Lateralization of norepinephrine, serotonin and choline uptake into hippocampal synaptosomes of sinistral rats

Gender differences in association between serotonin transporter gene polymorphism and resting-state EEG activity

Human brain oscillations represent important features of information processing and are highly heritable. Gender has been observed to affect association between the 5-HTTLPR (serotonin-transporter-linked polymorphic region) polymorphism and various endophenotypes. This study aimed to investigate the effects of 5-HTTLPR on the spontaneous electroencephalography (EEG) activity in healthy male and female subjects. DNA samples extracted from buccal swabs and resting EEG recorded at 60 standard leads were collected from 210 (101 men and 109 women) volunteers. Spectral EEG power estimates and cortical sources of EEG activity were investigated. It was shown that effects of 5-HTTLPR polymorphism on electrical activity of the brain vary as a function of gender. Women with the S/L genotype had greater global EEG power compared to men with the same genotype. In men, current source density was markedly different among genotype groups in only alpha 2 and alpha 3 frequency ranges: S/S allele carriers had higher current source density estimates in the left inferior parietal lobule in comparison with the L/L group. In women, genotype difference in global power asymmetry was found in the central-temporal region. Contrasting L/L and S/L genotype carriers also yielded significant effects in the right hemisphere inferior parietal lobule and the right postcentral gyrus with L/L genotype carriers showing lower current source density estimates than S/L genotype carriers in all but gamma bands. So, in women, the effects of 5-HTTLPR polymorphism were associated with modulation of the EEG activity in a wide range of EEG frequencies. The significance of the results lies in the demonstration of gene by sex interaction with resting EEG that has implications for understanding sex-related differences in affective states, emotion and cognition.

Cerebral serotonin transporter asymmetry in females, males and male-to-female transsexuals measured by PET in vivo

The serotonergic system modulates brain functions that are considered to underlie affective states, emotion and cognition. Several lines of evidence point towards a strong lateralization of these mental processes, which indicates similar asymmetries in associated neurotransmitter systems. Here, our aim was to investigate a potential asymmetry of the serotonin transporter distribution using positron emission tomography and the radioligand [(11)C]DASB in vivo. As brain asymmetries may differ between sexes, we further aimed to compare serotonin transporter asymmetry between females, males and male-to-female (MtF) transsexuals whose brains are considered to be partly feminized. Voxel-wise analysis of serotonin transporter binding in all groups showed both strong left and rightward asymmetries in several cortical and subcortical structures including temporal and frontal cortices, anterior cingulate, hippocampus, caudate and thalamus. Further, male controls showed a rightward asymmetry in the midcingulate cortex, which was absent in females and MtF transsexuals. The present data support the notion of a lateralized serotonergic system, which is in line with previous findings of asymmetric serotonin-1A receptor distributions, extracellular serotonin concentrations, serotonin turnover and uptake. The absence of serotonin transporter asymmetry in the midcingulate in MtF transsexuals may be attributed to an absence of brain masculinization in this region.

THE RELATIONSHIPS OF DOG HIPPOCAMPUS TO SEX AND PAW PREFERENCE

Previous studies have described paw preference and asymmetry in dog brains. Electrical activity of the dorsal hippocampus also indicated the existence of hippocampal asymmetry in dogs. In the present study, the possible paw and sex-related asymmetries and right-left differences in dog hippocampus were investigated. The hippocampus was dissected and weighed. Each hippocampus was cut into slices by the slicing apparatus placed horizontally on the tissues. The volumetric measurements were performed using the formula modified from the Cavalieri principle. The present study indicated the significant sex and paw differences and no right-left asymmetry in dog hippocampi. The morphological asymmetries in normal subjects might be related to functional hippocampal asymmetries in memory or in cognitive skills.

