Longitudinal Biochemical and Behavioral Alterations in a Gyrencephalic Model of Blast-Related Mild Traumatic Brain Injury

Blast-related traumatic brain injury (bTBI) is a major cause of neurological disorders in the U.S. military that can adversely impact some civilian populations as well and can lead to lifelong deficits and diminished quality of life. Among these types of injuries, the long-term sequelae are poorly understood because of variability in intensity and number of the blast exposure, as well as the range of subsequent symptoms that can overlap with those resulting from other traumatic events (e.g., post-traumatic stress disorder). Despite the valuable insights that rodent models have provided, there is a growing interest in using injury models using species with neuroanatomical features that more closely resemble the human brain. With this purpose, we established a gyrencephalic model of blast injury in ferrets, which underwent blast exposure applying conditions that closely mimic those associated with primary blast injuries to warfighters. In this study, we evaluated brain biochemical, microstructural, and behavioral profiles after blast exposure using in vivo longitudinal magnetic resonance imaging, histology, and behavioral assessments. In ferrets subjected to blast, the following alterations were found: 1) heightened impulsivity in decision making associated with pre-frontal cortex/amygdalar axis dysfunction; 2) transiently increased glutamate levels that are consistent with earlier findings during subacute stages post-TBI and may be involved in concomitant behavioral deficits; 3) abnormally high brain N-acetylaspartate levels that potentially reveal disrupted lipid synthesis and/or energy metabolism; and 4) dysfunction of pre-frontal cortex/auditory cortex signaling cascades that may reflect similar perturbations underlying secondary psychiatric disorders observed in warfighters after blast exposure.

The effect of developmental alcohol exposure on multisensory integration is larger in deeper cortical layers

Fetal Alcohol Spectrum Disorders (FASD) are one of the most common causes of mental disability in the world. Despite efforts to increase public awareness of the risks of drinking during pregnancy, epidemiological studies indicate a prevalence of 1-6% in all births. There is growing evidence that deficits in sensory processing may contribute to social problems observed in FASD. Multisensory (MS) integration occurs when a combination of inputs from two sensory modalities leads to enhancement or suppression of neuronal firing. MS enhancement is usually linked to processes that facilitate cognition and reaction time, whereas MS suppression has been linked to filtering unwanted sensory information. The rostral portion of the posterior parietal cortex (PPr) of the ferret is an area that shows robust visual-tactile integration and displays both MS enhancement and suppression. Recently, our lab demonstrated that ferrets exposed to alcohol during the "third trimester equivalent" of human gestation show less MS enhancement and more MS suppression in PPr than controls. Here we complement these findings by comparing in vivo electrophysiological recordings from channels located in shallow and deep cortical layers. We observed that while the effects of alcohol (less MS enhancement and more MS suppression) were found in all layers, the magnitude of these effects were more pronounced in putative layers V-VI. These findings extend our knowledge on the sensory deficits of FASD.

Development of multisensory processing in ferret parietal cortex

It is well known that the nervous system adjusts itself to its environment during development. Although a great deal of effort has been directed towards understanding the developmental processes of the individual sensory systems (e.g., vision, hearing, etc.), only one major study has examined the maturation of multisensory processing in cortical neurons. Therefore, the present investigation sought to evaluate multisensory development in a different cortical region and species. Using multiple single-unit recordings in anaesthetised ferrets (n = 18) of different ages (from postnatal day 80 to 300), we studied the responses of neurons from the rostral posterior parietal (PPr) area to presentations of visual, tactile and combined visual-tactile stimulation. The results showed that multisensory neurons were infrequent at the youngest ages (pre-pubertal) and progressively increased through the later ages. Significant response changes that result from multisensory stimulation (defined as multisensory integration [MSI]) were observed in post-pubertal adolescent animals, and the magnitude of these integrated responses also increased across this age group. Furthermore, non-significant multisensory response changes were progressively increased in adolescent animals. Collectively, at the population level, MSI was observed to shift from primarily suppressive levels in infants to increasingly higher levels in later stages. These data indicate that, like the unisensory systems from which it is derived, multisensory processing shows developmental changes whose specific time course may be regionally and species-dependent.

Effects of developmental alcohol exposure on cortical multisensory integration

Fetal alcohol spectrum disorder (FASD) is one of the most common causes of mental disabilities in the world with a prevalence of 1%-6% of all births. Sensory processing deficits and cognitive problems are a major feature in this condition. Because developmental alcohol exposure can impair neuronal plasticity, and neuronal plasticity is crucial for the establishment of neuronal circuits in sensory areas, we predicted that exposure to alcohol during the third trimester equivalent of human gestation would disrupt the development of multisensory integration (MSI) in the rostral portion of the posterior parietal cortex (PPr), an integrative visual-tactile area. We conducted in vivo electrophysiology in 17 ferrets from four groups (saline/alcohol; infancy/adolescence). A total of 1157 neurons were recorded after visual, tactile and combined visual-tactile stimulation. A multisensory (MS) enhancement or suppression is characterized by a significantly increased or decreased number of elicited spikes after combined visual-tactile stimulation compared to the strongest unimodal (visual or tactile) response. At the neuronal level, those in infant animals were more prone to show MS suppression whereas adolescents were more prone to show MS enhancement. Although alcohol-treated animals showed similar developmental changes between infancy and adolescence, they always 'lagged behind' controls showing more MS suppression and less enhancement. Our findings suggest that alcohol exposure during the last months of human gestation would stunt the development of MSI, which could underlie sensory problems seen in FASD.

Combined exposure to alcohol and cannabis during development: mechanisms and outcomes

Exposure to substances of abuse during pregnancy can have long-lasting effects on offspring. Alcohol is one of the most widely used substances of abuse that leads to the most severe consequences. Recent studies in the United States, Canada, and the United Kingdom showed that between 1% and 7% of all children exhibit signs and symptoms of fetal alcohol spectrum disorder (FASD). Despite preventive campaigns, the rate of children with FASD has not decreased during recent decades. Alcohol consumption often accompanies exposure to such drugs as tobacco, cocaine, opioids, and cannabis. These interactions can be synergistic and exacerbate the deleterious consequences of developmental alcohol exposure. The present review focuses on interactions between alcohol and cannabis exposure and the potential consequences of these interactions.

