Celeste R. Wirsig-Wiechmann

The nervus terminalis in the chick: a FMRFamide-immunoreactive and AChE-positive nerve

The chick terminal nerve (TN) was examined by immunocytochemical and histochemical methods. Molluscan cardioexcitatory peptide-immunoreactive (FMRFamide-ir) and acetylcholinesterase (AChE)-positive TN perikarya and fibers were distributed along olfactory and trigeminal nerves. FMRFamide-ir TN fibers terminated in the olfactory lamina propria and epithelium and in ganglia along the rostroventral nasal septum. This initial description of several populations of avian TN neurons should provide the foundation for future developmental studies of this system.

Melatonin Receptor Distribution in the Brain and Retina of a Lizard, Anolis carolinensis

Melatonin binding sites were identified in the brain and retina of the lizard Anolis carolinensis using in vitro autoradiography. Radioactive labeling was observed in areas which receive primary, secondary, and tertiary visual input: the superficial layers of the optic tectum, lateral geniculate nucleus, nucleus rotundus, dorsal ventricular ridge, and striatum. Other areas that demonstrated binding included the left medial habenular nucleus, the interpeduncular nucleus, medial cortex, dorsal cortex, mammillary nucleus, and septum. In the retina, melatonin binding was localized in the inner plexiform layer. Radioactive melatonin binding to the optic tectum was reduced in the presence of a nonhydrolyzable cyclic GMP analog, indicating that the melatonin receptor in the brain of this lizard is associated with a G-protein. These results suggest that melatonin receptor binding sites are widely distributed in the forebrain and midbrain of the iguanid lizard, and are prominent in areas of the nervous system that are associated with visual processing. The highest degree of melatonin binding appeared in the left medial habenular nucleus, interpeduncular nucleus, and dorsal ventricular ridge. This suggests that these brain regions may be important targets for the actions of melatonin, such as its effects on circadian rhythmicity, thermoregulation and photoperiodic reproduction.

Peripheral projections of nervus terminalis LHRH-containing neurons in the tiger salamander, Ambystoma tigrinum

The peripheral projections of the nervus terminalis (NT) have been difficult to examine due to the weak immunoreactivity of the processes to various antibodies. We performed two experimental manipulations in the tiger salamander in an attempt to increase the luteinizing hormone-releasing hormone-immunoreactive (LHRH-ir) labelling in the peripheral processes of the NT: 1) the NT was sectioned centrally, or 2) a 100 mg melatonin pellet was embedded subcutaneously for 3 days prior to sacriffice. Following these manipulations, animals were sacrifficed and tissue was processed with standard immunocytochemical techniques for the analysis of the distribution of LHRH-ir processes. In the nasal cavity, LHRH-ir fibers were observed projecting 1) into the rostral olfactory epithelium, 2) to Bowmans glands in the lamina propria of the rostromedial olfactory mucosa and ventrolateral mucosa between the main nasal cavity and Jacobsons organ, 3) into the naris constrictor muscle, and 4) along the palatine nerves and ganglia. These lesion and hormone manipulations have enabled the detection of peripheral projections of the NT not observed previously with immunocytochemical procedures alone. The wide distribution of LHRH-ir NT processes in the nasal cavity and cranium suggests that this nerve may influence many different cranial structures during appropriate pheromonal or neuroendocrine events.

Multiple cell targets for melatonin action in Xenopus laevis retina: distribution of melatonin receptor immunoreactivity.

In the retina of the African clawed frog (Xenopus laevis), melatonin is synthesized by the photoreceptors at night, and binds to receptors that likely mediate paracrine responses. Melatonin appears to alter the sensitivity of the retinal cells to light, and may play a key role in regulating important circadian events that occur in the eye. A polyclonal antibody was raised against a 13 amino acid peptide corresponding to a region of the third cytoplasmic loop of the Xenopus laevis Mel1c melatonin receptor. Western blot analysis revealed a major immunoreactive band of approximately 60 kD in neural retina and retinal pigment epithelium (RPE) membranes. Immunocytochemical labeling of sections of Xenopus eyes demonstrated intense melatonin receptor-like immunoreactivity in the inner plexiform layer (IPL). Immunolabeling with antibodies to glutamate decarboxylase (GAD) or tyrosine hydroxylase (TOH) appeared to co-localize with the melatonin receptor immunoreactivity in different sublaminas of the IPL. This suggests that both GABAergic and dopaminergic amacrine cells express melatonin receptor protein. There were also some melatonin receptor immunoreactive varicose fibers in the IPL that did not co-localize with either TOH or GAD, and may represent efferent fibers, since they could be followed into the optic nerve. Melatonin receptor immunoreactivity was also present on cell soma in the ganglion cell layer. Furthermore, a moderate level of melatonin receptor immunoreactivity was observed in the RPE and rod and cone photoreceptor cells. The presence of melatonin receptor immunoreactivity in these cells supports previous observations of melatonin receptor RNA expression in multiple cell types in the Xenopus retina. Expression of melatonin receptor protein in the photoreceptors suggests that melatonin may have a direct action on these cells.

