Assistant Professor

Research Interests:

Nicotine Addiction

The goal of this project is to elucidate the molecular mediators that lead to the association of contextual cues with the nicotine experience, a critical step in the process toward understanding and curing nicotine addiction.  Nicotine addiction is accompanied by striking associations between tobacco use and the context in which it is being experienced making it particularly difficult to maintain abstinence.  This problem is a significant health and social issue because tobacco use is the leading cause of preventable death in the United States.

Manipulation of the key mediators of these nicotine – context associations will facilitate their dissociation.  Since ERK MAPK plays a pivotal role in hippocampus-dependent contextual associative learning, and since nicotine both activates ERK MAPK in hippocampus and enhances hippocampus-dependent associative learning, we hypothesize that manipulations of ERK MAPK during different phases of nicotine – context associative learning will alter expression of those associations and hence enhance the extinction process.  Compulsion to take drugs of abuse and risk of relapse is, in part, an associative learning issue.   Pavlovian conditioning, one form of associative learning, describes the process by which a neutral stimulus becomes associated with a rewarding stimulus following repeated pairing of the two. For example the addictive drug nicotine serves as an unconditioned stimulus (US) that provides an unconditioned reward (UCR). After repeated pairings of nicotine with neutral environmental stimuli, these neutral stimuli gain significance (conditioned stimuli, CS).  As such, the context in which nicotine is repeatedly experienced becomes a CS associated with nicotine delivery and thus an important part of the stimulus complex that sustains nicotine use.

Nicotine-conditioned locomotor stimulation is a straightforward behavioral paradigm based on Pavlovian conditioning principles and serves as a model for nicotine – context associative learning.  We will utilize this paradigm to study the nicotine – context associative learning processes involved in the development, expression, and extinction of nicotine-conditioned cues in order to test the hypothesis that ERK MAPK manipulations during different phases of nicotine - context associative learning will alter expression of those associations and possibly enhance the extinction process. 

Alzheimer’s Disease

            Nicotinic Receptors in Alzheimer’s Disease

Elevation of beta-amyloid peptides (Ab) is considered a culprit in the cognitive decline of Alzheimer’s disease (AD), though these peptides are present in the brains and CSF of normal subjects.   The earliest detected cognitive dysfunction in AD occurs in the hippocampus: impairment in the encoding of new episodic memories is typical of early AD and this loss of episodic memory is linked to medial temporal pathology including the hippocampus.  Despite intensive study, the mechanism by which elevated Ab leads to AD-related hippocampal dysfunction remains mysterious, not to mention the lack of an understanding of the physiologic role for Ab in normal cognition, synaptic function, and signal transduction. 

An early depletion of nicotinic acetylcholine receptors (nAChRs) on the cholinergic projection neurons in the brains of AD patients is a universal feature of the disease; these receptors are the target for the current symptomatic strategy.  a7 nAChRs are expressed by these cholinergic projection neurons as well as being expressed pre- and post-synaptically in target brain regions.  a7 nAChRs flux the pluripotent second messenger Ca²⁺ and have been shown to modulate both neuron excitability and plasticity.  Furthermore, a7 nAChRs have been implicated in mediating some of the cognitive enhancing effects of in vivo administered nicotine. 

 Originating with the observation of an association between Ab and a7 nAChRs in postmortem tissue from AD brain, we and others have gone on to show that Ab binds to a7 nAChRs, leads to Ca²⁺-dependent activation of the extracellular signal-regulated kinase mitogen-activated protein kinase (ERK MAPK) cascade that results in phosphorylation of the transcription factor CREB.  The ERK MAPK cascade is crucial for many forms of synaptic plasticity, learning and memory.  We also demonstrated that Ab activates a7 nAChRs expressed in Xenopus oocytes, suggesting that Ab is an endogenous ligand for the a7 nAChR.  In the Tg2576 animal model for AD in which Ab production is elevated throughout the animals’ lifetime, we have shown age dependent dysregulation of ERK2 MAPK and CREB as well as a dramatic up-regulation of a7 nAChRs in the hippocampi of these mice, indicating that chronic exposure to Ab perturbs the normal functionality of this receptor system.  Furthermore, Tg2576 mice exhibit an age-dependent decline in cognition. 

This project strives to understand how Ab interaction with a7 nAChRs contributes to the molecular etiology of AD.  Currently, we are investigating whether a7 nAChRs mediate the toxic effects of elevated Ab by generating and studying genetic animal models in which Ab is over produced and a7 nAChR function is altered.  These animal models are analyzed at the behavioral, electrophysiological, biochemical and histopathological levels.  This work could potentially provide a mechanism for the cholinergic deficit in AD, as well as help delineate the emerging field of Ab / a7 nAChR biology as it pertains to normal physiological processes.  