Alterations in motor functional connectivity in Neonatal Hypoxic Ischemic Encephalopathy

BACKGROUND

Neonatal hypoxic-ischemic encephalopathy (HIE) is the result of global hypoxic-ischemic brain injury in neonates due to asphyxia during birth and is one of the most common causes of severe, long-term neurologic deficits in children. Methods: Resting state fMRI (rs-fMRI) was used to assess potential functional disruptions in the primary and association motor areas in HIE neonates (n = 16) compared to healthy controls (n = 11).

RESULTS

Results demonstrate reduced intra-hemispheric resting state functional connectivity (rs-FC) between primary motor regions (upper extremity and facial motor regions) as well as reduced inter-hemispheric rs-FC in the HIE group. In addition, HIE neonates demonstrated increased rs-FC between motor regions and frontal, temporal and parietal cortices but decreased rs-FC with the cerebellum.

DISCUSSION

These preliminary results provide initial evidence for the disruption of functional communication with the motor network in neonates with HIE. Further studies are necessary to both validate these findings in a larger dataset as well as to determine if rs-fMRI measurements collected at birth may have the potential to serve as a prognostic marker in addition to the traditional combination of clinical measurements and conventional MRI.

Impact of early postnatal exposure of red blood cell transfusions on the severity of retinopathy of prematurity

BACKGROUND

Postnatal exposure to red blood cell transfusion (RBCT) in premature infants is an important risk factor for Retinopathy of Prematurity (ROP) progression. We hypothesized that higher number and earlier timing of RBCT are associated with worse ROP severity and result in laser treatment at an earlier postmenstrual age (PMA) in very low birth weight (≤1500 g, VLBW) infants.

METHODS

A retrospective medical record review of 631 VLBW infants over a 5-year period was performed. Demographic features and potential clinical risk factors including number of RBCT, ROP severity, and progression to laser treatment were collected to evaluate predictors of severe ROP. ANCOVA, pairwise post-hoc analyses, and multivariate regression were used to determine associations between frequency and timing of RBCT and ROP severity.

RESULTS

Of the 456 eligible infants, 61 developed severe ROP (13%). There was significant correlation between number of RBCTs and ROP severity, adjusted for gestational age and birthweight (Adjusted R2 = 0.53; p <  0.001). Compared to infants with No/Mild and Type 2 ROP, infants with Type 1 ROP received more RBCTs, with higher number of RBCTs per week during the first month of life (mean RBCT in ROP No/Mild 5.7±0.4 vs Type 2 16.3±1.8 vs Type 1 22.4±1.5, p = 0.042). Laser-treated infants received a higher number of RBCTs than non-treated infants (mean RBCT 22.3 vs. 6.5, p <  0.001) but no correlation was observed between number of RBCTs and PMA at time of laser treatment.

CONCLUSION

Higher number of RBCTs in early postnatal life of VLBW infants was associated with more severe ROP.

Vinpocetine, cognition, and epilepsy

OBJECTIVE

Vinpocetine has been shown to enhance memory in animal models, with possible cognitive benefit in humans. The present study sought to demonstrate if vinpocetine can enhance cognition in healthy volunteers or patients with epilepsy. In addition, we compare blood levels of vinpocetine and its active metabolite (apovincaminic acid; AVA) in humans and animals to further characterize factors related to possible therapeutic benefit.

METHODS

The cognitive effects of vinpocetine were assessed in healthy adult volunteers (n = 8) using a double-blind, randomized, crossover design at single doses (placebo, 10, 20, and 60 mg oral). Cognitive effects of vinpocetine in patients with focal epilepsy (n = 8) were tested using a double-blind, randomized, crossover design at single doses (placebo, 20 mg oral) followed by one-month open label at 20 mg oral three times a day. The neuropsychological battery included both computerized and non-computerized tests. Levels of vinpocetine and AVA in the human studies were compared to levels in 45 mice across time dosed at 5-20 mg/kg intraperitoneal of vinpocetine.

RESULTS

No significant cognitive benefits were seen in healthy volunteers or patients with epilepsy. No appreciable side effects occurred. Vinpocetine and AVA levels were lower in humans than animals.

CONCLUSIONS

Vinpocetine was well tolerated, but was not associated with positive cognitive effects. However, blood levels obtained in humans were substantially less than levels in animals obtained from dosages known to be effective in one model. This suggests that higher dosages are needed in humans to assess vinpocetine's cognitive efficacy.

Mercury, lead, and cadmium exposure via red blood cell transfusions in preterm infants

BACKGROUND

Mercury, lead, and cadmium are developmental neurotoxicants. We predict that preterm newborns requiring packed red blood cell (PRBC) transfusions may be exposed to neurotoxic doses. We explored the relationship between donor concentration, number of donors, number of transfusions and mercury, lead and cadmium exposure.

METHODS

Single-donor PRBCs were analyzed for mercury, lead and cadmium concentration. Dose per transfusion was calculated and compared to intravenous reference doses (IVRfDs). Linear regression analyses were performed to correlate donor and infant exposure.

RESULTS

Thirty-six infants received 268 transfusions from 94 donors. Number of donors and transfusions were significantly correlated with birthweight and gestational age. All three metals were detected in ≥95% of donor PRBCs. Number of donors was significantly associated with cumulative dose, and there was a significant correlation between mercury and lead doses/transfusion. IVRfDs were exceeded for mercury and lead in 8.6% and 38% of transfusions, respectively. None exceeded the IVRfD for cadmium. For lead, infants exposed to three donors had more transfusions exceeding IVRfD than those exposed to 1-2 donors.

CONCLUSIONS

Preterm infants are exposed to heavy metals via transfusions. Doses exceeded the IVRfDs for mercury and lead. Cadmium did not pose a risk. Prescreening donor blood could reduce exposure risk.

Effects of Early Alcohol Exposure on Functional Organization and Microstructure of a Visual-Tactile Integrative Circuit

BACKGROUND

Children with fetal alcohol spectrum disorders (FASD) often have deficits associated with multisensory processing. Because ethanol (EtOH) disrupts activity-dependent neuronal plasticity, a process that is essential for refining connections during cortical development, we hypothesize that early alcohol exposure results in alterations in multisensory cortical networks, which could explain the multisensory processing deficits seen in FASD. Here, we use a gyrencephalic animal model to test the prediction that early alcohol exposure alters the functional connectivity and microstructural features of the rostral posterior parietal cortex (PPr), a visual-tactile integrative area.

METHODS

Ferrets were exposed to moderate doses of EtOH during the brain growth spurt period. Functional connectivity and microstructural features were assessed using resting-state functional magnetic resonance imaging and ex vivo diffusion kurtosis imaging (DKI), respectively, when the animals reached juvenile age and adulthood, respectively.