Gonadotropin-releasing hormone agonist binding in tiger salamander nasal cavity

Binding of the iodinated gonadotropin-releasing hormone (GnRH) agonist, buserelin, was examined in the nasal cavities of tiger salamanders using in vitro autoradiography. Binding of [125I]buserelin was seen within the chemosensory epithelium of the main nasal cavity and Jacobsons (vomeronasal) organ. Highest levels of binding were observed over the chemosensory neuron dendrites. Given the apparent lack of GnRH-immunoreactive fibers within the chemosensory epithelium as we have observed in a previous study, these observations suggest that GnRH may diffuse from fibers in the lamina propria of the chemosensory mucosa into the sensory epithelium to modulate chemosensory reception.

Localization and quantification of high‐affinity melatonin binding sites in Rana pipiens retina

Abstract: Melatonin binding was localized to the inner plexiform layer (IPL) of the frog retina by in vitro autoradiography, using 2‐125I‐melatonin as the radioligand. Radioreceptor binding assays of frog retinal homogehate demonstrated saturable melatonin binding. Scatchard analysis revealed a single population of binding sites with an apparent dissociation constant (Kd) of 125 pM, with a Bmax of 0.138 fmoles/mg of protein. These results suggest that high‐affinity melatonin binding sites are present in the IPL of the frog retina, which may reflect the presence of melatonin receptors in this synaptic layer.

Asymmetric distribution of melatonin receptors in the brain of the lizard Anolis carolinensis

The pineal hormone melatonin may regulate seasonal reproduction and entrainment of circadian rhythms by binding to specific brain receptors. An analysis of melatonin receptor distribution in the lizard brain revealed an asymmetry of melatonin binding in the diencephalon. A high degree of melatonin binding was present in the left habenular nucleus, but no binding was observed in the habenulum of the right brain hemisphere. It is intriguing that the left habenular nucleus, in contrast to the right habenulum, both possesses a high density of melatonin receptors and receives primary photic input from the parietal eye. Similarly, the optic tectum, which receives primary visual input from the retina, is also rich in melatonin receptors. These observations suggest that the left habenulum is under dual control (neuronal and hormonal) of the parietal eye/pineal complex, and that melatonin may play a significant role in neural processing of visual information.

LHRH-immunoreactive neurons in the pterygopalatine ganglia of voles: a component of the nervus terminalis?

Cranial tissue from adult and neonatal voles was examined with immunocytochemical techniques to determine the distribution of luteinizing hormone-releasing hormone-immunoreactive (LHRH-ir) neurons in extracerebral structures. The overall distribution of the LHRH-ir portion of the nervus terminalis in the nasal and extracranial cavities was comparable to that of other rodents. However, we observed a unique association of LHRH-ir neurons with the pterygopalatine ganglia of neonatal and adult voles. We also found LHRH-ir fibers in nasopalatine nerves, and trigeminal nerves and ganglia of neonatal voles. We speculate that these neurons may influence the autonomic control of the vascular pump in the vomeronasal organ.

Nervus terminalis lesions: I. No effect on pheromonally induced testosterone surges in the male hamster

The involvement of the nervus terminalis or terminal nerve in the pheromonally induced testosterone surge in the male hamster was investigated. Blood was collected from male hamsters not exposed to odor (baseline), and then a week later from the same hamsters exposed to the odor of vaginal discharge from an estrous female. Terminal nerve lesions, forebrain lesions, or sham surgeries were performed, and blood was collected again with and without odor stimulation. Serum testosterone levels were assessed by radioimmunoassay. None of the surgical procedures interrupted the ability of the male hamsters to demonstrate an increase in serum testosterone following exposure to the odor of an estrous female. We conclude that the terminal nerve is not necessary for this pheromonally mediated neuroendocrine reflex.

Biocytin : a neuronal tracer compatible with rapid decalcification procedures

The compatibility of neuronal tract-tracing and decalcification procedures was examined in salamander nasal chemosensory systems. Biocytin, but not horseradish peroxidase, retained its labeling capacity following rapid decalcification of the cranial bone. The combination of biocytin tract-tracing and decalcification procedures allows the visualization of labeled neurons and/or their projections within bony regions of intact specimens.