The size of non-hippocampal brain regions varies by season and sex in Richardson's ground squirrel.

Sex- and season-specific modulation of hippocampal size and function is observed across multiple species, including rodents. Other non-hippocampal-dependent behaviors exhibit season and sex differences, and whether the associated brain regions exhibit similar variation with sex and season remains to be fully characterized. As such, we examined the brains of wild-caught Richardson's ground squirrels (RGS; Urocitellus richardsonii) for seasonal (breeding, non-breeding) and sex differences in the volumes of specific brain areas, including: total brain volume, corpus callosum (CC), anterior commissure (AC), medial prefrontal cortex (mPFC), total neocortex (NC), entorhinal cortex (EC), and superior colliculus (SC). Analyses of variance and covariance revealed significant interactions between season and sex for almost all areas studied, primarily resulting from females captured during the breeding season exhibiting larger volumes than females captured during the non-breeding season. This was observed for volumes of the AC, mPFC, NC, EC, and SC. Where simple main effects of season were observed for males (the NC and the SC), the volume advantage favoured males captured during the NBr season. Only two simple main effects of sex were observed: males captured in the non-breeding season had significantly larger total brain volume than females captured in the non-breeding season, and females captured during the breeding season had larger volumes of the mPFC and EC than males captured in the breeding season. These results indicate that females have more pronounced seasonal differences in brain and brain region sizes. The extent to which seasonal differences in brain region volumes vary with behaviour is unclear, but our data do suggest that seasonal plasticity is not limited to the hippocampus and that RGS is a useful mammalian species for understanding seasonal plasticity in an ecologically relevant context.

The effects of season and sex on dentate gyrus size and neurogenesis in a wild rodent, Richardson's ground squirrel (Urocitellus richardsonii).

Sex and reproductive status affect hippocampal neurogenesis and dentate gyrus (DG) size in rodents. Relatively few studies, however, address these two effects simultaneously and even fewer studies address this issue in wild populations. Here, we examined seasonal and sex differences in neurogenesis and DG size in a wild, polygynous and social rodent, Richardson's ground squirrel (Uriocitellus richardsonii). Based on the behavioral ecology of this species, we predicted that both neurogenesis and DG size would be sexually dimorphic and the degree of dimorphism would be greatest in the breeding season. Using unbiased stereology and doublecortin (DCX) immunohistochemistry, we found that brain volume, DG size and number of DCX cells varied significantly between breeding and non-breeding seasons, but only brain volume and the number of DCX labeled cells differed between the sexes. Both sex and seasonal differences likely reflect circulating hormone levels, but the extent to which these differences relate to space use in this species is unclear. Based on the degree of seasonal differences in neurogenesis and the DG, we suggest that ground squirrels could be considered model species in which to examine hippocampal plasticity in an ecologically valid context.

Changes in human EEG alpha activity following exposure to two different pulsed magnetic field sequences.

The present study investigates the effects of a weak (+/-200 microT(pk)), pulsed, extremely low frequency magnetic field (ELF MF) upon the human electroencephalogram (EEG). We have previously determined that exposure to pulsed ELF MFs can affect the EEG, notably the alpha frequency (8-13 Hz) over the occipital-parietal region of the scalp. In the present study, subjects (n = 32) were exposed to two different pulsed MF sequences (1 and 2, used previously) that differed in presentation rate, in order to examine the effects upon the alpha frequency of the human EEG. Results suggest that compared to sham exposure, alpha activity was lowered over the occipital-parietal regions of the brain during exposure to Sequence 1, while alpha activity over the same regions was higher after Sequence 2 exposure. These effects occurred after approximately 5 min of pulsed MF exposure. The results also suggest that a previous exposure to the pulsed MF sequence determined subjects' responses in the present experiment. This study supports our previous observation of EEG changes after 5 min pulsed ELF MF exposure. The results of this study are also consistent with existing EEG experiments of ELF MF and mobile phone effects upon the brain.

Sex differences in object location memory and spatial navigation in Long-Evans rats.

In both humans and rodents, males typically excel on a number of tasks requiring spatial ability. However, human females exhibit advantages in memory for the spatial location of objects. This study investigated whether rats would exhibit similar sex differences on a task of object location memory (OLM) and on the watermaze (WM). We predicted that females should outperform males on the OLM task and that males should outperform females on the WM. To control for possible effects of housing environment, rats were housed in either complex environments or in standard shoebox housing. Eighty Long-Evans rats (40 males and 40 females) were housed in either complex (Complex rats) or standard shoebox housing (Control rats). Results indicated that males had superior performance on the WM, whereas females outperformed males on the OLM task, regardless of housing environment. As these sex differences cannot be easily attributed to differences in cognitive style related to linguistic processing of environmental features or to selection pressures related to the hunting gathering evolutionary prehistory of humans, these data suggest that sex differences in spatial ability may be related to traits selected for by polygynous mating strategies.

