Michael L. Molineux

Michael L. Molineux   PhD 2006
BSc Mechanical Eng.   State Univ. NY
BSc Biology   University of Miami
PhD Dissertation: T-type calcium channels in cerebellar output

Current Gig:
- San Francisco -
Address unknown

Training
1989
Diploma Mechanical Engineering
Lambton College
Sarnia Ontario

1994
BSc Mechanical Engineering
State University of New York
Albany New York

2001
BSc Biology
University of Miami
Miami Florida

2002 - 2006
PhD Neuroscience
University of Calgary
Calgary Alberta
Supervisor: R.W. Turner

Awards
MSc
Alberta Learning Scholarship
Teaching Assistantship

PhD
Alberta Provincial Graduate Scholarship
AHFMR Studentship
CIHR Canada Graduate Scholarship
AHFMR Postdoctoral Fellowship

Research Focus: Soma-dendritic ion channels underlying spike output in deep cerebellar nuclear neurons.

Approach:

Electrophysiology in vitro, pharmacology, immunocytochemistry, microscopy

Preparations:

In vitro slice preparations, tissue sections

Below are short summaries of my projects published from the Turner lab.

Biocytin-filled DCN neuron and MAP-2 labeled dendritic processes

Model - Deep nuclear neurons
Deep nuclear neurons represent the final output of cerebellum after integrating afferent excitatory pontine inputs and inhibitory input from cerebellar cortical Purkinje cells. These cells spontaneously discharge at rest but can respond to Purkinje cell inhibition with a transient rebound burst discharge. My project involves the use of immunocytochemistry, patch clamp recordings and focal ejection of ion channel blockers to identify identifying the role of ion channels that promote these different forms of output.

Biotin is endogenously expressed in select brain regions
Biotin is a vitamin with a high affinity for avidin compounds that is used in all immuno-cytochemical reactions that rely on the ABC technique to determine the distribution of antigens. A key assumption is that biotin is not expressed in the tissues examined. We show that biotin is endogenously expressed at high levels in specific brain regions, leading to potential false-positive results unless care is taken to prevent labeling of endogenous biotin. See McKay et al. (2003) PDF

Obtaining patch clamp recordings in the adult CNS
Patch clamp recordings are often difficult to obtain beyond P17 due to a peri-neuronal net in the extracellular space. I helped develop a method of "spread-printing", a novel approach to partially dissociate tissue slices and allow recordings from deep nuclear cells in animals up to 6 months old without the need for proteolytic enzymes. See Morales et al. (2004) PDF

Kv3 potassium channels exhibit frequency-dependent effects on cell output
This study describes a frequency-dependent effect of high threshold Kv3 potassium channels on the input-output relation of pyramidal cells and determined its underlying basis. A combination of patch recordings and modeling show that Kv3 channels rescue spike trains at high frequencies by decreasing both sodium channel inactivation and a cumulative increase in a low threshold potassium current. See Fernandez et al. (2005) PDF

Kv1 K+ channels regulate the climbing fiber EPSP

Kv1 potassium channels optimize rebound discharge in deep cerebellar neurons
In this study we examined the role of low threshold Kv1 K+ channels in controlling Purkinje cell discharge and its effect on the activity of postsynaptic deep cerebellar neurons. Kv1 channels lower Na+ spike frequency and raise the threshold for Ca2+ spike discharge in Purkinje cells. When these spike patterns are applied as stimulus templates to Purkinje cell axons, I found that Kv1 channels lower Purkinje cell output frequency to a range that optimizes rebound discharge in deep cerebellar neurons. See McKay et al. (2005) PDF

Measurement of stellate first spike latency

A-type K+ and T-type Ca2+ channels generate a novel first spike latency relationship
In this study we examined the mechanism underlying a non-monotonic voltage - first spike latency relationship in cerebellar stellate cells. We show through current and voltage clamp analysis and modeling that A-type and T-type inactivating channels interact to produce a voltage-dependent increase or decrease in first spike latency. The effect depends critically on the voltage-dependence of inactivation and relative density of the respective currents. See Molineux et al. (2005) PDF

