Research Portfolio

Funding Opportunities

Join our Mailing List
Join our mailing list to be notified of new funding opportunities.

Your Email

To receive information about funding opportunities, events, and program updates.



Nicotine toxicity acting on cardiac neurons

Institution: University of California, San Diego
Investigator(s): Darwin Berg, Ph.D.
Award Cycle: 1997 (Cycle 6) Grant #: 6RT-0050 Award: $446,920
Subject Area: Nicotine Dependence
Award Type: Research Project Awards
Abstracts

Initial Award Abstract
Cigarette smoking is the leading cause of premature deaths in the United States. A major contributor to the fatalities is increased heart disease caused by smoking. Nicotine is the primary drug in cigarette smoke that acts on molecules in the nervous system which controls cardiac output. These molecules, called nicotinic receptors, are proteins on the neuron surface and normally respond to chemicals released by other neurons at synapses. Nicotine, however, interacts more potently with the receptors and either can stimulate them or, in some cases, can produce long-lasting inactivation. Most interesting is an abundant class of nicotinic receptors in brain that is very efficient at letting calcium enter cells. The calcium, in turn, can activate a large array of calcium-dependent events in neurons, making the receptors potentially very important for a variety of physiological processes.

Recent evidence indicates that similar receptors are prominent in the clusters of neurons found on the heart wall. These neuron clusters relay information from the brain and also act as a local neural circuit to regulate heart function. The experiments proposed here will examine the role of such nicotinic receptors in transmitting information from the nervous system to the heart, and will assess how chronic exposure to nicotine at levels encountered in the blood of smokers produces long-lasting impairment of these processes.

The experimental approaches combine a number of techniques including the use of microelectrodes to measure electrical signals in rat cardiac neurons, the use of antibodies to study the composition of the receptors, and the use of fluorescent dyes to measure the influx of calcium into neurons. Direct visual monitoring of rhythmic heart contractions under the test conditions will also be performed to assess the overall impact of the receptors on neural control of heart function. In each experimental setting, the effects of nicotine will be examined to test the hypothesis that chronic exposure to the drug produces long-lasting inactivation of nicotinic receptors with developmental consequences for the heart. These studies will provide new insight into cellular and molecular mechanisms by which cigarette smoking can exacerbate heart disease. The information will be important for risk assessment by the public in considering acute effects such as cardiac arrhythmias, angina, and sudden cardiac arrest, as well as long-term dangers such as reduced cardiac output and endurance. Of greatest urgency is information about possible long-term consequences of nicotine exposure to the fetus during pregnancy. A direct clinical relevance of these studies is that they may suggest therapeutic strategies with drug combinations to lessen the risks and help restore balanced neural control of cardiac function.

Final Report
Obiective(s):

1. Identify the distinctive properties of aBgt-sensitive AChRs on rat intracardiac neurons and determine how the receptors are regulated by nicotine exposure.

2. Test the hypothesis that aBgt-sensitive AChRs on intracardiac neurons produce sustained elevations in intracellular calcium and influence the firing capabilities of the neurons. 3. Examine directly the contribution of aBgt-sensitive AChRs to signaling through cardiac ganglia and their impact on cardiac function.

3. Test the hypothesis that chronic exposure to nicotine in vivo produces long-lasting developmental effects on nicotinic transmission in cardiac ganglia.

Significant findings and conclusions:

A number of significant findings and conclusions were obtained relating to the original specific aims and extending beyond them. Most salient, we identified a new kind of a7containing nicotinic receptor in rat cardiac ganglion neurons and replicated the findings in rat superior cervical ganglion neurons (Cuevas and Berg, 1998; Cuevas et al., 2000). We also demonstrated the localization of a7-containing receptors on somatic spines and showed that they regulate calcium influx which has important consequences for receptor function and synaptic signaling (Shoop et al., 1999, 2000, 2001; Liu and Berg; 1999a, 1999b). We went on to examine the subunit composition of other nicotinic receptor subtypes in the CNS, and to examine the developmental regulation of a7-containing receptors (Conroy and Berg, 1998; Blumenthal et al., 1999). We also considered the role of specific organizing molecules in determining the location of a7-containing receptors on neurons (Kassner et al., 1998; Blumenthal et al., 1999; Conroy and Berg, 1999; Conroy et al, 2000; Paysan et al., 2000; Roth et al., 2000). Some of the results were also described in review articles and chapters (Berg et al., 1999, 2000; Lukas et al., 1999).

