Neurochemical asymmetries in the albino rat's cortex, striatum, and nucleus accumbens

Microstructural properties of attention-related white matter tracts are associated with the renewal effect of extinction

The tendency to show the renewal effect of extinction appears as an intra-individually stable, reproducible processing strategy associated with differential patterns of BOLD activation in hippocampus, iFG and vmPFC, as well as differential resting-state functional connectivity between prefrontal regions and the dorsal attention network. Also, pharmacological modulations of the noradrenergic system that influence attentional processing have partially different effects upon individuals with (REN) and without (NoREN) a propensity for renewal. However, it is as yet unknown whether REN and NoREN individuals differ regarding microstructural properties in attention-related white matter (WM) regions, and whether such differences are related to noradrenergic processing. In this diffusion tensor imaging (DTI) analysis we investigated the relation between microstructural properties of attention-related WM tracts and ABA renewal propensity, under conditions of noradrenergic stimulation by means of the noradrenergic reuptake inhibitor atomoxetine, compared to placebo. Fractional anisotropy (FA) was higher in participants with noradrenergic stimulation (ATO) compared to placebo (PLAC), the effect was predominantly left-lateralized and based on the comparison of ATO REN and PLAC REN participants. In REN participants of both treatment groups, FA in several WM tracts showed a positive correlation with the ABA renewal level, suggesting higher renewal levels were associated with higher microstructural integrity. These findings point towards a relation between microstructural properties of attention-related WM tracts and the propensity for renewal that is not specifically dependent on noradrenergic processing.

Brain Asymmetry: Towards an Asymmetrical Neurovisceral Integration

Despite the ancestral evidence of an asymmetry in motor predominance, going through the inspiring discoveries of Broca and Wernicke on the localization of language processing, continuing with the subsequent noise coinciding with the study of brain function in commissurotomized patients—and the subsequent avalanche of data on the asymmetric distribution of multiple types of neurotransmitters in physiological and pathological conditions—even today, the functional significance of brain asymmetry is still unknown. Currently, multiple evidence suggests that functional asymmetries must have a neurochemical substrate and that brain asymmetry is not a static concept but rather a dynamic one, with intra- and inter-hemispheric interactions between its various processes, and that it is modifiable depending on changing endogenous and environmental conditions. Furthermore, based on the concept of neurovisceral integration in the overall functioning of an organism, some evidence has emerged suggesting that this integration could be organized asymmetrically, using the autonomic nervous system as a bidirectional communication pathway, whose performance would also be asymmetric. However, the functional significance of this distribution, as well as the evolutionary advantage of an asymmetric nervous organization, is still unknown.

Cerebellar Modulation of Mesolimbic Dopamine Transmission Is Functionally Asymmetrical

Cerebral and cerebellar hemispheres are known to be asymmetrical in structure and function, and previous literature supports that asymmetry extends to the neural dopamine systems. Using in vivo fixed potential amperometry with carbon fiber microelectrodes in anesthetized mice, the current study assessed hemispheric lateralization of stimulation-evoked dopamine in the nucleus accumbens (NAc) and the influence of the cerebellum in regulating this reward-associated pathway. Our results suggest that cerebellar output can modulate mesolimbic dopamine transmission, and this modulation contributes to asymmetrically lateralized dopamine release. Dopamine release did not differ between hemispheres when evoked by medial forebrain bundle (MFB) stimulation; however, dopamine release was significantly greater in the right NAc relative to the left when evoked by electrical stimulation of the cerebellar dentate nucleus (DN). Furthermore, cross-hemispheric talk between the left and right cerebellar DN does not seem to influence mesolimbic release given that lidocaine infused into the DN opposite to the stimulated DN did not alter release. These studies may provide a neurochemical mechanism for studies identifying the cerebellum as a relevant node for reward, motivational behavior, saliency, and inhibitory control. An increased understanding of the lateralization of dopaminergic systems may reveal novel targets for pharmacological interventions in neuropathology of the cerebellum and extending projections.

Affective Circuitry Alterations in Patients with Trigeminal Neuralgia

Trigeminal neuralgia (TN) is a severe chronic neuropathic facial pain disorder. Affect-related behavioral and structural brain changes have been noted across chronic pain disorders, but have not been well-studied in TN. We examined the potential impact of TN (37 patients: 23 with right-sided TN, 14 with left-sided TN), compared to age- and sex-matched healthy controls, on three major white matter tracts responsible for carrying affect-related signals—i.e., cingulum, fornix, and medial forebrain bundle. Diffusion magnetic resonance imaging (dMRI), deterministic multi-tensor tractography for tract modeling, and a model-driven region-of-interest approach was used. We also used volumetric gray matter analysis on key targets of these pathways (i.e., hippocampus, cingulate cortex subregions, nucleus accumbens, and ventral diencephalon). Hypotheses included: (1) successful modeling of tracts; (2) altered white matter microstructure of the cingulum and medial forebrain bundle (via changes in dMRI metrics such as fractional anisotropy, and mean, axial, and radial diffusivities) compared to controls; (3) no alterations in the control region of the fornix; (4) corresponding decreases in gray matter volumes. Results showed (1) all 325 tracts were successfully modeled, although 11 were partially complete; (2) The cingulum and medial forebrain bundle (MFB) were altered in those with TN, with dMRI metric changes in the middle (p = 0.001) and posterior cingulum (p < 0.0001), and the MFB near the ventral tegmental area (MFB-VTA) (p = 0.001). The posterior cingulum and MFB-VTA also showed unilateral differences between right- and left-sided TN patients; (3) No differences were noted at any fornix subdivision; (4) decreased volumes were noted for the hippocampus, posterior cingulate, nucleus accumbens, and ventral diencephalon. Together, these results support the notion of selectively altered affective circuits in patients with TN, which may be related to the experience of negative affect and the increased comorbidity of mood and anxiety disorders in this population.

Hemispheric Asymmetry of Development Due to Drug Exposure

BACKGROUND

A previous survey of the literature of fMRI brain activation for two risk factors, impulsivity and craving, for addiction were lateralized to the right and left hemispheres respectively. Most articles reported these findings without consideration of how lateral asymmetries might be relevant to understanding the underlying factors leading to addiction.

OBJECTIVE

The current survey is intended to extend these observations by demonstrating hemispheric asymmetry of development due to pre-natal or adolescent/adult exposure to drugs of abuse.

METHOD

Articles that reported either pre-natal or adolescent/adult exposure to drugs of abuse were collected and the hemisphere of the affected structures was tabulated to determine if, and which, drugs affected more structures in one hemisphere or the other or both together.