RESULTS

While the whole brain volume was smaller in alcohol-treated animals, the relative size of the frontal brain area was larger when compared to control animals. Altered functional connectivity was observed in alcohol-treated animals, where increased connectivity was observed between PPr and the region that provides its major visual inputs (the caudal portion of the parietal cortex), but not with the region that provides its major somatosensory inputs (tertiary somatosensory cortex). DKI revealed reduced microstructural tissue complexity in all investigated sensory areas of alcohol-treated animals.

CONCLUSIONS

In this study, we observed alterations in cortical functional connectivity and microstructural integrity in a cortical area involved in multisensory processing in a ferret FASD model. These findings indicate an alteration in cortical networks that may be related to the multisensory processing deficiencies observed in FASD.

Effect of Postmortem Interval and Years in Storage on RNA Quality of Tissue at a Repository of the NIH NeuroBioBank

Brain tissue from 1068 donors was analyzed for RNA quality as a function of postmortem interval (PMI) and years in storage. Approximately 83% of the cortical and cerebellar samples had an RNA integrity number (RIN) of 6 or greater, indicating their likely suitability for real-time quantitative polymerase chain reaction research. The average RIN value was independent of the PMI, up to at least 36 hours. The RNA quality for specific donated brains could not be predicted based on the PMI. Individual samples with a low PMI could have a poor RIN value, while a sample with a PMI over 36 hours may have a high RIN value. The RIN values for control brain donors, all of whom died suddenly and unexpectedly, were marginally higher than for individuals with clinical brain disorders. Polymerase chain reaction (PCR) analysis of samples confirmed that RIN values were more critical than PMI for determining suitability of tissue for molecular biological studies and samples should be matched by their RIN values rather than PMI. Importantly, PCR analysis established that tissue stored up to 23 years at −80°C yielded high-quality RNA. These results confirm that postmortem human brain tissue collected by brain and tissue banks over decades can serve as high quality material for the study of human disorders.

Proceedings of the 2016 annual meeting of the Fetal Alcohol Spectrum Disorders Study Group

The 2016 Fetal Alcohol Spectrum Disorders Study Group (FASDSG) meeting was titled "Rehabilitation in FASD: Potential Interventions and Challenges". During the previous decades, studies with human subjects and animal models have improved much of our understanding of the mechanisms underlying FASD, putting the scientific community in a good position to test hypotheses that can lead to potential therapeutic interventions. During the conference, two keynote speakers addressed potential interventions used in different fields and their applicability to FASD research. The conference also included updates from several government agencies, short presentations by junior and senior investigators that showcased the latest in FASD research, and award presentations. The conference was closed by a talk by Dr. Charles Goodlett, the recipient of the 2016 Henry Rosett award.

Cortical multisensory connectivity is present near birth in humans

How the newborn brain adapts to its new multisensory environment has been a subject of debate. Although an early theory proposed that the brain acquires multisensory features as a result of postnatal experience, recent studies have demonstrated that the neonatal brain is already capable of processing multisensory information. For multisensory processing to be functional, it is a prerequisite that multisensory convergence among neural connections occur. However, multisensory connectivity has not been examined in human neonates nor are its location(s) or afferent sources understood. We used resting state functional MRI (fMRI) in two independent cohorts of infants to examine the functional connectivity of two cortical areas known to be multisensory in adults: the intraparietal sulcus (IPS) and the superior temporal sulcus (STS). In the neonate, the IPS was found to demonstrate significant functional connectivity with visual association and somatosensory association areas, while the STS showed significant functional connectivity with the visual association areas, primary auditory cortex, and somatosensory association areas. Our findings establish that each of these areas displays functional communication with cortical regions representing various sensory modalities. This demonstrates the presence of cortical areas with converging sensory inputs, representing that the functional architecture needed for multisensory processing is already present within the first weeks of life.

Structural and Functional Integrity of the Intraparietal Sulcus in Moderate and Severe Traumatic Brain Injury

Severe and moderate traumatic brain injury (sTBI) often results in long-term cognitive deficits such as reduced processing speed and attention. The intraparietal sulcus (IPS) is a neocortical structure that plays a crucial role in the deeply interrelated processes of multi-sensory processing and top down attention. Therefore, we hypothesized that disruptions in the functional and structural connections of the IPS may play a role in the development of such deficits. To examine these connections, we used resting state magnetic resonance imaging (rsfMRI and diffusion kurtosis imaging (DKI) in a cohort of 27 patients with sTBI (29.3 ± 8.9 years) and 27 control participants (29.8 ± 10.3 years). Participants were prospectively recruited and received rsfMRI and neuropsychological assessments including the Automated Neuropsychological Assessment Metrics (ANAM) at greater than 6 months post-injury. A subset of participants received a DKI scan. Results suggest that patients with sTBI performed worse than control participants on multiple subtests of the ANAM suggesting reduced cognitive performance. Reduced resting state functional connectivity between the IPS and cortical regions associated with multi-sensory processing and the dorsal attention network was observed in the patients with sTBI. The patients also showed reduced structural integrity of the superior longitudinal fasciculus (SLF), a key white matter tract connecting the IPS to anterior frontal areas, as measured by reduced mean kurtosis (MK) and fractional anisotropy (FA) and increased mean diffusivity (MD). Further, this reduced structural integrity of the SLF was associated with a reduction in overall cognitive performance. These findings suggest that disruptions in the structural and functional connectivity of the IPS may contribute to chronic cognitive deficits experienced by these patients.

Developmental alcohol exposure leads to a persistent change on astrocyte secretome