Calcineurin in Alzheimer’s Disease

The Tg2576 transgenic mouse is an extensively characterized animal model for Alzheimer’s disease (AD).  Similar to AD, these mice suffer from progressive decline in several forms of declarative memory including contextual fear conditioning and novel object recognition (NOR).  Recent work on this and other AD animal models suggests that initial cognitive deficits are due to synaptic dysfunction that is triggered by oligomeric forms of Ab peptide.  These early forms of cognitive dysfunction, we believe, are fully treatable with the correct intervention.   

Tg2576 at an early age have high central nervous system (CNS) activity of calcineurin (CaN), a phosphatase involved in negative regulation of memory function via inactivation of the transcription factor cAMP responsive element binding proteins (CREB), and display CaN-dependent memory deficits. These results thus suggested the involvement of prefibrillary forms of Abeta. To investigate this issue, we compared the effect of monomeric, oligomeric, and fibrillar Abeta on CaN activity, CaN-dependent pCREB and phosphorylated Bcl-2 Associated death Protein (pBAD) levels, and cell death in SY5Y cells and in rat brain slices, and determined the role of CaN on CREB phosphorylation in the CNS of Tg2576 mice. Our results show that oligomeric Abeta specifically induces CaN activity and promotes CaN-dependent CREB and Bcl-2 Asociated death Protein (BAD) dephosphorylation and cell death. Furthermore, Tg2576 mice display Abeta oligomers and reduced pCREB in the CNS, which is normalized by CaN inhibition. These findings suggest a role for CaN in mediating effects of oligomeric Abeta on neural cells. Because elevated CaN levels have been reported in the CNS of cognitively impaired aged rodents, our results further suggest that abnormal CaN hyperactivity may be a common event exacerbating the cognitive and neurodegenerative impact of oligomeric Abeta in the aging CNS.

Further studies have demonstrated that acute CaN inhibition rescues deficits in different forms of declarative memory in 5 months old Tg2576; specifically spontaneous object recognition, by employing the NOR paradigm, and contextual fear conditioning.  Furthermore, we determined whether FK506 rescue of NOR deficits depends on the retention interval employed and therefore is restricted to short-term, intermediate-term, or long-term memory (STM, ITM or LTM, respectively).  In object recognition, Tg2576 are unimpaired when NOR is tested as a STM task and CaN inhibition with FK506 does not influence NOR STM performance in Tg2576 or WT mice.  Tg2576 were impaired in NOR compared to WT mice when a 4 or 24 hour retention interval was employed to model ITM and LTM, respectively.  Acute CaN inhibition prior to and during the training session reversed these deficits in Tg2576 mice with no effect on WT performance. Our findings demonstrate that aberrant CaN activity mediates object recognition deficits in 5 months old Tg2576 when NOR is employed as a test for ITM and LTM.  Additionally, aberrant CaN activity mediates associative learning and memory deficits as well.  In human AD, CaN inhibition may lead the way for therapeutics to improve declarative memory performance as demonstrated in a mouse model for AD.

PPARg in Alzheimer’s Disease

Converging evidence associates gluco-regulatory abnormalities and cognitive function in AD.  As such, ongoing clinical trials are testing whether insulin-sensitizing drugs, such as the peroxisome-proliferator-activated receptor gamma agonist, rosiglitazone (RTZ), improve AD-related cognitive performance.  In this study, we used the AD mouse model Tg2576 to test the hypothesis that efficacy of one-month RTZ treatment to improve cognitive performance correlates with peripheral gluco-regulatory status.  We assessed cognition and peripheral gluco-regulatory status of Tg2576 mice following one month treatment with RTZ initiated at 4, 8, and 12 month of age. Our study shows that in 5 MO Tg2576, which are cognitively impaired and with normal glucose regulation, one month treatment with RTZ did not improve cognitive behavior.  In 9 and 13 MO Tg2576, RTZ treatment effectively normalized peripheral gluco-regulatory abnormalities; however, reversal of cognitive deficits only occurred in 9 MO mice.  These findings suggest that RTZ effectiveness at ameliorating cognitive deficits is greater when initiated prior to chronic peripheral gluco-regulatory abnormalities. 

Based on our studies, we propose a model in which RTZ treatment reverses learning and memory deficits that occur concomitant with insulin resistance through activation of CNS PPARg.  We showed that RTZ rescue of associative learning deficits in Tg2576 was reversed by acute intracerebroventricular (icv) injection of the specific and irreversible PPARg antagonist, GW9662 (GW; Seimandi et al., 2005), clearly demonstrating the RTZ effect was mediated specifically by the PPARg isoform in the CNS.  PPARg specificity was also shown by RTZ-dependent increase in hippocampal PPARg DNA binding activity which was reversed by acute icv GW, with no effects on the PPARa  or PPARd isoforms.  Regional specificity was observed since these pharmacological manipulations did not alter PPARa, PPARd, or PPARg in the cerebellum.  Collectively, these data suggest that RTZ improves cognitive function in hippocampus-dependent cognition specifically through forebrain activation of the PPARg isoform.  This is the first demonstration that PPARg plays a role in cognitive function.  As such, little is known about the regulation of the PPARg signaling axis in brain or the molecular mechanisms mediating RTZ-induced PPARg activity in the CNS.  Our research plan is focused on defining the CNS PPARg-specific signaling axis that rescues cognitive deficits in Tg2576. 

