UROPHYSIS AND CAUDAL
NEUROSECRETORY SYSTEM
HOWARD A. BERN
I.
11.
111.
IV.
V.
Introduction . . . . . . . . . . . . 399
Anatomy and Occurrence of the Caudal
Neurosecretory System
. . . . . . . . . 401
A. Caudal Neurosecretory System in Teleosts and Elasmobranchs . 401
B. Evidence for Caudal Neurosecretory Neurons
in Other Vertebrate Groups . . . . . . . . 407
C. Evolution of the Caudal Neurosecretory System . . . . 408
Cytophysiology and the Secretion Process . . . . . . 409
Physiology
. . . . . . . . . . . . 412
Perspectives . . . . . . . . . . . . 414
References . . . . . . . . . . . . . 416
I. INTRODUCTION
The caudal neurosecretory system is a neuroendocrine apparatus characteristic of the posterior spinal cord of elasmobranch and teleost fishes.
Despite the constant occurrence of this system in these large groups of
fishes, its physiological significance has yet to be definitively established
for even a single species. Nevertheless, its structure is such as to require
the conclusion that its function is an endocrine one. Its secretory cells,
modified neurons, project to a rich capillary network, and its secretory
product, prominent at both light and electron microscope levels, is concentrated in axonal enlargements that terminate on or near a basement
membrane region interposed between the axon terminals and the capillary endothelium (see Fig. 3). Thus, both the ubiquitousness and the
architecture of this system bespeak an important contribution to organismal physiology. It is regrettable that more than 14 years after the complete elucidation of its structural attributes by Masashi Enami, we still
399
NEUROSECRETORY SYSTEM
HOWARD A. BERN
I.
11.
111.
IV.
V.
Introduction . . . . . . . . . . . . 399
Anatomy and Occurrence of the Caudal
Neurosecretory System
. . . . . . . . . 401
A. Caudal Neurosecretory System in Teleosts and Elasmobranchs . 401
B. Evidence for Caudal Neurosecretory Neurons
in Other Vertebrate Groups . . . . . . . . 407
C. Evolution of the Caudal Neurosecretory System . . . . 408
Cytophysiology and the Secretion Process . . . . . . 409
Physiology
. . . . . . . . . . . . 412
Perspectives . . . . . . . . . . . . 414
References . . . . . . . . . . . . . 416
I. INTRODUCTION
The caudal neurosecretory system is a neuroendocrine apparatus characteristic of the posterior spinal cord of elasmobranch and teleost fishes.
Despite the constant occurrence of this system in these large groups of
fishes, its physiological significance has yet to be definitively established
for even a single species. Nevertheless, its structure is such as to require
the conclusion that its function is an endocrine one. Its secretory cells,
modified neurons, project to a rich capillary network, and its secretory
product, prominent at both light and electron microscope levels, is concentrated in axonal enlargements that terminate on or near a basement
membrane region interposed between the axon terminals and the capillary endothelium (see Fig. 3). Thus, both the ubiquitousness and the
architecture of this system bespeak an important contribution to organismal physiology. It is regrettable that more than 14 years after the complete elucidation of its structural attributes by Masashi Enami, we still
399