Fetal alcohol spectrum disorder is the most common cause of mental disabilities in the western world. It has been quite established that acute alcohol exposure can dramatically affect astrocyte function. Because the effects of early alcohol exposure on cell physiology can persist into adulthood, we tested the hypothesis that ethanol exposure in ferrets during a period equivalent to the last months of human gestation leads to persistent changes in astrocyte secretome in vitro. Animals were treated with ethanol (3.5 g/kg) or saline between postnatal day (P)10-30. At P31, astrocyte cultures were made and cells were submitted to stable isotope labeling by amino acids. Twenty-four hour conditioned media of cells obtained from ethanol- or saline-treated animals (ET-CM or SAL-CM) were collected and analyzed by quantitative mass spectrometry in tandem with liquid chromatography. Here, we show that 65 out of 280 quantifiable proteins displayed significant differences comparing ET-CM to SAL-CM. Among the 59 proteins that were found to be reduced in ET-CM we observed components of the extracellular matrix such as laminin subunits α2, α4, β1, β2, and γ1 and the proteoglycans biglycan, heparan sulfate proteoglycan 2, and lumican. Proteins with trophic function such as insulin-like growth factor binding protein 4, pigment epithelium-derived factor, and clusterin as well as proteins involved on modulation of proteolysis such as metalloproteinase inhibitor 1 and plasminogen activator inhibitor-1 were also reduced. In contrast, pro-synaptogeneic proteins like thrombospondin-1, hevin as well as the modulator of extracelular matrix expression, angiotensinogen, were found increased in ET-CM. The analysis of interactome maps through ingenuity pathway analysis demonstrated that the amyloid beta A4 protein precursor, which was found reduced in ET-CM, was previously shown to interact with ten other proteins that exhibited significant changes in the ET-CM. Taken together our results strongly suggest that early exposure to teratogens such as alcohol may lead to an enduring change in astrocyte secretome. Despite efforts in prevention, fetal alcohol spectrum disorders are a major cause of mental disabilities. Here, we show that developmental exposure to alcohol lead to a persistent change in the pattern of proteins secreted (secretome) by astrocytes. This study is also the first mass spectrometry-based assessment of the astrocyte secretome in a gyrencephalic animal. Cover Image for this issue: doi: 10.1111/jnc.13320.

Astrocytes Assemble Thalamocortical Synapses by Bridging NRX1α and NL1 via Hevin

Proper establishment of synapses is critical for constructing functional circuits. Interactions between presynaptic neurexins and postsynaptic neuroligins coordinate the formation of synaptic adhesions. An isoform code determines the direct interactions of neurexins and neuroligins across the synapse. However, whether extracellular linker proteins can expand such a code is unknown. Using a combination of in vitro and in vivo approaches, we found that hevin, an astrocyte-secreted synaptogenic protein, assembles glutamatergic synapses by bridging neurexin-1alpha and neuroligin-1B, two isoforms that do not interact with each other. Bridging of neurexin-1alpha and neuroligin-1B via hevin is critical for the formation and plasticity of thalamocortical connections in the developing visual cortex. These results show that astrocytes promote the formation of synapses by modulating neurexin/neuroligin adhesions through hevin secretion. Our findings also provide an important mechanistic insight into how mutations in these genes may lead to circuit dysfunction in diseases such as autism.

Proceedings of the 2015 Annual Meeting of the Fetal Alcohol Spectrum Disorders Study Group

The 2015 Fetal Alcohol Spectrum Disorders Study Group (FASDSG) meeting was titled "Basic Mechanisms and Translational Implications." Despite decades of basic science and clinical research, our understanding of the mechanisms by which ethanol affects fetal development is still in its infancy. The first keynote presentation focused on the role of heat shock protein pathways in the actions of ethanol in the developing brain. The second keynote presentation addressed the use of magnetoencephalography to characterize brain function in children with FASD. The conference also included talks by representatives from several government agencies, short presentations by junior and senior investigators that showcased the latest in FASD research, and award presentations. An important part of the meeting was the presentation of the 2015 Henry Rosett award to Dr. Michael Charness in honor of his achievements in research on FASD.

Hyperactivity and depression-like traits in Bax KO mice

The Bax gene is a member of the Bcl-2 gene family and its pro-apoptotic Bcl-associated X (Bax) protein is believed to be crucial in regulating apoptosis during neuronal development as well as following injury. With the advent of mouse genomics, mice lacking the pro-apoptotic Bax gene (Bax KO) have been extensively used to study how cell death helps to determine synaptic circuitry formation during neurodevelopment and disease. Surprisingly, in spite of its wide use and the association of programmed neuronal death with motor dysfunctions and depression, the effects of Bax deletion on mice spontaneous locomotor activity and depression-like traits are unknown. Here we examine the behavioral characteristics of Bax KO male mice using classical paradigms to evaluate spontaneous locomotor activity and depressive-like responses. In the open field, Bax KO animals exhibited greater locomotor activity than their control littermates. In the forced swimming test, Bax KO mice displayed greater immobility times, a behavior despair state, when compared to controls. Collectively, our findings corroborate the notion that a fine balance between cell survival and death early during development is critical for normal brain function later in life. Furthermore, it points out the importance of considering depressive-like and hyperactivity behavioral phenotypes when conducting neurodevelopmental and other studies using the Bax KO strain.

Overexpression of Serum Response Factor in Neurons Restores Ocular Dominance Plasticity in a Model of Fetal Alcohol Spectrum Disorders

BACKGROUND

Deficits in neuronal plasticity underlie many neurobehavioral and cognitive problems presented in fetal alcohol spectrum disorder (FASD). Our laboratory has developed a ferret model showing that early alcohol exposure leads to a persistent disruption in ocular dominance plasticity (ODP). For instance, a few days of monocular deprivation results in a robust reduction of visual cortex neurons' responsiveness to stimulation of the deprived eye in normal animals, but not in ferrets with early alcohol exposure. Previously our laboratory demonstrated that overexpression of serum response factor (SRF) exclusively in astrocytes can improve neuronal plasticity in FASD. Here, we test whether neuronal overexpression of SRF can achieve similar effects.

METHODS

Ferrets received 3.5 g/kg alcohol intraperitoneally (25% in saline) or saline as control every other day between postnatal day 10 to 30, which is roughly equivalent to the third trimester of human gestation. Animals were given intracortical injections of a Herpes Simplex Virus-based vector to express either green fluorescent protein or a constitutively active form of SRF in infected neurons. They were then monocularly deprived by eyelid suture for 4 to 5 days after which single-unit recordings were conducted to determine whether changes in ocular dominance had occurred.

RESULTS

Overexpression of a constitutively active form of SRF by neurons restored ODP in alcohol-treated animals. This effect was observed only in areas near the site of viral infection.

CONCLUSIONS

Overexpression of SRF in neurons can restore plasticity in the ferret model of FASD, but only in areas near the site of infection. This contrasts with SRF overexpression in astrocytes which restored plasticity throughout the visual cortex.

Effects of Developmental Alcohol Exposure on Potentiation and Depression of Visual Cortex Responses

BACKGROUND

Neuronal plasticity deficits are thought to underlie abnormal neurodevelopment in fetal alcohol spectrum disorders and in animal models of this condition. Previously, we found that alcohol exposure during a period that is similar to the last months of gestation in humans disrupts ocular dominance plasticity (ODP), as measured in superficial cortical layers. We hypothesize that exposure to alcohol can differentially affect the potentiation and depression of responses that are necessary for activity-dependent sprouting and pruning of neuronal networks. ODP is an established paradigm that allows the assessment of activity-dependent depression and potentiation of responses in vivo.

