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There appears to be specificity in the regrowth of nerve fibers in the fish central nervous system. However, the distribution of terminal boutons is unknown. This study was undertaken to ascertain the reinnervation of neurons by boutons in the regenerated goldfish spinal cord. The spinal cord of 60 goldfish was transected and a segment 2 cm caudal to the lesion was examined 5, 10, 15, 20, 25, 30, 45, and 60 days postoperatively. In another group of animals the spinal cord was retransected after 60 days regeneration time and examined 5 days later to show contributions of long regenerated tracts. The spinal cord segment was stained for boutons by the Rasmussen technique. Boutons were counted on the soma of neurons in medial intermediate gray, ventral horn motoneurons, and ventral horn interneurons and in addition, on primary dendrite of motoneurons. Animals were observed daily for the return of normal swimming. Neurons in the intermediate gray region showed a gradual linear decrease in boutons for 30 days and they remained at this level from 30 to 60 days. Motoneuron soma and primary dendrite showed an abrupt decrease in boutons at 5 days, with a linear increase in boutons to normal levels by 60 days. Retransection of the spinal cord after 60 days did not result in bouton loss on soma or dendrite. These data indicate that the motoneuron was originally innervated by descending long tracts but was now reinnervated by other tracts. Ventral-horn interneuron soma showed an initial loss of boutons followed by return to normal numbers by 30 days and hyperinnervation between 30 and 60 days. Retransection resulted in the return of boutons to normal levels. Thus, this interneuron was reinnervated by regenerated descending tracts. Despite this synaptic reorganization of spinal neurons, normal swimming returned. We conclude that specificity of regeneration is not selective for soma or dendrite of spinal neurons but is probably selective for the neuronal pools or circuits necessary for swimming.

The learning and retention of conditioned avoidance responses by goldfish were studied in a two-way avoidance task designed to minimize the demands of the task for forebrainless fish. Forebrainless fish were less active than normal fish in both pretraining response rate and between-trial cross rate. Forebrainless fish learned the avoidance response as well as normal fish with a minimal barrier and a 10-sec light-shock interval. Forebrainless fish were inferior to normal fish after insertion of a larger barrier which reduced the area for avoidance, concomitant with a 4-sec light-shock interval. Removal of the telencephalon produced significant deficits in the performance of a previously learned avoidance response; however, there was evidence for partial savings. It is proposed that the normal function of the telencephalon is best considered to be that of facilitating the processing of information.

Recent findings have shown that the spinalcord of mammals is capable of limited regeneration. The reparative process involves very limited regeneration of severed nerve fibers and growth of axonal sprouts. In addition, partially deafferented neurons proximal to the site of spinal cord lesion undergo morphological alteration. Following hemisection of the spinal cord nerve fibers reinnervate the morphologically altered neurons proximal to the site of lesion. The present paper reports an investigation of the process in rat, monkey, and man.

Although the central nervous system of the mammal is reported not to regenerate, axonal sprouting has recently been demonstrated in various regions of brain and spinal cord. The following study investigates the regenerative capacity of 72 rat spinal cords following left hemisection at T2. In addition to nine normals, rats were killed at 5, 7, 14, 30, 60, and 90 days after making the lesion. Three animals per groups were prepared for Golgi, Protargol-eosin-cresyl violet staining, and electron microscopy. Three additional animals had hemisections at C5 and the cord from C5 to T5 was stained by the Fink-Heimer method. Six animals had hemisections at T2 and the cords were subsequently rehemisected 90 days later at C5; three animals were prepared for the Fink-Heimer stain and three for electron microscopy. The dendrites of the reactive motor neurons proximal to the site of lesion became varicose from day 10 to day 60–90 after the lesion, until the entire dendrite was replete with irregularly shaped varicosities. At 15 days postoperatively, processes grew into the reactive neural zone and by day 30 could be identifified as axons (0.1–0.5 μ in diameter) and dendrites. The axons grew in fascicles, usually free of neuroglial cell processes. The amjority of the axons formed axodendritic synapses on the indentations of the dendritic varicosities by 60–90 days postoperatively. The Fink-Heimer stain reveled that a limited number of axons regenerated from long tracts into the reactive neural zone. Most regenerated axons appear to be axonal sprouts from the operated and unoporated portions of the spinal cord. The central nervous system of the rat does regenerate, but the regenerating axons do not grow past the reactive neural zone and thus do not reach the neuroglial scar.

