Deirdre M. McCarthy

Influence of dopamine on precursor cell proliferation and differentiation in the embryonic mouse telencephalon.

Dopamine and its receptor binding sites appear in the brain early in the embryonic period raising the possibility that dopamine may influence brain development. We show that one component of dopamine’s role in brain development is its ability to influence proliferation and differentiation of progenitor cells in the neostriatum and the dorsomedial prefrontal cortex on embryonic day 15 in mice. Dopamine and a D1-like receptor agonist reduce the relative proportion of progenitor cells incorporating the S phase marker bromodeoxyuridine. A D2-like agonist produces the opposite effect. Both the effects are evident in the lateral ganglionic eminence, neuroepithelial precursor of the neostriatum and in the neuroepithelium of the dorsomedial prefrontal cortex. Neostriatal progenitor cells are more responsive than cortical progenitor cells to the effects of dopamine receptor activation. Furthermore, progenitor cells in the ventricular zone are more responsive to D1-like agonists and progenitors in the subventricular zone more so to D2-like agonists. Thus, dopamine’s developmental effects show regional and progenitor cell type specificity, presumably due to heterogeneity in the distribution of its receptor binding sites.

Cocaine Alters BDNF Expression and Neuronal Migration in the Embryonic Mouse Forebrain

Prenatal cocaine exposure impairs brain development and produces lasting alterations in cognitive function. In a prenatal cocaine exposure mouse model, we found that tangential migration of GABA neurons from the basal to the dorsal forebrain and radial neuron migration within the dorsal forebrain were significantly decreased during the embryonic period. The decrease in the tangential migration occurred early in gestation and normalized by late gestation, despite ongoing cocaine exposure. The decrease in radial migration was associated with altered laminar positioning of neurons in the medial prefrontal cortex. The cocaine exposure led to transient decreases in the expression of Tbr2 and Tbr1, transcription factors associated with intermediate progenitor cells and newborn neurons of the dorsal forebrain, respectively, although neurogenesis was not significantly altered. Since cocaine can modulate brain derived neurotrophic factor (BDNF) expression in the mature brain, we examined whether cocaine can alter BDNF expression in the embryonic brain. We found a transient decrease in BDNF protein expression in the cocaine-exposed embryonic forebrain early in gestation. By late gestation, the BDNF expression recovered to control levels, despite ongoing cocaine exposure. In basal forebrain explants from cocaine-exposed embryos, cell migration was significantly decreased, corroborating the in vivo data on tangential GABA neuron migration. Since BDNF can influence tangential neuronal migration, we added BDNF to the culture medium and observed increased cell migration. Our data suggest that cocaine can alter tangential and radial neuronal migration as well as BDNF expression in the embryonic brain and that decreased BDNF may mediate cocaines effects on neuronal migration.

Plasma and brain concentrations of oral therapeutic doses of methylphenidate and their impact on brain monoamine content in mice

Methylphenidate is a frequently prescribed stimulant for the treatment of attention deficit hyperactivity disorder (ADHD). An important assumption in the animal models that have been employed to study methylphenidates effects on the brain and behavior is that bioavailability of methylphenidate in the animal models reflects that in human subjects. From this perspective, the dose and route of administration of methylphenidate assume critical importance because both these factors likely influence rate of uptake, plasma and brain concentrations of the drug. In the present study, plasma and brain concentrations of d- and l-methylphenidate and d- and l-ritalinic acid were measured in 2-month old mice (equivalent to young adulthood in humans) following a single oral administration of a racemic mixture. Our data show that oral administration of 0.75 mg/kg dose produced within 15 min, plasma levels of d-methylphenidate that correspond to the clinically effective plasma levels in human subjects (estimated to be 6-10 ng/ml). Brain concentrations of d- and l-methylphenidate tended to exceed their plasma concentrations, while the plasma concentrations of d- and l-ritalinic acid exceeded their brain concentrations. A single oral administration at 0.75 mg/kg dose increased dopamine content of the frontal cortex within 1 h, without producing statistically significant changes in serotonin or noradrenaline contents. Striatal monoamine levels remained unaltered. These data highlight disparities between plasma and brain concentrations of methylphenidate and its metabolites following oral administration and illustrate brain region- and monoamine-specific changes produced by the low oral dose of methylphenidate.

