Selective projections of cholecystokinin-8 immunoreactive fibers to galanin immunoreactive sympathetic preganglionic neurons in a teleost, Stephanolepis cirrhifer

Nervous control of photophores in luminescent fishes

Functional studies of the autonomic innervation in the photophores of luminescent fishes are scarce. The majority of studies have involved either the stimulation of isolated photophores or the modulatory effects of adrenaline-induced light emission. The fish skin is a highly complex organ that performs a wide variety of physiological processes and receives extensive nervous innervations. The latter includes autonomic nerve fibers of spinal sympathetic origin having a secretomotor function. More recent evidence indicates that neuropeptide-containing nerve fibers, such as those that express tachykinin and its NK1 receptor, neuropeptide Y, or nitric oxide, may also play an important role in the nervous control of photophores. There is no anatomical evidence that shows that nNOS positive (nitrergic) neurons form a population distinct from the secretomotor neurons with perikarya in the sympathetic ganglia. The distribution and function of the nitrergic nerves in the luminous cells, however, is less clear. It is likely that the chemical properties of the sympathetic postganglionic neurons in the ganglia of luminescent fishes are target-specific, such as observed in mammals.

The Sympathetic Nervous System of Anamniotes

The sympathetic nervous system develops as an evolutionary trait with gnathostomes (jawed vertebrates), but not with agnathan fishes (i.e., hagfishes and lampreys). Organization of the sympathetic preganglionic neuronal columns is different in teleosts and anurans. In the teleosts so far examined, the majority of sympathetic preganglionic neurons (SPNs) are located in the dorsal part of the spinal central gray matter. In Tetraodontiformes, the cell column occupies only two rostral spinal segments, which are distinct in their cytoarchitecture and projections. On the other hand, the SPNs of anurans form two cell columns segregated mediolaterally. The lateral and medial columns are also distinct in their cytoarchitecture and projections. The neuroactive substances expressed in the SPNs both in teleosts and anurans are coded to the projections. In anurans, the SPNs containing gonadotrophin-releasing hormone and those containing calcitonin gene-related peptide are involved in the regulation of blood vessels and cutaneous glands, respectively. In the filefish, the SPNs containing galanin project specifically to non-adrenergic non-cholinergic postganglionic neurons in the cranial sympathetic ganglia. Therefore, both anuran and teleost systems have different morphological and chemical-coded patterns for functional variation, although the anuran sympathetic nervous system has more organizational similarity with that of amniotes.

Effect of cholecystokinin on experimental neuronal aging

AIM: To observe the effect of cholecystokinin (CCK) on lipofusin value, neuronal dendrite and spine ultrastructure, and total cellular protein during the process of experimental neuronal aging.

METHODS: Experimental neuronal aging study model was established by NBA₂ cellular serum-free culture method. By using single intracellular lipofusin value from microspectrophotometry, morphology of neuronal dendrites and spines from the scanner electron microscopy, and total cellular protein as the indexes of experimental neuronal aging, we observed the effect of CCK₈ on the process of experimental neuronal aging.

RESULTS: Under the condition of serum-free culture, intracellular fluorescence value (%) increased with the extension of culture time (1 d 8.51±3.43; 5 d 10.12±3.03; 10 d 20.54±10.3; 15 d 36.88±10.49; ^bP<0.01). When CCK was added to serum-free culture medium, intracellular lipofusin value (%) decreased remarkably after consecutive CCK reaction for 10 and 15 d (control 36.88±10.49; 5 d 32.03±10.01; 10 d 14.37±5.55; 15 d 17.31±4.80; ^bP<0.01). As the time of serum-free culturing was prolonged, the number of neuronal dendrite and spine cells decreased. The later increased in number when CCK₈ was added. CCK₈ could improve the total cellular protein in the process of experimental neuronal aging.

CONCLUSION: CCK₈ may prolong the process of experimental neuronal aging by maintaining the structure and the number of neuronal dendrite and spine cells and changing the total cellular protein.

Choline acetyltransferase immunoreactive sympathetic ganglion cells in a teleost, Stephanolepis cirrhifer

The present study showed neurons immunoreactive for choline acetyltransferase (ChAT) in the cranial sympathetic ganglia lying close to the trigeminal-facial nerve complex of the filefish. In these ganglia, less than 1% of ganglion cells were positive for choline acetyltransferase. Choline acetyltransferase-positive neurons were significantly larger than the randomly sampled neurons in this ganglion. The majority of choline acetyltransferase-positive neurons were negative for tyrosine hydroxylase, but many of them were positive for galanin (GAL). Some neurons were positive for both choline acetyltransferase and tyrosine hydroxylase, but these neurons were rarely immunoreactive for dopamine beta hydroxylase, suggesting that they are not adrenergic. In the cranial sympathetic ganglia and the celiac ganglia, many nerve fibers immunoreactive for galanin were seen, and varicose terminals were in contact selectively with neurons negative for both choline acetyltransferase and tyrosine hydroxylase, but not with those positive for choline acetyltransferase or tyrosine hydroxylase. Nerve fibers immunoreactive for choline acetyltransferase were found to be present in contact with the deep layer of chromatophores, which was observed only in the labial region. These results suggest that cholinergic postganglionic neurons are present in the filefish cranial sympathetic ganglia, and that they also contain galanin. As few cholinergic sympathetic neurons express tyrosine hydroxylase and none express dopamine beta hydroxylase, they are unlikely to synthesize noradrenaline or adrenaline.