RESULTS

Some drugs, notably cocaine and alcohol, differentially affected left or right hemisphere structures which significantly differed depending on whether individuals were exposed prenatally or as an adolescent/adult. Cocaine tended to affect more left hemisphere structures when exposed prenatally and significantly affected more in the right when exposed as adults. Alcohol had the reverse pattern. The difference in patterns of effect between pre-natal or adult exposure was significant for both.

CONCLUSION

The results in this survey demonstrate that some drugs of abuse appear to have a right/left differential effect on structures of the brain. Further investigation into the reasons for this asymmetry may provide new insights into underlying factors of drug-seeking and addiction.

Hemispheric lateralization of resting-state functional connectivity of the ventral striatum: an exploratory study

Resting-state functional connectivity (rsFC) is widely used to examine cerebral functional organization. The ventral striatum (VS) is critical to motivated behavior, with extant studies suggesting functional hemispheric asymmetry. The current work investigated differences in rsFC between the left (L) and right (R) VS and explored gender differences in the extent of functional lateralization. In 106 adults, we computed a laterality index (fcLI) to query whether a target region shows greater or less connectivity to the L vs R VS. A total of 45 target regions with hemispheric masks were examined from the Automated Anatomic Labeling atlas. One-sample t test was performed to explore significant laterality in the whole sample and in men and women separately. Two-sample t test was performed to examine gender differences in fcLI. At a corrected threshold (p < 0.05/45 = 0.0011), the dorsomedial prefrontal cortex (dmPFC) and posterior cingulate cortex (pCC) showed L lateralization and the intraparietal sulcus (IPS) and supramarginal gyrus (SMG) showed R lateralization in VS connectivity. Except for the pCC, these findings were replicated in a different data set (n = 97) from the Human Connectome Project. Furthermore, the fcLI of VS-pCC was negatively correlated with a novelty seeking trait in women but not in men. Together, the findings may suggest a more important role of the L VS in linking saliency response to self control and other internally directed processes. Right lateralization of VS connectivity to the SMG and IPS may support attention and action directed to external behavioral contingencies.

Investigation of the effects of 'piperazine-containing party pills' and dexamphetamine on interhemispheric communication using electroencephalography

BACKGROUND

'Piperazine-containing party pills' were marketed and sold as legal alternatives to methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) until 2008 in New Zealand. The major constituents of these 'pills' were benzylphenylpiperazine (BZP) and trifluoromethylphenylpiperazine (TFMPP). Despite their popularity, there is a paucity of knowledge about their central effects in humans. This study investigated their effects on human neural processing using electroencephalographic techniques.

METHODS

A randomised, double-blind, placebo-controlled study investigated the effects of an acute dose of these compounds on the interhemispheric transfer of information (IHTT) using the Poffenberger task. Reaction time data were also collected. Healthy, right-handed males were given an oral dose of either BZP (n = 13) (200 mg), TFMPP (n = 15) (60 mg), a combination of BZP + TFMPP (n = 15) (100 mg/30 mg), dexamphetamine (n = 16) (20 mg), or placebo (n = 23) and tested both before and 120 min after drug administration.

RESULTS

A mixed factorial repeated measures analysis of variance of absolute N160 latency and contrast analysis revealed that only TFMPP (F (1,77) = 17.30, p ≤ 0.001) significantly reduced the absolute N160 latency. Analysis of the IHTT revealed that only TFMPP (F (1,77) = 5.266, p ≤ 0.02) significantly reduced the IHTT, while BZP, BZP + TFMPP and dexamphetamine had no effect. Contrast analysis revealed that both TFMPP (F (1,77) = 17.30, p ≤ 0.001) and placebo (F (1,77) = 15.08, p ≤ 0.001) preserved the laterality of information transfer from one hemisphere to the other. Reaction time (p > 0.05) was not significantly affected by any of the drug treatments.

CONCLUSIONS

The usual directional asymmetry (i.e. faster R-to-L transfer relative to L-to-R) observed in healthy control group was absent following the administration of either BZP, BZP + TFMPP or dexamphetamine. Surprisingly, lateralised hemispheric function was not affected by TFMPP. Our findings highlight how the administration of BZP, TFMPP and BZP + TFMPP leads to changes in the pattern of information transfer.

High Oestradiol Replacement Reverses Response Memory Bias in Ovariectomised Female Rats Regardless of Dopamine Levels in the Dorsal Striatum

Oestrogens influence memory system bias in female rats such that high levels of oestrogen are associated with place (or spatial) memory use, and low oestrogen levels with response (or habitual) memory use. Moreover, striatal-dependent response memory is sensitive to dopamine transmission in the dorsal striatum, and oestrogens have been shown to affect dopamine release in that brain area. In the present study, the effects of oestrogens and dopamine transmission on multiple memory system bias were explored in ovariectomised rats receiving low or high 17β-oestradiol replacement under saline, autoreceptor-activating doses of the dopamine D2 receptor agonist, apomorphine (50 and 80 μg/kg), or amphetamine (0.5 mg/kg) administration. Furthermore, dorsal striatal dopamine release was measured after administration of the same drug conditions using in vivo microdialysis. As expected, high oestradiol rats predominantly used place memory, whereas the opposite pattern was observed in low oestradiol rats. However, the high apomorphine dose statistically significantly altered memory bias in high oestradiol rats from predominant place to predominant response memory, with a similar trend in the low apomorphine dose and the amphetamine group. There was no effect of drugs on memory bias in low oestradiol rats. Rats with high oestradiol replacement receiving amphetamine exhibited greater dorsal striatal dopamine release than low oestradiol replacement rats, and this difference was amplified in the right hemisphere. Furthermore, a logistic regression analysis revealed that oestradiol, but not dorsal striatal dopamine levels, significantly predicted response memory bias. These findings provide further evidence that oestradiol modulates memory system bias, and also that memory bias is changed by systemic apomorphine administration. However, although oestradiol affects dopamine transmission in the dorsal striatum in a lateralised manner, this does not predict memory system bias.