Selected Publications:

1. Rodriguez-Rivera J, Denner, LA, Dineley KT (2009) Age-dependence of rosiglitazone reversal of cognitive deficits in an animal model for Alzheimer’s disease.  Neuropharmacology. In review.
2. Hernandez CM, Kayed R, Zheng H, Sweatt JD and Dineley KT (2009) Loss of a7 nicotinic receptors enhances Ab oligomer accumulation exacerbating early-stage cognitive decline and septo-hippocampal pathology in a mouse model for early Alzheimer’s disease.  Journal of Neuroscience. In revision.
3. Taglialatella G, Hogan D, Zhang W-R and Dineley KT (2009) Intermediate- and long-term recognition memory deficits in Tg2576 mice are reversed with acute calcineurin inhibition.  Behav Brain Res.  200(1):95-9.
4. Resse, L.C., Zhang, W., Dineley, K.T., Kayed, R., Taglialatela, G. (2008) Selective induction of calcineurin activity and signaling by oligomeric amyloid beta. Aging Cell. 7(6):824-35.
5. Dineley, K.T., Hogan, D., Ru, W., Taglialatela, G. (2007) Acute inhibition of calcineurin restores associative learning and memory in Tg2576 APP transgenic mice.  Neurobiol. Learn. Mem.  88(2):217-24, 2007 Sep.
6. Jones IW, Westmacott A, Chan E, Jones RW, Dineley K, O'Neill MJ, Wonnacott S. (2006) Alpha7 nicotinic acetylcholine receptor expression in Alzheimer's disease: receptor densities in brain regions of the APP(SWE) mouse model and in human peripheral blood lymphocytes. J Mol Neurosci. 30(1-2):83-84.
7. Bell, K.A., O’Riordan, K.J., Sweatt, J.D. and Dineley, K.T.  (2004) MAPK recruitment by b-amyloid in organotypic hippocampal slice cultures depends on physical state and exposure time.  J. Neurochem.  91:349-361.
8. Wang, R., Dineley, K.T., Sweatt, J.D. and Zheng, H. (2004) Presenilin 1 familial Alzheimer’s disease mutation leads to defective association learning and impaired adult neurogenesis.  Neurosci. 126:305-312.
9. Dineley K.T., Bell K.A., Bui D., and Sweatt J.D. (2002) b-amyloid peptide activates a7 nicotinic acetylcholine receptors expressed in Xenopus oocytes.  J. Biol. Chem. 277:25056-25061.
10. Dineley K.T., Xia X., Bui D., Sweatt J.D. and Zheng H. (2002) Accelerated plaque accumulation, associative learning deficits and up-regulation of a7 nicotinic acetylcholine receptor protein in transgenic mice co-expressing mutant human presenilin 1 and amyloid precursor proteins. J. Biol. Chem. 277:22768-22780.
11. Dineley K.T., Westerman M., Bui D., Bell K., Hsiao Ashe K. and Sweatt J.D. (2001) Beta-amyloid activates the mitogen-activated protein kinase cascade through hippocampal a7 nicotinic acetylcholine receptors: in vitro and in vivo mechanisms related to Alzheimer’s disease. J. Neurosci. 21:4125-4133.
12. Dineley K.T. and Patrick J. (2000) Molecular determinants of alpha7 nAChR surface expression. J. Biol. Chem. 275:13974-13985.
13. Goldner F., Dineley K.T., and Patrick J. (1997) Immunohistochemical localization of the nicotinic acetylcholine receptor subunit alpha6 to dopaminergic neurons in the substantia nigra and ventral tegmental area. Neuroreport  8:2739-2742.
14. Seguela P., Wadiche J., Dineley-Miller K.T., Dani J., and Patrick J. (1993) Molecular cloning, functional properties, and distribution of rat brain alpha7: a nicotinic cation channel highly permeable to calcium.  J. Neurosci. 13:596-604.
15. Dineley-Miller K.T., and Patrick J. (1992) Gene transcripts for the nicotinic acetylcholine receptor subunit, beta4, are distributed in multiple areas of the rat central nervous system.  Mol. Brain Res. 16:339-344.

Current Projects:

1) Physiological role of Ab – nAChR Interaction in Health and Disease
2) Hyperinsulinemia as a Risk Factor for AD
3) Role of NF-kB Signaling Axis in Ab – Induced Cognitive Impairment
4) Calcineurin as a Mediator of Ab – Induced Cognitive Impairment
5) Mass-Spectrometry Identification of Therapeutic Targets in Early and Late AD
6) Proteome of Nicotine – Conditioned Context Associations