Recent findings have shown that the spinalcord of mammals is capable of limited regeneration. The reparative process involves very limited regeneration of severed nerve fibers and growth of axonal spr

The effect of forebrain ablation on brightness discrimination in goldfish has been studied. Cardiac deceleration, a conditioned autonomic response, was used as the measure of discrimination in a series of goldfish. Normal and forebrainablated fish were trained to discriminate between two gray stimuli of different brightness. If the experimental animal made this brightness discrimination in thirty-five trials it was subsequently tested on a black and white stimulus pair to see whether the fish was capable of stimulus generalization. If the fish did not make the brightness discrimination, it was trained to discriminate a different set of stimuli to show that it was conditionable. It was found that forebrain ablation did not result in any loss in the ability of these operated fish to make a brightness discrimination. In fact, the operated animals learned the brightness discrimination more rapidly than normal animals. Furthermore, the forebrainless fish were able to generalize to another brightness problem. Control tests were run to substantiate this finding.

The blood-brain barrier may be demonstrated in mammals by the exclusion of certain dyes from the brain. In addition, anions such as thiocyanate, iodide, bromide, and sulfate are maintained in the brain at various brain/plasma ratios. In mammals, these ratios, in vivo have always been lower than the brain/plasma ratio for chloride. The present investigation was undertaken to study the blood-brain barrier of the goldfish by determining the entry of various dyes and ions into the brain parenchyma. The brains of the fish were examined 4 hr after intraperitoneal injection of 1% trypan blue, bromphenol blue, sodium phenolsulfonephthalein or sodium fluorescein. The dyes did not enter the brain parenchyma except at the anterior and posterior choroid plexus and the saccus vasculosus. The barrier could be disrupted by 70% alcohol or stab wounds in the brain. In addition, sodium thiocyanate was injected intraperitoneally or was introduced into the water of the aquarium. Tissue samples were taken 5–144 hr later and the thiocyanate space calculated. The chloride space of other fish was similarly calculated. The thiocyanate space of brain was significantly larger (p < 0.01) than the chloride space. The thiocyanate space of muscle was not significantly different from the chloride space. Since the thiocyanate space of brain exceeded the chloride space it is suggested that there are significant differences between the blood-brain barrier mechanisms of bony fish and mammals.

Raman spectra for the intensely colored salts of the tetracyanoethylene radical anion with sodium and potassium cations confirm previous assertions that the infrared salt spectra are completely dominated by vibronic interaction effects. As expected, strong Raman scattering has been observed at frequencies coincident with the intense infrared bands which have been assigned to totally symmetric modes activated by an ``electron‐vibration'' moment. The scattering intensities of the symmetric stretching modes (ν1, ν2, and ν3) reveal a complex dependence on excitation frequency which is qualitatively consistent with the observed vibronic structure of the electronic absorption band. By confirming the assignment of several of the radical anion internal modes, the Raman data have also permitted the evaluation of reliable stretching constants for comparison with the neutral molecule force constants and quantum chemical predictions of bond order changes. New data and a subsequent force constant analysis have required the reassignment of

The effect of forebrain ablation on hue discrimination in fish has been studied. Cardiac deceleration, a conditioned autonomic response, was used as the measure of discrimination in a series of goldfish. Electric shock was the unconditioned stimulus. Forebrain-ablated fish were trained to a red and a green stimulus selected to be of equal brightness. These fish were subsequently tested on red and green stimuli of known brightness, as perceived by these experimental animals. Normal fish in this situation reacted to the test stimuli on the basis of their wavelength characteristics, but forebrainless animals reacted only to the brightness and not to the wavelength characteristics of the test stimuli. Other control tests substantiate this finding.

