Laboratory of Molecular Neurobiology

Welcome to the Laboratory of Molecular Neurobiology at the Boston University School of Medicine. The members of the laboratory are working together as a team under the direction of David H. Farb, PhD, to elucidate the mechanisms by which receptors are regulated, how activation of these receptors modulates neural network activity in vivo and, how this in turn contributes to the onset and progression of memory deficits in age-related neurodegenerative diseases. The laboratory uses a systems neuroscience approach to understanding the functional interactions within neural networks implicated in neurological and psychiatric diseases. Dr. David Farb and the other members of the Laboratory of Molecular Neurobiology are among the first to use in vivo electrophysiological techniques to advanced our understanding of how drugs modulate neural network activities implicated in memory deficits associated with age-related amnestic mild cognitive impairment (Hippocampus, 2015). The Laboratory is currently using this same technology combined with ultra fine silicon microelectrode arrays (see figures and video below) to identify changes in local field potentials and single unit activity that underlie cognitive deficits associated with aging and disease and, to assess for the functional neural network correlates associated with effective therapeutics for Alzheimer’s disease.   Due to their unique design and flexible layouts, silicon probe microelectrode arrays permit for recording across strata within a subregion as well as from one or more subregions.  The figures below demonstrate how local field potential data is acquired and visualized for analysis of single unit activity associated with sharp wave ripples events in the CA1 hippocampal subregion (sharp wave ripple event is shown inside box in lower figure).  This research is funded in part by the National Institute on Aging.  The Laboratory of Molecular Neurobiology is part of the Boston University Center for Systems Neuroscience.

 

Sharp Wave Ripple with Associated Single Unit Activity

Silicon Probe Array Video

Hippocampal Place Cells

In vivo electrophysiological recordings have been used to study neuronal activity and hippocampal dependent learning and memory function since the Nobel Prize winning discovery of “Place Cells” by O’Keefe and Dostrovsky in 1971.  Place cells, are hippocampal pyramidal cells that fire with a greater frequency when an animal is in a specific location.  This activity pattern can be visualized in the video below of the Dancing Place Cells which was made from actual data recordings of hippocampal place cells.

The Dancing Place Cells

These cells establish stable place fields within a given environment and change their firing patterns (“remap”) when the animal is moved to a novel location in a classic remapping paradigm such as that shown in the video below.

Remapping Paradigm Video

The figure below shows the place fields of a rat “remapping” when the animal is moved from a familiar square environment to a novel cylindrical one.  The activity of these place cells is altered by aging and disease.  Place cell activity can also be modulated with drugs (a.k.a., cognitive enhancers).  In recent years, advances in vivo electrophysiology coupled with increased understanding of place cell firing dynamics has opened the door to the use of this technology as a research tool in the preclinical drug discovery process. Pyramidal cells with defined place fields in at least one environment are subsequently analyzed for drug-induced effects on firing rates, spatial correlations across environments, and spatial information content per spike.

Rat ephys 1

Place Fields

 

Analysis of In vivo Electrophysiological Data

Post-hoc differentiation of pyramidal “complex spike” cells (see top image below) and interneurons (see bottom image below) is facilitated in part by evaluation of auto-correlograms (far left panel), which show distinct patterns of activity, with pyramidal cells showing “complex spikes” characterized by bursts of action potentials immediately following the refractory period. Pyramidal cells are further differentiated from interneurons by the mean firing rates of the cell and the trough to peak width of their waveforms.  Note that the pyramidal cells also have distinct place fields (far right panel) while the interneurons do not.

Pyramidal Cells

Complex spike cell clusters

Interneurons

Interneurons figure

 

Custom Nichrome Tetrode Arrays

The Laboratory of Molecular Neurobiology also acquires in vivo electrophysiological data with custom made nichrome microtetrode arrays (such as the one pictured below).  The video below shows how these arrays are constructed.  These arrays allow us to simultaneously record drug-induced changes in the activity of single place cells and local field potentials from one or more hippocampal subregions (e.g., CA3 and CA1 ) in freely behaving rodents.The microelectrode arrays contain tetrodes, comprised of four nichrome micro-electrodes, such as the one pictured below (top) which can be lowered into the hippocampal subregion of interest by turning the screw on a microdrive (bottom).  

Microtetrode  Array

Microarray 1

Tetrode

Tetrode 1

Microelectrode Array Construction Video

These tetrodes allow for isolation of individual pyramidal cells based on the proximity of the cell to each of the four wires of the tetrode. The action potentials or “spikes” of individual neurons such as those pictured below are “sorted” manually using Plexon Offline Sorter software as shown below or via semi-automated sorting program for subsequent analysis. Well-isolated cells such as the one pictured below in yellow show amplitude differences reflecting their proximity to the four poles of the tetrode.

Observations and Results

We have effectively used the methods described above to demonstrate that co-administration of sub-therapeutic doses of the FDA approved anti-epileptic agents levetiracetam and valproic acid reduces hippocampal hyperactivity and increases spatial information content (SIC) per action potential (spike) in the CA3 and CA1 hippocampal subregions of aged rats (see histogram of these data below) (Hippocampus, 2015).

Pharmacologic Connectome

Pharmacological modulation of hippocampal circuitry implicated in learning and memory: Connectome shows interactions between inhibitory and excitatory inputs. Putative targets for treating age related learning and memory impairments include enhancement of GABA inhibitory tone and attenuation of glutamate mediated excitation. A loss of inhibitory interneurons in the hilar region has been implicated in CA3 pyramidal cell hyperactivity. Acute administration of LEV + VPA may attenuate the hyperactivity in this region of the hippocampus in part by enhancing GABAergic neurotransmission. Muscarinic and nicotinic acetylcholine receptors provide for suppression of feedback excitation and enhancement of afferent input respectively. Ach = acetylcholine; DA = dopamine; DG = dentate gyrus; ECI = entorhinal cortex layer I; ECII = entorhinal cortex layer II; ECIII = entorhinal cortex layer III; GABA = Gamma Amino Butyric Acid; Glu = glutamate; Loc. Cer. = Locus Coeruleus; Med. Sep. = Medial Septum; NE = norepinephrine; Raphe = raphe nucleus; Sub = subiculum; VTA = Ventral Tegmental Area (Hippocampus, 2015).