GABA and glycine immunoreactivity in the guinea pig superior olivary complex

Abstract

Immunoperoxidase immunocytochemistry was employed to examine the distribution of gamma-aminobutyric acid (GABA)-and glycine (GLY)-immunoreactive cells, fibers, and terminals in the guinea pig superior olivary complex. The nuclei studied were the lateral superior olive (LSO), medial superior olive (MSO), superior paraolivary nucleus (SPN), and the medial, ventral, and lateral nuclei of the trapezoid body (MNTB, VNTB, and LNTB, respectively). The majority of LSO neurons exhibited GABA-immunoreactive (+) labeling. These same neurons were also lightly GLY+. Extensive perisomatic punctate GLY + labeling was observed on most LSO neurons; these puncta most likely correspond to synaptic terminals. A very small number of MSO fusiform neurons were GABA +, and none were GLY +. The GLY positive perisomatic punctate labeling around most MSO neurons, although abundant, was not as profuse as that observed in the LSO. The MNTB neurons corresponding to the principal and elongate types were intensely GLY + and were contacted by small numbers of GLY + puncta. There was extensive GLY + punctate labeling in the SPN that surrounded the cell bodies of most of its large, radiate neurons and many of the smaller, fusiform neurons. The few large, radiate neurons that were lightly GLY + possessed far fewer GLY + puncta on their perikarya. The distribution of GABA + puncta was generally diffuse and scattered throughout the nuclei described above. In the VNTB and LNTB, several large neurons of various shapes were GLY + as were the small, oval neurons. The extent of GLY + punctate labeling was quite variable in both nuclei. The majority of perikarya in the VNTB and LNTB were GABA +. A light distribution of GABA + puncta was observed on most cell bodies in both nuclei. Peridendritic GABA + punctate labeling was dense in the VNTB neuropil. Two small populations of GLY + neurons were observed outside of the named nuclei of the SOC; one was located dorsal to the LSO, near its dorsal hilus, and the other was identified near the medial pole of the LSO. The somata of both populations possessed extremely sparse GLY + punctate labeling. In general, these results agree with and expand on findings in rodents from previous studies. There appears, however, to be differences between the guinea pig and cat with regard to the proportions of GABA + neurons in the LSO and GLY + punctate labeling in the MSO.

Responses of Neurons in the Rat's Ventral Nucleus of the Lateral Lemniscus to Monaural and Binaural Tone Bursts

“…Inhibitory postsynaptic potentials evoked by current pulse stimulation of lemniscal fibers are mediated primarily by glycine receptors, but in some cases by ␥-aminobutyric acid type A (GABA A ) receptors or both glycine and GABA A receptors (Irfan et al 2005). The most likely source of glycinergic inhibition is the MNTB, whose neurons have been shown by immunocytochemistry to contain glycine (Helfert and Aschoff 1997;Helfert et al 1989;Vater et al 1992). The less prominent GABAergic inhibition might originate from LNTB or VNTB, whose neurons label positively for GABA or a combination of GABA and glycine (Helfert et al 1989).…”

“…The most likely source of glycinergic inhibition is the MNTB, whose neurons have been shown by immunocytochemistry to contain glycine (Helfert and Aschoff 1997;Helfert et al 1989;Vater et al 1992). The less prominent GABAergic inhibition might originate from LNTB or VNTB, whose neurons label positively for GABA or a combination of GABA and glycine (Helfert et al 1989). The time course for activation of these inhibitory responses is similar to that for AMPA receptor-mediated excitation in VNLL.…”

Posthearing Developmental Refinement of Temporal Processing in Principal Neurons of the Medial Superior Olive

“…These interaural time delays (ITDs) are submillisecond cues, the physiological range of which is dependent on the diameter of the animal's head. The principal neurons of the MSO are able to extract these brief ITDs from converging binaural inputs that include an excitatory component from the ipsilateral and contralateral ventral cochlear nucleus (VCN) (Cant and Casseday, 1986;Smith et al, 1993;Beckius et al, 1999) and an inhibitory component from both the medial nucleus (MNTB) and lateral nucleus (LNTB) of the trapezoid body (Helfert et al, 1989;Adams and Mugnaini, 1990;Cant and Hyson, 1992;Vater, 1995). Although the mechanism for extracting ITDs from these excitatory and inhibitory inputs has yet to be fully elucidated (for review, see Joris et al, 1988;Grothe, 2003;Palmer, 2004), ITD information is conveyed to higher auditory centers through a rate code (Goldberg and Brown, 1969;Yin and Chan, 1990;Spitzer and Semple, 1995;Brand et al, 2002).…”

The Medial Nucleus of the Trapezoid Body in the Gerbil Is More Than a Relay: Comparison of Pre- and Postsynaptic Activity

“…The GABAergic terminals may originate from neurons in the ventral nucleus of the trapezoid body (Ostapoff et al 1997), which themselves receive excitatory input from axon collaterals of globular bushy cells . The superior paraolivary nucleus, in which most neurons label for GABA, might provide another source of GABAergic input to the MNTB (Helfert et al 1989). The glycinergic terminals arise, in part, from recurrent projections of MNTB neurons Smith et al 1998).…”