Hippocampome Usage Scenario

Consider the following scenario: a neuroscientist applies intracellular, stimulating current to a neuron in CA1 SLM and observes action potentials in a neuron with a soma in CA1 SO.  Examination of the axons and dendrites of the presynaptic cell shows that it has dendrites in CA1 SLM and axons in CA1 SR.  The Hippocampome indicates that this axo-dendritic pattern corresponds to the CA1 IS LM-R neuron type (also called CA1 IS2: Fig. 13 (Hajos et al., 1996) and Fig. 1 (Klausberger and Somogyi, 2008)).  Labeling of the axons and dendrites of the postsynaptic neuron is incomplete, but it shows that the cell has dendrites in CA1 SLM, SR, and SP and axons in CA1 SP. 

In addition to the Hippocampome providing a list of candidate neurons types, it provides biomarker expression properties to distinguish them.  Assume further that the postsynaptic neuron is CB-positive and PV-negative, which points strongly to its being a CA1 Oriens/alveus neuron.  These happen to be the only two biomarkers for which there is expression information for this neuron type; consequently, the researcher makes plans to extract the mRNA and preserves the slice in preparation for future experiments to ascertain a fuller biomarker profile for the neuron, thereby using the Hippocampome to illuminate targets for future work.

          In speculating about the role of the presynaptic CA1 IS LM-R neuron in vivo, the researcher uses the Hippocampome to identify neuron types with axons arborizing in CA1 SLM.  Interestingly, both excitatory and inhibitory neuron types have axons in this parcel.  The potential excitatory inputs come from either CA1, Sub, or EC neuron types, so the researcher is able to convert the slice experiment to stimulate subicular pyramidal neurons and monitor an EPSP response in the IS LM-R neuron. 

This information on the potential connection of Sub Pyramidal-CA1 projecting and CA1 IS LM-R neuron types is part of the wiring diagram for the CA1 SLM local environment that can be created from knowledge in the Hippocampome.  The researcher uses all of the wiring information, in combination with available electrophysiological properties in the Hippocampome for the neuron types, to create a realistic small network model centered on the CA1 IS LM-R neuron.

Hajos, N., Acsady, L., and Freund, T.F. (1996). Target selectivity and neurochemical characteristics of VIP-immunoreactive interneurons in the rat dentate gyrus. Eur. J. Neurosci. 8, 1415–1431.

Klausberger, T., and Somogyi, P. (2008). Neuronal diversity and temporal dynamics: the unity of hippocampal circuit operations. Science 321, 53–57.