Innate behaviors are shaped by contingencies built during evolutionary history. On the other hand, environmental stimuli play a significant role in shaping behavior. In particular, a short period of environmental enrichment can enhance cognitive behavior, modify effects of stress on learned behaviors and induce brain plasticity. It is unclear if modulation by environment can extend to innate behaviors which are preserved by intense selection pressure. In the present report we investigate this issue by studying effects of relatively short (14-days) environmental enrichment on two prominent innate behaviors in rats, avoidance of predator odors and ability of males to attract mates. We show that enrichment has strong effects on both the innate behaviors: a) enriched males were more avoidant of a predator odor than non-enriched controls, and had a greater rise in corticosterone levels in response to the odor; and b) had higher testosterone levels and were more attractive to females. Additionally, we demonstrate decrease in dendritic length of neurons of ventrolateral nucleus of hypothalamus, important for reproductive mate-choice and increase in the same in dorsomedial nucleus, important for defensive behavior. Thus, behavioral and hormonal observations provide evidence that a short period of environmental manipulation can alter innate behaviors, providing a good example of gene-environment interaction.
Viral vectors bearing protective transgenes can decrease neurotoxicity after varied necrotic insults. A neuron that dies necrotically releases glutamate, calcium and reactive oxygen species, thereby potentially damaging neighboring neurons. This raises the possibility that preventing such neuron death via gene therapy can secondarily protect neighboring neurons that, themselves, do not express a protective transgene. We determined whether such “good neighbor” effects occur, by characterizing neurons that, while uninfected themselves, are in close proximity to a transgene-bearing neuron. We tested two genes whose overexpression protects against excitotoxicity: anti-apoptotic Bcl-2, and a calcium-activated K+ channel, SK2. Using herpes simplex virus type 2-mediated transgene delivery to hippocampal cultures, we observed “good neighbor” effects on neuronal survival following an excitotoxic insult. However, in the absence of insult, “bad neighbor effects” could also occur (i.e., where being in proximity to a neuron constitutively expressing one of those transgenes is deleterious). We also characterized the necessity for cell-cell contact for these effects. These phenomena may have broad implications for the efficacy of gene overexpression strategies in the CNS.
ischemia; excitotoxicity; gene therapy; glutamate; kainic acid; HSV; hippocampus
Neuronal apoptosis following ischemia can be mediated by a caspase-dependent pathway, which involves the mitochondrial release of cytochrome c that initiates a cascade of caspase activation. In addition, there is a caspase-independent pathway, which is mediated by the release of apoptosis-inducing factor (AIF). Using caspase-inhibitor gene therapy, we investigated the roles of caspases on the mitochondrial release of cyt c and the release of AIF. Specifically, we used herpes simplex virus-1 amplicon vectors to ectopically express a viral caspase inhibitor (crmA or p35) in mixed cortical cultures exposed to oxygen/glucose deprivation. Overexpression of either crmA or p35 (but not the caspase-3 inhibitor DEVD) inhibited the release of AIF; this suggests that there can be cross-talk between the caspase-dependent and the ostensibly caspase-independent pathway. In addition, both crmA overexpression and DEVD inhibited cyt c release, suggesting a positive feedback loop involving activated caspases stimulating cyt c release.
Cytochrome c; Apoptosis-Inducing Factor; Oxygen Glucose Deprivation
The basolateral complex of the amygdala (BLA) is uniquely affected by steroid hormones. While glucocorticoids, the adrenal hormones released during stress, increase the excitability of BLA neurons, estrogen decreases it.
In this study, we used a vector designed to express a chimeric gene that contains the GC-binding domain of the GC receptor (GR) and the DNA binding domain of the E receptor (ER) (“ER/GR”) in infected neurons; as a result, it transduces GC signals into estrogenic ones. We microinfused ER/GR bilaterally into the BLA of rats to determine whether it would impair fear conditioning, a valuable BLA-dependent paradigm for studying the neural basis of emotional memory.
Expression of ER/GR in the BLA caused robust expression of the transgene and a significant disruption of both auditory and contextual long-term fear memory consolidation, while fear learning and post-shock freezing remained intact.
These data show that dual gene therapy with ER/GR may be a useful tool for understanding the role of steroid hormones in the storage of traumatic memories.
Fear conditioning; glucocorticoids; estrogen; amygdala; gene therapy; memory
Mice lacking the Kv1.1 potassium channel α subunit encoded by the Kcna1 gene develop recurrent behavioral seizures early in life. We examined the neuropathological consequences of seizure activity in the Kv1.1−/− (“knock-out”) mouse, and explored the effects of injecting a viral vector carrying the deleted Kcna1 gene into hippocampal neurons.