Sexual dimorphism and brain lateralization impact behavioral and histological outcomes following hypoxia-ischemia in P3 and P7 rats

Neonatal cerebral hypoxia-ischemia (HI) is a major cause of neurological disorders and the most common cause of death and permanent disability worldwide, affecting 1-2/1000 live term births and up to 60% of preterm births. The Levine-Rice is the main experimental HI model; however, critical variables such as the age of animals, sex and hemisphere damaged still receive little attention in experimental design. We here investigated the influence of sex and hemisphere injured on the functional outcomes and tissue damage following early (hypoxia-ischemia performed at postnatal day 3 (HIP3)) and late (hypoxia-ischemia performed at postnatalday 7 (HIP7)) HI injury in rats. Male and female 3- (P3) or 7-day-old (P7) Wistar rats had their right or left common carotid artery occluded and exposed to 8% O2 for 1.5h. Sham animals had their carotids exposed but not occluded nor submitted to the hypoxic atmosphere. Behavioral impairments were assessed in the open field arena, in the Morris water maze and in the inhibitory avoidance task; volumetric extent of tissue damage was assessed using cresyl violet staining at adult age, after completing behavioral assessment. The overall results demonstrate that: (1) HI performed at the two distinct ages cause different behavioral impairments and histological damage in adult rats (2) behavioral deficits following neonatal HIP3 and HIP7 are task-specific and dependent on sex and hemisphere injured (3) HIP7 animals presented the expected motor and cognitive deficits (4) HIP3 animals displayed discrete but significant cognitive impairments in the left hemisphere-injured females (5) HI brain injury and its consequences are determined by animal's sex and the damaged hemisphere, markedly in HIP3-injured animals.

Hormonal modulation of catecholaminergic neurotransmission in a prenatal stress model

Our laboratory has a long-standing interest in the effects of prenatal stress (PS) on various neurotransmitter pathways and the morphology of the developing brain as well as in behavioural aspects of the offspring. Employing a commonly used PS paradigm in which the dams were subjected to restraint stress during the last week of gestation, we observed that several of these pathways were altered in the offspring brain. In this chapter, we will summarize and discuss the results obtained with the main catecholaminergic pathways, namely dopamine (DA) and norepinephrine (NE). In our hands, PS produces an increase in dopamine D2-type receptors in limbic areas, a decreased DA release after amphetamine stimulation in prefrontal cortex (PFC) and an increase in NE release in the same area of the adult offspring brain. In addition, DA uptake is altered at prepubertal stages that persist through adulthood. However, the expression of the step-limiting enzyme of the DA synthesis, tyrosine hydroxylase (TH), is only impaired at early stages of development after PS in the neuronal bodies. At the nuclear regulation level, dopaminergic transcription factors Nurr1 and Ptx3 showed a high vulnerability to PS showing changes along the lifespan. It was striking to observe that many impairments observed in most of these pathways differed depending on whether they were tested before or after puberty indicating a particular sensitivity of the systems to variations in gonadal hormones peaks. In fact, we observed that PS induced long-term effects on the male offspring reproductive system and spermatogenesis development, particularly by inducing a long-term imbalance of circulating sexual hormone levels. Our findings suggest that PS exerts long-term effects on various neurotransmitter pathways altering the normal connectivity between brain areas. Since the developing forebrain was shown to be influenced by androgen exposure, and PS was shown to disrupt prenatal testosterone surges, our results suggest that prenatal insults might be affecting the organizational role of androgens during brain development and differentially modulating their activational role during pubertal brain maturation.

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.

A comparison of neural responses to appetitive and aversive stimuli in humans and other mammals

Distinguishing potentially harmful or beneficial stimuli is necessary for the self-preservation and well-being of all organisms. This assessment requires the ongoing valuation of environmental stimuli. Despite much work on the processing of aversive- and appetitive-related brain signals, it is not clear to what degree these two processes interact across the brain. To help clarify this issue, this report used a cross-species comparative approach in humans (i.e. meta-analysis of imaging data) and other mammals (i.e. targeted review of functional neuroanatomy in rodents and non-human primates). Human meta-analysis results suggest network components that appear selective for appetitive (e.g. ventromedial prefrontal cortex, ventral tegmental area) or aversive (e.g. cingulate/supplementary motor cortex, periaqueductal grey) processing, or that reflect overlapping (e.g. anterior insula, amygdala) or asymmetrical, i.e. apparently lateralized, activity (e.g. orbitofrontal cortex, ventral striatum). However, a closer look at the known value-related mechanisms from the animal literature suggests that all of these macroanatomical regions are involved in the processing of both appetitive and aversive stimuli. Differential spatiotemporal network dynamics may help explain similarities and differences in appetitive- and aversion-related activity.

Brain hemispheric differences in the neurochemical effects of lead, prenatal stress, and the combination and their amelioration by behavioral experience

Brain lateralization, critical to mediation of cognitive functions and to "multitasking," is disrupted in conditions such as attention deficit disorder and schizophrenia. Both low-level lead (Pb) exposure and prenatal stress (PS) have been associated with mesocorticolimbic system-mediated executive-function cognitive and attention deficits. Mesocorticolimbic systems demonstrate significant laterality. Thus, altered brain lateralization could play a role in this behavioral toxicity. This study examined laterality of mesocorticolimbic monoamines (frontal cortex, nucleus accumbens, striatum, midbrain) and amino acids (frontal cortex) in male and female rats subjected to lifetime Pb exposure (0 or 50 ppm in drinking water), PS (restraint stress on gestational days 16-17), or the combination with and without repeated learning behavioral experience. Control males exhibited prominent laterality, particularly in midbrain and also in frontal cortex and striatum; females exhibited less laterality, and this was primarily striatal. Lateralized Pb ± PS induced neurotransmitter changes were assessed only in males because of limited sample sizes of Pb + PS females. In males, Pb ± PS changes occurred in left hemisphere of frontal cortex and right hemisphere of midbrain. Behavioral experience modified the laterality of Pb ± PS-induced neurotransmitter changes in a region-dependent manner. Notably, behavioral experience eliminated Pb ± PS neurotransmitter changes in males. These findings underscore the critical need to evaluate both sexes and brain hemispheres for the mechanistic understanding of sex-dependent differences in neuro- and behavioral toxicity. Furthermore, assessment of central nervous system mechanisms in the absence of behavioral experience, shown here for males, may constitute less relevant models of human health effects.

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.

Gestational restraint stress and the developing dopaminergic system: an overview

Prenatal stress exerts a strong impact on fetal brain development in rats impairing adaptation to stressful conditions, subsequent vulnerability to anxiety, altered sexual function, and enhanced propensity to self-administer drugs. Most of these alterations have been attributed to changes in the neurotransmitter dopamine (DA). In humans; dysfunction of dopaminergic system is associated with development of several neurological disorders, such as Parkinson disease, schizophrenia, attention-deficit hyperactivity disorder, and depression. Evidences provided by animal research, as well as retrospective studies in humans, pointed out that exposure to adverse events in early life can alter adult behaviors and neurochemical indicators of midbrain DA activity, suggesting that the development of the DA system is sensitive to disruption by exposure to early stressors. The purpose of this article is to provide a general overview of published studies and our own study related to the effect of prenatal insults on the development of DA metabolism and biology, focusing mainly in articles involving prenatal-restraint stress protocols in rats. We will also attempt to make a correlation between theses alterations and DA-related pathological processes in humans.