METHODS

Mouse pups were exposed to 3.6 to 5 g/kg of ethanol in saline daily or every other day between postnatal days 4 and 9. Visual cortex plasticity was then assessed during the critical period for ODP using 2 techniques that separately record in layers 4 (visually evoked potentials [VEPs]) and 2/3 (optical imaging of intrinsic signals [OI]).

RESULTS

We discovered a layer-specific effect of early alcohol exposure. Recording of VEPs from layer 4 showed that while the potentiation component of ODP was disrupted in animals treated with alcohol when compared with saline controls, the depression component of ODP (Dc-ODP) was unaltered. In contrast, OI from layers 2/3 showed that Dc-ODP was markedly disrupted in alcohol-treated animals when compared with controls.

CONCLUSIONS

Combined with our previous work, these findings strongly suggest that developmental alcohol exposure has a distinct and layer-specific effect on the potentiation and depression of cortical responses after monocular deprivation.

Proceedings of the 2013 annual meeting of the Fetal Alcohol Spectrum Disorders Study Group

The 2013 Fetal Alcohol Spectrum Disorders Study Group (FASDSG) meeting was held in Orlando (Grand Cypress), FL with the theme "Developing Brain-Based Interventions for Individuals with Fetal Alcohol Spectrum Disorders." Children with fetal alcohol spectrum disorders have significant impairments in cognitive functioning and behavioral regulation skills, which lead to a lifetime of challenges for themselves and their families; thus, developing interventions that remediate or compensate for these deficits is of great importance. The conference included 2 keynote presentations, FASt data talks, award presentations, and updates by government agencies. In addition, a lively panel discussion addressed the challenges faced by FASDSG researchers in the translation of intervention strategies developed in preclinical studies to clinical trials and, ultimately, to clinical practice.

Synaptic dysfunction in the hippocampus accompanies learning and memory deficits in human immunodeficiency virus type-1 Tat transgenic mice

BACKGROUND

Human immunodeficiency virus (HIV) associated neurocognitive disorders (HAND), including memory dysfunction, continue to be a major clinical manifestation of HIV type-1 infection. Viral proteins released by infected glia are thought to be the principal triggers of inflammation and bystander neuronal injury and death, thereby driving key symptomatology of HAND.

METHODS

We used a glial fibrillary acidic protein-driven, doxycycline-inducible HIV type-1 transactivator of transcription (Tat) transgenic mouse model and examined structure-function relationships in hippocampal pyramidal cornu ammonis 1 (CA1) neurons using morphologic, electrophysiological (long-term potentiation [LTP]), and behavioral (Morris water maze, fear-conditioning) approaches.

RESULTS

Tat induction caused a variety of different inclusions in astrocytes characteristic of lysosomes, autophagic vacuoles, and lamellar bodies, which were typically present within distal cytoplasmic processes. In pyramidal CA1 neurons, Tat induction reduced the number of apical dendritic spines, while disrupting the distribution of synaptic proteins (synaptotagmin 2 and gephyrin) associated with inhibitory transmission but with minimal dendritic pathology and no evidence of pyramidal neuron death. Electrophysiological assessment of excitatory postsynaptic field potential at Schaffer collateral/commissural fiber-CA1 synapses showed near total suppression of LTP in mice expressing Tat. The loss in LTP coincided with disruptions in learning and memory.

CONCLUSIONS

Tat expression in the brain results in profound functional changes in synaptic physiology and in behavior that are accompanied by only modest structural changes and minimal pathology. Tat likely contributes to HAND by causing molecular changes that disrupt synaptic organization, with inhibitory presynaptic terminals containing synaptotagmin 2 appearing especially vulnerable.

Sodium valproate exposure during the brain growth spurt transiently impairs spatial learning in prepubertal rats

The brain is extremely vulnerable to teratogenic insults during the brain growth spurt, a period that starts during the third trimester of human gestation and is characterized by synaptogenesis establishment of neuronal circuits. While the treatment of epilepsy during pregnancy increases the risk of neurodevelopmental disorders in offspring, the consequences of exposure to anticonvulsants during the brain growth spurt remain poorly known. Here we investigate whether exposure to sodium valproate (VPA) during a similar period in rats impairs spatial learning of juvenile rats. Long-Evans rats were exposed to VPA (200mg/kg) or saline solution (SAL) every other day between postnatal day (PN) 4 and PN10. At PN23 and PN30, Morris water maze performance was evaluated during 6 consecutive days. In the group of animals which started their tests at PN23, the VPA exposure impaired both, swimming speed and learning/memory performance. Interestingly, no differences were observed between VPA and control animals tested from PN30 to PN35. Our data suggests that the neurobehavioral deficits caused by VPA exposure during the brain growth spurt are transitory.

Early alcohol exposure disrupts visual cortex plasticity in mice

There is growing evidence that deficits in neuronal plasticity underlie the cognitive problems seen in fetal alcohol spectrum disorders (FASD). However, the mechanisms behind these deficits are not clear. Here we test the effects of early alcohol exposure on ocular dominance plasticity (ODP) in mice and the reversibility of these effects by phosphodiesterase (PDE) inhibitors. Mouse pups were exposed to 5 g/kg of 25% ethanol i.p. on postnatal days (P) 5, 7 and 9. This type of alcohol exposure mimics binge drinking during the third trimester equivalent of human gestation. To assess ocular dominance plasticity animals were monocularly deprived at P21 for 10 days, and tested using optical imaging of intrinsic signals. During the period of monocular deprivation animals were treated with vinpocetine (20mg/kg; PDE1 inhibitor), rolipram (1.25mg/kg; PDE4 inhibitor), vardenafil (3mg/kg; PDE5 inhibitor) or vehicle solution. Monocular deprivation resulted in the expected shift in ocular dominance of the binocular zone in saline controls but not in the ethanol group. While vinpocetine successfully restored ODP in the ethanol group, rolipram and vardenafil did not. However, when rolipram and vardenafil were given simultaneously ODP was restored. PDE4 and PDE5 are specific to cAMP and cGMP respectively, while PDE1 acts on both of these nucleotides. Our findings suggest that the combined activation of the cAMP and cGMP cascades may be a good approach to improve neuronal plasticity in FASD models.