Morphological techniques were used to assess neuropathological patterns in hippocampus of Kv1.1−/− animals. Immunohistochemical and biochemical techniques were used to monitor ion channel expression in Kv1.1−/− brain. Both wild-type and knockout mice were injected (bilaterally into hippocampus) with an HSV1 amplicon vector that contained the rat Kcna1 subunit gene and/or the E.coli lacZ reporter gene. Vector-injected mice were were examined to determine the extent of neuronal infection.
Video/EEG monitoring confirmed interictal abnormalities and seizure occurrence in Kv1.1−/− mice. Neuropathological assessment suggested that hippocampal damage (silver stain) and reorganization (Timm stain) occurred only after animals had exhibited severe prolonged seizures (status epilepticus). Ablation of Kcna1 did not result in compensatory changes in expression levels of other related ion channel subunits. Vector injection resulted in infection primarily of granule cells in hippocampus, but the number of infected neurons was quite variable across subjects. Kcna1 immunocytochemistry showed “ectopic” Kv1.1 α channel subunit expression.
Kcna1 deletion in mice results in a seizure disorder that resembles – electrographically and neuropathologically – the patterns seen in rodent models of temporal lobe epilepsy. HSV1 vector-mediated gene transfer into hippocampus yielded variable neuronal infection
Epilepsy; Gene therapy; Hippocampal pathology; Knock-out; Potassium channel; Seizures
Mental stress modifies both cholinergic neurotransmission and alternative splicing in the brain, via incompletely understood mechanisms. Here, we report that stress changes brain microRNA (miR) expression and that some of these stress-regulated miRs regulate alternative splicing. Acute and chronic immobilization stress differentially altered the expression of numerous miRs in two stress-responsive regions of the rat brain, the hippocampal CA1 region and the central nucleus of the amygdala. miR-134 and miR-183 levels both increased in the amygdala following acute stress, compared to unstressed controls. Chronic stress decreased miR-134 levels, whereas miR-183 remained unchanged in both the amygdala and CA1. Importantly, miR-134 and miR-183 share a common predicted mRNA target, encoding the splicing factor SC35. Stress was previously shown to upregulate SC35, which promotes the alternative splicing of acetylcholinesterase (AChE) from the synapse-associated isoform AChE-S to the, normally rare, soluble AChE-R protein. Knockdown of miR-183 expression increased SC35 protein levels in vitro, whereas overexpression of miR-183 reduced SC35 protein levels, suggesting a physiological role for miR-183 regulation under stress. We show stress-induced changes in miR-183 and miR-134 and suggest that, by regulating splicing factors and their targets, these changes modify both alternative splicing and cholinergic neurotransmission in the stressed brain.
Stress; microRNA; miR-183; miR-134; SC35; Cholinergic
Research with experimental stroke models has identified a wide range of therapeutic proteins that can prevent the brain damage caused by this form of acute neurological injury. Despite this, we do not yet have safe and effective ways to deliver therapeutic proteins to the injured brain, and this remains a major obstacle for clinical translation. Current targeted strategies typically involve invasive neurosurgery, whereas systemic approaches produce the undesirable outcome of non-specific protein delivery to the entire brain, rather than solely to the injury site. As a potential way to address this, we developed a protein delivery system modeled after the endogenous immune cell response to brain injury. Using ex-vivo-engineered dendritic cells (DCs), we find that these cells can transiently home to brain injury in a rat model of stroke with both temporal and spatial selectivity. We present a standardized method to derive injury-responsive DCs from bone marrow and show that injury targeting is dependent on culture conditions that maintain an immature DC phenotype. Further, we find evidence that when loaded with therapeutic cargo, cultured DCs can suppress initial neuron death caused by an ischemic injury. These results demonstrate a non-invasive method to target ischemic brain injury and may ultimately provide a way to selectively deliver therapeutic compounds to the injured brain.
Dephosphorylated and activated glycogen synthase kinase (GSK) 3β hyperphophorylates β-catenin, leading to its ubiquitin-proteosome-mediated degradation. β-catenin-knockdown increases while β-catenin overexpression prevents neuronal death in vitro; in addition, protein levels of β-catenin are reduced in the brain of Alzheimer’s patients. However, whether β-catenin degradation is involved in stroke-induced brain injury is unknown. Here we studied activities of GSK3 β and β-catenin, and the protective effect of moderate hypothermia (30 °C) on these activities after focal ischemia in rats. The results of Western blot showed that GSK3 β was dephosphorylated at 5 and 24 hours after stroke in the normothermic (37 °C) brain; hypothermia augmented GSK3β dephosphorylation. Because hypothermia reduces infarction, these results contradict with previous studies showing that GSK3β dephosphorylation worsens neuronal death. Nevertheless, hypothermia blocked degradation of total GSK3β protein. Corresponding to GSK3β activity in normothermic rats, β-catenin phosphorylation transiently increased at 5 hours in both the ischemic penumbra and core, and the total protein level of β-catenin degraded after normothermic stroke. Hypothermia did not inhibit β-catenin phosphorylation, but it blocked β-catenin degradation in the ischemic penumbra. In conclusion, moderate hypothermia can stabilize β-catenin, which may contribute to the protective effect of moderate hypothermia.