Since the a7-containing nicotinic receptor is widely expressed in the nervous system and since it regulates numerous calcium=dependent cellular events due to its high relative calcium permeability, the receptor has been implicated in numerous brain functions and neurodegenerative diseases. The findings presented in the indicated publications provide a molecular and cellular basis for considering receptor function and regulation in neural circuits.
Publications

Nicotinic receptor subtypes in the developing chick brain: appearance of a species containing the alpha 4, beta 2, and alpha 5 gene products.
Periodical: Molecular Pharmacology Index Medicus:
Authors: Conroy WG, Berg DK ART
Yr: 1998 Vol: 53 Nbr: Abs: Pg: 392-401

Organizing effects of rapsyn on neuronal nicotinicacetylcholine receptors
Periodical: Molecular and Cellular Neuroscience Index Medicus:
Authors: Kassner PD, Conroy WG, Berg DK ART
Yr: 1998 Vol: Nbr: Abs: Pg:

Functional blockade of neuronal AChRs by intracellular dialysis with monoclonal antibodies: identification of an a7-containing receptor subtypes
Periodical: Society for Neuroscience Abstracts Index Medicus:
Authors: Cuevas J, Berg DK ABS
Yr: 1998 Vol: 24 Nbr: 834 Abs: Pg:

Transport of a7-containing neuronal AChRs along the sciatic nerve
Periodical: Society for Neuroscience Abstracts Index Medicus:
Authors: Roth AL, Conroy WG, Berg DK ABS
Yr: 1998 Vol: 24 Nbr: 834 Abs: Pg:

Neuronal AChRs containing a7 subunits are concentrated on somatic spines
Periodical: Society for Neuroscience Abstracts Index Medicus:
Authors: Shoop RD, Martone ME, Yamada N, Ellisman MH, Berg DK ABS
Yr: 1998 Vol: 24 Nbr: 834 Abs: Pg:

Three-dimensional analysis of a presynaptic calyx of confocal microscopy
Periodical: Society for Neuroscience Abstracts Index Medicus:
Authors: Paysan J, Coggan JS, Conroy WG, Berg DK ABS
Yr: 1998 Vol: 24 Nbr: 567 Abs: Pg:

Calcium regulation of nicotinic receptors with alpha7 subunits on somatic spines
Periodical: Society for Neuroscience Abstracts Index Medicus:
Authors: Liu Q-S, Berg DK ABS
Yr: 1999 Vol: 25 Nbr: Abs: Pg:

The role of actin filaments in constraining alpha7-containing nicotinic receptors to somatic spines
Periodical: Society for Neuroscience Abstracts Index Medicus:
Authors: Shoop RD, Conroy WG, Berg DK ABS
Yr: 1999 Vol: 25 Nbr: Abs: Pg:

Targeting alpha7-containing nicotinic receptors on neurons to distal locations
Periodical: European Journal of Pharmacology Index Medicus:
Authors: Roth AL, Shoop RD, Berg DK ART
Yr: 2000 Vol: 393 Nbr: Abs: Pg: 105-112

Two distinct classes of functional alpha7-containing nicotinic receptors on rat superior cervical ganglion neurons
Periodical: Journal of Physiology Index Medicus:
Authors: Cuevas J, Roth AL, Berg DK ART
Yr: 2000 Vol: 525 Nbr: Abs: Pg: 735-746

Cytoskeletal links of neuronal acetylcholine receptors containing alpha7 subunits
Periodical: Journal of Neuroscience Index Medicus:
Authors: Shoop RD, Yamada N, Berg DK ART
Yr: 2000 Vol: 20 Nbr: Abs: Pg: 4021-4029

The neurofilament infrastructure of a developing presynaptic calyx
Periodical: Journal of Comparative Neurology Index Medicus:
Authors: Paysan J, Coggan JS, Conroy WG, Berg DK ART
Yr: 2000 Vol: 425 Nbr: Abs: Pg: 284-294

Cluster formation of alpha7-containing nicotinic receptors at interneuronal interfaces in cell cultures
Periodical: Neuropharmacology Index Medicus:
Authors: Conroy WG, Ogden LF, Berg DK ART
Yr: 2000 Vol: 39 Nbr: Abs: Pg: 2699-2705