Two experiments were performed to determine whether regenerating preganglionic sympathetic fibers establish synapses randomly with any postganglionic neuron or selectively with specific postganglionic neurons. Experiment I . In normal cats the cervical sympathetic trunk (CST) is composed of nerve fibers deriving from the thoracic sympathetic rami T1 to T7. Of these rami, T1 contributes largely pupillodilator fibers and T4 contributes largely vasoconstrictor fibers (i.e., electrical stimulation of T1 produces pupillary dilation without decrease in ear temperature and stimulation of T4 produces a decrease in ear temperature without pupillary dilation). Following transection and regeneration of the CST, these relationships are re-established, indicating that the sympathetic preganglionics from T1 have established synapses preferentially with pupillary postganglionic cells and that the preganglionics from T4 have established synapses preferentially with vasomotor postganglionic cells. Experiment II . In normal cats pupillary dilation is elicited by electrical stimulation of rami T1 to T3, but not T4 to T7. However, stimulation of T4 to T7 does produce pupillary dilation 1 month after crushing T1 to T3 (i.e., before the crushed fibers have regenerated). This effect results from the formation of terminal collateral connections between the residual nonpupillary (T4 to T7) preganglionic nerve fibers and pupillary postganglionic cells (11). Six months postoperatively, pupillary dilation is elicited by stimulation of T1 to T3, but not T4 to T7. Apparently, after T1 to T3 fibers have regenerated, the nonpupillary collaterals (T4 to T7) become functionally inactive and the regenerated fibers again establish functional connections with the pupillary postganglionic cells. From these two experiments we conclude that there is a strong specific affinity between regenerating sympathetic preganglionic fibers and their appropriate postganglionic nerve cells.

Experiments were performed to determine if the fibers of the sciatic or tibial nerves that normally innervate the soleus and plantaris muscles will, after regeneration, selectively reinnervate these muscles. In addition to nine unoperated control rats, thirty-seven operated animals were studied 4 months after one of the following procedures: sciatic nerve transection and resuture in adults (9), sciatic nerve crush in adults (8), tibial nerve transection and resuture in adults (5), tibial nerve crush in adults (5), sciatic nerve transection in neonatal rats (5), sciatic nerve crush in neonatal rats (5). Recordings were made of the isometric tensions (T) developed by the soleus and plantaris muscles during supramaximal tetanic stimulation of lumbar nerves L4 and L5 singly and simultaneously (L4 + 5). In normal rats L4 supplies a proportionately greater functional innervation to the plantaris than to the soleus, the ratio TL4/TL5 being significantly higher in the plantaris than in the soleus. In none of the six operated groups could any such difference in the ratio of the two muscles be demonstrated. Consequently there is no evidence of selectivity in the regeneration of the plantaris and soleus nerve fiber constituents of the sciatic or tibial nerves. Both the plantaris and soleus muscles of each operated group showed greater tension overlap than the corresponding muscles of the unoperated control group. Tension overlap was computed as follows: (TL4 + TL5 − TL4 + 5) TL4 + 5 . Gold chloride impregnations of motor end plates indicate that the increased overlap results only in part from increased numbers of dually innervated (presumably bisegmentally innervated) muscle fibers.

Although the spinal cord of goldfish normally regenerates, 30 or more days of blockage by Teflon inserts will result in the loss of this regenerative capacity. The following studies were undertaken to investigate the ultrastructure of normal regeneration and the loss of regenerative capacity following Teflon blockage. The spinal cords of 13 normal and 27 cord-transected goldfish were examined with the electron microscope. Cord-transected goldfish were killed 1 day to 3 months postoperatively. In 15 additional goldfish the spinal cords were transected and Teflon sheet placed between the severed stumps for 1–3 months, after which time it is known the spinal cord will not regenerate following Teflon removal. The spinal cords were immersed in buffered 1% osmic acid and prepared for electron microscopy. In the absence of Teflon, regenerating axons were repelte with smooth endoplasmic reticulum and mitochondria. The majority of axons had regenerated across the site of lesion by day 30 and synapsed in the first segment of the caudal spinal cord stump. Dendrites regenerated in neurite fascicles along with axons. After blockage by Teflon, the nerve fiber tips grew into juxtaposition in zones subjacent to a glialependymal scar. These axons possessed multibulbous processes at the tip which usually formed axoaxonic and axodendritic synapses. Retransection (five goldfish) of the spinal cord one segment rostral to the Teflon block resulted in the degeneration of approximately 50% of all the synapses in the synaptic zone subjacent to the glial-ependymal scar.

