Fluorescent latex microspheres as a retrograde neuronal marker for in vivo and in vitro studies of visual cortex

Abstract

The use of retrograde axonal transport of various substances (for example, enzymes, lectins, synthetic fluorescent compounds) has yielded much information on the organization of neuronal pathways. Each type of retrograde tracer has its own set of attributes which define the scope of problems it can address. We describe here a new class of retrograde tracer, rhodamine-labelled fluorescent latex microspheres (0.02-0.2 micron diameter), which have distinct advantages over other available tracers for in vivo and in vitro applications. When injected into brain tissue, these microspheres show little diffusion and consequently produce small, sharply defined injection sites. Once transported back to neuronal somata, the label persists for at least 10 weeks in vivo and 1 yr after fixation. Microspheres have no obvious cytotoxicity or phototoxicity as assessed by intracellular recording and staining of retrogradely labelled cells in a cortical brain slice preparation. This approach was further used to visualize and compare, in cat visual cortex slices, neurones with different projection patterns, and revealed significant differences in patterns of intrinsic axons and dendrites. These properties of microspheres open new avenues for anatomical and physiological studies of identified projection neurones in slices as well as in dissociated cell cultures.

Spatial selectivity and binaural responses in the inferior colliculus of the great horned owl

“…Retrograde tracers were injected into the optic tecta of 3 owls to label neurons in IC. In one owl we used fluorescent latex microspheres (Luma Fluor; Katz et al, 1984), and in 2 others, HRP. For the first method, we first recorded with a metal electrode and located an appropriate injection site in the optic tectum by crudely mapping the visual receptive fields.…”

Transient D1Dopamine Receptor Expression on Prefrontal Cortex Projection Neurons: Relationship to Enhanced Motivational Salience of Drug Cues in Adolescence

“…spheres were used because fibers of passage are not affected such that only direct projections are stained (Katz et al, 1984). Correct placement within the dorsomedial region of the NAc core was verified under 10ϫ magnification using a Cy5 filter to view the bolus of fluosphere injection.…”

Three Kinetically Distinct Ca2+-Independent Depolarization-Activated K+ Currents in Callosal-Projecting Rat Visual Cortical Neurons

“…In previous studies on neocortical neurons, for example, the cells either were not identified directly (Foehring and Surmeier 1993;Spain et al 1991) or were identified based on in vitro morphology (Hamill et al 1991), which, as we have shown previously, is not a reliable method for identifying cortical neurons (Giffin et al 1991). To circumvent these difficulties, we have exploited in vivo retrograde labeling to permit the in vitro identification of cortical neurons (Giffin et al 1991;Katz and Iarovici 1990;Katz et al 1984;Solomon et al 1993). In the experiments described here, we have characterized the detailed time-and voltage-dependent properties of the Ca 2+ -independent, depolarizationactivated K + currents in isolated, identified callosal-projecting (CP) neurons from postnatal rat primary visual cortex.…”