Lateralized and sex-dependent behavioral and morphological effects of unilateral neonatal cerebral hypoxia-ischemia in the rat

Neonatal cerebral hypoxia-ischemia (HI) is an important cause of neurological deficits. The Levine-Rice model of unilateral HI is a useful experimental tool, but the resulting brain damage is mainly restricted to one hemisphere. Since the rat presents morphological and biochemical asymmetries between brain hemispheres, behavioral outcome from this model is probably dependent on which hemisphere is damaged. We here investigated the effects of sex and lesioned hemisphere on the outcome of open field, plus maze, inhibitory avoidance and water maze tasks in adult rats previously submitted to neonatal unilateral HI. Females were more active than males in some of studied parameters and males presented better spatial learning. Hypoxia-ischemia caused spatial deficits independently of sex or damaged hemisphere. Right-HI increased locomotion only in males and caused working memory in females and on aversive learning in both males and females. Morphological analysis showed that right-HI animals presented greater reduction of ipsilateral striatum area, with females being more affected. Interestingly, males showed greater hippocampal volume. These results show that task performance and cerebral damage extension are lateralized and sex-dependent, and that the right hemisphere, irrespective of sex, is more vulnerable to neonatal cerebral hypoxia-ischemia.

Effects of reversible inactivation of the ventral tegmental area on the acquisition and expression of morphine-induced conditioned place preference in the rat

The mesolimbic dopaminergic system that projects from the ventral tegmental area (VTA) to the nucleus accumbens is critical for initiation of opioid reinforcement and reward-related effects of drugs of abuse. In the present study, the effects of reversible inactivation of VTA on acquisition and expression of morphine-induced conditioned place preference (CPP) were investigated in rats. One hundred and eighty-one adult male albino Wistar rats were used in these experiments. Reversible inactivation of VTA was done through the unilateral and bilateral intra-VTA microinjection of 2% lidocaine during the acquisition and expression of morphine (5 mg/kg; s.c.)-induced CPP. Animal displacement, conditioning score and locomotor activity were recorded by Ethovision software. The results showed that bilateral but not unilateral intra-VTA administration of lidocaine significantly decreases the acquisition (P<0.01) and expression (P<0.05) of morphine-induced CPP compared to their respective saline-microinjected groups. Moreover, intra-VTA administration of lidocaine had no effect on locomotor activity in these experiments. Our results further support the idea that VTA may play an important role in the acquisition of morphine-induced CPP. In addition, there is no functional lateralization in the VTA for acquisition and/or expression of morphine-induced CPP in the rat.

Hippocampal asymmetry in exploratory behavior to vasoactive intestinal polypeptide

The effects of vasoactive intestinal polypeptide (VIP) microinjected uni- or bilaterally into the CA1 hippocampal area of male Wistar rats at a dose of 10, 50 and 100 ng on exploratory behavior were examined. VIP microinjected bilaterally at a high dose (100 ng) significantly decreased the horizontal movements, while at low doses (10 and 50 ng) had no effect on the exploratory activity. Microinjections of VIP into the left hippocampal CA1 area at doses 50 and 100 ng suppressed the exploratory activity, while right-side VIP administration at a dose 100 ng significantly increased horizontal movements compared to the respective controls. Vertical activity was stimulated only by VIP administered into the right hippocampal CA1 area at the three doses used. Neither bilateral nor left injections of VIP induced changes in the vertical movements. The main finding was the presence of hippocampal asymmetry in exploratory behavior to unilateral microinjections of VIP depending on the dose and the microinjected hemisphere.

Hippocampal asymmetry in serotonergic modulation of learning and memory in rats

The modulation of learning and memory after left or right microinjections of the selective 5-HT1A receptor agonist 8-OH-DPAT and of the 5-HT1A receptor antagonist NAN190 into the hippocampal CA1 area of male Wistar rats was studied. Microinjections of 8-OH-DPAT (1 microg) into the right or left CA1 hippocampal area produced a significant decrease in the number of avoidances in a shuttle box. The impairing effect of 8-OH-DPAT was more pronounced when injected into the right hippocampus compared to the left one. Microinjections of NAN190 (1 microg) into the right or left CA1 hippocampal area produced a significant increase in the number of avoidances in a shuttle box. Right microinjections of NAN190 increased the number of avoidances more strongly than compared to left injections. These effects on learning and memory were more pronounced after injection of either of the serotonergic agents into the right CA1 hippocampal area compared to the left. The stronger memory-modulating effect after injection of 8-OH-DPAT or NAN190 into the right CA1 hippocampal area suggests a rightward bias in the rat.

Memory enhancement induced by post-training intrabasolateral amygdala infusions of beta-adrenergic or muscarinic agonists requires activation of dopamine receptors: Involvement of right, but not left, basolateral amygdala

Previous findings indicate that the noradrenergic, dopaminergic, and cholinergic innervations of the basolateral amygdala (BLA) modulate memory consolidation. The current study investigated whether memory enhancement induced by post-training intra-BLA infusions of a beta-adrenergic or muscarinic cholinergic agonist requires concurrent activation of dopamine (DA) receptors in the BLA. Rats with implanted BLA cannulae were trained on an inhibitory avoidance (IA) task and, 48 h later, tested for retention. Infusions of the beta-adrenergic agonist clenbuterol into the right BLA, but not the left, enhanced retention, and concurrent infusions of the nonspecific DA receptor antagonist cis-Flupenthixol (Flu) blocked the enhancement. Post-training infusions of the muscarinic agonist oxotremorine into the right BLA also enhanced retention, and concurrent infusions of Flu blocked this effect. Additional experiments investigated whether memory modulation was lateralized to the right BLA. Post-training DA infusions into the right BLA, but not the left, enhanced retention. Post-training infusions of lidocaine or muscimol, which impair retention when infused bilaterally, had no effect when infused unilaterally into either the right or left BLA. These findings, together with earlier work, suggest that the dopaminergic system in the BLA is critically involved in memory modulation induced by noradrenergic and cholinergic influences. Additionally, these findings indicate that the enhancement, but not impairment, of memory consolidation is lateralized to the right BLA.

