Patrick A. Forcelli, Ph.D. - US grants

DESCRIPTION (provided by applicant): The use of antiepileptic drugs (AEDs) in pregnancy and early infancy poses special challenges and concerns, as even transient exposure to certain drugs during CNS development may impede subsequent neuronal and synaptic development. Several AEDs, including phenobarbital and phenytoin, when given in therapeutically relevant doses to rats during the early postnatal period, cause a pronounced increase in apoptotic cell death in several brain regions. Other drugs such as lamotrigine (in low or moderate doses) and levetiracetam are devoid of this effect. We have recently discovered a single exposure to phenobarbital, at the time of peak vulnerability to the propapoptotic action (postnatal day 7 in the rat), resulted In the suppression of the normal, developmental increase in the frequency of inhibitory post-synaptic currents (IPSCs) recorded via patch clamp from striatal medium spiny neurons (MSNs) in slices taken between postnatal day 10 and 14. We have also identified impairments in adult rotorod performance in rats treated at P7 with a proapoptotic dose of phenytoin, a reduction in prepulse inhibition (a measure of sensory-motor gating) and a reduction in seizure threshold to pentylenetetrazol In animals treated in the first postnatal week with phenobarbital. Each of these behavioral assays are sensitive to damage or altered function in the striatum. The proposed experiments will follow up on these exciting preliminary findings to determine if there is a consistent and predictive (potentially causative) relationship between AED-induced neuronal apoptosis and impaired maturation of I PSC frequency in the striatum and/or adult behavioral toxicitiy. This will be assessed by comparing AED treatments that are proapoptotic with those that avoid this toxicity. We hypothesize that AEDs that do not cause cell death will not cause impaired maturation of IPSC frequency in striatal MSNs, nor will they result in impaired rotorod performance, reduced seizure threshold, and impaired prepulse inhibition ofthe acoustic starle response. Moreover, the extent to which a neuroprotective treatment can prevent impaired maturation of IPSC frequency in striatal MSNs and/or behavior will be evaluated to test the hypothesis that neuronal death is necessary for this adverse functional outcome. The results ofthe proposed experiments will allow us to better understand the potential functional outcomes of exposure to AEDs in late gestation or early infancy, and the extent to which induction of excessive neuronal death is a valid marker of subsequent functional impairment. Furthermore, it will identify strategies to avoid deleterious functional sequelae of AED therapy during critical developmental periods. GOALS FOR KIRSCHSTEIN-NRSA FELLOWSHIP TRAINING AND CAREER I am seeking this fellowship tp support my dissertation research in Dr. Karen Gale and Dr. Stefano Vicini's laboratories, investigating the impact of neonatal anticonvulsant drug exposure. My goal for dissertation research is to develop a broad skill set of experimental techniques that will allow me to address scientific questions at the level of molecules, cells, networks and behavior. The complementary expertise of my mentors provides such exposure. A limited portion of this support is also requested to allow me to continue to teach (present lectures to graduate and undergraduate students, and continue to direct a course entitled, "Diseases and Disorders of the Brain". A key goal of my training is to complete and publish a series of focused studies on outcomes following drug exposure during development. My long-term goals are predicated on the broad training I am receiving at Georgetown. Following Georgetown I will seek post-doctoral training and then I hope to develop an independent, productive research program at an academic institution where I can ask and answer questions of interest at multiple levels of function, to maintain an active Involvement in teaching and mentoring, and to contribute to scientific discourse.

Epilepsy is the second most prevalent neurological disorder, affecting approximately 2 million people in the United States. While many patients achieve satisfactory seizure control with pharmacotherapy, there is a significant proportion (20-40%) who have medically intractable seizures. For these patients identification of novel methods for seizure control is a high priority. One such method may be to harness endogenous seizure suppressive circuits in the brain. Because seizures may have multiple or unknown sites of initiation, focal stimulation approaches (e.g., deep brain stimulation [DBS]) that can control seizures originating in diverse brain networks are highly desirable. The circuitry of the basal ganglia has received particular attention in this regard. Here, we propose to employ optogenetic methodologies to analyze the contribution of the nigrotectal pathway and its descending projections to the pedunculopontine nucleus to seizure control. The SNpr is major source of inhibitory input to DLSC. Moreover, both DLSC and SNpr both provide synaptic input to PPN. In Aim 1, we will test the hypothesis that optogenetic silencing of the SNpr, activation of DLSC, or silencing of SNpr to DLSC projections will control spontaneous recurrent seizures in a post-status epilepticus model. In Aim 2, we will determine if projections from SNpr/DLSC to the PPN are necessary and sufficient to account for basal-ganglia mediated seizure control. We will dissect the contribution of multiple cell types within the PPN, separately analyzing glutamatergic and cholinergic cell groups. In the service of these aims, we will examine the effects of optogenetic manipulations on complementary spontaneous and evoked seizure models to map the contributions of this network to seizure suppression within divergent seizure circuits. Together the proposed studies will provide proof of principle for optogenetic modulation of seizures in diverse networks from a single circuit. Moreover, this approach allows us to examine previously untestable hypotheses about the connections that mediate basal ganglia seizure control. Finally, the proposed experiments aim to uncover the circuit and neurotransmitter mechanism by which focal manipulations in motor control regions (i.e., SNpr/DLSC) translate into brain-wide changes in excitability.