Exposure to ELF magnetic and ELF-modulated radiofrequency fields: the time course of physiological and cognitive effects observed in recent studies (2001-2005).

In 2002, we published a review of the cognitive and physiological effects of extremely low frequency magnetic fields (ELF MFs) and ELF-modulated radiofrequency fields associated with mobile phones. Since the original preparation of that review, a significant number of studies have been published using techniques such as electroencephalography, event-related potentials and positron emission tomography to investigate electromagnetic field effects upon human physiology and various measures of performance (cognitive, perceptual, behavioral). We review these recent studies, and when effects were observed, we reference the time course of observed effects (immediate or delayed). In our concluding remarks, we discuss a number of variables that are not often considered in human bioelectromagnetics studies, such as personality, individual differences and the specific laterality of ELF MF and mobile phone exposure over the brain. We also consider the sensitivity of various physiological assays and performance measures in the study of biological effects of electromagnetic fields.

Further evidence for a role of the anterior claustrum in epileptogenesis.

The anatomy of the claustrum (CLA) has been well characterized, but its functional role remains uncertain. The results of recent research suggest that the CLA may be part of a network of structures involved in seizure generalization, and we set out to test this idea. To test persistence, seizures were kindled in the anterior CLA. Following a 14-day suspension of kindling, all rats required only one stimulation to evoke a stage 5 seizure. In another experiment, groups of rats received bilateral lesions of the anterior CLA before and after amygdaloid kindling. We found that small lesions of the anterior CLA retard amygdaloid kindling, but do not block the expression of generalized seizures. Lesions produced after amygdaloid kindling resulted in a shorter seizure duration, but had no marked effect on seizure expression. Another group of rats was tested for transfer of kindling between the anterior CLA and contralateral amygdala. We found an asymmetrical transfer of kindling to the CLA from the amygdala wherein amygdaloid kindling facilitated subsequent kindling of the CLA but kindling of the anterior CLA failed to facilitate kindling of the amygdala. The results add support to the notion that the CLA contributes to the development of generalized limbic seizures.

Handedness and depression in university students: a sex by handedness interaction.

Previous research has indicated that there is an increased incidence of left-handedness in samples of depressed individuals. We administered the Beck Depression Inventory (BDI) to a sample of 541 undergraduate students. Left-handed males showed significant elevation of BDI scores. It is unlikely that this result is due to decreased right hemisphere activity or sex-role conflicts. However, one possibility is that known differences in male steroid hormones levels between right- and left-handers contributed to this effect. Press

Susceptibility to kindling and neuronal connections of the anterior claustrum.

The claustrum has been implicated in the kindling of generalized seizures from limbic sites. We examined the susceptibility of the anterior claustrum itself to kindling and correlated this with an anatomical investigation of its afferent and efferent connections. Electrical stimulation of the anterior claustrum resulted in a pattern of rapid kindling with two distinct phases. Early kindling involved extremely rapid progression to bilaterally generalized seizures of short duration. With repeated daily kindling stimulations, early-phase generalized seizures abruptly became more elaborate and prolonged, resembling limbic-type seizures as triggered from the amygdala. We suggest that the rapid rate of kindling from the anterior claustrum is an indication that the claustrum is functionally close to the mechanisms of seizure generalization. In support of our hypothesis, we found significant afferent, efferent, and often reciprocal connections between the anterior claustrum and areas that have been implicated in the generation of generalized seizures, including frontal and motor cortex, limbic cortex, amygdala, and endopiriform nucleus. Additional connections were found with various other structures, including olfactory areas, nucleus accumbens, midline thalamus, and brainstem nuclei including the substantia nigra and the dorsal raphe nucleus. The anatomical connections of the anterior claustrum are consistent with its very high susceptibility to kindling and support the view that the claustrum is part of a forebrain network of structures participating in the generalization of seizures.

Lateral and sex differences in manual gesture during conversation.

To examine whether sex differences in cerebral lateralisation for speech can be observed through lateral differences in manual gesturing during natural conversation, 100 individuals (50 male and 50 female) were observed following a procedure similar to that described by Kimura (1973a,b). For males, there was a significant increase in the number of gestures made with the right hand during speech. When males were listening, there was a significant increase in the number of gestures made with the left hand. This result was not observed in the females studied, who did not demonstrate significant manual asymmetries in gesturing during either speech or listening. This result is consistent with claims that there is a sex difference in hemispheric specialisation wherein males are more functionally lateralised than females.

The NMDA receptor antagonist, NPC 12626, reduces the pronociceptive effects of orphanin FQ and kappa opiate antinociception in the land snail, Cepaea nemoralis.

