Neuropeptide‐ and neurotransmitter‐related immunoreactivities in the developing rat olfactory bulb

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Abstract
The development of neuropeptide and neurotransmitter‐related immunoreactivities in the rat olfactory bulb were investigated immunohistochemically by using antisera raised against substance P (SP), cholecystokinin‐8 (CCK), neurotensin (NT), leucine‐enkephalin or methionine‐enkephalin‐Arg6‐Gly7‐Leu8 (ENK), somatostatin (SOM), neuropeptide Y (NPY) and tyrosine hydroxylase (TH).Results obtained for the adult olfactory bulb confirmed previous observations, except for SP‐like immunoreactive (SP‐IR) granule cells in the main olfactory bulb (MOB) and NT‐IR neurons around the modified glomerular complex (MGC) (Teicher et al., Brain Res. 194:530‐535, 1980).SP‐, CCK‐ and NT‐IR neurons were observed in the MOB of the rat fetus. SP‐IR neurons also appeared in the accessory olfactory bulb (AOB). Among them, NT‐IR neurons in the MOB and SP‐IR neurons in the AOB were observed on embryonic day 16. SP‐ and CCK‐IR neurons in the MOB appeared on embryonic day 18. Most of these neurons were presumed to be projecting neurons. SOM‐, NPY‐, ENK‐ and TH‐IR neurons appeared in the newborn rats. The number and intensity of immunostaining of these neurons continued to increase with age, producing the adult pattern, except for NT‐IR neurons in the MGC and SP‐IR neurons in the mitral cell layer of the AOB, which were more numerous and intensely stained in young animals.