Fetal alcohol spectrum disorders and abnormal neuronal plasticity

The ingestion of alcohol during pregnancy can result in a group of neurobehavioral abnormalities collectively known as fetal alcohol spectrum disorders (FASD). During the past decade, studies using animal models indicated that early alcohol exposure can dramatically affect neuronal plasticity, an essential property of the central nervous system responsible for the normal wiring of the brain and involved in processes such as learning and memory. The abnormalities in neuronal plasticity caused by alcohol can explain many of the neurobehavioral deficits observed in FASD. Conversely, improving neuronal plasticity may have important therapeutic benefits. In this review, the author discuss the mechanisms that lead to these abnormalities and comment on recent pharmacological approaches that have been showing promising results in improving neuronal plasticity in FASD.

Therapeutic utility of phosphodiesterase type I inhibitors in neurological conditions

Neuronal plasticity is an essential property of the brain that is impaired in different neurological conditions. Phosphodiesterase type 1 (PDE1) inhibitors can enhance levels of the second messengers cAMP/cGMP leading to the expression of neuronal plasticity-related genes, neurotrophic factors, and neuroprotective molecules. These neuronal plasticity enhancement properties make PDE1 inhibitors good candidates as therapeutic agents in many neurological conditions. However, the lack of specificity of the drugs currently available poses a challenge to the systematic evaluation of the beneficial effect of these agents. The development of more specific drugs may pave the way for the use of PDE1 inhibitors as therapeutic agents in cases of neurodevelopmental conditions such as fetal alcohol spectrum disorders and in degenerative disorders such as Alzheimer's and Parkinson's.

Early valproic acid exposure alters functional organization in the primary visual cortex

Epilepsy is one of the most common neurologic disorders and affects 0.5 to 1% of pregnant women. The use of antiepileptic drugs, which is usually continued throughout pregnancy, can cause in offspring mild to severe sensory deficits. Neuronal selectivity to stimulus orientation is a basic functional property of the visual cortex that is crucial for perception of shapes and borders. Here we investigate the effects of early exposure to valproic acid (Val) and levetiracetam (Lev), commonly used antiepileptic drugs, on the development of cortical neuron orientation selectivity and organization of cortical orientation columns. Ferrets pups were exposed to Val (200mg/kg), Lev (100mg/kg) or saline every other day between postnatal day (P) 10 and P30, a period roughly equivalent to the third trimester of human gestation. Optical imaging of intrinsic signals or single-unit recordings were examined at P42-P84, when orientation selectivity in the ferret cortex has reached a mature state. Optical imaging of intrinsic signals revealed decreased contrast of orientation maps in Val- but not Lev- or saline-treated animals. Moreover, single-unit recordings revealed that early Val treatment also reduced orientation selectivity at the cellular level. These findings indicate that Val exposure during a brief period of development disrupts cortical processing of sensory information at a later age and suggest a neurobiological substrate for some types of sensory deficits in fetal anticonvulsant syndrome.

Activation of NMDA receptors is necessary for the recovery of cortical binocularity

Classic experiments have indicated that monocular deprivation (MD) for a few days during a critical period of development results in a decrease in the strength of connections mediating responses to the deprived eye, leading to a dramatic breakdown of cortical neuron binocularity. Despite the substantial functional change in the visual cortex, recovery from the effects of MD can be obtained if binocular vision is promptly restored. While great efforts have been made to elucidate the mechanisms regulating loss of deprived eye function, the mechanisms that underlie the recovery of cortical binocularity are poorly understood. Here, we examined whether activation of the N-methyl-d-aspartate receptor (NMDAR) is required for the recovery of cortical binocularity by pharmacologically blocking the NMDAR using d,l-2-amino-5-phosphonopentanoic (APV). Ferrets (n = 10) were monocularly deprived for 6 days, and osmotic minipumps, filled with APV (5.6 mg/ml) or saline, were surgically implanted into the primary visual cortex. One day after surgery, the deprived eye was reopened, and the animals were allowed 24 h of binocular vision. Extracellular recordings showed that intracortical infusion of the NMDAR antagonist, APV, prevented recovery of cortical binocularity while preserving neuronal responsiveness. These findings provide an important new insight for a specific role of NMDARs in the recovery of cortical binocularity from the effects of MD.

Phosphodiesterase type 1 inhibition improves learning in rats exposed to alcohol during the third trimester equivalent of human gestation

Deficits in learning and memory have been extensively observed in animal models of fetal alcohol spectrum disorders (FASD). Here we use the Morris maze to test whether vinpocetine, a phosphodiesterase type 1 inhibitor, restores learning performance in rats exposed to alcohol during the third trimester equivalent of human gestation. Long Evans rats received ethanol (5g/kg i.p.) or saline on alternate days from postnatal day (P) 4 to P10. Two weeks later (P25), the latency to find a hidden platform was evaluated (2 trials per day spaced at 40-min inter-trial intervals) during 4 consecutive days. Vinpocetine treatment started on the first day of behavioral testing: animals received vinpocetine (20mg/kg i.p.) or vehicle solution every other day until the end of behavioral procedures. Early alcohol exposure significantly affected the performance to find the hidden platform. The average latency of ethanol-exposed animals was significantly higher than that observed for the control group. Treatment of alcohol-exposed animals with vinpocetine restored their performance to control levels. Our results show that inhibition of PDE1 improves learning and memory deficits in rats early exposed to alcohol and provide evidence for the potential therapeutic use of vinpocetine in FASD.

Phosphodiesterase type 4 inhibition does not restore ocular dominance plasticity in a ferret model of fetal alcohol spectrum disorders

BACKGROUND

There is growing evidence that deficits in neuronal plasticity account for some of the neurological problems observed in fetal alcohol spectrum disorders (FASD). Recently, we showed that early alcohol exposure results in a permanent impairment in visual cortex ocular dominance (OD) plasticity in a ferret model of FASD. This disruption can be reversed, however, by treating animals with a Phosphodiesterase (PDE) type 1 inhibitor long after the period of alcohol exposure.

AIM

Because the mammalian brain presents different types of PDE isoforms we tested here whether inhibition of PDE type 4 also ameliorates the effects of alcohol on OD plasticity.

MATERIAL AND METHODS

Ferrets received 3.5 g/Kg alcohol i.p. (25% in saline) or saline as control every other day between postnatal day (P) 10 to P30, which is roughly equivalent to the third trimester equivalent of human gestation. Following a prolonged alcohol-free period (10 to 15 days), ferrets had the lid of the right eye sutured closed for 4 days and were examined for ocular dominance changes at the end of the period of deprivation.