Hemisphere-specific effects on serotonin but not dopamine innervation in the nucleus accumbens of gerbils caused by isolated rearing and a single early methamphetamine challenge

The aim of this study was twofold: We examined whether serotonin (5-HT) and dopamine (DA) innervations of the nucleus accumbens are lateralised and whether the environment or the combination with an early pharmacological impact might interfere with the postnatal maturation of the monoaminergic innervation. Male gerbils were assigned to either enriched rearing (ER) or isolated rearing (IR). Animals from both rearing conditions additionally received a single dose of either methamphetamine [MA (50 mg/kg ip)] or saline on postnatal day 14. DA and 5-HT fibres of the adult animals (postnatal day 90-110) were immunocytochemically stained and fibre densities were quantified in nucleus accumbens core and shell of both the left and right hemisphere. Our data demonstrate that the DA and 5-HT innervation is not lateralised in saline-treated animals of both rearing conditions. IR increases the DA fibre density in both hemispheres of saline controls, whereas an additional MA treatment reverses this effect. In both ER and IR groups, MA provokes an excessive 5-HT fibre in growth of only the right hemisphere. The combination of IR with MA induces right-side asymmetries of the 5-HT fibre density in both the core and shell. From the data obtained, we conclude that the maturation of the monoaminergic innervation of the nucleus accumbens is vulnerable to postnatal stimuli. The subtle "innervation imbalance" observed in our studies is consistent with previously reported effects in other brain regions of this animal model and may be causative for behavioural disturbances.

Postnatal maturation of cortical serotonin lateral asymmetry in gerbils is vulnerable to both environmental and pharmacological epigenetic challenges

Long-term effects of postnatal differential rearing conditions and/or early methamphetamine (MA) application on serotonin (5-HT) fibre density were investigated in several cortical areas of both hemispheres of gerbils. The aim of this study was twofold: (1) Is the 5-HT fibre innervation of the cerebral cortex lateralised, and (2) if so, do postnatal environmental conditions and/or an early drug challenge interfere with development of 5-HT cerebral asymmetries? For that purpose, male gerbils were reared either under semi-natural or restricted environmental and social conditions, under both conditions once (on postnatal day 14) being treated with either a single dose of MA (50 mg/kg, i.p.) or saline. On postnatal day 110, 5-HT fibres were immunohistochemically stained and innervation densities quantified in prefrontal cortex, insular cortex, frontal cortex, parietal cortex, and entorhinal cortex. It was found that (1) 5-HT innervation in the cerebral cortex was clearly lateralised; (2) direction and extent of this asymmetry were not uniformly distributed over the different areas investigated; (3) both early methamphetamine challenge and rearing condition differentially interfered with adult 5-HT cerebral asymmetry; (4) combining MA challenge with subsequent restricted rearing tended to reverse the effects of MA on 5-HT cerebral asymmetry in some of the cortical areas investigated; and (5) significant responses in 5-HT cerebral asymmetry only occurred in prefrontal and entorhinal association cortices. The present findings suggest that the ontogenesis of cortical laterality is influenced by epigenetic factors and that disturbances of the postnatal maturation of lateralised functions may be associated with certain psychopathological behaviours.

The acetylcholine fiber density of the neocortex is altered by isolated rearing and early methamphetamine intoxication in rodents

Alterations in the cholinergic physiology of the brain were the first to be observed when research on environmental influences on postnatal brain development began 35 years ago. Since then, the effects of isolated rearing (IR) or early pharmacological insults have been shown not only on the physiology, but also the anatomy of a variety of transmitter systems. The cholinergic fiber density, however, still remained to be assessed. We therefore used a histochemical procedure to stain cholinergic fibers in the brains of young adult gerbils reared either in groups in enriched environments or isolated in standard makrolon cages. Half of the animals from each rearing condition had received a single high dose of methamphetamine on postnatal day 14. Fiber densities were measured by computerized image analysis in the medial and orbital prefrontal cortex (PFC), dysgranular and granular insular cortex, sensorimotor cortices, and the entorhinal cortex of both hemispheres. Isolation rearing increased the cholinergic fiber densities in the prefrontal cortices of the left hemisphere and in the entorhinal cortex of the right hemisphere by about 10%, with no effect in the respective contralateral side. The early methamphetamine intoxication showed no influence in prefrontal and entorhinal cortices, but diminished the acetylcholine (ACh) innervation of the forelimb area of cortex in both hemispheres in IR gerbils and of the left hemisphere in ER gerbils, and reduced the acetylcholine innervation in the hindlimb area in both sides in both rearing groups. These results demonstrate that (a) cholinergic fiber density is differentially regulated in different cortical areas and (b) the plasticity of the cholinergic system can only be understood in the interplay with other neuromodulatory innervations.

Sex-specific development of cortical monoamine levels in mouse

Several mental health disorders exhibit sex differences in monoamine levels associated with dimorphic cortical ontogeny. Studies in rodents support the notion that monoamines can profoundly modulate morphogenesis. Here, we show significant sex and hemisphere differences in BALB/cByJ mice on postnatal day 3 for dopamine (DA) and serotonin (5-TH), supporting the notion that sex differences in early monoaminergic ontogeny may result in dimorphic cortical development. Such sex differences may also influence differential behavioral and/or clinical outcomes.

Neonatal cerebral hypoxia-ischemia causes lateralized memory impairments in the adult rat

Neonatal hypoxia-ischemia (HI) has been extensively studied in a rat model characterized by unilateral brain damage (Rice-Vannucci Model). However, as well as in humans, each rat brain hemisphere is distinctly involved in cognitive functions, as for example retrieval of emotionally based memory, and neurochemical asymmetries have been described. In this paper we investigated whether hypoxia-ischemia could cause distinct cognitive deficits depending on which hemisphere is damaged. Seven-day-old male Wistar rats were submitted to permanent occlusion of left or right common carotid artery and were exposed to a mixture of 8% oxygen-92% nitrogen for 2.5 h. On adulthood, these rats were trained in step-down inhibitory avoidance and in two tasks in the Morris water maze. Both experimental groups (right and left lesioned) showed a deficit of retrieval in the inhibitory avoidance task compared to controls, although rats with right hemisphere lesion showed a significantly greater deficit than the left damaged group (P<0.05). In the Morris maze, both damaged groups presented cognitive deficits in the reference memory task (P<0.05), however only the right damaged group had an impairment in the working memory task. Brain coronal areas, at levels +1.20 and -3.30 mm from bregma of both HI groups were smaller than those of control, with no differences between the right and left damaged groups (P<0.05). These results show that cerebral hypoxia-ischemia in neonatal rats causes asymmetric behavioral outcomes depending on which of the hemispheres is lesioned and support the hypothesis of lateralization of cognitive functions in the rodent brain.