The heptadecapeptide, orphanin FQ or nociceptin (Phe-Gly-Phe-Thr-Gly-Ala-Arg-Lys-Ser-Ala-Arg-Lys-Leu-Ala-Asn-Gln), originally isolated from rat brain has been identified as an endogenous ligand for the orphan opioid-like receptor. Although orphanin FQ shares some sequence and structural homology with kappa-opioid peptides, it has been speculated to exert its effects through novel nonopioid mechanisms. Kappa opioids have also been suggested to have nonopioid actions in rodents involving the N-methyl-D-aspartate (NMDA) receptor. The present study examined the effects of the competitive NMDA antagonist, NPC 12626, on the antinociceptive effects of the specific kappa-opiate receptor agonist, U69,593, and the pronociceptive effects of orphanin FQ in an invertebrate system, the land snail, Cepaea nemoralis. NPC 12626 had no effect on the basal nociceptive sensitivity of snails, as measured by the latency of response to a thermal (40 degrees C) surface. As reported for rodents, NPC 12626 dose-dependently reduced U69,593-induced antinociception in a manner comparable to that produced by the specific kappa-opiate antagonist, nor-binaltorphimine, while slightly enhancing the antinociceptive effects of the predominately mu-opiate agonist, morphine. Similarly, NPC 12626 dose-dependently reduced the pronociceptive effects of orphanin FQ. These findings with the snail, Cepaea, indicate that NMDA systems/receptors are associated with the mediation of the nociceptive effects of both kappa opioids and orphanin FQ. They suggest an early evolutionary development and phylogenetic continuity of NMDA opioid and related neuropeptide interactions in the mediation of nociception.

Dermatoglyphic asymmetry is related to perceptual asymmetry and to interhemispheric transmission.

The numbers of ridges on the fingertips is asymmetrical between hands and is also sexually dimorphic. Most people have more ridges on the right hand (rightward dermatoglyphic asymmetry; R >) and men typically have more ridges than women. The direction of dermatoglyphic asymmetry has been shown to be related to patterns of cognitive abilities in men and women and to perceptual asymmetry in homosexual men. W e assessed presumptively heterosexual, right-handed men and women who had either R > (n = 35) or L > (n = 30) ridge count, on: (1) dichotic listening to words; (2) two tachistoscopic tasks sampling visual field asymmetries (dot location and letter identification); and (3) a tachistoscopic task designed to examine interhemispheric transmission. L > subjects had a smaller right-ear advantage than R > subjects, but this was accounted for by an increased incidence of an atypical left-ear advantage in the L > group. Visual field asymmetries were also smaller in the L > group but the asymmetry measures did not reach significance, with the exception of an increased incidence of an atypical field advantage (left) for letter recognition only. On the interhemispheric transfer task, L > subjects performed relatively faster on tasks requiring interhemispheric comparisons than did R > subjects. These findings confirm an association between the direction of dermatoglyphic asymmetry and aspects of brain organisation.

Antagonistic effects of the selective, competitive N-methyl-D-aspartate (NMDA) receptor antagonist, NPC 12626, on kappa opiate-induced analgesia in male deer mice.

The present study examined the effects of the competitive NMDA antagonist, NPC 12626, on the analgesic effects of the specific kappa opiate receptor agonist, U69,593, in male deer mice. Intraperitoneal (i.p.) administration of NPC 12626 had no effect on the basal nociceptive sensitivity of reproductive male deer mice, as measured by latency of response to a thermal (50 degrees C) surface. NPC 12626 dose-dependently (0.05-1.0 mg/kg) reduced U69,593-induced analgesia. NPC 12626 at 1.0 mg/kg attenuated U69,593-induced analgesia in a manner comparable to that produced by the specific kappa opiate antagonist, nor-binaltorphimine. In contrast, this dose of NPC 12626 potentiated the analgesia produced by the predominantly mu agonist morphine (1.0 mg/kg). The non-competitive NMDA antagonist, MK-801, which has been previously indicated to affect kappa opiate analgesia, significantly reduced at 1.0 mg/kg, but did not block, the analgesia produced by U69,593 and in contrast to NPC 12626, slightly reduced morphine-induced analgesia. These findings suggest that the NMDA antagonist, NPC 12626, may, either directly or indirectly, have effects on kappa opiate receptor mediated mechanisms.

Characteristics of dorsal and ventral striatal kindling in rats.

We examined the characteristics of kindling of seizures with stimulation of the dorsal or ventral striatum in rats. Different groups of rats carried electrodes directed towards the nucleus accumbens or the head, middle, or tail of the caudate. Thresholds for afterdischarge (AD) were high at all sites, and stimulation often produced forced motor responses (motor responses that occurred during the stimulation and were not a consequence of kindling). Kindling at sites in the accumbens proceeded more slowly than at the sites in the caudate, which did not differ among themselves. The duration of accumbens seizures increased dramatically over the course of kindling, whereas the duration of caudate seizures remained relatively short and invariant. Although the kindled seizures resembled seizures kindled from limbic sites, they also contained aspects of seizures triggered from stimulation of the anterior neocortex. We conclude that striatal kindling comprises elements of both limbic and neocortical kindling.