Sex dependent behavioral response to frontal cortical suction lesions in the rat

Evolution of hemispheric specialisation of antagonistic systems of management of the body's energy resources

Excellent and rich reviews of lateralised behaviour in animals have recently been published indexing renewed interest in biological theorising about hemispheric specialisation and yielding rich theory. The present review proposes a new account of the evolution of hemispheric specialisation, a primitive system of "management of the body's energy resources". This model is distinct from traditionally evoked cognitive science categories such as verbal/spatial, analytic/holistic, etc., or the current dominant neuroethological model proposing that the key is approach/avoidance behaviour. Specifically, I show that autonomic, immune, psychomotor, motivational, perceptual, and memory systems are similarly and coherently specialised in the brain hemispheres in rodents and man. This energy resource management model, extended to human neuropsychology, is termed here the "psychic tonus" model of hemispheric specialisation.

Combined 192 IgG-saporin and 5,7-dihydroxytryptamine lesions in the male rat brain: a neurochemical and behavioral study

In a previous experiment [Eur J Neurosci 12 (2000) 79], combined intracerebroventricular injections of 5,7-dihydroxytryptamine (5,7-DHT; 150 microg) and 192 IgG-saporin (2 microg) in female rats produced working memory impairments, which neither single lesion induced. In the present experiment, we report on an identical approach in male rats. Behavioral variables were locomotor activity, T-maze alternation, beam-walking, Morris water-maze (working and reference memory) and radial-maze performances. 192 IgG-saporin reduced cholinergic markers in the frontoparietal cortex and the hippocampus. 5,7-DHT lesions reduced serotonergic markers in the cortex, hippocampus and striatum. Cholinergic lesions induced motor deficits, hyperactivity and reduced T-maze alternation, but had no other effect. Serotonergic lesions only produced hyperactivity and reduced T-maze alternation. Beside the deficits due to cholinergic lesions, rats with combined lesions also showed impaired radial-maze performances. We confirm that 192 IgG-saporin and 5,7-DHT injections can be combined to produce concomitant damage to cholinergic and serotonergic neurons in the brain. In female rats, this technique enabled to show that interactions between serotonergic and basal forebrain cholinergic mechanisms play an important role in cognitive functions. The results of the present experiment in male rats are not as clear-cut, although they are not in obvious contradiction with our previous results in females.

Effects of neonatal cholinergic basal forebrain lesions on excitatory amino acid receptors in neocortex

The role of cholinergic basal forebrain projections in the modulation of cortical plasticity and associated functional changes is currently the subject of renewed attention. Excitatory amino acid receptors have been identified as mediators of cortical topographic efferent and afferent information. In addition some of these receptors, notably the NMDA and metabotropic [mGluR] type, participate in cortical plasticity. Growing evidence suggests that interactions between cholinergic and glutamatergic systems contribute to cognitive cortical functions and their anatomical and physiological substrates. Though cholinergic and glutamatergic mechanisms have both been shown to be involved in cortical morphogenesis, few studies have attempted to study their interactions in development. The present study investigates the effect of neonatal lesions to the cholinergic basal forebrain on NMDA, AMPA and mGluR receptors in BALB/CByJ mice, at two different developmental ages. We demonstrated previously that nBM lesions at birth result in transient cholinergic depletion for the first two postnatal weeks, substantial morphogenetic alterations in neocortex and cognitive deficits by adulthood. We show here that unilateral neonatal lesions result in decreases in NMDA and AMPA receptors but increases in mGluRs during the second postnatal week (PND 14). At 30 days postnatal, lesion mediated changes were attenuated, compared with PND 14, but significant sex differences in control and nBM lesioned mice were apparent. These data support the notion that cholinergic/glutamatergic interactions are important during early cortical morphogenesis. Moreover, our results highlight the fact that cholinergic as well glutamatergic developmental mechanisms are sexually dimorphic.

Sex differences in EEG in adult gonadectomized rats before and after hormonal treatment

EEG activity was recorded from the left and right parietal cortex in adult male and female Wistar rats that were gonadectomized (GNX) after puberty during 2 days without and 3 days with hormonal treatment (either testosterone propionate, 5 alpha-DHT or vehicle in males and progesterone, estradiol benzoate or vehicle in females). In contrast to EEG characteristics reported for intact rats, GNX abolished right over left parietal activation in both sexes and, sex differences in EEG interhemispheric correlation and in theta and delta relative power in the right parietal; additionally GNX males showed higher absolute power than females. Hormonal treatment reestablished interparietal asymmetry in both sexes and a lack of sex differences in absolute power, however, it was not enough to reestablish sex differences in delta and theta proportion in the right parietal nor in interhemispheric correlation. Differential effects were obtained with testosterone propionate and 5 alpha-DHT in males suggesting that activational effects of testosterone on EEG are probably exerted through testosterone or its aromatized metabolites. The results of our study indicate that the activational effects of gonadal steroids after puberty are necessary for maintaining sex differences in the EEG of the adult rat.