Asymmetry of neuron numbers in the hippocampal formation of prenatally malnourished and normally nourished rats: a stereological investigation

There is considerable evidence for lateralization of hippocampal function and hemispheric asymmetry in humans. In the rat, studies have reported asymmetries in the thicknesses of layers, the volumes of hippocampal subfields, and the density of cells at specific points along the septotemporal axis. To determine if there is an asymmetry of neuron numbers and whether prenatal malnutrition affects any asymmetries, 90-day old male Sprague-Dawley rats that were either normally nourished or malnourished prenatally were perfused with 4% paraformaldehyde and the brains cut into 30-micro m sections. One interrupted series of sections through the entire hippocampus was analyzed stereologically to estimate the total number of neurons in the hilus of the dentate gyrus, the CA3/CA2 stratum pyramidale (SP), the CA1 SP, and the SP of the prosubiculum/subiculum of both hemispheres. Significant asymmetries (P < 0.05) were found in the CA1 and CA3/CA2 subfields, with the right hemisphere containing 21 and 6% fewer neurons, respectively. Malnutrition reduced neuron numbers in the CA1 subfield by 12%, but did not alter the hemispheric asymmetry. Our findings agree with previous reports of left dominant asymmetries in the rat brain and suggest that this may result from differences in total numbers of neurons.

Asymmetries in thigmotactic scanning: evidence for a role of dopaminergic mechanisms

In two experiments, the influence of spontaneous asymmetries in thigmotactic scanning was analyzed on spontaneous and drug-induced behavior in the rat. The side of the face with which an animal performed more scanning in a baseline test was defined as the dominant vibrissae side. In experiment 1, repeated testing of either spontaneous thigmotactic scanning, or scanning after apomorphine or amphetamine, yielded no evidence that rats would preferably use one side of the face for scanning, when re-exposed to the same environment. However, an asymmetry in turning was observed both under apomorphine and amphetamine, that is, turning away from the dominant vibrissae side. In experiment 2, an influence of spontaneous asymmetries in scanning was found on behavioral asymmetries induced by unilateral vibrissae removal. Only animals, in which the vibrissae of the non-dominant side had been removed, showed more scanning with the intact vibrissae side, both undrugged and after apomorphine. Turning under apomorphine was more pronounced in animals in which the vibrissae on the dominant side had been removed. These animals showed an asymmetry in turning towards the intact vibrissae side. Furthermore, in both experiments we found evidence for left/right differences in turning or scanning. The results are discussed with respect to possible endogenous substrates of asymmetry, such as within the mesostriatal dopamine system.

Directed drug distribution: adding controlled brain activity to a drug

Environmental factors can alter the state of an organism so as to influence the response to drugs. This fact is widely recognized even though the responsible mechanisms are difficult to understand and control. The capacity of environmental influences to alter local drug pharmacokinetics is rarely considered. Drug localization and resulting action within the brain are influenced by vascular blood flow factors, local concentration differences in competing neurohumours, and receptor density. These are all frequently asymmetrically represented in the brain and drug effects are correspondingly laterality dependent. Attention to regional brain pharmacokinetics and the influence of environment on regional blood flow, local neurohumor concentration, and receptor density represents an untapped opportunity to enhance the desired effect of a centrally active drug at its site of action without enhancing general systemic toxicity. Combined pharmacotherapy and psychotherapy may result in superior therapeutic responses. Psychotherapy is a potential tool deliberately to manipulate environmental factors that influence physiological and physical chemical parameters that determine drug disposition.

Aminopeptidase activity is asymmetrically distributed in selected zones of rat brain

Levels of soluble aminopeptidase (AP), measured as arylamidase activity using L-Leucine-2-Naphthylamide (Leu-2-NA) as substrate, were determined in the soluble fraction of eleven zones of rat brain. Results showed that AP activity is asymmetrically distributed in frontal cortex and hypothalamus with both left sides having significantly higher levels of AP activity, respectively, than the right sides. Simultaneously, the activities of lactate dehydrogenase (LDH) and glutamate-oxalacetate aminotransferase (GOT) were measured in the same cerebral regions; no significant difference was recorded in these activities between either side of the rat brain in any of the zones studied. Provided that aminopeptidases are involved in the degradation of some endogenously released neuropeptides, the results suggest a new mode of expression of cerebral lateralization.

Asymmetry in the hippocampal region specific for one of two closely related species of wild mice

The volumes of the components of the left and right hippocampal regions were compared in male, adult specimens of the two closely related species of wild mice, Apodemus flavicollis (yellow-necked wood mice) and Apodemus sylvaticus (long-tailed wood mice). In one of the species, Apodemus flavicollis, the component containing the deep layers of the subiculum was found to be significantly larger in the hippocampal region of the left side than it was in that of the right side. No other significant asymmetries were found in the hippocampal components of the two species. These findings indicate that significant asymmetries in localized brain regions can arise during a single speciation event.