Focal ischemia; hypothermia; GSK-3β; β-catenin
Apoptosis, a predominant cause of neuronal death after stroke, can be executed in a caspase-dependent or apoptosis inducing factor (AIF)-dependent manner. Herpes Simplex Virus (HSV) vectors expressing caspase inhibitors p35 and crmA have been shown to be neuroprotective against various excitotoxic insults. Here we further evaluated the possible neuroprotective role of p35 and crmA in a rat stroke model. Overexpression of p35, but not crmA, significantly increased neuronal survival. Results of double immunofluorescence staining indicate that compared with neurons infected with crmA or control vectors, p35-infected neurons had less active caspase-3 expression, cytosolic cytochrome c and nuclear AIF translocation.
cerebral ischemia; apoptosis; caspase inhibitor; crmA; p35; gene therapy; stroke
Parasite Toxoplasma gondii blocks the innate aversion of rats for cat urine, putatively increasing the likelihood of a cat predating a rat. This is thought to reflect an adaptive behavioral manipulation, because Toxoplasma can reproduce only in cat intestines. While it will be adaptive for the parasite to cause an absolute behavioral change, fitness costs associated with the manipulation itself suggest that the change be optimized and not maximized. We investigate these conflicting suggestions in the present report. Furthermore, exposure to cat odor causes long-lasting acquisition of learnt fear in the rodents. If Toxoplasma manipulates emotional valence of cat odor rather than just sensory response, infection should affect learning driven by the aversive properties of the odor. As a second aim of the present study, we investigate this assertion. We demonstrate that behavioral changes in rodents induced by Toxoplasma infection do not represent absolute all-or-none effects. Rather, these effects follow a non-monotonous function dependent on strength of stimulus, roughly resembling an inverted-U curve. Furthermore, infection affects conditioning to cat odor in a manner dependent upon strength of unconditioned stimulus employed. Non-monotonous relationship between behavioral manipulation and strength of cat odor agrees with the suggestion that a dynamic balance exists between benefit obtained and costs incurred by the parasite during the manipulation. This report also demonstrates that Toxoplasma affects emotional valence of the cat odor as indicated by altered learned fear induced by cat odor.
fear; behavioral manipulation; dose-response; parasitism; parasite; conditioning
In recent years the classic view that glucocorticoids, the adrenal steroids secreted during stress, are universally anti-inflammatory has been challenged at a variety of levels. It was first observed that under some circumstances, acute GC exposure could have pro-inflammatory effects on the peripheral immune response. More recently, chronic exposure to GCs has been found to have pro-inflammatory effects on the specialized immune response to injury in the central nervous system. Here we review the evidence that in some cases, glucocorticoids can increase pro-inflammatory cell migration, cytokine production, and even transcription factor activity in the brain. We consider how these unexpected effects of glucocorticoids can co-exist with their well-established anti-inflammatory properties, as well as the considerable clinical implications of these findings.
Glucocorticoids; stress; inflammation; LPS; stroke; ischemia; cytokines; NFκB; brain; central nervous system
Reactive oxygen species contribute to neuronal death following cerebral ischemia. Prior studies using transgenic animals have demonstrated the neuroprotective effect of the antioxidant, copper/zinc superoxide dismutase (SOD1). In this study we investigated whether SOD1 overexpression using gene therapy techniques in non-transgenic animals would increase neuronal survival. A neurotropic, herpes simplex virus-1 (HSV-1) vector containing the SOD1 gene was injected into the striatum either before or after transient focal cerebral ischemia. Striatal neuron survival at two days was improved by 52% when vector was delivered 12–15 hours prior to ischemia and by 53% when vector delivery was delayed 2 hours following ischemia. These data add to the growing literature which suggests that an antioxidant approach, perhaps by employing gene therapy techniques, may be beneficial in the treatment of stroke. (According to the guidline, it is mandatory to include classification terms here. But I did not find them –HZ)
copper; zinc superoxide dismutase; gene therapy; stroke, focal ischemia, cerebral ischemia
In recent decades, the general trend in the criminal justice system in the USA has been to narrow the range of insanity defences available, with an increasing dependence solely on the M'Naghten rule. This states that innocence by reason of insanity requires that the perpetrator could not understand the nature of their criminal act, or did not know that the act was wrong, by reason of a mental illness. In this essay, I question the appropriateness of this, in light of contemporary neuroscience. Specifically, I focus on the role of the prefrontal cortex (PFC) in cognition, emotional regulation, control of impulsive behaviour and moral reasoning. I review the consequences of PFC damage on these endpoints, the capacity for factors such as alcohol and stress to transiently impair PFC function, and the remarkably late development of the PFC (in which full myelination may not occur until early adulthood). I also consider how individual variation in PFC function and anatomy, within the normative range, covaries with some of these endpoints. This literature is reviewed because of its relevance to issues of criminal insanity; specifically, damage can produce an individual capable of differentiating right from wrong but who, nonetheless, is organically incapable of appropriately regulating their behaviour.
