Seizure sensitivity and GABAergic modulation of ethanol sensitivity in selectively bred FAST and SLOW mouse lines

FAST and SLOW selected mouse lines were bred for differences in locomotor response to low-dose ethanol. FAST mice exhibit an extreme stimulant response and SLOW mice exhibit locomotor depression at the same ethanol dose. We tested the hypothesis that gamma-aminobutyric acid (GABA) systems modulate ethanol's stimulant effects by examining convulsant responses to GABAA receptor ligands, and by assessing the effects of GABAA and GABAB ligands on locomotor activity in the presence and absence of EtOH. FAST mice were more sensitive to the convulsant effects of GABAA drugs, and to one of two non-GABAergic drugs also tested. FAST and SLOW mice differed in locomotor responses to two benzodiazepines, but not to other GABAA receptor ligands. Ethanol's stimulant effects were not selectively altered by bicuculline or picrotoxin. The selected lines differed in sensitivity to the locomotor depressant effects of the GABAB agonist, baclofen. Ethanol-stimulated activity of FAST mice was inhibited by baclofen, and this effect was reversed by administration of the GABAB antagonist, CGP-35348. These GABAB receptor mediated effects were replicated in DBA/2J inbred mice that exhibit extreme sensitivity to ethanol's stimulant effects. In summary, we found moderate to strong evidence that some sites on the GABAA receptor complex were altered as a consequence of selection of FAST and SLOW mice, but found little support for GABAA mediation of EtOH-stimulated activity. In contrast, we found moderate evidence for differential alteration of GABAB receptor function; however, GABAB receptor involvement in ethanol-stimulated activity was strongly supported by results in the selected lines and an inbred strain.     

Electrophysiological interactions of ethanol with GABAergic mechanisms in the rat cerebellum in vivo

Induction of neonatal H-2 tolerance is highly efficient in most allodisparate strain combinations, with the exception of those in which neonatal recipients do not, but donor cells do, express I-E molecules. For example, less than 25% of I-E-nonexpressing B10.S mice become tolerant following neonatal injection with I-E+ (B10.AxB10.S)F1 cells. It has been hypothesized that the high rate of nontolerance observed in I-E-nonexpressing neonatal recipients of injections of I-E-bearing cells is caused by a failure to delete V beta 11+ cells in the immediate postnatal period. To test this possibility, we have examined V beta 11 expression and tolerogen-responsiveness among T cells of thymus and spleens harvested periodically from B10.S mice after neonatal inoculation of (B10.AxB10.S) F1 cells. We found that V beta 11+ cells were selectively eliminated within 1-2 days from the thymus glands of all recipient mice, B10.A-specific proliferative T cells disappeared concordantly, and the thymus glands contained donor-derived chimeric cells. Subsequently, an increasing proportion of injected mice acquired V beta 11+ thymocytes and B10.A-responsive T cells, while losing chimeric cells. However, deletion and in vitro nonreactivity were still apparent in the majority of mice at 60 days of age. We conclude that neonatal inoculation of I-E-expressing cells established thymic chimerism and caused profound elimination of V beta 11+ cells from the thymus glands of all injected mice. Therefore, the failure of the majority of neonatally injected B10.S mice to display transplantation tolerance of B10.A antigens as adults cannot be ascribed to an inability to delete I-E-reactive thymocytes.     

Role of GABA in the actions of ethanol in rats selectively bred for ethanol sensitivity

Rats from the N/Nih heterogeneous stock have been selectively bred for high (HAS) or low (LAS) initial sensitivity to injected ethanol as measured by duration of the loss of the righting reflex. The selection for ethanol sensitivity in these lines apparently has reached a maximum. These lines are useful to elucidate the central nervous system mechanisms of the genetic differences between the lines and also provide clues to the mechanisms of ethanol's action. We have found that: 1) ethanol, etomidate, and ketamine but not propofol produce different sleep times and brain levels of the drug on awakening between these two lines; 2) only ethanol, etomidate, and ketamine produced significant differences between the HAS and LAS rats in GABA-mediated stimulation of chloride uptake into brain microsacs; 3) GABA, propofol, and etomidate decreased the Kd for flunitrazepam binding to whole-brain membranes but equally in both lines. Neither ethanol nor ketamine had an effect; 4) only GABA, ethanol, and etomidate increased the Kd for TBPS binding and only GABA decreased Bmax of TBPS binding. As with the previous selection for ethanol sensitivity in mice (short and long sleep) these lines of rats have very marked line differences in GABA-mediated events, and these are correlated with the sedative effects of ethanol. From these and previous studies we know that the major differences between selected lines of mice and rats are that the mouse lines are not differentially sensitive to halothane or pentobarbital while the rat lines are. However, the mouse lines are differentially sensitive to propofol and the rat lines are not. These data should be useful in dissecting the actions of ethanol at the GABA(A) receptor.     

