Cerebrospinal fluid-contacting (CSF) cells in both the septal and the tuberal areas in the brain of the ring dove are labeled by RET-P1, a monoclonal antibody to opsin that reacts with inner and outer segment membranes of rod photoreceptors in a variety of vertebrates. Immunoblot analysis of proteins from diverse brain regions, however, revealed bands of anti-RET-P1 immunoreactivity that did not correspond to opsin. Binding of RET-P1 to opsin-containing membranes, was not inhibited by membranes rich in muscarinic and beta-adrenergic receptor proteins (red blood cells, heart, lung) taken from doves. RET-P1-immunoreactive CSF-contacting cells emit a dendritic process that penetrates the ependyma and ends in a knob-like terminal suspended in the ventricle. These cells also possess other processes that penetrate more or less deeply into the neuropil. Additionally, a band of labeled fibers occurs in the external layer of the median eminence. A double-label technique demonstrated that RET-P1-positive cells coexpress VIP-like immunoreactivity. VIP-positive cells in other brain areas are not RET-P1-positive.

No abstract

Brains of nonmammalian vertebrates typically contain multiple forms of gonadotropin-releasing hormone (GnRH). Until recently, only the mammalian form of GnRH (mGnRH) had been isolated in placental mammals. Biochemical and histological data show that both mGnRH and chicken-II GnRH (cGnRH-II) are present in a primitive placental mammal, the musk shrew (Suncus murinus). Similar to the case in nonmammalian species, in the musk shrew, neurons that express cGnRH-II are located in a discrete cluster in the midbrain. We have used a combination of radioimmunoassay and immunocytochemistry, analyzed at the light level and with electron microscopy, to describe the distribution of cGnRH-II cell bodies and fibers in the musk shrew brain. All cGnRH-II-immunoreactive (ir) neurons reside in the midbrain, and this area contains the greatest concentration of cGnRH-II peptide in the brain. At the light and electron micrographic levels, we have identified synaptic terminals containing dense core vesicles that are immunoreactive for cGnRH-II in the medial habenula. Radioimmunoassay reveals that this region contains the second greatest concentration of cGnRH-II in the brain. Widely scattered cGnRH-II-ir fibers are present throughout the forebrain, particularly in the medial septum, hypothalamus, and midbrain central gray. Scant cGnRH-II fibers are present in the median eminence, arcuate nucleus, and infundibular stem, and only low concentrations of the peptide are detected in these areas. Finally, intravenous administration of mGnRH is ten times more effective than cGnRH-II in promoting ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Golgi impregnation and neurobiotin injection were used to examine details of the neural pathways in the olfactory system of the freshwater crayfish, Procambarus clarkii. Deutocerebral projection neurons (globuli cells) were directly injected with neurobiotin. These neurons have dendritic arborizations in the ipsilateral olfactory and accessory lobes, and they project axons to the lateral protocerebrum, where they terminate in microglomeruli of the hemi-ellipsoid body. The axons of the deutocerebral projection neurons are readily impregnated by Golgi procedures, and they terminate as an expanded membranous knot about 5 microns in diameter. Electron microscopy on Golgi-stained terminals has revealed that each knot makes several hundred synapses with small spine-like or shaft-like processes of postsynaptic neurons. Injection of neurobiotin into local interneurons of the hemi-ellipsoid body and subsequent examination of stained preparations with the electron microscope reveals that these cells are a major postsynaptic target of the deutocerebral projection neurons. Furthermore, the local interneurons make extensive efferent synaptic connections with unidentified neurons in the terminal medulla.

Little knowledge is available concerning the detailed anatomy of the crusctacean central olfactory pathway. We are using radiolabeling, Golgi and biocytin/neurobiotin tracer methodologies, at the correlated light and electron microscopical levels, to study the olfactory midbrain of the freshwater crayfish. We have found that primary afferent fibers from the antennular olfactory receptor cells branch extensively throughout the length of the glomerular columns within the olfactory lobes in the midbrain. Globuli cells of the lateral cell clusters ramify as dendritic arborizations within both the olfactory and accessory lobes; their axons project out the olfactory-globular tracts to the lateral protocerebrum, often branching to both sides. Developmental plasticity involving the connections made by afferent fibers within the olfactory lobes may permit detailed examination of organizational changes within the midbrain as the animal grows and adds new afferent input from the periphery.