1. ANATOMY AND PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
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pathway, appears to be rather a universal fcature of the neuroendocrine
system of vertebrates and thus fish can serve as a model for neuroendocrine function.
Kandel ( 1964) studied the electrophysiological properties of neuroendocrine cells in the magnocellular area of thc preoptic nucleus of
goldfish. These cells usually range in size from 12 to 30 with occasional
large cells up to 5 O p . Single cell recordings wcre made with glass fluidfilled pipettes. Antidromic stimulation of the preoptic cells was accomplished by stimulation of the pituitary gland proper. The average
latency for antidromic activation was 6.0 mscc. Since axon length was 2.8
mm, a conduction velocity of 0.46 meters/sec was calculated for the
axons of the neuroendocrine cells. A similar conduction velocity for the
axons of the preoptic neurons (0.5 meters/sec) was observed in Lophius
(Potter and Loewenstein, 1955). Spike heights of the neuroendocrine
cells ranged up to 117 mV and were distinguished by long durations of
discharge up to 3.5 msec (Kandel, 1964).
The neuroendocrine cells demonstrated a slow spontaneous firing rate
of 2-8 impulses/sec. Action potentials and afterpotentials similar to those
occurring spontaneously were initiated by this stimulation. Afferent stimulation of preoptic neurons was produced by stimulation of the olfactory
tract which produced a long latency depolarizing excitatory postsynaptic
potential (EPSP). This response was graded and triggered an action
potential when the critical discharge potential was attained. The EPSP
was multiphasic and most probably polysynaptic. Suprathreshold stimuli
produce a faster firing EPSP and a shorter latency spike.
Antidromic stimulation, from stimulation of the pituitary gland, activated the neurohypophysial tract and produced antidromic action
potentials in the preoptic nucleus. This type of stimulation resulted in
inhibitory postsynaptic potentials (IPSP) in 80% of the neurons in the
preoptic nucleus. The IPSP was also a graded response and proved to be
sensitive to polarizing current; that is, the potential change was increased
by depolarizing current pulses and decreased or abolished by hyperpolarizing current pulses ( Kandel, 1964 ).
Flushing the gills of goldfish with water containing as little as 0.10.35% sodium chloride ( NaCl) produced effects localized in the preoptic
nucleus. Higher percentages of saltwater tended to produce small positive extracellular potential changes in surrounding areas of the brain.
Single infusions of saltwater produced little or no effect, but multiple
infusions appeared to summate the response and produced significant
slowing of spontaneous activity in preoptic neurons. However, infusion
of seawater three, four, and five times with 10-60 seclpulse interval
will elicit a slowing of spontaneous discharge rate. Multiple infusions of
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pathway, appears to be rather a universal fcature of the neuroendocrine
system of vertebrates and thus fish can serve as a model for neuroendocrine function.
Kandel ( 1964) studied the electrophysiological properties of neuroendocrine cells in the magnocellular area of thc preoptic nucleus of
goldfish. These cells usually range in size from 12 to 30 with occasional
large cells up to 5 O p . Single cell recordings wcre made with glass fluidfilled pipettes. Antidromic stimulation of the preoptic cells was accomplished by stimulation of the pituitary gland proper. The average
latency for antidromic activation was 6.0 mscc. Since axon length was 2.8
mm, a conduction velocity of 0.46 meters/sec was calculated for the
axons of the neuroendocrine cells. A similar conduction velocity for the
axons of the preoptic neurons (0.5 meters/sec) was observed in Lophius
(Potter and Loewenstein, 1955). Spike heights of the neuroendocrine
cells ranged up to 117 mV and were distinguished by long durations of
discharge up to 3.5 msec (Kandel, 1964).
The neuroendocrine cells demonstrated a slow spontaneous firing rate
of 2-8 impulses/sec. Action potentials and afterpotentials similar to those
occurring spontaneously were initiated by this stimulation. Afferent stimulation of preoptic neurons was produced by stimulation of the olfactory
tract which produced a long latency depolarizing excitatory postsynaptic
potential (EPSP). This response was graded and triggered an action
potential when the critical discharge potential was attained. The EPSP
was multiphasic and most probably polysynaptic. Suprathreshold stimuli
produce a faster firing EPSP and a shorter latency spike.
Antidromic stimulation, from stimulation of the pituitary gland, activated the neurohypophysial tract and produced antidromic action
potentials in the preoptic nucleus. This type of stimulation resulted in
inhibitory postsynaptic potentials (IPSP) in 80% of the neurons in the
preoptic nucleus. The IPSP was also a graded response and proved to be
sensitive to polarizing current; that is, the potential change was increased
by depolarizing current pulses and decreased or abolished by hyperpolarizing current pulses ( Kandel, 1964 ).
Flushing the gills of goldfish with water containing as little as 0.10.35% sodium chloride ( NaCl) produced effects localized in the preoptic
nucleus. Higher percentages of saltwater tended to produce small positive extracellular potential changes in surrounding areas of the brain.
Single infusions of saltwater produced little or no effect, but multiple
infusions appeared to summate the response and produced significant
slowing of spontaneous activity in preoptic neurons. However, infusion
of seawater three, four, and five times with 10-60 seclpulse interval
will elicit a slowing of spontaneous discharge rate. Multiple infusions of