Electrophysiological responses to ethanol, pentobarbital, and nicotine in mice genetically selected for differential sensitivity to ethanol.

Examined cortical EEG changes induced by ethanol (4.3 and 1.4 g/kg, ip), pentobarbital (50 and 16 mg/kg), and nicotine (1.0 g/kg) in long-sleep (LS) and short-sleep (SS) male mice that were genetically selected for differential sleep times induced by a hypnotic dosage of ethanol. Ethanol (4.3 g/kg) caused EEG changes that paralleled the behavioral differences, whereas no differences between selected lines were observed following the activating dose (1.4 g/kg). Data support the notion that the known difference in ethanol sleep times is due not to greater SS sensitivity to ethanol activation but rather to greater LS sensitivity to ethanol hypnosis. No differences between selected lines were observed following 50 mg/kg pentobarbitol, which again parallels previous behavioral data. SS mice were more responsive to pentobarbital activation (16 mg/kg). Nicotine more severely reduced EEG power and heart rate in LS Ss; a continuous infusion of nicotine elicited a distinct pattern of behavioral stereotypy for each selected line, with more profound motor and reflex depression in LS Ss. The lines do not differ in rate of nicotine metabolism, hence they must differ in CNS sensitivity to nicotine. Thus, mice selectively bred for differential sensitivity to ethanol also differ in electrophysiological and behavioral responses to nicotine. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of ethanol on structural parameters of rat brain membranes: relationship to genetic differences in ethanol sensitivity

Equine leukoencephalomalacia (ELEM) affected 6 of 10 pleasure horses in adjacent paddocks at a boarding facility. Four of the 6 affected horses died or were euthanized. Two of 3 horses presented for treatment survived with complete resolution of clinical signs. Treatment was primarily supportive. Dimethyl sulfoxide, dexamethasone, flunixin meglumine and thiamine were administered as anti-inflammatory agents and to decrease or prevent cerebral edema. Fusarium monileforme was cultured from ear corn fed the affected horses. Fumonisin B1, B2 and B3 were isolated.     

Behavioral, physiological, and neuroendocrine stress responses and differential sensitivity to diazepam in two Wistar rat lines selectively bred for high- and low-anxiety-related behavior

Two Wistar rat lines, selectively bred for high-anxiety-related behavior (HAB) and low-anxiety-related behavior (LAB) in the elevated plus-maze test, were tested for the susceptibility of their behavioral characteristics to anxiolytic treatment and for their endocrine and physiological reactivity to different stressors. Injection of 1 mg/kg diazepam failed to affect line differences in coping strategy but resulted in a marked (20-fold) decrease in plus-maze anxiety in HAB rats; whereas, the anxiolytic effect was less pronounced in LAB animals. Biotelemetrical measurements revealed that HAB and LAB rats do not significantly differ in their baseline body temperature, locomotor activity, food and water intake, or in stress-induced alterations of the diurnal rhythms in these parameters. However, line differences were found in acute changes in body temperature and locomotor activity following stress exposure, LAB rats responding with a greater, albeit shorter, increase in body temperature and activity than HAB animals. Basal ACTH and corticosterone plasma levels as well as pituitary reactivity to intravenously administered CRH (40 ng/kg) were similar in both lines, although, especially in response to plus-maze exposure, HAB rats tended toward higher ACTH secretion than LAB rats. These data confirm that animals with high or low basal levels of anxiety may be a promising model for studying the mechanisms of action of anxiolytic substances. Nevertheless, the endocrine findings support the notion that the reactivity of the hypothalamo-pituitary-adrenocortical system and anxiety-related behavior can be regulated independently.     

