New version page

Morphology of GABAergic Neurons in the Inferior Colliculus of the Cat

Upgrade to remove ads

This preview shows page 1-2-3-4-5 out of 16 pages.

Save
View Full Document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience

Upgrade to remove ads
Unformatted text preview:

THE JOURNAL OF COMPARATIVE NEUROLOGY 340:2742 (1994) Morphology of GABAergic Neurons in the Inferior Colliculus of the Cat DOUGLAS L. OLIVER, JEFFERY A. WINER, GRETCHEN E. BECKIUS, AND RICHARD L. SAINT MARIE Department of Anatomy, The University of Connecticut Health Center, Farmington, Connecticut 06030-3405 (D.L.O., G.E.B.); Department of Molecular and Cell Biology, Division of Neurobiology, University of California, Berkeley, California 94720-2097 (J.A.W.); Department of Neuroanatomy, House Ear Institute, 2100 West Third St., Los Angeles, California 90057 (R.L.S.M) ABSTRACT The goal of the present study was to provide a comprehensive and quantitative description of neurons immunoreactive for y-aminobutyric acid (GABA) in the inferior colliculus (IC) of the cat. Neurons were investigated with two different antisera and two different incubation methods. Free-floating frozen or vibratome-cut sections were incubated either with an antiserum to glutamic acid decarboxylase (GAD) or to GABA conjugated to protein with glutaraldehyde. Additional 1.5-~m-thick sections were incubated with the GABA antiserum after embedding and removal of the plastic. Quantitative data were obtained from much of this material. Despite the use of these different antisera and reaction methods, the results obtained were remarkably similar. The results show that GAD- or GABA-positive neurons represent a significant population of cells in the central nucleus of the IC, up to 20% of the neurons. Most of these neurons have large or medium-sized perikarya. In contrast, immunonegative neurons are medium-sized or small. Many GABA-positive neurons had proximal dendrites or somata oriented in parallel to the fibrodendritic laminae of the central nucleus and are presumed to be disc-shaped neurons. Others have an orthogonal orientation and are presumed to be stellate cells. Large GABA- positive neurons form two groups, those with many axosomatic endings and those with few. Collectively, these observations suggest that there are several types of GABAergic neuron in the central nucleus and, by extension, that these may participate in many types of inhibitory Circuits. e 1994 Wiley-Liss, Inc. Key words: auditory pathways, inhibitory synapses, axosomatic endings, neuropil Neural responses in the inferior colliculus (IC) may depend upon local circuits. When IC neurons are injected intracellularly in vivo with horseradish peroxidase (HRP), almost every type of neuron elaborates a local axon collat- eral (Oliver et al., '91). Local axons terminate near the cell of origin and in a symmetric position in the opposite IC (Saldaba and Merchan, '92). Some local axons are surpris- ingly extensive and could provide a structural substrate for feed forward excitation/inhibition, sharpened tuning, or amplification/suppression of lateral interactions. If these axons are excitatory, their intrinsic connections could supplement the effects of ascending afferent systems. How- ever, if local axons suppress other IC neurons, then the intrinsic collaterals might have an entirely different set of physiologic implications. An essential first step toward understanding the function of the local connections within the IC is to establish which neurons use inhibitory neuro- transmitters. Despite the potential importance of local inhibitory trans- mission, there have been few studies to identify inhibitory neurons within the IC. Surveys of neurons immunopositive for y-aminobutyric acid (GABA) or its synthetic enzyme, glutamic acid decarboxylase (GAD), in the gerbil (Roberts and Ribak, '87a), rat (Roberts and Ribak, '87b), guinea pig (Thompson et al., '851, and bat (Winer et al., '94) describe many such neurons. However, only brief reports have related GABA immunoreactivity and neuron type in the cat (Oliver et al., '88; Oliver and Beckius, '89; Paloff et al., '91). GABA immunoreactivity reveals that the transmitter is present in axonal endings (Oliver and Beckius, '92). How- ever, the GABAergic synapses remain to be associated with Accepted August 23, 1993. Address reprint requests to Douglas L. Oliver, PhD, Department of Anatomy, The University of Connecticut Health Center, Farmington, CT 06030-3405. o 1994 WILEY-LISS, INC.28 D.L. OLIVER ET AL. Winer, '91, '92). Sections were incubated in the primary antiserum, GAD-1440 (Oertel et al., '811, at a 1:2,000 dilution and immunostained with either the peroxidase- antiperoxidase (Sternberger and Joseph, '79) or the avidin- biotin (Hsu et al., '81) method. The latter, using a double- bridge technique (Roberts et al., '85), produced superior immunostaining, and the contrast of these sections was further enhanced by the osmium-thiocarbohydrazide- osmium procedure (Willingham and Rutherford, '84). GABA immunocytochemistry To show GABA-immunoreactive neurons and axonal terminals, six cats were anesthetized as noted above and perfused with phosphate buffer (50-100 ml, 0.12 M, pH 7.2-7.4, 0.004% CaC12, 2% sucrose, 0.06% lidocaine) fol- lowed by two successively more concentrated mixtures of buffered paraformaldehyde and glutaraldehyde (Oliver and Beckius, '92). Solutions were delivered by gravity at 37°C. Brains remained in the final perfusate (1% paraformalde- hyde, 3% glutaraldehyde, and 0.004% CaClz in 0.12 M phosphate buffer; pH 7.2-7.4) overnight at 4°C. The next day, the brainstem was sectioned on a vibratome while submerged in chilled phosphate buffer (0.12 M, pH 7.4; 0.004% CaC12). Sometimes 6% sucrose was added. For preembedding immunocytochemistry, 50-100-pm- thick tissue slices were placed in 5% normal goat serum in phosphate buffer (1 hour) and then incubated overnight with affinity-purified GABA antiserum diluted 1: 1,000-1: 16,000 in buffer (Wenthold et al., '86). Binding of the GABA antibodies was detected by biotinylated goat antirabbit IgG and an avidin-biotin-peroxidase complex (Vectastain ABC Kit; Vector Laboratories, Burlingame, CA) with diaminoben- zidine as the chromagen (Hsu et al., '81). All procedures preceding the peroxidase reaction were performed at 4°C with continuous agitation. Treated sections were some- times postfixed with buffered 0.5-2.0% osmium tetroxide for 15-120 minutes, stained with 2% uranyl acetate over- night, and flat embedded in Durcupan ACM or Polybed 812


Download Morphology of GABAergic Neurons in the Inferior Colliculus of the Cat
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Morphology of GABAergic Neurons in the Inferior Colliculus of the Cat and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Morphology of GABAergic Neurons in the Inferior Colliculus of the Cat 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?