Spinal cord hemisection results in limited regeneration of nerve fibers and the sprouting of intact nerve fibers proximal to the site of lesion. Electron microscopically the nerve fibers form new synaptic complexes. The following study was undertaken in the rat to determine the synaptic profile of neurons during the regenerative process. The spinal cords of 40 rats were hemisected at vertebral segment T-2 and 5 animals per group (in addition to 5 normals) were utilized 10, 20, 30, 45, 60, and 90 days posthemisection. Tissue was prepared by the Rasmussen technique for the light microscopic demonstration of boutons. In addition, five animals had the cord hemisected and the spinal cord tissue was prepared for electron microscopy 40 days postoperatively. Bouton counts were made on perikaryon and primary dendrite (of the same neuron) of neurons in lamina IV, lamina VII, and on motoneurons. Statistical analysis of counts from coded material was carried out utilizing a polynomial regression, analysis of variance, and a Neuman-Keuls a posteriori analysis. The number of boutons on the perikaryon of neurons on the operated side demonstrated a significant decrease in boutons at 10–20 days postoperative followed by a significant increase in boutons at 30 days to levels below normal innervation. This reinnervation was followed by a significant secondary loss of boutons from 30 to 60 days. This trend of bouton alteration was repeated (with minor variations) on the perikaryon of neurons on the unoperated side of the spinal cord. This general trend was repeated on the primary dendrite on both operated and unoperated side of the spinal cord. However, the number of boutons on primary dendrite usually returned to normal. The regenerated boutons (30 days) frequently contained granular vesicles (predominantly 900 A). The boutons that degenerated 30–60 days had all combinations of synaptic vesicles. This is an indication that former and new synaptic complexes were degenerating. The alteration of boutons on perikaryon and primary dendrite following hemisection suggests: that there is a critical period of initial denervation (0–20 days); that reinnervation occurs within the first 30 days; and that a secondary denervation occurs after 30–60 days. This recombination of neuronal circuits may represent an accelerated view of a dynamic continuum which imparts information to denervated neurons about altered neuronal circuitry adding a further dimension to the plasticity of the adult nervous system.

The intra-hippocampal organization of theta rhythm was examined in chronically implanted rats. Small lesions were placed in the posterior aspects of the hippocampal formation and the subsequent effect of the lesion ascertained electrophysiologically. Lesions of the subiculum significantly diminished the amount of theta rhythm present and the effect appeared to be permanent. Lesions of the lateral entorhinal region produced a large, but transient, increase in the amount of theta rhythm present. The electrophysiological consequences of these lesions were organized in ‘lamellae’ as previously suggested. In addition, the effects of the discrete lesions were expressed ipsilaterally only. The fiber connections underlying these effects were reviewed and the subiculum was postulated to be a critical region for the maintenance of normal ‘on-going’ hippocampal electrical activity. The increase in theta rhythm following lateral entorhinal lesions was postulated to be result of the loss of high-frequency influences from other neural regions. It was concluded that, although paced by the septal regions, hippocampal theta rhythm is dependent upon intra-hippocampal formation maintenance and modulation. In particular, the present data indicate the importance of the subiculum in this maintenance. Furthermore, the data suggest an important role of the hippocampal formation in the organization of theta rhythm.

The ultrastructure of a neuroma within the spinal cord of a paraplegic patient is described. The neuroma consisted of a discrete circular collection of cells and nerve fibers surrounded by a capsule of glial fibrils. The axis cylinders of the nerve fibers present often did not fill the myelin sheath. The myelin sheaths formed by Schwann-like cells were replete with Schmidt-Lanterman incisures and nodes of Ranvier. These data indicate that this central neuroma is of dorsal root or perivascular origin.