RESULTS

Using in vivo electrophysiology we show that inhibition of PDE4 by rolipram does not restore OD plasticity in alcohol-treated ferrets.

CONCLUSION

This result suggests that contrary to PDE1, PDE4 inhibition does not play a role in the restoration of OD plasticity in the ferret model of FASD.

Phosphodiesterase inhibition increases CREB phosphorylation and restores orientation selectivity in a model of fetal alcohol spectrum disorders

Background

Fetal alcohol spectrum disorders (FASD) are the leading cause of mental retardation in the western world and children with FASD present altered somatosensory, auditory and visual processing. There is growing evidence that some of these sensory processing problems may be related to altered cortical maps caused by impaired developmental neuronal plasticity.

Methodology/Principal Findings

Here we show that the primary visual cortex of ferrets exposed to alcohol during the third trimester equivalent of human gestation have decreased CREB phosphorylation and poor orientation selectivity revealed by western blotting, optical imaging of intrinsic signals and single-unit extracellular recording techniques. Treating animals several days after the period of alcohol exposure with a phosphodiesterase type 1 inhibitor (Vinpocetine) increased CREB phosphorylation and restored orientation selectivity columns and neuronal orientation tuning.

Conclusions/Significance

These findings suggest that CREB function is important for the maturation of orientation selectivity and that plasticity enhancement by vinpocetine may play a role in the treatment of sensory problems in FASD.

Neocortical plasticity deficits in fetal alcohol spectrum disorders: lessons from barrel and visual cortex

Fetal Alcohol Spectrum Disorder (FASD) is characterized by a constellation of behavioral and physiological abnormalities, including learning and sensory deficits. There is growing evidence that abnormalities of neuronal plasticity underlie these deficits. However, the cellular and molecular mechanisms by which prenatal alcohol exposure disrupts neuronal plasticity remain elusive. Recently, studies with the barrel and the visual cortex as models to study the effects of early alcohol exposure on neuronal plasticity shed light on this subject. In this Mini-Review, we discuss the effects of ethanol exposure during development on neuronal plasticity and suggest environmental and pharmacological approaches to ameliorate these problems.

Do cross-modal projections always result in multisensory integration?

Convergence of afferents from different sensory modalities has generally been thought to produce bimodal (and trimodal) neurons (i.e., exhibit suprathreshold excitation to more than 1 sensory modality). Consequently, studies identifying cross-modal connections assume that such convergence results in bimodal (or trimodal) neurons that produce familiar forms of multisensory integration: response enhancement or depression. The present study questioned that assumption by anatomically identifying a projection from ferret auditory to visual cortex Area 21. However, electrophysiological recording within Area 21 not only failed to identify a single bimodal neuron but also familiar forms of multisensory integration were not observed either. Instead, a small proportion of neurons (9%; 27/296) showed subthreshold multisensory integration, in which visual responses were significantly modulated by auditory inputs. Such subthreshold multisensory effects were enhanced by gamma-aminobutyric acid antagonism, whereby a majority of neurons (87%; 20/23) now participated in a significant, multisensory population effect. Thus, multisensory convergence does not de facto result in bimodal (or trimodal) neurons or the traditional forms of multisensory integration. However, the fact that unimodal neurons exhibited a subthreshold form of multisensory integration not only affirms the relationship between convergence and integration but also expands our understanding of the functional repertoire of multisensory processing itself.

Restoration of neuronal plasticity by a phosphodiesterase type 1 inhibitor in a model of fetal alcohol exposure

Although some studies showed the efficacy of phosphodiesterase (PDE) inhibitors as neuronal plasticity enhancers, little is known about the effectiveness of these drugs to improve plasticity in cases of mental retardation. Fetal alcohol syndrome (FAS) is the leading cause of mental retardation in the western world. Using a combination of electrophysiological and optical imaging techniques, we show here that vinpocetine, a PDE type I inhibitor, restores ocular dominance plasticity in the ferret model of fetal alcohol exposure. Our finding should contribute to a better understanding and treatment of cognitive deficits associated with mental disorders, such as FAS.

Protein synthesis-independent plasticity mediates rapid and precise recovery of deprived eye responses

Monocular deprivation (MD) for a few days during a critical period of development leads to loss of cortical responses to stimulation of the deprived eye. Despite the profound effects of MD on cortical function, optical imaging of intrinsic signals and single-unit recordings revealed that deprived eye responses and orientation selectivity recovered a few hours after restoration of normal binocular vision. Moreover, recovery of deprived eye responses was not dependent upon mRNA translation, but required cortical activity. Interestingly, this fast recovery and protein synthesis independence was restricted to the hemisphere contralateral to the previously deprived eye. Collectively, these results implicate a relatively simple mechanistic process in the reactivation of a latent set of connections following restoration of binocular vision and provide new insight into how recovery of cortical function can rapidly occur in response to changes in sensory experience.

Early alcohol exposure impairs ocular dominance plasticity throughout the critical period

Animal models of fetal alcohol syndrome (FAS) have revealed an impairment of sensory neocortex plasticity. Here, we examine whether early alcohol exposure leads to a permanent impairment of ocular dominance plasticity (OD) or to an alteration in the timing of the critical period. Ferrets were exposed to alcohol during a brief period of development prior to eye opening and effects of monocular deprivation examined during early, mid and late critical period. Single-unit electrophysiology revealed markedly reduced OD plasticity at every age examined. This finding provides evidence that early alcohol exposure does not affect the timing or duration of the critical period of OD plasticity and suggests an enduring impairment of neural plasticity in FAS.

Early alcohol exposure induces persistent alteration of cortical columnar organization and reduced orientation selectivity in the visual cortex

Fetal alcohol syndrome (FAS) is a major cause of learning and sensory deficits in children. The visual system in particular is markedly affected, with an elevated prevalence of poor visual perceptual skills. Developmental problems involving the neocortex are likely to make a major contribution to some of these abnormalities. Neuronal selectivity to stimulus orientation, a functional property thought to be crucial for normal vision, may be especially vulnerable to alcohol exposure because it starts developing even before eye opening. To address this issue, we examined the effects of early alcohol exposure on development of cortical neuron orientation selectivity and organization of cortical orientation columns. Ferrets were exposed to ethanol starting at postnatal day (P) 10, when the functional properties and connectivity of neocortical neurons start to develop. Alcohol exposure ended at P30, just before eye opening at P32. Following a prolonged alcohol-free period (15-35 days), long-term effects of early alcohol exposure on cortical orientation selectivity were examined at P48-P65, when orientation selectivity in normal ferret cortex has reached a mature state. Optical imaging of intrinsic signals revealed decreased contrast of orientation maps in alcohol- but not saline-treated animals. Moreover, single-unit recordings revealed that early alcohol treatment weakened neuronal orientation selectivity while preserving robust visual responses. These findings indicate that alcohol exposure during a brief period of development disrupts cortical processing of sensory information at a later age and suggest a neurobiological substrate for some types of sensory deficits in FAS.

