Dendritic morphology of neurons in sympathetic ganglia of the goldfish, Carassius auratus

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.

Nitric oxide synthase- and neuropeptide Y-containing subpopulations of sympathetic neurons in the coeliac ganglion of the Atlantic cod, Gadus morhua, revealed by immunohistochemistry and retrograde tracing from the stomach

In this study retrograde tracing was used to locate sympathetic ganglion cells innervating the stomach of a teleost fish, Gadus morhua. A subpopulation of small neurons in the coeliac ganglion was retrogradely labelled after Fast Blue injection in the stomach wall. Neurons projecting to the myenteric plexus and muscle layers contained tyrosine hydroxylase immunoreactivity, and neurons projecting to submucosal layers and blood vessels contained neuropeptide Y immunoreactivity in addition to being tyrosine hydroxylase immunoreactive. A population of nitric oxide synthase containing tyrosine hydroxylase immunoreactive neurons was also found in the coeliac ganglion. These neurons were not frequently labelled after injection in any layer of the stomach. The presence of entero-enteric pathways was also surveyed, but too few enteric neurons were labelled with Fast Blue after injection in the coeliac ganglion to indicate a presence of an entero-enteric reflex. We conclude that in teleost fish, as previously reported in a variety of mammals, a pattern of target specific chemical coding of sympathetic neurons exists, but that all reflex systems of mammalian vertebrates are perhaps not present in fish.

Sympathetic vasoconstrictor neurons projecting from the guinea-pig superior cervical ganglion to cutaneous or skeletal muscle vascular beds can be distinguished by soma size

We have used a combination of retrograde axonal tracing and intracellular dye injections to determine the soma size of sympathetic vasoconstrictor neurons projecting from the superior cervical ganglion to the cutaneous vascular bed of the eartips, or to the vascular beds of the masseter muscle, of guinea-pigs. Neurons projecting to vasculature of the masseter muscle had a cross-sectional area of 956 +/- 295 microns2 (mean +/- SD; n = 45 cells) and were significantly larger than neurons projecting to the vasculature of the eartip skin (mean cross-sectional area +/- SD, 604 +/- 251 microns2; n = 39 cells). These results are consistent with physiological observations showing that muscle vasoconstrictor neurons have faster conduction velocities than cutaneous vasoconstrictor neurons. Furthermore, they suggest that muscle vasoconstrictor neurons may innervate a larger volume of vasculature compared with cutaneous vasoconstrictor neurons.