The actions of some cannabinoid receptor ligands in the rat isolated mesenteric artery

Premature ovarian failure (POF) is a defect of ovarian development and is characterized by primary or secondary amenorrhea, with elevated levels of serum gonadotropins, or by early menopause. The disorder has been attributed to various causes, including rearrangements of a large "critical region" in the long arm of the X chromosome. Here we report identification, in a family with POF, of a gene that is disrupted by a breakpoint. The gene is the human homologue of the Drosophila melanogaster diaphanous gene; mutated alleles of this gene affect spermatogenesis or oogenesis and lead to sterility. The protein (DIA) encoded by the human gene (DIA) is the first human member of the growing FH1/FH2 protein family. Members of this protein family affect cytokinesis and other actin-mediated morphogenetic processes that are required in early steps of development. We propose that the human DIA gene is one of the genes responsible for POF and that it affects the cell divisions that lead to ovarian follicle formation.     

Effects of prenatal ethanol exposure on parvalbumin-expressing GABAergic neurons in the adult rat medial septum

Exposure of human fetuses to ethanol often results in the fetal alcohol syndrome. Animal models of fetal alcohol syndrome have been developed and used to examine the consequences of prenatal ethanol exposure on the central nervous system. The objective of this study was to determine the long-term effects of prenatal ethanol exposure on parvalbumin-expressing (PA+) GABAergic neurons of the rat medial septum. Pregnant Long-Evans rats were maintained on 1 of 3 diets from gestational day 0 to 21: an ethanol-containing liquid diet in which ethanol accounted for 35% of the total calories, a similar diet with the isocaloric substitution of sucrose for ethanol, or a lab chow control diet. Offspring were killed on postnatal day 60, and their brains were prepared for parvalbumin immunocytochemistry. Female rats exposed to the ethanol-containing diet during gestation had 42% fewer PA+ neurons in the medial septum and reduced PA+ cell density when compared with female rats exposed to the sucrose diet. Ethanol females also had fewer PA+ neurons per unit volume than sucrose females. Male rats exposed to ethanol did not display a similar reduction in PA+ neurons or density. No effect of prenatal diet was found on the area or volume of the medial septum, nor were cell diameters affected. As such, prenatal exposure to ethanol seems to reduce permanently the number of PA+ neurons in the female rat medical septum without affecting area, volume, or neuronal size. Functional implications and possible relations to the fetal alcohol syndrome are discussed.     

Contribution of GABAergic inhibition to sensitivity to cross-like figures in striate cortex

Many neurons in the cat primary visual cortex are sensitive to cruciform and corner figures consisting of two oriented lines. To determine the contribution of inhibition to this property we investigated 85 V1 neurons before and after local blockade of GABAergic inhibition by microiontophoretic application of bicuculline. Cross sensitivity was generated or enhanced by inhibition in roughly 1/3 and suppressed or diminished in another 1/3 of the cells. In the remaining 1/3 cross sensitivity was either absent or not influenced by inhibition. The results demonstrate a substantial contribution of intracortical inhibition to either establish sharp single bar orientation tuning or to generate or modulate the sensitivity of visual cortical neurons to line crossings.     

Role of rat strain in the differential sensitivity to pharmaceutical agents and naturally occurring substances

The development of drugs to combat diseases, chemicals to improve food production, or compounds to enhance the quality of life necessitates, by law, the use of laboratory animals to test their safety. In order to simulate the human condition it is necessary to choose a species in which pharmacokinetic and toxicokinetic mechanisms are established and resemble those of humans. The advantages of the use of the rat in drug and chemical toxicity testing include (a) metabolic pathway similarities to humans; (b) numerous similar anatomical and physiological characteristics; (c) a large database, which is extremely important for comparative purposes; and (d) the ease of breeding and maintenance of animals at relatively low cost. However, the choice of rat can be complicated, especially when over 200 different strains of rat are known to exist. The aim of this review is to summarize genetically determined differences in the responsiveness of rat strains to drugs and naturally occurring chemicals and to show that susceptibility is dependent on the target organ sensitivities, which may also be strain dependent. It is suggested that detailed studies of strain differences may help to clarify toxic mechanisms. Such studies are usually best conducted using inbred strains in which the genetic characteristics have been fixed, rather than in outbred stocks in which individual samples of animals may differ, the phenotype is variable, and the stocks are subject to substantial genetic drift. The fact that strains may differ also needs to be taken into account in assessing the potential hazard of the chemical, particularly when a study involves only a single strain and therefore provides no assessment of likely strain variation.     