Retinoic acid influences neuronal migration from the ganglionic eminence to the cerebral cortex

J. Neurochem. (2011) 119, 723–735.

Effects of prenatal exposure to cocaine on brain structure and function.

Drug abuse during pregnancy affects the mother and has adverse effects on the unborn child. This chapter highlights our recent findings at the neuroanatomical, molecular, and behavioral levels in a prenatal cocaine exposure mouse model. In the embryonic brains of prenatally cocaine-exposed mice, we observed a delay in the tangential migration of GABA neurons to the cerebral cortex as a result of a significant but transient decrease in the expression of the neurotrophin brain-derived neurotrophic factor (BDNF). These developmental changes lead to lasting deficits in the numerical density of GABA neurons in the mature medial prefrontal cortex (mPFC). In adult prenatally cocaine-exposed mice, we observed a behavioral deficit in the recall of an extinguished cue-conditioned fear, which was rescued by administration of exogenous recombinant BDNF protein directly into the infralimbic cortex of the mPFC, which may result from altered activity-driven transcriptional regulation of BDNF.

Prenatal Cocaine Exposure Decreases Parvalbumin-Immunoreactive Neurons and GABA-to-Projection Neuron Ratio in the Medial Prefrontal Cortex

Cocaine abuse during pregnancy produces harmful effects not only on the mother but also on the unborn child. The neurotransmitters dopamine and serotonin are known as the principal targets of the action of cocaine in the fetal and postnatal brain. However, recent evidence suggests that cocaine can impair cerebral cortical GABA neuron development and function. We sought to analyze the effects of prenatal cocaine exposure on the number and distribution of GABA and projection neurons (inhibitory interneurons and excitatory output neurons, respectively) in the mouse cerebral cortex. We found that the prenatal cocaine exposure decreased GABA neuron numbers and GABA-to-projection neuron ratio in the medial prefrontal cortex of 60-day-old mice. The neighboring prefrontal cortex did not show significant changes in either of these measures. However, there was a significant increase in projection neuron numbers in the prefrontal cortex but not in the medial prefrontal cortex. Thus, the effects of cocaine on GABA and projection neurons appear to be cortical region specific. The population of parvalbumin-immunoreactive GABA neurons was decreased in the medial prefrontal cortex following the prenatal cocaine exposure. The cocaine exposure also delayed the developmental decline in the volume of the medial prefrontal cortex. Thus, prenatal cocaine exposure produced persisting and region-specific effects on cortical cytoarchitecture and impaired the physiological balance between excitatory and inhibitory neurotransmission. These structural changes may underlie the electrophysiological and behavioral effects of prenatal cocaine exposure observed in animal models and human subjects.

Expression of cellular FLICE inhibitory proteins (cFLIP) in normal and traumatic murine and human cerebral cortex

Cellular Fas-associated death domain-like interleukin-1-beta converting enzyme (FLICE) inhibitory proteins (cFLIPs) are endogenous caspase homologues that inhibit programmed cell death. We hypothesized that cFLIPs are differentially expressed in response to traumatic brain injury (TBI). cFLIP-alpha and cFLIP-delta mRNA were expressed in normal mouse brain—specifically cFLIP-delta (but not cFLIP-alpha) protein was robustly expressed. After controlled cortical impact (CCI), cFLIP-alpha expression increased initially then decreased to control levels at 12 h, increasing again at 24-72 h (P<0.05). cFLIP-delta expression was decreased in brain homogenates by 12 h after CCI, then increased again at 24 to 72 h (P<0.05). cFLIP-delta immunostaining was markedly reduced in injured cortex, but not hippocampus, at 3 to 72 h after CCI. In cortex, reduced cFLIP-delta staining was found in TUNEL-positive cells, but in hippocampus TUNEL-positive cells expressed cFLIP-delta immunoreactivity. cFLIP-delta was increased in a subset of reactive astrocytes in pericontusional cortex and hippocampus at 48 to 72 h. Low levels of both cFLIP isoforms were detected in human cortical tissue with no TBI, from four patients undergoing brain surgery for epilepsy and <24 h post mortem from three patients without CNS pathologic assessment. In cortical tissue surgically removed <18 h after severe TBI (n = 3), cFLIP-alpha expression was increased relative to epilepsy controls (P<0.05) but not relative to post-mortem controls. The data suggest differential spatial and temporal regulation of cFLIP-alpha and cFLIP-delta expression that may influence the magnitude of cell death and further implicate programmed mechanisms of cell death after TBI.