Poikilotherms that are stored in the cold often do not give normal visual responses. This experiment was undertaken to examine the electrophysiological and morphological changes in the retina during cold stress. Twenty-two goldfish (Carassius auratus) were placed in a refrigerated aquarium and the temperature reduced from 20 to 6 C (±2) for up to 31 days after which temperature was gradually returned to 20 C. During the period of cold stress and recovery, recordings were made of the electroretinogram, fast retinal potential, and tectal evoked response. Eyes of 22 animals were removed at various intervals for histological examinations. Electrical signals of nine animals were tested during cold stress and recovery to monitor for cold effects on retinal and visual pathway discharge. The temperature of two normal goldfish was reduced from room temperature to 5 C during 2 hr to control for the effect of temperature on visual signals. This resulted in minimal physiological changes. All visual signals nearly disappeared within 14 days of exposure to continuous cold stress. Slow recovery to 20–100% of normal was achieved within 52 days after return to room temperature. Statistical analysis of results from samples of retinal tissue indicated that electrical signal loss and return was paralleled by depletion and restitution of many cone outer segments. The return of visual behavior was correlated with the return of nearly normal complements of cone outer segments.

This study investigated the regenerative capacity of the long tracts in the goldfish spinal cord. The spinal cord was transected anterior to the dorsal fin and the regenerative capacity of the descending fiber tracts (tectospinal, cerebellospinal, ventral tract group) assessed. Degenerating axons were stained 9 and 60 days later. Seven animals in the 60-day group underwent a subsequent cord retransection, one segment rostral to the original site of lesion and stained 9 days later. The degenerative patterns of the descending and ascending tracts were determined for a spinal cord segment 2 cm caudal to the original site of lesion. Following spinal cord transection all fish were paralyzed but normal swimming returned by day 25. Nine days postoperatively, the descending tracts were completely degenerated, with no evidence of degeneration in the ascending tracts. Sixty days postoperatively regenerated nerve fibers in the descending tracts were approximately 35–49% of the usual complement of axons. Approximately 94% of the regenerated nerve fibers were 4–8 times of normal diameter. Retransection of the spinal cord one segment rostral to the first lesion resulted in degeneration of the large diameter regenerated axons but not the normal diameter component. The relationship of the return of function to the quality and quantity of regenerated nerve fibers is discussed.

Historically, injury of the mammalian spinal cord resulted in abortive regeneration. Recent findings have shown regeneration of the spinal cord occurs by limited regrowth of severed nerve fibers and massive regrowth of axonal sprouts of normal axons. The foregoing study investigates the regenerative capacity of the spinal cord in 14 Rhesus monkeys (Macaca mulatto) following left hemisection at vertebral segment T2. In addition to three normals, animals were utilized 7, 14, 21 days and 1, 2, 3, and 4 months posthemisection. Tissue was prepared for Golgi impregnation, Protargol-cresyl violet-eosin staining, and electron microscopy. The motor horn rostral to the site of lesion was investigated. Dendrites of motor horn cells adjacent to and facing the lesion developed varicosities which formed at the terminal end of the dendrite by day 7 and progressed to include the entire dendrite by day 14–30 posthemisection. Motor horn cell dendrites (0–5 mm from lesion) were varicose and many possessed only two short, va...

Raman spectra for the intensely colored salts of the tetracyanoethylene radical anion with sodium and potassium cations confirm previous assertions that the infrared salt spectra are completely dominated by vibronic interaction effects. As expected, strong Raman scattering has been observed at frequencies coincident with the intense infrared bands which have been assigned to totally symmetric modes activated by an ``electron‐vibration'' moment. The scattering intensities of the symmetric stretching modes (ν1, ν2, and ν3) reveal a complex dependence on excitation frequency which is qualitatively consistent with the observed vibronic structure of the electronic absorption band. By confirming the assignment of several of the radical anion internal modes, the Raman data have also permitted the evaluation of reliable stretching constants for comparison with the neutral molecule force constants and quantum chemical predictions of bond order changes. New data and a subsequent force constant analysis have required the reassignment of

Publisher Summary The primary function of the central nervous system is integration. This chapter discusses the integrative function within the central nervous system. Integration results in adaptive behavior, which is initiated by the perception of peripheral events. These peripheral events are encoded; information is transmitted to different areas of the central nervous system; messages converge on and divert to the appropriate central nervous system centers; this information is transmitted to appropriate efferent centers with the resultant appropriate messages going to the efferent organs of the body, resulting in the final behavior of the animal. Anatomically, information is carried over the fiber tracts of the central nervous system to the various neural centers; physiologically, this results in the dendritic summation of excitatory and/or inhibitory effects on the neural components of the nervous system center. The neuroanatomical relationships of the various centers in the central nervous system have been advanced by the use of modern techniques such as the use of specific stains for the degeneration of neural pathways and the utilization of radioactive tracers for the study of axoplasmic flow. In addition, electron microscopy has revealed several unusual features of the fish nervous system. There have been many experimental methods and designs developed to ascertain the integrative function of various portions of the nervous system of fish. The study of the integrative function of the central nervous system of fish is aided by one of the most remarkable features of the system that is its ability to regenerate.