Comparison of innate EEG parameters in rat lines selected for ethanol preference

Through bidirectional selective breeding, lines of rats that differ greatly in their voluntary alcohol drinking behavior have been developed--namely, the alcohol-preferring (P) and high-alcohol-drinking (HAD) lines and the alcohol-nonpreferring (NP) and low-alcohol-drinking (LAD) lines. The present experiments were designed to determine if an association exists between ethanol preference and features of the electroencephalogram (EEG) during various sleep-wake behaviors. Of the EEG parameters measured, only theta activity in the hippocampus revealed differences in the lines. However, these differences were not generally associated with ethanol preference. The peak frequency and distribution mean of hippocampal theta activity during REM sleep were significantly higher in NP rats than in P, HAD, and LAD rats. In addition, theta frequency during alert immobility tended to be higher in NP rats than in P, HAD, and LAD rats. A qualitative comparison of these data with published data from unselected rats further suggested that the NP rats are uniquely different with respect to theta frequency.     

Differential sensitivity of human neuroblastoma cell lines to ethanol: correlations with their proliferative responses to mitogenic growth factors and expression of growth factor receptors

Early ethanol exposure depletes neurons in the developing nervous system, however the effects on neuronal precursors are not homogeneous. Some cells are more susceptible to ethanol toxicity than others. Growth factors are important mitogens for neuronal precursors. We tested the hypothesis that the differential sensitivity of neuronal precursors to ethanol is determined by their responses to growth factors using an in vitro model (SH-SY5Y, SK-N-SH, and IMR32 neuroblastoma cells) of neuronal precursors. The three cell lines were raised in a medium containing 10% or 0% fetal calf serum. Cells were exposed to ethanol and/or a growth factor. These factors included basic fibroblast growth factor, epidermal growth factor, insulin-like growth factor-I, nerve growth factor, and platelet-derived growth factors AA and BB. The numbers of cells per culture were counted both before and after 3 days of ethanol and/or growth factor treatment. In addition, the effect of ethanol exposure on the expression of receptors for these growth factors was examined. Neuroblastoma cells displayed differential sensitivity to ethanol. The growth of SH-SY5Y and SK-N-SH cells was inhibited by ethanol in a concentration-dependent manner. Ethanol did not affect cell viability. Thus, this inhibition resulted from a reduction of cell proliferation. In contrast, IMR32 cells were not affected by ethanol (even at concentrations as high as 800 mg/dl). The response to growth factors was also heterogeneous. In serum-supplemented medium, SH-SY5Y and SK-N-SH cells were stimulated by all of the tested growth factors. For cells raised in a serum-free medium, only the nerve growth factor was ineffective. IMR32 cells, however, were unaffected by most of these growth factors, regardless of the medium conditions. Ethanol blocked the action of all growth factors tested. In general, all cells expressed the specific receptors for the six growth factors. Only the expression of the basic fibroblast growth factor, insulin-like growth factor-I, and nerve growth factor receptors were reduced by ethanol exposure. In summary, neuroblastoma cells exhibit differential susceptibility to ethanol, and this correlates with their response to mitogenic growth factors. Some growth factors are a target of ethanol toxicity. These heterogeneous effects seem to parallel ethanol-induced changes of proliferating neuronal precursors in vivo.     

Sensitivity to low doses of ethanol and pentobarbital in mice selected for sensitivity to hypnotic doses of ethanol.

Assessed sensitivity to low doses of ethanol and pentobarbital in mice that had been selectively bred with respect to ethanol sleep time (the length of time an animal remains on its back following a hypnotic dose of ethanol). The hypothesis investigated was that short-sleep (SS) Ss might be more sensitive than long-sleep (LS) Ss to excitatory effects produced by low doses of depressants. In support of this hypothesis, SS Ss were more active in an open-field test after ethanol than were LS Ss. Two experiments were conducted, using 88 LS and 88 SS Ss. The lines did not differ in performance on a rotating-rod apparatus after these same doses of ethanol, suggesting that the difference in open-field activity was not attributable to a greater impairment of locomotor activity in LS Ss. A similar difference in the open-field activity of the selected lines was observed with pentobarbital. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic determinants of sensitivity to ethanol in inbred mice.

