Lorenz S. Neuwirth

Clozapine Functions Through the Prefrontal Cortex Serotonin 1A Receptor to Heighten Neuronal Activity via Calmodulin Kinase II-NMDA Receptor Interactions

J. Neurochem. (2012) 120, 396–407.

Effects of Taurine on Anxiety-Like and Locomotor Behavior of Mice

Taurine is one of the most abundant free amino acids especially in excitable tissues, with wide physiological actions. We have previously reported that chronic supplementation of taurine in drinking water to mice increases brain excitability, mainly through alterations in the inhibitory GABAergic system. In this study we investigated the effects of chronic versus acute taurine treatment on anxiety-like and locomotor behaviors using two behavioral tests: elevated plus-maze and open-field. These two test conditions generated different levels of anxiety, and both anxiolytic and anxiogenic effects of taurine could be assessed. We used two paradigms for taurine treatment: Acute injection versus chronic supplementation. In the open field test, taurine supplementation increased whereas taurine injection suppressed locomotor activity. We found that taurine supplementation induced an increase in the total distance traveled, the overall movement speed, the time the animals spent mobile, the number of line crossings, and the time the animals entered the center zone. In the elevated arm maze, taurine injection suppressed anxiety whereas taurine supplementation was anxiogenic. The major findings of this are two folds: First these results suggest that taurine might play a role in the modulation of anxiety and locomotor activity. Second, taurine when injected acutely had opposite effects than when administered chronically.

Taurine Regulation of Blood Pressure and Vasoactivity

Taurine plays an important role in the modulation of cardiovascular function by acting not only within the brain but also within peripheral tissues. We found that IV injection of taurine to male rats caused hypotension and tachycardia. A single injection of taurine significantly lowered the systolic, diastolic, and mean arterial blood pressure in freely moving Long-Evans control rats. We further confirm the vasoactive properties of taurine using isolated aortic ring preparations. Mechanical responses of circular aortic rings to pharmacological agents were measured by an isometric force transducer and amplifier. We found that bath application of taurine to the aortic rings caused vasodilation which was blocked by picrotoxin. Interestingly, picrotoxin alone induced a constriction of the aortic ring in the absence of exogenously added taurine, suggesting a tonic activation of GABA(A)receptors by circulating either taurine or GABA. Additionally, we found that the endothelial cells express high levels of taurine transporters and GABA(A)receptors. We have previously shown that taurine activates GABA(A)receptors and thus we suggest that the functional implication of GABA(A)receptor activation is the relaxation of the arterial muscularis, vasodilation, and a decrease in blood pressure. Interestingly however, the effects of acute taurine injection were very different than chronic supplementation of taurine. When rats were supplemented taurine (0.05%, 4 weeks) in their drinking water, taurine has significant hypertensive properties. The increase in blood pressure was observed however only in females; males supplemented with taurine did not show an increase in systolic, diastolic, or mean arterial pressure. In both genders however, taurine supplementation caused a significant tachycardia. Thus, we suggest that acute administration of taurine may be beneficial to lowering blood pressure. However, our data indicate that supplementation of taurine to females caused a significant increase in blood pressure. The effect of taurine supplementation on hypertensive rats remains to be seen.

Taurine regulation of short term synaptic plasticity in fragile X mice

BackgroundFragile X Syndrome is the most common known genetic cause of autism. The Fmr1-KO mouse, lacks the fragile X mental retardation protein (FMRP), and is used as a model of the syndrome. The core behavioral deficits of autism may be conceptualized either as excessive adherence to patterns as seen in repetitive actions and aberrant language, or as insensitivity to subtle but socially important changes in patterns. The hippocampus receives information from the entorhinal cortex and plays a crucial role in the processing of patterned information. To gain more insight into the physiological function of FMRP and the neuronal mechanisms underlying fragile X syndrome, we examined the electrophysiological response of the hippocampus to pair pulse stimulation as a measure of patterned information processing and how it is affected in the Fmr1-KO mouse.MethodsIn this study, we used paired-pulse stimulation of the afferent perforant path and recorded from the CA1 region of the hippocampus. Two-month-old FVB/NJ male mice and age-matched Fmr1-KO mice were used in this study. Hippocampal slices were prepared, equilibrated in artificial cerebrospinal fluid (aCSF), and excitatory post synaptic potentials (EPSPs) measured by stimulating the perforant path of the dentate gyrus (DG) while recording from the molecular layer of CA1. Stimulation occurred by setting current and pulse width to evoke a fixed percentage of maximal EPSP amplitude. This stimulation paradigm allowed us to examine the processing capabilities of the hippocampus as a function of increasing interstimulus intervals (ISI) and how taurine, a GABAA receptor agonist, affects such information processing.ResultsWe found that hippocampal slices from wild type (WT) showed pair-pulse facilitation at ISI of 100-300 ms whereas slices from Fmr1-KO brains showed a consistent pair-pulse depression at a comparable ISI. Addition of 10 μM taurine to WT slices resulted in a drastic decrease of the peak response to the second stimulus, resulting in an initial depression at 100 ms ISI followed by potentiation at higher ISI (150 ms and above). In the presence of taurine, the amplitude of the second response remained significantly lower than in its absence. Fmr1-KO mice however, were completely insensitive to taurine application and pair-pulse stimulation always resulted in a depression of the response to the second stimulus.ConclusionsPreviously we reported that Fmr1-KO mice have reduced beta subunits of the GABAA receptors. We also showed as well as others that taurine acts as an agonist or a modulator for GABAA receptors. Therefore, the insensitivity of Fmr1-KO slices to taurine application could be due to the reduced binding sites on the GABAA receptors in the Fmr1-KO mice.

