Adaptive changes in responses to repeated locomotor perturbations in cerebellar patients.

This study examined the responses of cerebellar patients and a group of age- and sex-matched control subjects to repeated changes in treadmill speed in order to test whether cerebellar patients can adapt their gait to this type of perturbation and, if so, whether their responses are comparable to those of controls. While the subject walked on the treadmill, a perturbation consisting of a sudden slowing of the treadmill followed by a sudden increase back to the original speed was applied repeatedly at a specific time during the step cycle. Both the control subjects and cerebellar patients were able to compensate for the perturbations by minimizing their postural sway and changing step length. However, the nature of the compensatory changes in step length differed between these subject groups. Control subjects compensated for the perturbation by consistently using the same leg to initiate the response to the perturbation and by adapting a pattern of stepping such that the EMG characterizing the response occurred in a manner that was entrained to the timing of the normal locomotor cycle. In contrast, the patients, although undergoing modifications in step length, employed a much less consistent motor pattern from trial to trial than that of the normal subjects. An inconsistent pattern among their responses was apparent in both the analysis of stepping and in the EMG activity of the gastrocnemius and anterior tibial muscles. These results suggest that, although the cerebellar patients can adapt their behavior in response to locomotor perturbations, they do not establish a motor pattern comparable to that employed by normal subjects.

Ataxia reflected in the simulated movements of patients with cerebellar lesions.

Previous studies demonstrated that the time required to simulate mentally a complex movement is highly correlated with the time required to execute the same task. The purpose of this experiment was to examine whether this relationship exists when execution times are prolonged as a consequence of the motor abnormalities exhibited by patients with substantial cerebellar pathology. The paradigm required subjects to alternate between moving a hand-held stylus horizontally on a digitizing tablet through a four-segment template and imagining the same movement through the same template. These two modes of performance were compared based on the times required to complete the two types of trials. Performance using both upper extremities was assessed using templates with two different levels of difficulty. Difficulty was varied by interposing gates that narrowed the path through the template. Using a MANOVA, measurements of actual and simulated movement times were compared between the group of cerebellar patients and a group of age- and sex-matched controls. The results showed that: (1) both movement times and mental-simulation times were greater for cerebellar patients than for control subjects under all experimental conditions, (2) both the movement times and the mental-simulation times of the patients were greater on the more-affected side than on the less-affected side, and (3) on the more-affected side, there was no significant difference between the patients' simulation and movement times for either the more difficult or less difficult condition. Thus, the consequence of cerebellar dysfunction on the time required to execute a volitional movement is reflected in the time needed to simulate the same behavior.

Microinjections of anisomycin into the intermediate cerebellum during learning affect the acquisition of classically conditioned responses in the rabbit.

The purpose of this study was to examine the effects of protein synthesis inhibition in the intermediate cerebellum on the acquisition and expression of classically conditioned nictitating membrane responses in the rabbit. Animals were conditioned for three days in a standard delay paradigm. Before each training session, either a solution of anisomycin (a protein synthesis inhibitor) or vehicle was bilaterally injected into the interposed cerebellar nuclear. Following these three training sessions, rabbits were tested to determine whether the previous training under the influence of anisomycin or vehicle resulted in the acquisition of conditioned responses. In this test, animals that were injected previously with the protein synthesis inhibitor exhibited significantly less retention of conditioned responses than rabbits injected with vehicle. Additional experiments demonstrated that anisomycin does not block the expression of conditioned responses during conditioning or in well-trained animals. Microinjections of muscimol at the same sites of the previous drug infusions suppressed the expression of conditioned responses, indicating that the protein synthesis inhibitor was applied to the eyeblink-related parts of cerebellar circuits. The obtained data are the first to demonstrate that a manipulation of cerebellar circuits, which does not affect the performance of learned behavior, can affect the process of learning. These results suggest that the synthesis of new proteins in the intermediate cerebellum participates in the formation of plastic changes responsible for eyeblink conditioning.