It has been known for decades that wild baboons are naturally infected with Treponema pallidum, the bacterium that causes the diseases syphilis (subsp. pallidum), yaws (subsp. pertenue), and bejel (subsp. endemicum) in humans. Recently, a form of T. pallidum infection associated with severe genital lesions has been described in wild baboons at Lake Manyara National Park in Tanzania. In this study, we investigated ten additional sites in Tanzania and Kenya using a combination of macroscopic observation and serology, in order to determine whether the infection was present in each area. In addition, we obtained genetic sequence data from six polymorphic regions using T. pallidum strains collected from baboons at two different Tanzanian sites. We report that lesions consistent with T. pallidum infection were present at four of the five Tanzanian sites examined, and serology was used to confirm treponemal infection at three of these. By contrast, no signs of treponemal infection were observed at the six Kenyan sites, and serology indicated T. pallidum was present at only one of them. A survey of sexually mature baboons at Lake Manyara National Park in 2006 carried out as part of this study indicated that roughly ten percent displayed T. pallidum-associated lesions severe enough to cause major structural damage to the genitalia. Finally, we found that T. pallidum strains from Lake Manyara National Park and Serengeti National Park were genetically distinct, and a phylogeny suggested that baboon strains may have diverged prior to the clade containing human strains. We conclude that T. pallidum infection associated with genital lesions appears to be common in the wild baboons of the regions studied in Tanzania. Further study is needed to elucidate the infection's transmission mode, its associated morbidity and mortality, and the relationship between baboon and human strains.
Reports exist of transmission of culture in nonhuman primates. We examine this in a troop of savanna baboons studied since 1978. During the mid-1980s, half of the males died from tuberculosis; because of circumstances of the outbreak, it was more aggressive males who died, leaving a cohort of atypically unaggressive survivors. A decade later, these behavioral patterns persisted. Males leave their natal troops at adolescence; by the mid-1990s, no males remained who had resided in the troop a decade before. Thus, critically, the troop's unique culture was being adopted by new males joining the troop. We describe (a) features of this culture in the behavior of males, including high rates of grooming and affiliation with females and a “relaxed” dominance hierarchy; (b) physiological measures suggesting less stress among low-ranking males; (c) models explaining transmission of this culture; and (d) data testing these models, centered around treatment of transfer males by resident females.
A unique less-aggressive suite of behaviors that affects the overall structure and social atmosphere of a wild baboon troop potentially represents an intergenerational transfer of social culture
Gene therapy has demonstrated the protective potential of a variety of genes against stroke. However, conventional gene therapy vectors are limited due to the inability to temporally control their expression, which can sometimes lead to deleterious side effects. Thus, an inducible vector that can be temporally controlled and activated by the insult itself would be advantageous. Using hypoxia responsive elements (HRE) and antioxidant responsive elements (ARE), we have constructed an insult-inducible vector activated by hypoxia and reactive oxygen species (ROS). In COS7 cells, the inducible ARE−HRE-luciferase vectors are highly activated by oxygen deprivation, hydrogen peroxide treatment, and the ROS-induced transcription factor NF-E2-related factor 2 (Nrf2). Using a defective herpes virus, the neuroprotective potential of this inducible vector was tested by over-expressing the transcription factor Nrf2. In primary cortical cultures, expression of the inducible ARE−HRE–Nrf2 protects against oxygen glucose deprivation, similar to that afforded by the constitutively expressed Nrf2. This ARE+HRE vector system is advantageous in that it allows the expression of a transgene to be activated not only during hypoxia but also maintained after reperfusion, thus prolonging the transgene expression during an ischemic insult. This insult-inducible vector system will be a valuable gene therapy tool for activating therapeutic/protective genes in cerebrovascular diseases.
Insult-inducible; Gene therapy; Hypoxia; HIF1; Nrf2; Reactive oxygen species