Cell types and response properties of neurons in the ventral division of the medial geniculate body of the rabbit

Abstract

Although there is evidence for multiple classes of thalamic relay neurons in the auditory thalamus, correlative anatomical and physiological studies are lacking. We have used the juxtacellular labeling technique, in conjunction with Nissl, Golgi, and immunocytochemical methods, to study the morphology and response properties of cells in the ventral division of the medial geniculate body of the rabbit. Single units in the ventral division of the medial geniculate body (MGV) were characterized extracellularly with monaural and binaural tone and noise bursts (100- to 250-msec duration). Characterized units were filled with biocytin and visualized with an antibody enhanced diaminobenzidine reaction. A total of 31 neurons were physiologically characterized and labeled with the juxtacellular technique. Labeled neurons were fully reconstructed from serial sections by using a computer microscope system. Three subregions of the rabbit MGV were identified, each characterized by differences in Nissl architecture, calcium-binding protein expression, and by the dendritic orientation of tufted relay neurons. In general, the dendritic fields of relay neurons were closely aligned with the cellular laminae. Qualitative and quantitative analyses revealed two types of presumptive relay neurons within the MGV. Type I cells had thick dendrites with a greater total volume and morphologically diverse appendages compared with the Type II cells whose dendrites were thin with a moderate number of small spines. Both classes were acoustically responsive and exhibited a variety of response patterns, including onset, offset, and sustained responses. In terms of binaural characteristics, most (ca. 53%) labeled neurons were of the EE type, with the remaining cells classified as EO (27%) or EI (20%) response types. Two types of presumptive interneurons were also seen: bipolar neurons with large dendritic fields and a small neurogliaform variety. Cell types and dendritic orientation within the MGV are discussed in terms of the physiological organization of the rabbit auditory thalamus.

Functional Subregions in Primary Auditory Cortex Defined by Thalamocortical Terminal Arbors: An Electrophysiological and Anterograde Labeling Study

“…No preference for contralateral or binaural stimulation was classified as excitatory/occlusion (EO) (Imig and Adrian, 1977;Middlebrooks and Zook, 1983). Afterward, spike rasters, poststimulus time histograms (PSTHs) and tuning curves were obtained (Cetas et al, 2002a). The binaurality determined for noise bursts was used to set the mode of stimulus presentation (contra or binaural) when the automated tuning curve program was run.…”

“…(2) More importantly, experimental animals served as their own controls; adjacent cortical penetrations in which one electrode passed through a TC patch while the other did not were comparable in frequency progression, latency, sharpness of tuning, and response strength. (3) In some cases, the multi-unit responses within a TC patch (Cetas et al, , 2002a(Cetas et al, , 2002b. TC axons originating from binaural-specific relay neurons (red, blue) located in frequency slabs terminate in patches along a frequency strip in AI.…”

“…A model incorporating both of these features of TC circuitry based on anatomical and physiological data (Cetas et al, 1999(Cetas et al, , 2002a is shown in Figure 10. In this model, TC axons originating from binaural-specific relay neurons located in frequency slabs in the MGV terminate in patches along a frequency strip in AI.…”

Two thalamic pathways to primary auditory cortex

“…MGBv neurons in turn project to AI, where these features are represented in layer III and layer IV (Read et al, 2002), forming a two dimensional projection plane (Huang and Winer, 2000;Smith and Populin, 2001). Previous studies in cat and rabbit found a single low-to-high BF organization or tonotopy in MGBv (Aitkin and Webster, 1972;Imig and Morel, 1985;Brandner and Redies, 1990;Cetas et al, 2002;Cetas et al, 2003). Neurons with similar BFs form isofrequency laminae which extend ~3 mm in the dorsal-ventral dimension of MGBv in both species and which correspond anatomically to fibrodendritic laminae (Morest, 1965).…”

“…Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. (Imig and Morel, 1985) or up to 1 octave in rabbit (Cetas et al, 2001;Cetas et al, 2002) MGBv. Reconstruction of physiological recording tracks in cat MGBv (Imig and Morel, 1985) suggests two distinct regions within the laminar subdivision, one with a fine and the other with a coarser tonotopic frequency resolution (Escabí and Read, 2005).…”