Patients with cerebellar lesions cannot acquire but are able to retain conditioned eyeblink reflexes.

The purpose of these experiments was to examine the role of the human cerebellum in the acquisition and retention of conditioned reflexes. Normal human subjects and patients with cerebellar lesions were tested for their capacity to acquire, retain and express conditioned eyeblink responses. In acquisition tests, subjects were trained in a delay classical conditioning paradigm using a tone conditioned stimulus and a midline forehead tap as an unconditioned stimulus. While normal subjects developed anticipatory eyeblinks to the tone in one session, patients with cerebellar lesions failed to acquire conditioned responses in four consecutive training sessions. The conditioning deficit was bilateral even in patients with a unilateral cerebellar pathology. The same groups of subjects were tested for the presence of eyeblinks to a visual threat. In these experiments, both normal subjects and patients with cerebellar lesions exhibited a high level of responding when they saw an object approaching their face. These eyeblinks to the visual threat are probably naturally acquired conditioned responses because they extinguish in normal subjects if they are not reinforced by the unconditioned cutaneous stimulus. In addition, the stimulus of seeing an approaching object blocks the acquisition of classically conditioned eyeblinks to a new conditioned stimulus in normal subjects. These data imply that patients with cerebellar lesions who cannot acquire new classically conditioned responses are able to retain and express conditioned eyeblinks which were acquired before the onset of the pathology. Consequently, cerebellum-dependent neural substrates which are involved in learning new conditioned reflexes do not seem to be required for the storage of naturally learned conditioned responses.

Impaired capacity of cerebellar patients to perceive and learn two-dimensional shapes based on kinesthetic cues.

This study addresses the issue of the role of the cerebellum in the processing of sensory information by determining the capability of cerebellar patients to acquire and use kinesthetic cues received via the active or passive tracing of an irregular shape while blindfolded. Patients with cerebellar lesions and age-matched healthy controls were tested on four tasks: (1) learning to discriminate a reference shape from three others through the repeated tracing of the reference template; (2) reproducing the reference shape from memory by drawing blindfolded; (3) performing the same task with vision; and (4) visually recognizing the reference shape. The cues used to acquire and then to recognize the reference shape were generated under four conditions: (1) "active kinesthesia," in which cues were acquired by the blindfolded subject while actively tracing a reference template; (2) "passive kinesthesia," in which the tracing was performed while the hand was guided passively through the template; (3) "sequential vision," in which the shape was visualized by the serial exposure of small segments of its outline; and (4) "full vision," in which the entire shape was visualized. The sequential vision condition was employed to emulate the sequential way in which kinesthetic information is acquired while tracing the reference shape. The results demonstrate a substantial impairment of cerebellar patients in their capability to perceive two-dimensional irregular shapes based only on kinesthetic cues. There also is evidence that this deficit in part relates to a reduced capacity to integrate temporal sequences of sensory cues into a complete image useful for shape discrimination tasks or for reproducing the shape through drawing. Consequently, the cerebellum has an important role in this type of sensory information processing even when it is not directly associated with the execution of movements.

Visuomotor learning in cerebellar patients.

The aim of the present study was to demonstrate that patients with pathology affecting substantial regions of the cerebellum can improve their performance in a series of two-dimensional tracing tasks, thus supporting the view that this type of motor behavior can be acquired even when the integrity of this structure is compromised. Eight patients with chronic, isolated cerebellar lesions and eight age- and sex-matched healthy controls were tested. Three patients had mild, five had moderate upper limb ataxia. The experiment was divided into two parts. In the first, subjects traced an irregularly shaped outline over 20 consecutive trials ('Trace 1' task). Next, subjects were asked to redraw the object without any underlying template as a guide ('Memory 1' task). In the second part of the study, subjects were asked to trace a different, irregularly shaped outline over 20 consecutive trials ('Trace 2' task). Next, they were required to redraw it by memory with its axis rotated 90 degrees ('Memory 2' task). In each of the memory tasks the template was placed over the drawn image after each trial and shown to the subjects. The error of performance was determined by calculating three different measurements, each focused on different aspects of the task. Based on these measurements, the cerebellar patients showed improvement in both memory tasks. In the 'Memory 1' task the calculated error decreased significantly for the patients with mild ataxia. In the 'Memory 2' task all cerebellar patients improved their performance substantially enough to reduce significantly the magnitude of all three error measurements. The experiments demonstrate that patients with cerebellar lesions are capable of improving substantially their performance of a complex motor task involving the recall of memorized shapes and the visuomotor control of a tracing movement.

