Light and electron microscopic immunohistochemical localization of N-acetylaspartylglutamate NAAG in the olivocerebellar pathway of the rat

Abstract

The inferior olive (IO) is the sole contributor of climbing fibers (CF) to the Purkinje cells of the cerebellar cortex. Although the anatomy and the connectivity between the IO and the cerebellum have been well established, there is still controversy regarding the neurotransmitter systems mediating olivocerebellar projections. The excitatory amino acids, glutamate (Glu) and aspartate (Asp), have both been considered as neurotransmitter candidates of olivocerebellar projections in the rat. More recently N-acetylaspartylglutamate (NAAG) has also been proposed as a transmitter of cerebellar climbing fibers based on biochemical and electrophysiological data. The aim of the present study was to determine whether NAAG immunoreactivity is present in the IO and CF at the light and electron microscopic levels and to quantitate the amount of immunogold labeling in olivary neurons and climbing fiber terminals containing this dipeptide. A polyclonal antisera against NAAG was utilized with a peroxidase-labeled avidin-biotin procedure to demonstrate these immunoreactive neurons in the IO at the light microscopic level. Approximately 45% of olivary neurons display NAAG-like immunoreactivity, and their distribution is unevenly clustered throughout the inferior olive. Using postembedding immunogold electron microscopy in combination with quantitative procedures, we found the highest densities of gold particles in the axonal terminals synapsing on olivary neurons (101.0 particles/microns2), in CF terminals (96.3 particles/microns2), and in some mossy fiber terminals (101.0 particles/microns2). Approximately half of the climbing fiber terminals examined were unlabeled. Moderate labeling occurred in CF axons (70.8 particles/microns2), while IO neuronal perikarya were lightly but significantly labeled (41.6 particles/microns2). The localization of NAAG in the subset of cerebellar climbing fiber terminals provides anatomical support for the hypothesis that NAAG may serve as a neurotransmitter/neuromodulator candidate in the olivocerebellar pathway.

Glutamate Carboxypeptidase II Gene Expression in the Human Frontal and Temporal Lobe in Schizophrenia

“…NAAG is the most prevalent and widely distributed neuropeptide in the mammalian nervous system (reviewed in Coyle, 1997;Neale et al, 2000). It meets criteria for classification as a neurotransmitter, being concentrated in synaptic vesicles (Williamson and Neale, 1988a;Renno et al, 1997) released in a calcium-dependent manner upon depolarization (Williamson and Neale, 1988b;Tsai et al, 1990), and is hydrolyzed by membrane-bound peptidase. Immunocytochemical studies reveal colocalization of NAAG in many putative glutamatergic pathways in the human brain (Passani et al, 1997).…”

Effects of convection on the removal of the multiplicity of stable states in one‐dimensional vertical models

“…Such a multiplicity of stable states arises from the non-grey absorption only, since cases with weak to high absorption within the atmospheric window give a single stable state (as for current values of the earth's atmospheric opacity). Therefore, it differs from the multiple equilibria in RCMs found by Li et al (1997), Rennó (1997), Lorenz et al (1999) and Ide et al (2001). Such a multiplicity of stable states has been analysed by Pujol and Fort (2002) and North (2002, 2003) in planetary atmospheres, and solved with an angular approximation for the radiation field and a stratosphere in monochromatic radiative equilibrium.…”

“…It implies that the multiplicity of stable states found in Fig. 4 is intrinsically different from that obtained in RCMs applied to earth's current state (Li et al 1997;Rennó 1997;Ide et al 2001). Indeed, the multiple equilibria found by Li et al (1997) in a RCM is caused by the assumption that the surface albedo is a function of surface temperature, being very similar in nature to the multiple solutions found in vertically averaged, latitude-dependent energy-balance model with ice-albedo feedback (see, e.g.…”

Immunohistological and electrophysiological evidence that N‐acetylaspartylglutamate is a co‐transmitter at the vertebrate neuromuscular junction

“…Using ultrastructural immunocytochemistry, we and others previously localised NAAG in synaptic vesicles in the central nervous system (Williamson & Neale, ; Renno et al ., ). The localisation of NAAG within the presynaptic terminal and the loss of immunoreactivity following depolarisation in high K + (Fig.…”