Eye movement-related activities in cells of the lateral suprasylvian cortex of the cat

Investigation of eye movement-related activities and photic responsiveness using behaving cats demonstrated distinctive representations of eye movement signals in different areas of the lateral suprasylvian cortex: visual reafference in the medial bank of the middle suprasylvian sulcus and non-visual signals (proprioceptive reafference or efference copy) in the lateral bank.     

Early coping experience and later aversive conditioning in cats

Kittens were given differential early experience in order to compare an objective coping behavior with the result of an inescapable aversive experience. Separate groups of kittens were treated in a shock motivated runway task at either 4 or 12 weeks of age, by allowing one member of a weight matched sibling pair to acquire an escape behavior, while the other member was confined; a third subject served as a handled control. Escape behavior was significantly different for 4 and 12 week old subjects, since the older kittens reached a running asymptote within the first few shock trials. At 6 months of age, the subjects were tested for effects of differential early treatment; heart rate, respiration rate and amplitude, and somatic activity were measured during classical conditioning. While all groups gave evidence of acquisition in one or more response measures, only a potentiated heart rate response in 4 week kittens could be related to early experience. Heart rate did not differentiate escaping kittens from confined ones. Rather, heart rate was related to early treatment with shock, perhaps reflecting an increased tendency to react with a passive defensive response.     

Posttraumatic Early Epilepsy and Minor Head Injury

The mechanism of “early epilepsy” sometimes observed after trivial head injury is controversial. Also, the risk of developing late epilepsy after these convulsions, so far, have not been clear.

In order to clarify the mechanism of this posttraumatic early epilepsy after trivial head injury, an attempt was made to observe the role of extracellular potassium ion concentration ([K⁺]_o) in initiation of seizure discharges, in both adult cats and kittens, with K-sensitive microelectrodes.

It was concluded that an increase of [K⁺]_o was not a simple factor for epileptogenesis but minor head injury actually increased seizure slisceptability of immature cat cortex.     

Analysis of monocular optokinetic nystagmus in normal and visually deprived kittens

The asymmetry of monocular OKN was assessed in normal, monocularly deprived (non-deprived eye) and strabismic cats. No significant differences were observed between the responses of these 3 groups. In young kittens, the gain of OKN for nasalward stimulus was larger than that for temporalward. This asymmetry declined to a low residual level by about one year of age. Neurophysiological recordings indicated that the symmetry of OKN is not related to cortical binocularity.     

Development of the optical surfaces of the kitten eye

In the intact post-natal kitten eye, an extensive vascular network severely limits optical quality. We have used scanning electron microscopy to find the locations of this network, to examine all optical surfaces of the eye, and to trace changes with age. Standard preparative procedures were used to view anterior and posterior surfaces of the cornea and lens of 11-, 16-, and 25-day-old kittens and an adult. No significant differences with age are found for the cornea. The vascular network that engulfs the anterior, lateral, and posterior lens is very prominent at 11 days but substantially reduced at 16 days. The anterior surface seems to clear first, and by the 25th day the network is gone although some debris remains. The period of absorption of the vascular system coincides with a marked improvement in optical quality.     

The localization of cytochrome oxidase in the LGN and striate cortex of postnatal kittens

The distribution of cytochrome oxidase (C.O.) was examined in the lateral geniculate nucleus of the kitten during the first postnatal month and compared with the adult pattern. During the first week, most of the C.O. was localized within the perikarya of geniculate neurons. Perigeniculate neurons had darkly reactive dendrites as well as perikaya. A population of relatively large, darkly reactive neurons became distinguishable around the end of the first week, as the level of reactivity diminished to moderate-to-light within most medium and small neurons. On the basis of their relative size and pattern of distribution, most of the darkly reactive neurons are likely to represent ones that will later have class 1 morphology and develop Y receptive field properties. These cells normally undergo rapid growth earlier, and their growth is more adversely affected by early short-term monocular suture than other classes of less reactive geniculate neurons. Thus, in the LGN of developing kitten, C.O. histochemistry may be used as a functional marker for future class 1 Y-cells. The reactivity of the neuropil gradually increases as synapses with dendrites mature. At the electronmicroscopic level the increased reactivity of the neuropil is due mainly to an increase in the number of reactive mitochondria localized within the growing dendrites. In the developing striate cortex of postnatal kittens dark reactivity is localized in the outer part of layer II for the first 2 weeks and then disappears. Dark reactivity gradually increases in layer IV after the third week. The changes in C.O. reactivity accompany pathway-specific physiological and anatomical changes that occur during early postnatal development.     

Influence of binocular competition on the expression profiles of CRMP2, CRMP4, Dyn I, and Syt I in developing cat visual cortex

The visual cortex is vulnerable to changes in visual input, especially during the critical period when numerous molecules drive the refinement of the circuitry. From a list of potential actors identified in a recent proteomics study, we selected 2 collapsin response mediator proteins (CRMP2/CRMP4) and 2 synaptic proteins, Dynamin I (Dyn I) and Synaptotagmin I (Syt I), for in-depth analysis of their developmental expression profile in cat visual cortex. CRMP2 and CRMP4 levels were high early in life and clearly declined toward adulthood. In contrast, Dyn I expression levels progressively augmented during maturation. Syt I showed low levels at eye opening and in adults, high levels around the peak of the critical period, and maximal levels at juvenile age. We further determined a role for each molecule in ocular dominance plasticity. CRMP2 and Syt I levels decreased in area 17 upon monocular deprivation, whereas CRMP4 and Dyn I levels remained unaffected. In contrast, binocular removal of pattern vision had no influence on CRMP2 and Syt I expression in kitten area 17. This study illustrates that not the loss of quality of vision through visual deprivation, but disruption of normal binocular visual experience is crucial to induce the observed molecular changes.     

