1. ANATOMY AM, PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
77
to the muscles responsible for opening and closing the mandible can be
transected and cross-united ( Arora and Sperry, 1957). The nerve which
normally innervated muscles responsible for closing the mandible now
was innervating muscles that were responsible for opening the mandible
and vice versa. In four specimens ( Astronotus), the nerve cross-unions
completely regenerated and innervated the muscles with normally opposite function. In these animals, the muscles reacted properly and mandibular movement returned to normal. Electrical stimulation of the
cross-united nerves resulted in muscle contraction demonstrating that
the foreign nerve had indeed grown into the muscle (Arora and Sperry,
1957). These experiments demonstrated that regenerating motor fibers
did establish functional connections with foreign mandibular muscles
and that these muscles induced a local muscle specificity so that information derived from the regenerated motor axons resulted in the return of
function specific for the muscle (myotypic respecification).
Regeneration of the oculomotor nerve of Astronotus resulted in return
of normal function following regeneration into extraocular muscles. However, cross-union of the original branches to the different extraocular
muscles of the eye in the anglefish, Pterophyllum scalure, did not result
in normal restitution of function (Arora, 1962). It would appear then
that there was no myotypic respecification of the regenerated nerve fibers
of this cranial nerve. This also appears to be the case in the regeneration
of transposed peripheral nerves to pectoral fins.
Regeneration of spinal axons to peripheral fin musculature has been
studied in Astronotus (Mark, 1965). In this cichlid fish, there were three
groups of antagonistic muscles that moved the pectoral fins. Each of
these muscle groups was innervated by a separate nerve bundle derived
from the brachial plexus. The muscles were elevators, adductors, or
abductors of the pectoral fins, Following transection of the root from
the brachial plexus on one side, or partial transection of the root (leaving
the nerve fibers to abductor muscles intact), there was an initiation of
recovery of function following 7-10 days of paralysis. Recovery was completed in all five animals tested 3 weeks postoperative. Cross-union and
regeneration of the innervation of the abductor muscle to the distal
stump of the nerve innervating of the adductor musculature (and vice
versa) resulted, in the majority of animals, in uncoordinated movements
of the fin for up to 10 months postoperatively (Mark, 1965).
Neither respecification of muscle specificity nor central nervous SYStem plasticity of the fish was adequate to compensate for inappropriate
nerve muscle connection in the fin musculature. This suggested that the
reconstitution of muscular control as seen in the work with the trigeminal
nerve primarily depends on the selective reestablishment of peripheral
77
to the muscles responsible for opening and closing the mandible can be
transected and cross-united ( Arora and Sperry, 1957). The nerve which
normally innervated muscles responsible for closing the mandible now
was innervating muscles that were responsible for opening the mandible
and vice versa. In four specimens ( Astronotus), the nerve cross-unions
completely regenerated and innervated the muscles with normally opposite function. In these animals, the muscles reacted properly and mandibular movement returned to normal. Electrical stimulation of the
cross-united nerves resulted in muscle contraction demonstrating that
the foreign nerve had indeed grown into the muscle (Arora and Sperry,
1957). These experiments demonstrated that regenerating motor fibers
did establish functional connections with foreign mandibular muscles
and that these muscles induced a local muscle specificity so that information derived from the regenerated motor axons resulted in the return of
function specific for the muscle (myotypic respecification).
Regeneration of the oculomotor nerve of Astronotus resulted in return
of normal function following regeneration into extraocular muscles. However, cross-union of the original branches to the different extraocular
muscles of the eye in the anglefish, Pterophyllum scalure, did not result
in normal restitution of function (Arora, 1962). It would appear then
that there was no myotypic respecification of the regenerated nerve fibers
of this cranial nerve. This also appears to be the case in the regeneration
of transposed peripheral nerves to pectoral fins.
Regeneration of spinal axons to peripheral fin musculature has been
studied in Astronotus (Mark, 1965). In this cichlid fish, there were three
groups of antagonistic muscles that moved the pectoral fins. Each of
these muscle groups was innervated by a separate nerve bundle derived
from the brachial plexus. The muscles were elevators, adductors, or
abductors of the pectoral fins, Following transection of the root from
the brachial plexus on one side, or partial transection of the root (leaving
the nerve fibers to abductor muscles intact), there was an initiation of
recovery of function following 7-10 days of paralysis. Recovery was completed in all five animals tested 3 weeks postoperative. Cross-union and
regeneration of the innervation of the abductor muscle to the distal
stump of the nerve innervating of the adductor musculature (and vice
versa) resulted, in the majority of animals, in uncoordinated movements
of the fin for up to 10 months postoperatively (Mark, 1965).
Neither respecification of muscle specificity nor central nervous SYStem plasticity of the fish was adequate to compensate for inappropriate
nerve muscle connection in the fin musculature. This suggested that the
reconstitution of muscular control as seen in the work with the trigeminal
nerve primarily depends on the selective reestablishment of peripheral