Rebound burst discharge in deep cerebellar neurons

T-type Ca2+ channel isoforms correlate with distinct burst phenotypes
In this study we determined the distribution of the three isoforms of T-type currents (Cav3.1, 3.2, 3.3) in rat cerebellar neurons, revealing a greater range of expression and contribution to rebound discharge than realized. Moreover, a distinct expession pattern for Cav3 isoforms in deep cerebellar nuclear neurons is shown to correlate to either a strong or weak rebound discharge capability. See Molineux et al. (2006) PDF

Cav3 immunolabel in cortical pyramidal dendrites

T-type calcium channel isoforms differentially distribute to soma and dendrites
In this study we used antibodies specific to each of the Cav3 family of T-type calcium channels (Cav3.1, 3.2, 3.3) to compare the distribution of these isoforms over the soma-dendritic axis of cells in neocortex, hippocampus, thalamus and cerebellum. We find a general subcellular pattern for the three isoforms between cells, with Cav3.3 preferentially targeted to both somatic and dendritic compartments. See McKay et al. 2006. PDF

CF discharge converts Purkinje cell output

Climbing fiber input regulates intrinsic properties of Purkinje cells
In this study we show that climbing fiber input activated at physiological frequencies blocks an intrinsic trimodal pattern inherent to Purkinje cells studied in vitro, restoring tonic Na+ spike discharge similar to that found in vivo. Moreover, all the effects of direct climbing fiber stimulation were reproduced by simulating climbing fiber input with an injected EPSC in the presence of synaptic blockers, emphasizing a key role for the postsynaptic complex spike depolarization in determining Purkinje cell activity. See McKay et al. 2007. PDF

Distinct ion channel contributions to burst phenotype in deep cerebellar neurons
The large diameter putative projection neurons of rat deep cerebellar nuclei have been shown to generate either a Transient or Weak rebound Burst phenotype that was linked to the selective expression of T-type calcium channel isoforms. Here we show that the two burst phenotypes also reflect a differential functional availability of LVA T type calcium current at burst threshold, and different contributions of repolarizing potassium currents that shape burst properties. See Molineux et al. (2008). PDF

KChiP3 mediated shift in Kv4 inactivation

Distinct roles for IT and IH in controlling deep cerebellar rebound responses
Here we examined the role for IT and IH in generating the rebound responses that are evoked in deep cerebellar neurons in response to inhibitory input from Purkinje cells. We used recordings in vitro and modeling to find that only a small fraction of the total IT and IH available to a cell are activated by physiological levels of hyperpolarization. However, the currents activated are still sufficient to differentially control the latency, frequency and precision of spike firing during the immediate phase of a rebound response. See Engbers et al. (2011).

Peer-reviewed Publications

McKay B.E, Molineux ML, and Turner RW. (2004) Biotin is endogenously expressed in select regions of the rat central nervous system. J. Comparative Neurology 473(1): 86-96. PDF

Morales E, Fernandez FR, Sinclair S, Molineux ML, Mehaffey HW and Turner RW. (2004) Releasing the peri-neuronal net to patch clamp neurons in the adult CNS. Pflugers Archiv 448(2):248-58. PDF

Fernandez F, Mehaffey WH, Molineux ML and Turner RW. (2005) High threshold K+ channels increase gain by offsetting a frequency-dependent increase in low threshold K+ current. J. Neuroscience 25(2): 363-371. PDF

McKay BE, Molineux ML, Mehaffey WH and Turner RW. (2005) Kv1 potassium channels control Purkinje cell output to facilitate post-synaptic rebound discharge in deep cerebellar neurons. J. Neuroscience 25(6): 1481-1492. PDF

Molineux ML*, Fernandez FR*, Mehaffey WH and Turner RW (2005) A-type and T-type currents interact to produce a novel spike latency-voltage relationship in cerebellar stellate cells. J. Neuroscience 25(47): 10863-10873. * Shared first author. PDF

Molineux ML, McRory JE, McKay BE, Hamid J, Mehaffey WH, Snutch TP, Zamponi GW and Turner RW (2006) Specific T-type calcium channel isoforms are associated with distinct burst phenotypes in deep cerebellar nuclear neurons. PNAS 103(14): 5555-5560. PDF Supplementary data

McKay, B.E., McRory, J.E., Molineux, M.L., Hamid, J., Snutch, T.P., Zamponi, G.W. and Turner, R.W. (2006) Cav3 T-type calcium channel isoforms differentially distribute to somatic and dendritic compartments in rat central neurons. European J. Neuroscience 24: 2581-2594. PDF

