Differential Changes of Extracellular Aspartate and Glutamate in the Striatum of Domestic Chicken Evoked by High Potassium or Distress: An In Vivo Microdialysis Study

Age-related and function-dependent regional alterations of free L- and D-aspartate in postembryonic chick brain

D-aspartate (D-Asp) modulates adult neural plasticity and embryonic brain development by promoting cell proliferation, survival and differentiation. Here, developmental changes of the excitatory amino acids (EAAs) L-Glu, L-Asp and D-Asp were determined during the first postembryonic days, a time window for early learning, in selected brain regions of domestic chickens after chiral separation and capillary electrophoresis. Extracellular concentration (ECC) of EAAs was measured in microdialysis samples from freely moving chicks. ECC of D-Asp (but not L-EAAs) decreased during the first week of age, with no considerable regional or learning-related variation. ECC of L-Asp and L-Glu (but not of D-Asp) were elevated in the mSt/Ac in response to a rewarding stimulus, suggesting importance of Asp-Glu co-release in synaptic plasticity of basal ganglia. Potassium-evoked release of D-Asp, with a protracted transient, was also demonstrated. D-Asp constitutes greater percentage of total aspartate in the extracellular space than in whole tissue extracts, thus the bulk of D-Asp detected in tissue appears in the extracellular space. Conversely, only a fraction of tissue L-EAAs can be detected in extracellular space. The lack of changes in tissue D-Asp following avoidance learning indicates a tonic, rather than phasic, mechanism in the neuromodulatory action of this amino acid.

Comparison and effects of acute lamotrigine treatment on extracellular excitatory amino acids in the hippocampus of PTZ-kindled epileptic and PTZ-induced status epilepticus rats

In this communication, the effect of acute treatment with lamotrigine (LTG) was investigated on release of main excitatory amino acids (EAA) such as glutamate (Glu) and aspartate (Asp) in the hippocampus of pentylenetetrazol (PTZ)-induced and PTZ-kindled freely moving rats using micro dialysis. The results show that, levels of Glu and Asp significantly increased in the rat hippocampus during the seizure/interical periods for PTZ-status epilepticus (SE) and PTZ-kindled epileptic (EP) rats. The levels of Glu and Asp increased more in EP rat hippocampus than in SE rat hippocampus. After administration of 20 mg/kg LTG, the levels of Glu and Asp significantly decreased in the SE and EP rat hippocampus. The results indicate that: (a) excitability of the PTZ-kindled epileptogenic model is higher than that of the status epilepticus model; (b) the modulation of LTG on the EAA neurotransmitters certainly plays an important role in antiepileptic efficacy, especially in PTZ-kindled epileptic model where the release of EAA was influenced more markedly by acute application of 20 mg/kg LTG.

Amygdalofugal axon terminals immunoreactive for L-aspartate or L-glutamate in the nucleus accumbens of rats and domestic chickens: a comparative electron microscopic immunocytochemical study combined with anterograde pathway tracing

Several studies have shown that L-aspartate (Asp) is present in synaptic vesicles and released exocytotically from presynaptic terminals, possibly by Ca(2+)-dependent corelease of Asp and L-glutamate (Glu). It has been demonstrated that both excitatory amino acids (EAAs) are released from the rat striatum as part of corticostriatal neurotransmission. The single or colocalized occurrence of Asp and Glu in specific synaptic boutons of the chicken medial striatum/nucl. accumbens has been demonstrated by our group using ultrastructural immunocytochemistry. However, evidence for the presence of EAAs in any specific striatal pathway was only circumstantial. Here, we report on the distribution of Asp and Glu in specific synaptic terminals of the amygdalostriatal pathway, both in rat and chicken brains, combining anterograde tracing with postembedding immunogold labeling of Asp or Glu. Immunoreactivity for Asp and Glu was observed in amygdalofugal terminals with asymmetrical synaptic junctions (morphologically representing excitatory synapses) in both species. The postsynaptic targets were either dendritic spines or small dendrites, whereas axosomatic or axo-axonic connections were not observed. Ultrastructurally, the synaptic terminals immunoreactive for Asp were indistinguishable from those immunoreactive for Glu. The findigs are consistent with an Asp-Glu corelease mechanism, with a distinct synaptic contingent, evolutionarily conserved in the amygdalostriatal pathway.