Transgenic mice and transhybridomas producing chimeric mouse/human anti-human interleukin-2 receptor recombinant antibodies.

Transgenic mice were developed that secreted chimeric mouse/human anti-human interleukin-2 receptor (IL-2R) antibodies (Ab) into their serum. In addition, hybridomas producing the chimeric Ab in tissue culture were generated from the transgenic mice. The presence of the mouse/human immunoglobulin (Ig) transgene did not appear to affect rearrangement of endogenous murine Ig in the hybridomas. Serum levels of the chimeric Ab correlated with transgene copy number. Although many of the transgenic lineages had serum titers of the chimeric Ab comparable to endogenous mouse IgG, there was no apparent correlation with endogenous mouse IgG levels.

Accelerated growth of mammary tumor cells in normal and athymic mice after treatment in vitro with dexamethasone.

The tumorigenicity of dexamethasone-treated tissue-cultured mammary tumor cells was compared to that of untreated mammary tumor cells. The dexamethasone-induced cells progressed faster in normal syngeneic animals than did untreated mammary tumor cells. The fact that the growth rate differential was also observed in athymic mice suggests that T-lymphocyte-mediated immunity was not a factor in the accelerated progression in vivo of the tumor cells that had been cultured in the presence of dexamethasone.

Resistance to syngeneic lymphoma cells as a result of immunization with chemically modified allogeneic lymphoma cells in mice.

Immunization with trinitrophenyl (TNP)-derivatized allogeneic lymphoma cells resulted in significant immunity to poorly immunogenic syngeneic lymphoma cells. Neither TNP-treated nor X-irradiated syngeneic lymphoma cells were immunogenic under similar experimental conditions. Immunization with untreated allogeneic lymphoma cells produced only minimal levels of resistance to challenge with syngeneic lymphoma cells. The complete set of antigens responsible for the immunity was carried exclusively on transformed lymphocytes because allogeneic TNP-derivatized lymph node and thymus cells also did not immunize. The immunity was transferred to nonimmune inbred BALB/c and A/J mice by spleen cells from immune donors. The Winn assay was used to measure the antilymphoma immunity in vivo. When immune spleen cell-lymphoma mixtures were inoculated sc at a ratio of 1,000:1, nonimmune mice were completely protected. Reactivity of immune lymphocytes to syngeneic lymphoma cells was also demonstrated in vitro by the 51Cr-release method. Immunization with TNP-derivatized allogeneic lymphoma cells resulted in measurable immune resistance to inocula of viable syngeneic tumor cells in excess of 100 times the tumorigenic dose. Induction of immunity to syngeneic lymphoma cells strictly required that the immunizing cells be histoincompatible at the major H-2 locus and possess tumor-specific antigen(s). Maximum immune sensitivity was observed only after chemical modification of the immunizing allogeneic lymphoma cells.

Retarded growth of lymphoma in immunodepressed mice.

Lymphoma cells were inoculated iv into normal and immunodepressed mice. In most instances the immunodepressed animals survived longer than their normal counterparts. This was true both with athymic and thymectomized animals that had been lethally irradiated and reconstituted with syngeneic bone marrow. The route of administration was critical, since increased survival of immunodeficient animals was not observed when the lymphoma cells were injected ip.