McKay, B.E., Engbers, J.D.T., Mehaffey, W.H., Gordon, G., Molineux, M.L., Bains, J. and Turner, R.W. (2007) Climbing fiber discharge regulates cerebellar functions by controlling the intrinsic characteristics of Purkinje cell output. J. Neurophysiology 97: 2590-2604. PDF

Molineux, M.L., Mehaffey, W.H., Tadayonnejad, R., Anderson, D., Tennent, A.F. and Turner, R.W. (2008) Ionic factors governing rebound burst phenotype in rat deep cerebellar neurons. J. Neurophysiology 100:2684-2701. PDF

Engbers, J.D.T.*, Anderson, D.*, Tadayonnejad, R.*, Mehaffey, W.H., Molineux, M.L. and Turner, R.W. (2011) Distinct roles for IT and IH in controlling the frequency and timing of rebound spike responses. J. Physiol (Lond.), eprint, Oct 3, 2011. * Shared first authors.

Invited Chapters:
McKay, B.E., Molineux, M.L., and Turner, R.W. (2007) Endogenous expression of biotin in central neurons. Methods in Molecular Biology , vol. 418: Avidin-Biotin Interactions. R. J. McMahon (ed) Methods Mol Biol. © Humana Press Inc., Totowa, NJ 418:111-128.

Tadayonnejad, R., Anderson, D., Molineux, M.L., Mehaffey, W.H., Jayasuriya, K. and Turner, R.W. (2011) Rebound discharge in deep cerebellar nuclear neurons in vitro. Cerebellum 9(3): 352-374. PDF

Key Abstracts
Molineux ML and Turner RW. The role of TEA sensitive K^+ channels in the output of deep cerebellar neurons. Proc Soc Neurosci 2003.

Turner RW, Molineux ML, McKay BE. Endogenous Biotin in the Rat CNS – Implications for False-Positive Avidin-Biotin Reactions. Proc Soc Neurosci 2003.

Molineux ML and Turner RW. The ionic basis of deep cerebellar neuron tonic firing. Proc Soc Neurosci 2004.

Fernandez FR, Mehaffey WH, Molineux ML and Turner RW. Incomplete activaton of high threshold K+ channels allows feedback stabilization of high frequency firing. Proc Soc Neurosci 2004.

McKay BE, Molineux, ML and Turner RW. Kv1 K+ channels regulate excitability of rat cerebellar Purkinje cells and climbing fibers. Proc Soc Neurosci 2004.

Molineux ML, McRory JE, McKay B., Mehaffey WH, Hamid ., Snutch TP, Zamponi GW, and Turner RW. Specific Cav3 T-type calcium channel isoforms are associated with bursting and nonbursting cerebellar neurons. Proc. Soc. Neurosci. 2005.

Hamid J, Molineux ML, Snutch TP, Rehak R, Turner RW, Zamponi GE and McRory JE. Generation and characterization of novel and specific antibodies directed to the Cav3 family of calcium channels. Biophys Mtg, 2006.

Turner, R.W., Molineux, M.L., McRory, J.E., Snutch, T. and Zamponi, G.W. T type calcium channel function in deep cerebellar nuclei. Calcium Channel Conference, Moorea 2007.

McKay BE, Engbers JDT, Mehaffey WH, Gordon GRJ, Molineux ML, Bains JS and Turner RW. Climbing fibre control of Purkinje cell spike output. Can Assoc Neurosci 2007 [Can J. Neurol. Sci., 34 (Supplement 3): S87].

Molineux ML, Tennent AF, Mehaffey HM and Turner RW. Ionic mechanisms of spike firing in two distinct types of rat deep cerebellar neurons. Proc. Soc. Neurosci. 2007.

Tadayonnejad R, Molineux ML, Mehaffey HM and Turner RW. Transient and Weak Bursting Deep Cerebellar neurons exhibit differential coding properties for membrane hyperpolarizations. Proc. Soc. Neurosci. 2007.

Iftinca, M., Anderson, D.M., Rehak, R., Molineux, M.L., Zamponi, G.W. and Turner, R.W. T type calcium channels provide calcium-dependent modulation of A type potassium currents. Can. Assoc. Neurosci. 2008.

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