Asymmetrical development of the monoamine systems in 2,4-dichlorophenoxyacetic acid treated rats

The purpose of this study was to determine whether the regional brain biogenic amine levels in adult rats were altered by pre- and post-natal exposure to 2,4-dichlorophenoxyacetic acid (2,4-D). Pregnant rats were daily orally exposed to 70 mg/kg per day of 2,4-D from gestation day (GD) 16 to post-partum day (PPD) 23. After weaning, the pups were assigned to one of two subgroups: T1 fed with untreated diet up to post-natal day (PND) 90 and T2 (maintained with 2,4-D diet up to PND 90). In addition, we wanted to know the effect of 2,4-D on lateralization in the monoamine systems of the basal ganglia of these adult rats and whether there was any correlation with the behavioral developmental pattern previously reported by us. In this study the content of noradrenaline (NA) was significantly increased in substantia nigra (SN) while it decreased in cerebellum in male and female rats of T2 group. The decreased dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovallinic acid (HVA) contents in cerebellum, midbrain, ventral tegmental area (VTA) and prefrontal cortex (PFc) showed an alteration in the mesocorticolimbic system. However, an increase of DA in SN and of DOPAC and HVA in nucleus accumbens (NAc) in both sexes and of DA and DOPAC (only in females) in striatum was detected. The contents of serotonin (5-hydroxytryptamine, 5-HT) were significantly increased in both sexes in PFc, striatum (St), midbrain, SN and cerebellum. Variations of any monoamine levels in NAc and VTA were determined. T1 rats were irreversibly altered: a diminution in DA and/or DOPAC levels in PFc, midbrain, VTA and cerebellum was determined. Indolamines of these rats were increased in both sexes in PFc and St. There was also a large increase in 5-HT levels in midbrain of male rats. Although no changes in the dopaminergic system with respect to their control values in any side of these brain structures were observed, DA and DOPAC levels were found to be decreased in the right side with respect to the left side in striata and accumbens nuclei in T2 female rats supporting the behavioral rotation previously registered by us in these rats. In addition, the increased 5-HT content detected in both the right and left striata observed in this study could be the answer to the behaviors observed and to the early alterations in dopamine in basal ganglia by 2,4-D in neonatal exposed rats, mediated by a serotonergic modulation on the dopaminergic system.

The neurobiological consequences of early stress and childhood maltreatment

Early severe stress and maltreatment produces a cascade of neurobiological events that have the potential to cause enduring changes in brain development. These changes occur on multiple levels, from neurohumoral (especially the hypothalamic-pituitary-adrenal [HPA] axis) to structural and functional. The major structural consequences of early stress include reduced size of the mid-portions of the corpus callosum and attenuated development of the left neocortex, hippocampus, and amygdala. Major functional consequences include increased electrical irritability in limbic structures and reduced functional activity of the cerebellar vermis. There are also gender differences in vulnerability and functional consequences. The neurobiological sequelae of early stress and maltreatment may play a significant role in the emergence of psychiatric disorders during development.

Developmental neurobiology of childhood stress and trauma

Severe early stress and maltreatment produces a cascade of events that have the potential to alter brain development. The first stage of the cascade involves the stress-induced programming of the glucocorticoid, noradrenergic, and vasopressin-oxytocin stress response systems to augment stress responses. These neurohumors then produce effects on neurogenesis, synaptic overproduction and pruning, and myelination during specific sensitive periods. Major consequences include reduced size of the mid-portions of the corpus callosum; attenuated development of the left neocortex, hippocampus, and amygdala along with abnormal frontotemporal electrical activity; and reduced functional activity of the cerebellar vermis. These alterations, in turn, provide the neurobiological framework through which early abuse increases the risk of developing post-traumatic stress disorder (PTSD), depression, symptoms of attention-deficit/hyperactivity, borderline personality disorder, dissociative identity disorder, and substance abuse.

Dopaminergic lateralisation in the forebrain: relations to behavioural asymmetries and anxiety in male Wistar rats

Neurochemical lateralisation has been demonstrated in dopaminergic systems in the rat brain, and it has been suggested that such lateralisation might contribute to asymmetric and emotional behaviour. Here, we investigated dopaminergic brain lateralisation in relation to spontaneous and drug-induced behavioural asymmetries, and to emotional behaviour in a sample of 24 male Wistar rats. Asymmetric behaviour was measured in the open field in the undrugged state and after a systemic challenge with the muscarinic receptor antagonist scopolamine (0.5 mg/kg). Emotional behaviour was measured in the elevated plus-maze. Dopaminergic lateralisation was assessed by means of a post-mortem analysis of tissue dopamine (DA) and dihydroxyphenyl acetic acid (DOPAC) content. We found higher DOPAC/DA ratios in the neostriatum, ventral striatum, frontal cortex and amygdala of the right hemisphere. In the open field, the complete sample of rats did not show a left/right asymmetry in spontaneous behaviour, whereas systemic scopolamine induced a left-sided preference in thigmotactic scanning. A correlational analysis yielded individual relationships between behaviour and post-mortem neurochemistry, since lateralisation of DOPAC/DA ratios in favour of the right ventral striatum was related to right-side thigmotaxis. Furthermore, a right dopaminergic lateralisation in the frontal cortex was associated with lower anxiety. The study indicates that asymmetries in ventral striatal dopamine might contribute to side preferences in thigmotactic scanning while frontal dopaminergic lateralisation might influence emotional processing.

Lateralized learning and memory effects of angiotensin II microinjected into the rat CA1 hippocampal area

The effects of angiotensin II (ANG II) microinjected unilaterally (left or right) and bilaterally (left and right) at a dose of 0.5 microg (0.5 nmol) into the CA1 hippocampal area of male Sprague Dowley rats on learning and memory (shuttle box) were studied. Bilateral microinjections of ANG II improved learning, i.e. increased the number of avoidances during the two training days as compared to the respective controls microinjected with saline. ANG II facilitated learning and memory, especially when microinjected into the left CA1 hippocampal area as compared to the respective controls microinjected with saline. Left-side microinjection of ANG II increased the number of avoidances on the first and second training day as compared to the right-side microinjection of ANG II. These findings suggest asymmetric effects of ANG II on cognitive processes in hippocampus.

Behaviour laterality in male rats: influence of practice and stress

During recent decades, the existence of cerebral and behavioural asymmetries has been manifested in many different animal species. In this work, the asymmetric spatial preference recorded in the water T-maze has been analysed. Fifty-five male rats were tested in this maze for 8 consecutive days. Spatial preference, the number of times each arm was chosen, and the percentages of animals that showed right, left, or no spatial preference were calculated. The results show the evolution of this asymmetric behaviour. Most of the animals tested preferred the right arm (populational laterality). Recently, the influence of factors such as stress and practice in the process of acquiring this behaviour has been investigated. We used 40 male rats divided into two groups with two different stress levels: water temperature at 21 degrees C and 14 degrees C. Our results, based on these two criteria, hypothesize that both variables, stress and practice, are involved in the acquisition of spatial preference behaviour.