Developmental and hormonal factors in the sexually dimorphic, asymmetrical response to focal cortical lesions

The developmental and hormonal determinants of the lateralized response to focal cortical suction lesions were examined in a series of experiments. In an initial study, Sprague-Dawley male rats 25, 30, 55 or 90 days of age, received right unilateral focal frontocortical suction lesions. Only 90-day-old rats developed hyperactivity, suggesting a specific role for maturational factors in the production of this response. Prepubertally castrated adult male rats receiving right frontocortical suction lesions at 90 days also failed to develop hyperactivity, suggesting that sexual maturational factors and/or the presence of testosterone are necessary for the expression of this response. Testosterone implants, producing physiological relevant levels of circulating testosterone reinstated the hyperactivity response to adult cortical lesions in prepubertally castrated male rats. Similar lesions in the left hemisphere, however, did not produce hyperactivity in castrated male rats with testosterone replacement. Finally, in ovariectomized adult female rats, testosterone did not allow the expression of a hyperactivity response to right frontocortical suction lesions. Together, these results demonstrate both an organizational and permissive role for sex steroids in the sexually dimorphic asymmetrical response to cortical injury.

New evidence for distinct patterns of brain organization in rats differentiated on the basis of inherent laterality

The purpose of the present study was to search for possible relationships among diverse measures of behavioral laterality in a non-human species or to identify an index of laterality that was predictive of other non-lateralized functions. Several indices of behavioral laterality and open field activity were assessed in male and female rats before and after asymmetric neocortical ablations. Plasma adrenocorticotropin, corticosterone, and prolactin were measured following stress at sacrifice. Sex-dependent population-level lateral biases were observed preoperatively in the choice of arms in a T-maze and initial direction out of a corner of an open field. Unilateral left neocortical ablation induced a leftward bias in the T-maze in both male and female rats. The direction of rotation following the peripheral administration of amphetamine was correlated with: (a) the degree of sensitization to amphetamine; (b) preoperative open field activity in females; (c) the induction of hyperactivity following right neocortical ablation in males; (d) rotational responses to amphetamine in male rats sustaining bilateral ablations; and (e) the effect of left neocortical ablation on prolactin levels in males. We propose that these data provide new evidence for distinct patterns of brain organization in rats differentiated by a measure of inherent cerebral laterality.

Role of gender in the behavioral effects of peripheral sympathetic ingrowth

Following cholinergic denervation of the hippocampal formation, peripheral sympathetic nerves originating from the superior cervical ganglia grow into the hippocampus. As gender is known to alter the anatomy of hippocampal sympathetic ingrowth, we assessed the effect of this variable on the behavioral recovery following ingrowth. Adult male or female rats were trained on a standard version of a radial-8-arm maze task until they reached a specific learning criterion. Animals from each sex then underwent one of three surgical procedures: sham surgery, medial septal lesions plus superior cervical ganglionectomy, or medial septal lesion plus sham ganglionectomy. Reacquisition of the maze was then assessed. Prior to surgery, male animals acquired the task significantly faster than female animals. Following surgery male and female rats recovered overall performance at similar rates. However, marked group differences were observed. In males, the control group recovered faster than the group with medial septal lesion plus ganglionectomy, which recovered faster than the medial septal lesion group. In females, the control group recovered faster than the medial septal lesion group, which in turn recovered faster than the medial septal ganglionectomy group. The results of this study clearly demonstrate that gender can influence the behavioral effects of hippocampal sympathetic ingrowth. We believe that this is the first report in which gender has been shown to alter the behavioral effect of a neuronal reorganization.

Estrogen formation in the mammalian brain: possible role of aromatase in sexual differentiation of the hippocampus and neocortex

Recent studies suggest that sex differences in cognitive function may involve effects of circulating androgens on the developing cerebral cortex and hippocampus. The mechanism of these effects is not understood. In rhesus monkeys, aromatase activity is present in the hippocampus and several areas of the cerebral cortex during late fetal and early postnatal life. Similarly, work in rats and mice indicates that the hippocampus and cerebral cortex may be capable of estrogen biosynthesis during early development. These results are consistent with the hypothesis that the actions of androgens on the developing cerebral cortex and hippocampus may involve local estrogen-mediated effects similar to those responsible for differentiation of the hypothalamic mechanisms controlling reproductive function.