Neurogenesis and Neuronal Migration in the Forebrain of the TorsinA Knockout Mouse Embryo

Early-onset generalized torsion dystonia, also known as DYT1 dystonia, is a childhood onset heritable neurological movement disorder involving painful, involuntary muscle contractions, sustained abnormal postures, and repetitive movements. It is caused by a GAG deletion in the Tor1A gene located on chromosome 9. TorsinA, the product of the Tor1A gene, is expressed throughout the brain beginning early in embryonic development. It plays a role in the regulation of nuclear envelope-cytoskeletal interactions, and presumably nuclear translocation. Since nuclear translocation, powered by cytoskeletal traction, is critical for cell proliferation and migration, we examined whether neurogenesis and neuronal migration are affected in Tor1A–/– mouse brain. Our data show that interkinetic nuclear migration and the pattern of migration of newly generated neurons are impaired in the dorsal forebrain of the Tor1A–/– embryo. However, neurogenesis is not altered significantly. The rate of migration of cells from explants of the medial ganglionic eminence is also impaired in the Tor1A–/– embryo. Thus, loss of torsinA results in subtle but significant alterations in cell proliferation and migration in the embryonic forebrain. These subtle developmental changes are consistent with a lack of significant changes in neuronal numbers, neuronal positioning or size of brain regions in DYT1 dystonia patients.

Prenatal L-DOPA exposure produces lasting changes in brain dopamine content, cocaine-induced dopamine release and cocaine conditioned place preference

Dopamine, its receptors and transporter are present in the brain beginning from early in the embryonic period. Dopamine receptor activation can influence developmental events including neurogenesis, neuronal migration and differentiation raising the possibility that dopamine imbalance in the fetal brain can alter development of the brain and behavior. We examined whether elevated dopamine levels during gestation can produce persisting changes in brain dopamine content and dopamine-mediated behaviors. We administered L-3,4-dihydroxyphenylalanine (L-DOPA) in drinking water to timed-pregnant CD1 mice from the 11th day of gestation until the day of parturition. The prenatal L-DOPA exposure led to significantly lower cocaine conditioned place preference, a behavioral test of reward, at postnatal day 60 (P60). However, in vivo microdialysis measurements showed significant increases in cocaine-induced dopamine release in the caudate putamen of P26 and P60 mice exposed to L-DOPA prenatally, ruling out attenuated dopamine release in the caudate putamen as a contributor to decreased conditioned place preference. Although dopamine release was induced in the nucleus accumbens of prenatally L-DOPA exposed mice at P60 by cocaine, the dopamine release in the nucleus accumbens was not significantly different between the L-DOPA and control groups. However, basal dopamine release was significantly higher in the prenatally L-DOPA exposed mice at P60 suggesting that the L-DOPA exposed mice may require a higher dose of cocaine for induction of cocaine place preference than the controls. The prenatal L-DOPA exposure did not alter cocaine-induced locomotor response, suggesting dissociation between the effects of prenatal L-DOPA exposure on conditioned place preference and locomotor activity. Tissue concentration of dopamine and its metabolites in the striatum and ventral midbrain were significantly affected by the L-DOPA exposure as well as by developmental changes over the P14-P60 period. Thus, elevation of dopamine levels during gestation can produce persisting changes in brain dopamine content, cocaine-induced dopamine release and cocaine conditioned place preference.

Cocaine‐induced neurodevelopmental deficits and underlying mechanisms

Exposure to drugs early in life has complex and long-lasting implications for brain structure and function. This review summarizes work to date on the immediate and long-term effects of prenatal exposure to cocaine. In utero cocaine exposure produces disruptions in brain monoamines, particularly dopamine, during sensitive periods of brain development, and leads to permanent changes in specific brain circuits, molecules, and behavior. Here, we integrate clinical studies and significance with mechanistic preclinical studies, to define our current knowledge base and identify gaps for future investigation. Birth Defects Research (Part C) 108:147-173, 2016.