Two types of periglomerular cells in the olfactory bulb of the macaque monkey (Macaca fascicularis)

The olfactory bulb (OB) of mammals is the brain region that receives the sensory information coming from the olfactory epithelium. The entrance of the olfactory information occurs in spherical structures of neuropil named olfactory glomeruli and is modulated by a population of interneurons known as periglomerular cells (PG). It has been demonstrated that there are two types of PG in the OB of some macrosmatic mammals, including rats and mice. Type 1 PG (PG-1) receive synapses from the olfactory nerve, whereas type 2 PG (PG-2) do not receive synapses from the olfactory axons. To date, the presence of the two types of PG has not been investigated in microsmatic mammals. In this context, we analyze the presence of PG-1 and PG-2 in the OB of the long-tailed macaque (Macaca fascicularis). For that, we used the enzyme tyrosine hydroxylase, the neuronal isoform of the enzyme nitric oxide synthase and the calcium-binding proteins calbindin D-28k and calretinin as neurochemical markers. Our results demonstrate that the OB of the macaque contains PG-1 and PG-2. A subpopulation of PG-1 expresses tyrosine hydroxylase and another expresses the neuronal isoform of nitric oxide synthase. In addition, a subpopulation of PG-2 expresses calbindin D-28k and another expresses calretinin. Double immunofluorescence demonstrates that there is no colocalization of two markers in the same PG. These results mimic those found in macrosmatic animals. The presence of two types of PG in the glomerular circuits seems to be a key principle for the organization of the OB of mammals.