Project Summary Pharmacotherapy during critical periods of brain development can adversely affect nervous system function. This poses a challenge for the treatment of neurological disorders, where the underlying illness and the treatment both may have adverse effects. One example of this is balancing the choice of medication for the treatment of seizures, one of the most common neurological disorders of infancy. Seizures in neonates are a common occurrence after hypoxia (or hypoxia-ischemia); these seizures are typically aggressively treated with anticonvulsant drugs. Hypoxia-induced seizures are associated with a profound increase in risk for later-in-life seizures, as well as significant developmental delays and intellectual disabilities. However, the outcomes due to the seizures and the outcomes due to the drug therapy are confounded. In this application, we propose to evaluate: (1) the effect of hypoxia-induced seizures, (2) the effect of the three most common anti-seizure drugs used in babies (phenobarbital, phenytoin, levetiracetam), and (3) the efficacy of a neuroprotective intervention (melatonin). We will determine the degree to which seizures and drugs influence brain development at the level of biochemistry (assessment of programmed cell death, oxidative stress), neurophysiology (patch-clamp recordings from neurons in hippocampal CA1 subfield), and behavior (tests of learning and memory in adult animals exposed to drugs and/or seizures as babies). We will also evaluate biomarkers of drug safety through peripheral measurement of oxidative stress and high-resolution magnetic resonance imaging of animals exposed to these early life insults. Finally, we will determine if our neuroprotective intervention ameliorates some, or all, of the adverse outcomes associated with seizures and/or drug treatment.

Exaggerated emotional reactivity, impaired social function, aberrant regulation of defense behaviors, and autonomic dysregulation are a constellation of debilitating symptoms that are present in a range of anxiety disorders. Anxiety disorders, as a group, impact about 20% of the US population and treatments for anxiety disorders are only partially effective and often associated with side effects. While most attention has focused on fronto-limbic circuitry, a current gap in knowledge is the contribution of hindbrain circuits. A second major gap is how hindbrain and forebrain sites interact. Moreover, the vast majority of circuit-level characterization has occurred in rodent models, which leads to the third major gap in knowledge: the functional organization of these circuits in non-human primates. Indeed, as evidenced by findings in our lab and by others, the primate brain is organized in often surprisingly different manners than the rodent brain. Thus, understanding the organization of these circuits in the primate brain is essential to understanding the organization of the human brain. We have previously found that acute disinhibition of the deep layers of the superior colliculus (DLSC), a midbrain structure, by focal infusions of the GABAA antagonist, bicuculline, precipitated a state of exaggerated defensive and emotional reactivity (DER). Concurrent inhibition of the basolateral amygdala (BLA) reduced some but not all of the defense responses, suggesting differential circuitry underlying individual components of the defensive response. In this application, we propose to determine the circuit architecture by which hindbrain (DLSC, PAG) and forebrain (BLA, central nucleus of the amygdala, pulvinar) regions interact to produce defensive emotional reactions, unconditioned fear, dysregulation of social behavior, and autonomic arousal. In the two proposed specific aims, we will test the hypotheses that induced inhibition of the limbic components will attenuate the DER evoked from the midbrain structures and that induced inhibition of midbrain structures will attenuate the DER evoked from the forebrain. Using MRI-guided intracerebral microinfusions, we will transiently activate and inactivate components of this network and determine the resulting impact on anxiety- relevant behavioral responses. Following these experiments, we will employ anatomical tracer techniques to characterize projection pathways of interest. We will also perform validation experiments using Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), which have grown in use in rodents, but remain rarely used in primates, to help move this translational technology forward. We expect that our data will have implications for understanding the pathology of anxiety disorders.