Hey, this is my first post, I needed a good excuse to join this board, and here we are. I'm currently doing my masters in pharmacology, but my education so far has been very light on cellular neuroanatomy. In a review paper I'm reading, there is constant reference to interneurons of various sizes (i.e. small, medium and large), and asymmetric synapses.

I was hoping someone could a) tell me if there is going to a general or specific correlation between neurotransmitter type and the size of interneuron, B) what's the story with asymmetric synapses is, and c) if there is a good text I can read for further readings/citations.

This is just off the top of my head:

"Interneurons" typically refer to local circuit neurons which, in primates, and in areas like the thalamus and cortex, refer to GABAergic neurons that may additionally also contain neuropeptides such as VIP, Substance P, and Enkephalins. A correlation between size and neurotransmitter type I don't think I'm aware of, though I have read of correlations between immunoreactivity for different calcium binding proteins (parvalbumin, calbindin, and calretinin) and interneuron sub-type in the cerebral cortex. My own experience suggests parvalbumin-immunopositive GABAergic interneurons in cerebral cortex are larger than other interneurons, for the most part.

Asymmetric synapses are made by excitatory neurons which use, for the most part, glutamate (and sometimes aspartate) as neurotransmitter, and will be found being made onto inhibitory interneurons, as well as onto other neurons, and will often occur on dendritic spines (when made on excitatory neurons). On the other hand, symmetric synapses are made by inhibitory neurons onto other neuron types, usually on the proximal dendrites and soma.

I'll get back to you on a good text. None come to mind at the moment, but I'll have to look into it further.