rabbits at later post-injection times after the largest dose. Quantitative analysis of the unit activity revealed several major effects of ethanol. Individual rabbits varied significantly in their degree of response. The effects of ethanol included phasic decreases and increases, which varied with the brain area and the dose. A predominant depression of MUA occurred in the septum, fimbria/fornix, entorhinal cortex, and CA1 zone of the hippocampus. Large transient increases in MUA were noted in the CA1, hippocampal commissure, and entorhinal cortex. Overall, regional differences in unit activity consisted of a relatively greater effect in the septum, CA1, and the entorhinal cortex. Conspicuously smaller effects were evident in the CA3 and dentate zones of the hippocampus.

Ethanol-induced regional and dose-response differences in multiple-unit activity in rabbits

Multiple-unit activity (MUA), recorded simultaneously from many brain areas, was used to detect the existence ahd location of "target sites" for ethanol action in rabbits with chronically implanted electrodes in 14 areas. Each of 12 rabbits received intraperitoneal injection of 300, 600, 900, and 1200 mg/kg of 20% ETOH and a saline control injection given in random order with at least a 4-day interval between injections. Large amounts of MUA data, recorded continuously for a 2-min pre-injection control period and a 15-min post-injection period, were quantified by a sensitive and unique technique. MUA changes did not correlate with alcohol-induced changes in the corresponding EEG for the same locus. Whereas visual inspection of the EEG did not disclose any regional differences in response to ethanol, both temporal and topographical differences in ethanol effect on MUA were observed. There were 14 histologically verified brain areas with adequate sample size for statistical evaluation of MUA response. At high doses, all brain areas were affected. Included among the brain areas which were least affected by low doseas were the caudate nucleus, septum, fornix, and medial forebrain bundle. Those areas that met the criteria for target sites of responding quickly (less than 5 min) to low doses (300 mg/kg) were: cerebellar cortex, cerebral cortex, hippocampus, lateral and medial geniculate nuclei, midbrain reticular formation, and pyriform cortex. In conjunction with the preliminary study [Brain Res. 70, 361 (1974], the data indicate that the most ethanolsensitive tissue is found in the various kinds of cortex, cerebellar and cerebral (both paleocortex and neocortex).