Taurine Effects on Emotional Learning and Memory in Aged Mice: Neurochemical Alterations and Differentiation in Auditory Cued Fear and Context Conditioning

Previously we have shown FVB/NJ mice given taurine acutely (i.e. 43 mg/kg/s.c. [aTau]) is anxiolytic, whereas chronically (0.05% w/v for >4 weeks [cTau]) produces anxiogenic phenotypes under select aversive behavioral experiments, but negated emotional contributions to acquisition learning and retention. Hyperexcitability induced in c-Tau mice is further exacerbated under stressful conditions compromising discrimination between cognitive vs. emotional learning. In the present study, we investigated differences between a-Tau and c-Tau mice using the auditory cued tone (ACTC) and context conditioning (CC) tests. Consistent with previous results, a-Tau mice exhibit less fear and increased inhibition, whereas c-Tau mice exhibit increased fear and decreased inhibition to ACTC and CC. Once fear conditioned, taurine mice become hypersensitive to novel environments and ACTC. Taurine brain levels are noted to increase in response to stressors as a neuroprotective mechanism against hyperexcitability. We suggest that c-Tau mice have increased accumulation of cysteamine (Cyst) and depleted somatostatin (SS) expression resulting in fear disregulation through GABAergic projection neurons in the limbic system, which are not seen in a-Tau mice. Our findings suggest that taurine causes not only varied phenotypic profiles of emotional fear learning, but are further complicated by the inability to associate cues with aversive stimuli due to potential auditory sensory overloading.

Taurine Recovery of Learning Deficits Induced by Developmental Pb 2+ Exposure

Lead (Pb2+) is a historically well-documented environmental neurotoxin that produces developmental cognitive learning and memory impairments. These early neurodevelopmental impairments cause increased brain excitability via disruption of Ca2+ mediated signaling during critical periods of synaptogenesis inducing competition with Ica2+ through NMDARs resulting in altered brain development and functioning across the lifespan. Interestingly, Pb2+ has been shown to decrease GABA transport and uptake, decrease spontaneous and depolarization-evoked GABA neurotransmission and lower the expression of glutamic acid decarboxylase (GAD); thereby, limiting excitatory GABAergic influences that regulate early developmental brain excitability and reducing inhibition across mature GABAergic networks. Taurine has been shown to regulate brain excitability in the mature brain through GABAAR mediated inhibition, thereby attenuating improper brain excitability. Mechanistically, taurine is developmentally a potent neuromodulator that acts as a GABAAR agonist and more recently has been reported as a partial agonist for NMDARs through glycine sites. We investigated the effects of developmental Pb2+ exposure on the rats mature inhibitory cognitive control abilities pharmacologically through anxiety and emotional learning-related behaviors and whether taurine could recover Pb2+ induced neurodevelopmental behavioral deficits later in life. Results showed that Pb2+ increased anxiety symptoms in the open field and hole board test, increased sensitivity to context fear training with cognitive deficits in both acquisition and extinction learning while producing learning deficits and inabilities in acquiring inhibitory learned associations through the acoustic startle response and pre-pulse inhibition (ASR-PPI) test. Interestingly, taurine recovered Pb2+ developmentally induced behavioral deficits in the open field and hole board test evidenced by decreased freezing and increased exploration behaviors and facilitated inhibitory dependent ASR-PPI learning to levels higher than controls. In contrast, Baclofen, a GABABR agonist, dose dependently showed no interaction with Pb2+ effects on ASR-PPI learning. Thus, taurine may work as an important neuromodulator at both GABAARs and NMDARs glycine sites, thereby increasing inhibition, enhancing Ca2+-mediated signaling, and decreasing the altered brain excitability, which impedes learning and memory from early Pb2+ exposure. Taken together our data suggests that GABAAR dependent inhibitory learning is altered by early Pb2+ exposure and taurine was able to recover these Pb2+ induced deficits through neuromodulation of GABAARs and potentially NMDARs later in life. These findings may pave the way for further exploration of taurine as a pharmacotherapy for neurodevelopmental lead poisoning in both animal and clinical models.