Asymmetrical influence of mesocortical dopamine depletion on stress ulcer development and subcortical dopamine systems in rats: implications for psychopathology

The effects of left, right or bilateral depletion of the mesocortical dopamine innervation (medial prefrontal and anterior cingulate) with 6-hydroxydopamine were examined in male Sprague-Dawley rats tested for susceptibility to cold restraint-induced gastric stress pathology. All three types of lesions tended to potentiate the development of stress pathology (i.e. ulceration) in comparison to restrained shams, but only right cortical dopamine depletion produced a highly significant increase. The results support a protective role for mesocortical dopamine in helping the organism cope with stressful situations, and extend previous findings suggesting that dopamine activation in the right cortex is preferentially associated with uncontrollable stress. The right cortex is hypothesized to be at the top of a hierarchy in the processing of such stressful inputs, and endogenous dopaminergic modulation facilitates adaptive responses. Subcortical dopamine terminal regions were also examined for dopamine content and turnover. In addition to depleting cortical dopamine, the three lesion groups showed highly specific alterations in the status of subcortical dopamine systems, compared to either restrained or non-restrained shams. Left brain lesions resulted in significant bilateral increases in amygdala dopamine turnover. Right cortical lesions induced significant bilateral reductions of striatal dopamine content. Bilateral lesions increased dopamine content in the left amygdala and decreased dopamine in the right nucleus accumbens. Also in this group, dopamine turnover was increased in the right nucleus accumbens and decreased in the right amygdala. The data suggest that increases in stress vulnerability induced by cortical lesions may be related, in part, to neurochemical alterations in subcortical structures previously shown to modulate gastric stress pathology. The results also indicate that brain organization is inherently asymmetrical with respect to the regulation of responses to stress, which may be of significance for human psychopathology and its exacerbation by stress.

Asymmetrical modulation of immune reactivity in left- and right-biased rats after ipsilateral ablation of the prefrontal, parietal and occipital brain neocortex

We report here on the lateralized brain immunomodulation in male Wistar rats, a phenomenon related to the rotational bias of animal and the site of cortical lesion. Rats assigned to left- and right-rotators in a cylindrical Plexiglass rotometer were subjected to the ablation of the ipsilateral prefrontal cortex (PFC), parietal cortex (PC) and occipital cortex (OC) and sensitized with bovine serum albumin (BSA) in complete Freund's adjuvant. Intact and sham-lesioned left-biased animals demonstrated increased Arthus and delayed hypersensitivity skin reactions and antibody production to BSA in comparison with corresponding right-biased animals. PFC ablation decreased humoral and cellular immune responses to BSA in left- but increased in right-biased rats. Lesioning of PC decreased humoral immune reactions in left- but increased in right-rotating animals. OC ablation failed to produce immunological abnormalities. These results suggest that immunopotentiation is associated with the left neocortex, and immunosuppression with the right neocortex. The prefrontal cortex appears to be particularly associated with immune reactions.

Left/right nigrostriatal asymmetry in susceptibility to neurotoxic dopamine depletion with 6-hydroxydopamine in rats

Male Sprague-Dawley rats were investigated for the existence of a left/right hemispheric population asymmetry in the extent of striatal dopamine depletion following unilateral lesions with 6-hydroxydopamine (6-OHDA) in the left or right substantial nigra. Four doses of 6-OHDA were employed (with left and right lesion groups at each dose). Analysis of striatal dopamine depletion revealed significant main effects not only for dose of 6-OHDA, but also for side of lesion, with right-lesioned rats having greater dopamine depletion across doses. In a group of non-lesioned rats, randomly selected from this population, striatal dopamine turnover showed a significant right-sided bias. It is suggested that the latter functional asymmetry may have been responsible for the neurotoxic depletion asymmetry seen in lesioned animals, and that side of lesion should be considered when attempting to produce consistent and maximal dopamine depletion in large scale studies with the unilateral 6-OHDA lesion paradigm.

Hippocampal asymmetry in the behavioral responses to the 5-HT1A receptor agonist 8-OH-DPAT

The present study examined the behavioral responses of rats to unilateral and bilateral injections of the selective serotonin 1A (5-HT1A)-receptor agonist 8-hydroxydipropylaminotetralin hydrobromide (8-OH-DPAT) 1 microgram into the hippocampal CA1 area of male Wistar rats. 8-OH-DPAT increased locomotor activity, which was most pronounced with injections into the left hippocampus. The agonist impaired learning and memory (shuttle-box), especially when injected into the right hippocampus. The elevated plus-maze experiments showed that neither left nor right nor bilateral hippocampal injections of 8-OH-DPAT produced any anxiogenic effect. However, with Vogel's conflict test, right injections of 8-OH-DPAT produced anxiety. The present study has revealed hippocampal asymmetry in the behavioral responses to the 5-HT1A-receptor agonist 8-OH-DPAT.

Distribution of brain monoamines in left- and right-handed mice injected with bacillus Calmette-Guerin

Concentrations of brain monoamines from various cerebral structures were determined in right and left sides of the brain from female mice selected for paw preference and injected or not with BCG 8 weeks before. BCG-induced changes in brain monoamine distribution in prefrontal cortex, medial hypothalamus and brain stem were only observed in right-handers. In the posterior hypothalamus, even though there was no BCG effect, norepinephrine asymmetry observed in right-handed controls was suppressed after BCG-injection. Moreover, BCG-induced brain monoamine changes in right-handers mainly involved the right hemisphere except the NE decrease in brain stem which was left-sided. This work demonstrates that the injection of BCG leads to long lasting asymmetrical changes in brain monoamine distribution that furthermore depend on behavioral lateralization of mice.

Brain lateralization and immunomodulation

The two sides of the brain may be differently involved in the modulation of immune responses as demonstrated by lesional and behavioral approaches in rodents. Lesions of right or left neocortex induced opposite effects on various immune parameters including mitogen-induced lymphoproliferation, interleukin-2 production, macrophage activation or natural killer cell activity. This animal model, useful to elucidate whereby the brain and the immune system can communicate, appears to be suitable for studying the immune perturbations observed during stroke in humans. Brain asymmetry in modulation of immune reactivity may also be demonstrated in intact animal using a behavioral paradigm. The direction of a lateralized motor behavior ie paw preference in a food reaching task, correlated with an asymmetrical brain organization, was shown to be associated with lymphocyte reactivity, natural killer cell activity and auto-antibody production. The association between paw preference and immune reactivity in mice varies according to the immune parameters tested and is a sex-dependent phenomenon in which genetic background may be involved. The experimental models for investigating asymmetrical brain modulation of the immune system should be useful for studying several physiological, pathological and genetic aspects of neuroimmunomodulation.