The Purkinje cell dendritic tree: a computer-aided study of its development in the cat and in culture

Golgi-prepared cerebella from 1, 10, 13 and 30-day-old kittens were analyzed and compared with 30-45 days in vitro (DIV) HRP-stained organotypic cultures of newborn kitten cerebella. Computer reconstructions and morphometric parameters allowed a quantitative analysis of the Purkinje cell (P-cell) dendritic trees. In intact animals the dendritic organization appeared monoplanar as early as one day after birth and biplanar in 85% of the cells at day 13; however, by day 30, 90% of the cells were monoplanar. During the first 4 postnatal weeks, the dendritic expansion was due mostly to an increase in the total number of segments and the total dendritic length, whereas the overall mean segment length remained almost unchanged. In culture, the 30-45 DIV P-cell dendritic trees always appeared reduced in size when compared to their in vivo counterparts due mostly to a reduction in the total number of segments. Nevertheless, these cells retained several primary dendritic trunks and their overall mean segment length was longer. These supposedly 'mature' cultured P-cells never reached full adult development: a discriminant analysis classified them as resembling those from intact animals of 13 days but often maintaining some properties of newborn animals. These results demonstrate that the presence of all normal inputs is required to achieve the full elaboration and the planar disposition of the P-cell dendrites.     

The organization of immature callosal connections

In newborn kittens, the anterograde transport of horseradish peroxidase, alone or bound to wheat-germ agglutinin, indicates that callosal axons have entered selectively the restricted portions of the neocortical gray matter (e.g., the area 17/18 border) which receive callosal afferents in adults. The callosal axons do also reach regions where they lack in the adult, but there they seem not to penetrate far into the gray matter. Neonatal injections of retrograde fluorescent tracers restricted to the gray matter in areas 17, 18, and posteromedial lateral suprasylvian area (PMLS) label neurons in the contralateral hemisphere only when the tracers were directed into regions known to receive callosal axons. In particular, injections near the 17/18 border label neurons in the contralateral hemisphere at the homologous site and at restricted, retinotopically corresponding locations in other visual areas: a pattern similar to the adult one. In contrast, an injection reaching the white matter of areas 17 or 18 labels a wider, continuous territory extending mediolaterally over most visual areas from 17 to posterolateral lateral suprasylvian area (PLLS) and including regions which later become acallosal; in addition, labeled neurons are found in the limbic cortex medial to area 17 and in the auditory cortex lateral to PLLS, none of which is known to project to either 17 or 18 in the adult. In flattened reconstructions of the cortex, the shape of the territory labeled by each of these injections is characteristically, although somewhat irregularly, crescent shaped; its rostrocaudal position varies with that of the injection. An injection extending into the white matter of more lateral visual areas (19, 21a, PMLS) labels callosal neurons over a similar territory, which extensively overlaps that labeled by the 17/18 border injections and likewise includes regions which are acallosal in the adult. In spite of the overlapping distribution of labeling obtained from separate injection sites, as in adults, each cytoarchitectonically (or retinotopically) defined area seems to receive from a different set of neurons, although a few neurons send bifurcating axons to more than one area. In conclusion, injections restricted to the cortical gray matter reveal a topographic organization of juvenile callosal connections similar to that of the adult. In contrast, injections extending into the white matter and adequate to reach the transitory callosal axons which appear to be confined there reveal what appears to be an earlier organization. These two organizations probably reflect different morphogenetic factors.     

Brain stem auditory evoked response development in the kitten

The development of brain stem auditory evoked responses (BAERs), recorded from a surface electrode as short-latency, volume-conducted potentials, was studied in a series of kittens over a postnatal period ranging from birth to 60 days. Repeated, longitudinal observations on particular kittens were supplemented with observations on additional kittens during the first and second postnatal week to determine age of onset of the BAERs. The position of the animal and sound source within the recording chamber were held constant across recording sessions, as was click intensity except during recordings in which intensity effects were specifically studied. Click rates of 1, 10, 50 and 100/sec were routinely presented. Reference electrodes at the tongue, pinna and neck showed volume-conducted responses to the click stimuli and resulted in considerable distortion of the activity recorded by the vertex electrod; the forepaw, in contrast, showed no activity and a vertex-forepaw electrode configuration provided good resolution of the BAERs across development.A number of new observations were made. BAERs were first observed at 4 days of age, approximately the same age at which depth evoked potentials are first recorded in brain stem auditory nuclei. Initially the BAERs were diffuse, high threshold and fatigued rapidly, characteristics shared with depth evoked potentials in the early postnatal period. Over the first two weeks, the potentials showed marked decrease in threshold, increased resistance to fast click rates, and better definition of wave forms. All BAER components showed exponential decreases in latency. Because all of the brain stem evoked potentials could be recorded concurrently and longitudinally in the same subject a number of developmental comparisons were possible among the BAER components. Wave 1, related to the acoustic nerve in the adult cat, showed a developmental time course and adult latency similar to that reported for N₁. Wave 2, related to the cochlear nucleus in the adult, showed a marked bimodality over the first month; wave 2a was a large amplitude clearly separated wave which gradually fused as an inconspicuous conspicuous leading shoulder on wave 2b. Wave 2b developed with a time course and adult latency similar to that reported for the ventral cochlear nucleus. Wave 3, related to the region of the superior olivary complex in the adult, showed a clear but transient bimodality during the third week of development. Wave 5, related to the inferior colliculus in the adult, appeared later than waves 1–4 and showed a significantly slower rate of development than waves 1–4. These data indicate that differential developmental changes occur within the brain stem auditory pathway and that the BAERs provide a dynamic probe of concurrent maturational interactions.