The Effects of Chronic Taurine Supplementation on Motor Learning

Taurine is one of the most abundant nonprotein amino acids shown to be essential for the development, survival, and growth of vertebrate neurons. We previously demonstrated that chronic taurine supplementation during neonatal development results in changes in the GABAergic system (El Idrissi, Neurosci Lett 436:19-22, 2008). The brains of mice chronically treated with taurine have decreased levels of GABA(A)β subunits and increased expression of GAD and GABA, which contributes to hyperexcitability. This down regulation of GABA(A)receptor subunit expression and function may be due to a sustained interaction of taurine with GABA(A)receptors. This desensitization decreases the efficacy of the inhibitory synapses at the postsynaptic membrane. If changes occur in the GABAergic system as a possible compensatory mechanism due to taurine administration, then it is important to study all aspects by which taurine induces hyperexcitability and affects motor behavior. We therefore hypothesized that modification of the GABAergic system in response to taurine supplementation influences motor learning capacity in mice. To test this hypothesis, the rotarod task was employed after chronic taurine supplementation in drinking water (0.05% for 4 weeks). Control animals receiving no taurine supplementation were also tested in order to determine the difference in motor learning ability between groups. Each animal was trained on the rotarod apparatus for 7 days at an intermediate speed of 24 rpm in order to establish baseline performance. On the testing day, each animal was subjected to eight different predefined speeds (5, 8, 15, 20, 24, 31, 33, and 44 rpm). From our observations, the animals that underwent chronic taurine supplementation appeared to have a diminished motor learning capacity in comparison to control animals. The taurine-fed mice displayed minor improvements after repeated training when compared to controls. During the testing session the taurine-fed mice also exhibited a shorter latency to fall, as the task requirements became more demanding.

Taurine Recovers Mice Emotional Learning and Memory Disruptions Associated with Fragile X Syndrome in Context Fear and Auditory Cued-Conditioning

Previously, we have assessed the administration of chronic taurine (i.e. 0.05 % w/v for >4 weeks [c-Tau]) producing anxiogenic neurobehaviors, whereas acute taurine (i.e. 43 mg/kg/s.c. [a-Tau]) induces anxiolytic outcomes on anxiety based measures of behavior in the FVB/NJ mouse strain. Here we compared our findings with the FVB/NJ Fragile X knock out mouse (KO), the most inheritable form of intellectual disability characterized by a reduced efficiency in GABAergic signaling, to assess whether or not taurine, a GABAAR agonist, (i.e. acute and chronic) could stabilize and recover the emotional learning and memory profiles consistent with wild type (WT) mice. When compared to WT mice, KO mice exhibited reduced learning on the context fear task over four trials. Interestingly, both KO a-Tau and KO c-Tau evidenced recovered emotional learning acquisition during the context fear task when compared to KO which was comparable to WT; with marked improvements in the KO a-Tau condition more than the KO c-Tau. In addition, memory retention was increased in the KO a-Tau condition when compared to KO, while KO c-Tau was not significantly affected. These findings suggest that KO a-Tau treatment can be utilized as a potential pharmacotherapeutic intervention for treating KO’s in enhancing GABAergic modulation of emotional learning conditions consistent with this genetic disorder.

Changes in Gene Expression at Inhibitory Synapses in Response to Taurine Treatment

We have previously shown that chronic supplementation of taurine to mice significantly ameliorated the age-dependent decline in memory acquisition and retention. We also showed that concomitant with the amelioration in cognitive function, taurine caused significant alterations in the GABAergic and somatonergic system. These changes include increased levels of the neurotransmitters GABA and glutamate, increased expression of both isoforms of GAD and the neuropeptide somatostatin, decreased hippocampal expression of the beta (β) 2/3 subunits of the GABA(A) receptor, an increase in the number of somatostatin-positive neurons, and an increase in the amplitude and duration of population spikes recorded from CA1 in response to Schaefer collateral stimulation and enhanced paired pulse facilitation in the hippocampus. These specific alterations of the inhibitory system caused by taurine treatment oppose those naturally induced by aging, suggesting a protective role of taurine in this process. In this study, we further investigated the effects of taurine on gene expression of relevant proteins of the inhibitory synapses using qRT-PCR method and found that taurine affects gene expression of various subunits of the GABA(A) receptors and GAD. Increased understanding the effects of taurine on gene expression will increase our understanding of age-related taurine-mediated neurochemical changes in the GABAergic system and will be important in elucidating the underpinnings of the functional changes of aging. Taurine might help forestall the age-related decline in cognitive functions through interaction with the GABAergic system.

Making the Case for Real Diversity: Redefining Underrepresented Minority Students in Public Universities

Immigration to the United States has been a major catalyst for population growth and is the significant factor in the changing racial/ethnic composition of our population. The specific changes in the racial/ethnic mix in United States in recent times are due in large part to a surge in immigration from diverse sending countries. However, much of the terminology that continues to be used in the context of higher education to describe diversity in the student populations are anachronistic and serves actually to occlude true diversity. We argue that variables such as country of birth of the student, the country of origin of the parent, and parental educational achievement, all have significant impact on the academic progress and success of undergraduate underrepresented minority students. These are variables that should be used to disaggregate the traditional racial and ethnic categories, to really serve the needs of the increasingly diverse student body. These are not data typically collected by institutions of higher education, but without which appropriate needs assessments and targeted interventions cannot occur.