Serotonergic mechanisms in the nucleus accumbens affected by chronic desipramine treatment

The effects of repeated treatment of rats with desipramine on 5-HT mechanisms within the nucleus accumbens (NAS) have been studied in a functional model. Local microinjections of 5-HT, quipazine as well as 5-HT1A receptor agonist buspirone, 8-OH-DPAT and NDO-008, inhibited rat locomotor activity in the open-field test. The effect of 5-HT and buspirone was blocked by serotonergic receptor antagonists methysergide and cyanopindolol, respectively. Chronic, but not acute treatment of rats with desipramine (10 mg/kg, PO, twice a day for 21 days, tests were performed 24 h after the last dose) significantly attenuated behavioral depression after 5-HT and quipazine microinjections, while the effect of buspirone was left unchanged. On the basis of present data, it may be concluded that whereas both accumbens 5-HT1A and 5-HT2 receptors appear to be important to regulation of animals' motility, only 5-HT2 receptors seem to be the most likely targets of antidepressive treatment. These data, along with previously reported changes in limbic noradrenergic and dopaminergic activity after antidepressive treatment, may explain the energizing influence of drugs and electroconvulsive shocks on psychomotor retardation, a part of endogenous depression.

Asymmetrical effects of cortical ablation on brain monoamines in mice

Neurochemical changes induced by right or left cortical ablation which have previously been described to have immunological effects were investigated in mice. Catecholamine and indolamine levels were determined in the contralateral cortex and in subcortical structures involved in immunoregulation 14 and 60 days after unilateral cortical ablation. Unilateral cortical ablation induced profound and widespread changes in the contralateral cortex but also in subcortical regions of both sides at 14 days after surgery. Lesions of the left neocortex appeared mainly to affect the activity of serotoninergic inputs to the right neocortex, whereas ablations of the right cortex influenced the activity of the catecholaminergic inputs to the left. Sixty days after surgery, modifications in monoamine levels were observed only in the ipsilateral, but not contralateral, subcortical regions, the only exception being that DA turnover in the tuberoinfundibular system remained lowered in both hemispheres after either right or left cortical ablations. Furthermore, some asymmetrical effects of cortical lesions depended on functional brain lateralization as assessed by paw preference. It may be hypothesized that some neurochemical modifications induced by unilateral cortical lesions are, at least partially, responsible for the immunological perturbations observed after cortical ablation.

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.

Asymmetric distribution of brain monoamines in left- and right-handed mice

Biogenic amine distributions analyzed in the cerebral neocortex, striatum, anterior hypothalamus, and bulbospinal region, were compared between both hemispheres of left- and right-handed mice. The handedness of mice was determined using a paw preference test. The animals were tested 5 times, once every two weeks, and the biochemical analysis was performed two weeks after the last behavioral evaluation. The results indicated that (1) asymmetrical monoaminergic concentrations exist in the mouse brain. Monoamine contents were found to be higher in the right parietal cortex and anterior hypothalamus than in the left ones; (2) besides the behavioral expression of handedness, left- and right-handed subpopulations of mice differ according to asymmetrical distributions of cortical and bulbospinal NE contents as well as DA turnover of the tuberoinfundibular system.

Cerebral lateralization as a source of interindividual differences in behavior

Cerebral laterality can no longer be considered an exclusively human trait, as over the last 15 years there has been an emergence of data to suggest that animal brains are also lateralized. Morphologic, chemical and behavioral indices of brain asymmetry in the rodent have been reported, and it is suggested that variations in the magnitude and direction of these indices are determined by a complex interaction of genetic, hormonal and experiential factors. Interindividual differences in cerebral laterality have been shown to covary with, or predict, individual differences in spatial behavior and stress reactivity, as well as susceptibility to stress pathology and drug sensitivity. Such findings suggest that it is possible to study individual differences in lateralized brain function through the use of animal models.

Alterations in behavioral and striatal dopamine asymmetries induced by prenatal stress

We investigated the effects of maternal noise and light stress, randomly applied throughout pregnancy, on the development of behavioral and neurochemical asymmetries in the rat offspring. This form of maternal stress resulted in a rightward positioning of the tail of both sexes soon after birth as opposed to the leftward bias in controls. At adulthood, prenatally stressed offspring showed a change in directional bias compared to controls with a preponderance of left turns after amphetamine. In the males, this was expressed as a reduction in directional preference, while in females a reversal occurred of their dominant turning direction from right (controls) to left. We also observed a reduction in dopamine turnover rates in the left corpora striata of stressed offspring of both sexes. Again, in the females, this change was particularly marked and resulted in a reversal towards the right hemisphere. The findings from this study are consistent with the possibility that the alterations in cerebral asymmetries induced by prenatal stress may underly the decrease in the ability of the offspring to cope with anxiety provoking situations.

Sodium diethyldithiocarbamate protects against the MPTP-induced inhibition of immune responses in mice

The effects of 1-methyl-4-phenyl - 1,2,3,6-tetrahydropyridine (MPTP) on immune parameters, and the restorative influence of sodium diethyldithiocarbamate (DTC) or deprenyl were evaluated in mice. The concentrations of dopamine (DA), 3-methoxytyramine (3-MT), 3-4-dihydroxyphenyl acetic acid (DOPAC), and homovanillic acid (HVA), were concomitantly measured in the striatum. MPTP depressed T-cell responses. DTC restored these responses as well as the concentration of striatal DA. Deprenyl had no effect on the concentrations of DA and its metabolites, yet it modified the immune responses alike MPTP. The findings suggest a dopamine pathway could be involved in the brain-controlled immunostimulation afforded by DTC.

The asymmetry of 3H-imipramine binding may predict psychiatric illness

The Bmax and Kd values for 3H-imipramine binding were measured in post-mortem human brains from drug-free selected psychiatric subject homicide victims (n = 15) and normal controls (n = 15). The two groups were comparable in age and gender. The number of imipramine binding sites (Bmax) in the frontal cortices of psychiatric subjects had significantly higher Bmax values in the left hemisphere than in the right hemisphere. Inversely, the number of imipramine binding sites (Bmax) in the frontal cortices of normal controls were significantly higher in the right brain than in the left brain. It was postulated that the inhibiting effect of central serotonin (5-HT) has weakened in psychiatric cases, therefore the change of presynaptic serotonergic activity might be associated with psychiatric illness in the left hemisphere of human brain.