Recovery of Cortical Binocularity and Orientation Selectivity After the Critical Period for Ocular Dominance Plasticity

Cortical binocularity is abolished by monocular deprivation (MD) during a critical period of development lasting from approximately postnatal day (P) 35 to P70 in ferrets. Although this is one of the best-characterized models of neural plasticity and amblyopia, very few studies have examined the requirements for recovery of cortical binocularity and orientation selectivity of deprived eye responses. Recent studies indicating that different mechanisms regulate loss and recovery of binocularity raise the possibility that different sensitive periods characterize loss and recovery of deprived eye responses. In this report, we have examined whether the potential for recovery of binocularity and orientation selectivity is restricted to the critical period. Quantitative single unit recordings revealed recovery of cortical binocularity and full recovery of orientation selectivity of deprived eye responses following prolonged periods of MD (i.e., >3 wk) starting at P49, near the peak of plasticity. Surprisingly, recovery was present when binocular vision was restored after the end of the critical period for ocular dominance plasticity, as late as P83. In contrast, ferrets that had never received visual experience through the deprived eye failed to recover binocularity even though normal binocular vision was restored at P50, halfway through the critical period. Collectively, these results indicate that there is potential for recovery of cortical binocularity and deprived eye orientation selectivity after the end of the critical period for ocular dominance plasticity.

Neonatal alcohol exposure induces long-lasting impairment of visual cortical plasticity in ferrets

Fetal alcohol syndrome is a major cause of learning and sensory deficits. These disabilities may result from disruption of neocortex development and plasticity. Alcohol exposure during the third trimester equivalent of human gestation may have especially severe and long-lasting consequences on learning and sensory processing, because this is when the functional properties and connectivity of neocortical neurons start to develop. To address this issue, we used the monocular deprivation model of neural plasticity, which shares many common mechanisms with learning. Ferrets were exposed to ethanol (3.5 mg/kg, i.p.) on alternate days for 3 weeks starting on postnatal day (P) 10. Animals were then monocularly deprived at the peak of ocular dominance plasticity after a prolonged alcohol-free period (15-20 d). Quantitative single-unit electrophysiology revealed that alcohol exposure disrupted ocular dominance plasticity while preserving robust visual responses. Moreover, optical imaging of intrinsic signals revealed that the reduction in visual cortex area driven by the deprived eye was much less pronounced in ethanol-treated than in control animals. Alcohol exposure starting at a later age (P20) did not disrupt ocular dominance plasticity, indicating that timing of exposure is crucial for the effects on visual plasticity. In conclusion, alcohol exposure during a brief period of development impairs ocular dominance plasticity at a later age. This model provides a novel approach to investigate the consequences of fetal alcohol exposure and should contribute to elucidate how alcohol disrupts neural plasticity.

Sex differences in the incidence of total callosal agenesis in BALB/cCF mice

Corpus callosum (CC) development and adult morphology seems to be affected by sex. Here we analyzed the incidence of total callosal agenesis in 341 adult male and 318 female BALB/cCF mice. This strain of mice presents total or partial callosal agenesis in approximately 20-30% of its population. No significant differences were found in overall distributions of CC lengths and in average callosal lengths (totally acallosal excluded) between male and female mice. However, a highly significant difference in the incidence of total callosal agenesis was demonstrated: 18% (n=56) of the female mice presented such trait as opposed to 10% of males (n=34). This last result suggests that sex is a relevant factor in callosal development in its earliest stages of formation.

The effects of callosal agenesis on the susceptibility to seizures elicited by pentylenetetrazol in BALB/cCF mice

The effects of callosal agenesis in sensitivity to pentylenetetrazol (PTZ) were studied in 199 (95 males and 104 females) mice of the BALB/cCF strain. This strain presents agenesis of the corpus callosum (CC) in approximately 30% of its population. Seizures were elicited by intraperitoneally injected PTZ. Animals were tested with doses of 40 and 50 mg/kg. Seizure severity was expressed by the following scoring scale: 0 (no abnormal behavior, NAB); 1 (myoclonus, M); 2 (running bouncing clonus, RBC); 3 (tonic hindlimb extension, THE). For the 40-mg/kg dose, abnormal mice were found to be more susceptible, displaying more severe seizures more often then normal mice. Normal female mice were also more susceptible to PTZ than males for this dose. No significant differences were found for the 50-mg/kg dose as a result of the fact that most animals displayed RBC. These data indicate that callosal development and sex are important factors affecting seizure susceptibility.

Do NMDA receptor kinetics regulate the end of critical periods of plasticity?

Increasing NR2A subunit expression and the associated shortening of the NMDA-EPSC are thought to underlie the loss of diverse types of sensory cortical plasticity. Lu and colleagues (Lu et al., 2001 [this issue of Neuron]) now report that mice lacking the NR2A subunit display normal duration of critical periods of barrel cortex plasticity. Shortening of the NMDA-EPSC is therefore not responsible for the end of these critical periods.

Sex differences in sensitivity to seizures elicited by pentylenetetrazol in mice

Sex differences in sensitivity to seizures elicited by intraperitoneally injected pentylenetetrazol (PTZ) were studied in 240 (120 males and 120 females) adult Swiss mice. Animals were separated into four groups according to the dose that was injected: 40, 50, 60 and 70 mg/kg. Seizure severity was expressed by the following scoring scale: (0) no abnormal behavior; (1) myoclonus; (2) running bouncing (RB) clonus; (3) tonic hind limb extension (THE). The analyses of the dose-response curves indicated that females were more susceptible than males when the 50- and 60-mg/kg doses were used. Specifically, females often displayed RB clonus, while males frequently displayed only myoclonus or no abnormal behavior. No significant sex differences were demonstrated when either the 40- or the 70-mg/kg doses were used. These data indicate that, for a specific range of doses, sex differences in seizure susceptibility can be clearly demonstrated with the use of intraperitoneally injected PTZ. In this sense, this method could be used as a tool to investigate the role played by sexual hormones in regulating the sensitivity of the gamma-aminobutiric acid (GABA(A)) receptor complex (GRC).