The regenerative capacity of the central nervous system appears to be related to phylogenetic level. The present studies in the goldfish and rat were undertaken to ascertain the regenerative capacity of the telencephalon. Five types of telencephalic lesions performed in goldfish were total removal, removal of one hemisphere, removal of lateral portion of hemispheres, partial section of hemisphere, and stab wound in hemisphere. In the rat a stab wound was made in occipital cortex. Animals were killed up to 2 years postoperatively. In the goldfish regardless of age at operation, removal of a mass of tissue did not result in restitution of the ablated parenchyma. After partial transection, cysts were observed in the telencephalic parenchyma partially or completely lined with pseudostratified columnar epithelial cells which were often ciliated. Giant pleomorphic reactive neuroglial cells were found in the area of the lesion. These cells usually became necrotic after 60 days. Severed axons regenerated around the lesions and reformed characteristic tracts. Ninety days after transection the area of the lesion was sometimes filled with epithelial cells which subsequently became glial in form so that the area of lesion was characterized by cysts and increased vascularity. Cortical regeneration in the rat was abortive. The cellular reaction to injury was compared in these two animals.

The role of the telencephalon in hue discrimination and interocular transfer of hue discrimination has been studied. Cardiac deceleration, a conditioned autonomic response, was used as the measure of discrimination in goldfish. Electric shock was the unconditioned stimulus. After occluding one eye, normal fish were trained to a red and a green stimulus selected to be of equal brightness. The naive or transfer eye was then tested on red and green stimuli of known brightness as perceived by these experimental animals. Normal fish and fish with the forebrain contralateral to the trained eye ablated demonstrated interocular transfer of a hue discrimination. Following ablation of the forebrain homolateral to the trained eye or bilateral forebrain ablation, operated fish demonstrated a loss in ability to make an interocular transfer to generalizations of hue. However, the ability to make an interocular transfer of a hue discrimination returns if a suitable period is allowed postoperatively. It was concluded that the telencephalon is not essential for color vision or for the interocular transfer of color vision in fish.

Two infants with anomalous ossification centers for the inferior articular processes of several lumbar vertebrae are reported. The possible origin of these centers and their adult equivalent are discussed.

In the fish and amphibia the regenerative capacity of the spinal cord decreases from the embryonic stages of life to adulthood. The present experiments examine the relationship between age and the regeneration of severed spinal elements in the adult goldfish. The spinal cord of 1-, 2-, and 3-year old fish was transected in the mid dorsal fin region. The operation resulted in paralysis caudal to the lesion. Normal swimming and turning movements occurred in 20–25 days for 1-year olds, 25–30 days for 2-year olds, and 35–40 days for 3-year olds. In all age groups stimulation of the cervical spinal cord 30 days postoperatively elicited electromyographic responses in the myotomes caudal to the lesion. By 7 days post-operatively, small branching nerve fibers had grown from both proximal and distal stumps into the connective tissue scar in the gap. By 90 days postoperatively regeneration was complete. At this time there was a 26% decrease in cord diameter in the 2-year olds, a 28% decrease in the 3-year olds, but only 0.5% decrease in 1-year olds. In the region of transection the percentage of regenerated fibers was significantly greater in the 1-year olds than in the 2- and 3-year olds; in the 1-year olds the number of fibers was 90% of normal whereas in the 2- and 3-year olds it was 50% of normal. There were no motor horn cells in the regenerated area, and Mauthner's axon did not regenerate. It is concluded that spinal cord regeneration in the goldfish is age dependent; however, regeneration was sufficient in all age groups studied to result in complete restitution of function.