Calbindin-D28k and neuronal nitric oxide synthase expression in the lateral nucleus of the sheep amygdala

The amygdala is an heterogeneous structure that comprises numerous nuclei and subnuclei. In the amygdala activity a central role is played by lateral nucleus which is the major input region for sensory-related thalamic and cortical information directed to the amygdala and provides the most extensive intraamigdaloid projections (Sah, Physiol. Rev. 83, 2003). The lateral nucleus presents pyramidal neurons, that employ glutamate as an excitatory neurotransmitter, and non-pyramidal neurons that utilize GABA as an inhibitory neurotransmitter (McDonald, Neurosci. Lett. 53, 1985; McDonald, J. Comp. Neurol. 365, 1996). This study is about the expression of calbindin-D28k (CB), of neuronal nitric oxide synthase (nNOS) and their colocalization in the sheep lateral nucleus of the amygdala. CB-immunoreactive (IR) neurons were especially non-pyramidal, but few pyramidal cells were also present. The non-pyramidal neurons showed a multipolar and, rarely, a fusiform morphology. nNOS-IR neurons were only non-pyramidal with multipolar and fusiform morfology. Double immunolabelling (CB/nNOS) was found mostly in non-pyramidal multipolar neurons and only in a few non-pyramidal fusiform cells. From quantitative and morphometric analysis it results that the nNOS-IR neurons were more numerous and smaller than CB-IR neurons. Moreover CB and nNOS coexist in a minority of neurons.