Mice from 15 inbred strains (n?=?27–40 per strain) differed in sensitivity to ethanol-induced effects on open-field activity, hypothermia, rotarod ataxia, and anesthesia. Sensitivities to the different behavioral responses were generally uncorrelated. This suggests that the genetic determinants of behavioral sensitivity to one domain of ethanol effects are unrelated to those determining other responses. On the other hand, some variables were genetically related. For example, those strains sensitive to the loss of righting reflex induced by higher doses of ethanol showed reduced activity in the open field at lower doses and were more sensitive to ethanol-induced decreases in rearing. More generally, the pattern of results suggests that genetically influenced sensitivity to ethanol is not a monolithic phenomenon. Rather, it is specific to the particular response variable studied. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of binding parameters of sigma 1 and sigma 2 binding sites in rat and guinea pig brain membranes: novel subtype-selective trishomocubanes

Comparisons of binding parameters of [3H](+)-pentazocine and [3H]1,3-di-o-tolylguanidine (DTG) at sigma binding sites in guinea pig and rat brain membranes demonstrated that [3H](+)-pentazocine binds to a single high-affinity site, whereas [3H]DTG binds to two high-affinity sites in both species. The Kd values of the radioligands were similar in both types of membranes. However, the density of sigma 1 sites in guinea pig was significantly higher than that of rat. Novel trishomocubanes were tested for their affinities at sigma 1 and sigma 2 binding sites in guinea pig brain membranes using [3H](+)-pentazocine and [3H]DTG as the radioligands. N-(4-Phenylbutyl)-3-hydroxy-4- azahexacyclo[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecane (ANSTO-14) showed the highest affinity for the sigma 1 site (Ki = 9.4 nM) and 19-fold sigma 1/sigma 2 selectivity, as a result of increasing the alkyl chain between the cubane moiety and the aromatic ring. N-(3'-Fluorophenyl)methyl- 3-hydroxy-4-azahexacyclo[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11]dodeca ne (ANSTO-19), displayed the highest affinity for sigma 2 sites (Ki = 19.6 nM) and 8-fold sigma 2/sigma 1 selectivity due to a fluoro substitution in the meta position of the aromatic ring. These represent structurally novel lead compounds, especially for the development of selective sigma 2 receptor ligands.     

Increased sensitivity of adriamycin-selected tumor lines to CTL-mediated lysis results in enhanced drug sensitivity

The emergence of drug resistance to chemotherapeutic agents is a major cause of treatment failure in cancer therapy. Therefore, much effort has been aimed at circumventing or reversing this undesired effect. Recently, we found that tumor cell lines selected for their multidrug-resistant phenotype can also exhibit increased levels of TAP mRNA and MHC class I proteins. This raised the question of whether drug-resistant tumors are more readily recognized by MHC-restricted CTLs. In this report, we show that five of five MHC class I+ tumor cell lines grown in medium containing Adriamycin developed into variants that expressed higher levels of MHC class I than did their corresponding parental cell lines. This was not observed with a MHC class I- cell line. No similar association was noted for changes in the expression of either HER-2 or intercellular adhesion molecule 1 protein. We also found that MHC class I+ drug-selected variants were more readily lysed by MHC-restricted, tumor-associated CTLs than were the drug-sensitive parental cell lines. When the drug-selected variants were cocultured with the same CTLs to eliminate tumor cells expressing higher levels of MHC-I (MHC-Ihi), the CTL-resistant tumor cells exhibited a drug sensitivity profile similar to that of the parental cell lines that were not exposed to Adriamycin. These findings suggest that certain chemotherapeutic drugs may increase the immunogenicity of some tumors, and that CTL immunotherapy may help reverse drug resistance.     

Projections of GABAergic and cholinergic basal forebrain and GABAergic preoptic-anterior hypothalamic neurons to the posterior lateral hypothalamus of the rat

