Serotonin-containing cell bodies in novel brain locations: effects of light input.

Cell bodies staining positively for serotonin (5HT) appear in the suprachiasmatic nuclei (SCN) of hamsters that have been held in constant darkness (DD) for several months but are otherwise untreated. No such cell bodies are found in the SCN of animals that have been bilaterally enucleated for the same amount of time; however, in enucleated hamsters 5HT-containing cell bodies appear in the superior colliculus. These data provide the first indication that changes in sensory input can modulate 5HT levels in cells bodies outside of the raphe nuclei.

Light perception in the vertebrate brain: an ultrastructural analysis of opsin- and vasoactive intestinal polypeptide-immunoreactive neurons in iguanid lizards.

Recent biochemical and immunocytochemical evidence indicates that a population of circadian and reproductive rhythm-entraining photoreceptors lies in the basal diencephalon of iguanid lizards. Here, we report the results of correlated light and electron microscopy of opsin-immunoreactive cells in the basal brain, and we discuss their ultrastructural relationship to known photoreceptors. Cerebrospinal fluid (CSF)-contacting bipolar neurons in the lizards Anolis carolinensis and Iguana iguana were immunolabeled with antisera generated against vertebrate retinal opsins and vasoactive intestinal polypeptide (VIP). Within the brain, opsin-immunoreactive cells were found exclusively in the ependyma of the basal region of the lateral ventricles (adjacent to nucleus paraolfactorius/nucleus ventromedialis and neostriatum/paleostriatum). Cells in the same anatomical location and with the same morphology were labeled with anti-VIP antisera. These cells possessed a dendritic process that extended toward the lateral ventricle, ending in a bulbous terminal that protruded into the ventricle. Axonal processes travelled ventrally and caudally. The entire cell, including the axonal process, exhibited opsin-like and VIP-like immunoreactivity. By light microscopy, opsin-like immunostaining appeared punctate, with immunoreactivity greatest in the bulbous terminal. Opsin- and VIP-immunostained thick sections were resectioned, and individual cells observed by light microscopy were then characterized using electron microscopy. We found that all immunostained cells were morphologically similar and that they were morphologically distinct from neighboring nonimmunoreactive cells. CSF-contacting opsin- and VIP-immunoreactive cells lacked the membranous stacks characteristic of retinal photoreceptors but were ciliated and contained numerous large electron-dense vesicles. Multiple synaptic contacts were made on the soma and putative dendritic processes of opsin- and VIP-immunoreactive CSF-contacting neurons. Our results provide the first ultrastructural characterization of opsin-immunostained encephalic CSF-contacting neurons in a vertebrate animal, and they indicate that these putative photoreceptors share structural features with pineal photoreceptors and with certain invertebrate extraretinal photoreceptors, but they are morphologically and biochemically distinct from visual photoreceptors of the retina.

Distribution of chicken-II gonadotropin-releasing hormone in mammalian brain.

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)

Coexpression of opsin- and VIP-like-immunoreactivity in CSF-contacting neurons of the avian brain.

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.