Behavioral lateralization in the T-maze and monoaminergic brain asymmetries

Recently we have reported a marked rat lateralization in the T-maze choice. The present study examines the relationship between the ascending monoaminergic systems and the T-maze behavioral asymmetry. There were no significant differences for serotonin or norepinephrine between the T-maze preferred and non-preferred brain sides in the s. nigra, ventral tegmental area, striatum, acumbens, frontal lobe or hippocampus. Only in the hippocampus was dopamine concentration significantly greater for the brain site ipsilateral to the T-maze choice side. Previously, we reported that both apomorphine, a dopamine receptor agonist, and 6-hydroxydopamine lesion in the medial forebrain bundle of the catecholaminergic neurons affect the T-maze asymmetry; we therefore suggested that the T-maze choice could be related with the ascending dopaminergic systems. The present data strongly support this hypothesis and suggest that the DA cells involved in the spatial asymmetry in the T-maze are included in the dopaminergic mesohippocampal system.

Lateralization of spike and wave complexes produced by hallucinogenic compounds in the cat

The ability of four hallucinogenic compounds--ketamine, phencyclidine, quipazine, and SKF-10 047--to produce some specific electrical pattern in portions of the limbic system and the hemispheric lateralization of such effects were studied in cats with permanently implanted electrodes. Electronic frequency and area integrators were used to analyze the results, and the percentage change in electrographic alterations was calculated. All compounds studied produced trains of spike and wave complexes in the cingulum, rapid discharges in the amygdala complex, and slow-wave synchronous activity in the septal nucleus. Those changes predominated in the left hemisphere. At small but hallucinatory concentrations of these drugs, the cortical EEG was not affected. Exploratory movements directed toward nonexistent objects, classified as hallucinatory-like behavior, appeared simultaneous with these changes in the EEG recordings. We concluded that there could exist a relationship between the appearance of spike and wave complexes in the limbic system without epileptic signs (twitching or myoclonus) and the presence of hallucinations, and that there is a left side hemispheric lateralization of the electrographic effects, viewing cerebral dominance phenomena as a functional and fluctuating state.

Asymmetrical distribution of aminopeptidase activity in the cortex of rat brain

The levels of soluble aminopeptidase (AP) activity were measured in the right and left frontal (FC), parietotemporal (PTC) and occipital (OC) cortex of male albino rat brains. The results showed more AP activity in the left cortex than in the right. Analyzing these results further, we found that the differences are significant for frontal cortex but not for parietotemporal nor occipital cortex. However, 76% of the rats were left-predominant for AP activity in the 3 cortical areas studied.

Lack of asymmetrical distribution of receptor binding sites and of neurally active peptides within rat brain

The high affinity binding of 5 tritiated (naloxone, spiroperidol, serotonin, quinuclidinylbenzilate, dihydroalprenolol) ligands to left and right frontal cortex, hippocampus and striatum has been compared in 8-week-old male rats. No lateralization of specific binding was observed between paired brain regions. Also, no regional asymmetry of protein content was found. No significant differences in met-enkephalin and substance P contents were found between paired striata, frontal cortex, and hippocampi. These data suggest that several neurotransmitter and neuromodulator indices are symmetrically distributed within the rat brain.

Lateralization of zinc in rat brain and its relationship to a spatial behavior

Essential metals are differentially accumulated within the brain and have been related to normal neurotransmitter metabolism. Hippocampal glutaminergic pathways have the highest zinc levels in the brain, and lesions to these pathways disrupt behaviors with a spatial component. Zinc distribution may thus reflect glutaminergic activity or innervation and may have functional consequences for spatial behavior. The present data support this hypothesis, indicating that the lateral distribution of zinc between the right and left hippocampus is strongly correlated with the spatial preference of the animal (r = + 0.72). Other parameters tested but shown not to be significantly correlated with spatial preference were zinc in corpus striatum and cortex, and copper in hippocampus corpus striatum and cortex.