Within the basal forebrain, gamma-aminobutyric acid (GABA)-synthesizing neurons are codistributed with acetylcholine-synthesizing neurons (Gritti et al. [1993] J. Comp. Neurol. 329:438-457), which constitute one of the major forebrain sources of subcortical afferents to the cerebral cortex. In the present study, descending projections of the GABAergic and cholinergic neurons were investigated to the lateral posterior hypothalamus (LHp) through which the medial forebrain bundle passes and where another major forebrain source of subcortical afferents is situated. Retrograde transport of cholera toxin b subunit (CT) from the LHp was combined with immunohistochemical staining for glutamic acid decarboxylase (GAD) and choline acetyl transferase (ChAT) using a sequential peroxidase-antiperoxidase (PAP) technique. A relatively large number of GAD+ neurons (estimated at approximately 6,200), which represented > 15% of the total population of GAD+ cells in the basal forebrain (estimated at approximately 39,000), were retrogradely labeled from the LHp. These cells were distributed through the basal forebrain cell groups, where ChAT+ cells are also located, including the medial septum and diagonal band nuclei, the magnocellular preoptic nucleus, and the substantia innominata, with few cells in the globus pallidus. In these same nuclei, a small number of ChAT+ cells were retrogradely labeled (estimated at approximately 800), which represented only a small percentage (< 5%) of the ChAT+ cell population in the basal forebrain (estimated at approximately 18,000). Both the GAD+ and ChAT+ LHp-projecting neurons represented a small subset of their respective populations in the basal forebrain, distinct from the magnocellular, presumed cortically projecting, basal neurons. In addition to the GAD+ cells in the basal forebrain, GAD+ cells in the adjacent preoptic and anterior hypothalamic regions were also retrogradely labeled in significant numbers (estimated at approximately 5,500) and proportion (> 20%) of the total population (estimated at approximately 30,000) from the LHp. The retrogradely labeled GAD+ neurons were distributed in continuity with those in the basal forebrain through the lateral preoptic area, medial preoptic area, bed nucleus of the stria terminals, and anterior and dorsal hypothalamic areas. Of the large number of cells that project to the LHp in the basal forebrain and preoptic-anterior hypothalamic regions (estimated at approximately 66,000), the GAD+ neurons represented a significant proportion (> 15%) and the ChAT+ neurons a very small proportion (approximately 2%). The relative magnitude of the GABAergic projection suggests that it may represent an important inhibitory influence of the descending efferent output from the basal forebrain and preoptic-anterior hypothalamic regions.(ABSTRACT TRUNCATED AT 400 WORDS)     

The actions of avenaciolide and ethanol on glucose metabolism and on related enzyme activities in the isolated perfused rat liver

Six hundred and seventy five cases of attempted suicide observed in a resuscitation department were confronted with a certain number of biometeorological factors recorded daily: atmospheric pressure, air temperature, degree of insolation, precipitation, relative humidity, water vapour pressure, wind (speed and direction), hydrometeores, index of solar eruption, density of F2 layer. The confrontation is made for the two days before the intoxication and for the day when suicide is attempted. Parameters are then studied by statistical calculation (calculation of X2 and of the number of degrees of freedom). There does not seem to be any significant relationship, in spite of disconcerting series, between most meteorological factors and the number of attempted suicides observed. However, it is noted that no suicides were recorded during periods of solar eruption, and that there seems to be a marked correlation between suicide and winds, particularly according to their direction. Thus, winds charged with ionised particles seem to coincide with a high rate of self-destruction.     

Sources of GABAergic input to the inferior colliculus of the rat

We have studied the GABAergic projections to the inferior colliculus (IC) of the rat by combining the retrograde transport of horseradish peroxidase (HRP) and immunohistochemistry for gamma-amino butyric acid (GABA). Medium-sized (0.06-0.14 microliter) HRP injections were made in the ventral part of the central nucleus (CNIC), in the dorsal part of the CNIC, in the dorsal cortex (DCIC), and in the external cortex (ECIC) of the IC. Single HRP-labeled and double (HRP-GABA)-labeled neurons were systematically counted in all brainstem auditory nuclei. Our results revealed that the IC receives GABAergic afferent connections from ipsi- and contralateral brainstem auditory nuclei. Most of the contralateral GABAergic input originates in the IC and the dorsal nucleus of the lateral lemniscus (DNLL). The dorsal region of the IC (DCIC and dorsal part of the CNIC) receives connections mostly from its homonimous contralateral region, and the ventral region from the contralateral DNLL. The commissural GABAergic projections originate in a morphologically heterogeneous neuronal population that includes small to medium-sized round and fusiform neurons as well as large and giant neurons. Quantitatively, the ipsilateral ventral nucleus of the lateral lemniscus is the most important source of GABAergic input to the CNIC. In the superior olivary complex, a smaller number of neurons, which lie mainly in the periolivary nuclei, display double labeling. In the contralateral cochlear nuclei, only a few of the retrogradely labeled neurons were GABA immunoreactive. These findings give us more information about the role of GABA in the auditory system, indicating that inhibitory inputs from different ipsi- and contralateral, mono- and binaural auditory brainstem centers converge in the IC.