Progressive limb ataxia following inferior olive lesions.

Cerebellar climbing fibres originate in the inferior olive (IO). Temporary IO inactivation produces movement deficits. Does permanent inactivation produce similar deficits and, if so, do they recover? The excitotoxin, kainic acid, was injected into the rostral IO of three cats. Behaviour was measured during reaching and locomotion. Two cats were injected during the reaching task. Within minutes, grasping became difficult and the trajectories of the reaches showed higher arcing than normally seen. During locomotion, both cats showed head and trunk deviation to the injected side, walking paths curved to the injected side, and the paws were lifted higher than normal. Limbs contralateral to the injections became rigid. Within 1 day, posture had normalized, locomotion was unsteady and high lifting of the paws had reversed to a tendency to drag the dorsum of the paws. Passive body movement produced vestibular signs. Over a few days, locomotion normalized and vestibular signs disappeared. Reach trajectories were normal but grasping deficits persisted. Over the first week, the amplitude of limb lift during reaching and locomotion began to increase. The increase continued over time and, after several months, limb movements became severely ataxic. The effects followed the somatotopy of the rostral IO: a loss of cells in medial rostral IO only affected the forelimb, whereas a loss of cells in medial and lateral IO affected both forelimb and hindlimb. Deficits produced by IO lesions involve multiple mechanisms; some recover rapidly, some appear stable, and some worsen over time. The nature of the progressive deficit suggests a gradual loss of Purkinje cell inhibition on cerebellar nuclear cells.

Functional specialization within the cat red nucleus.

Magnocellular (RNm) and parvicellular (RNp) divisions of the cat red nucleus (RN) project to the cervical spinal cord. RNp projects more heavily to upper cervical levels and RNm projects more heavily to lower levels. The cells in RN are active during reaching and grasping, and the differences in termination suggest that the divisions influence different musculature during this behavior. However, the spinal termination may not reflect function because most rubrospinal terminations are to interneuronal regions, which can influence motor neurons at other spinal levels. To test for functional differences between RNm and RNp, we selectively stimulated RNm and RNp as well as the efferent fibers from each region. Electromyographic activity was recorded from seven muscles of the cat forelimb during reaching. The activity from each muscle was averaged over several thousand stimuli to detect influences of stimulation on muscle activity. Stimulation within the RN produced a characteristic pattern of poststimulus effects. The digit dorsiflexor, extensor digitorum communis (edc), was most likely to show facilitation, and several other muscles showed suppression. The pattern of activation did not differ between RNm and RNp. In contrast, stimulation of RNp fibers favored facilitation of shoulder muscles (spinodeltoideus and supraspinatus), and stimulation of RNm fibers favored facilitation of digit and wrist muscles (edc, palmaris longus, and extensor carpi ulnaris). Fiber stimulation produced few instances of poststimulus suppression. The results from fiber stimulation indicate that the physiological actions of RNm and RNp match their levels of spinal termination. The complex pattern of facilitation and suppression seen with RN stimulation may reflect synaptic actions within the nucleus.

Prolactin receptor expression in the epithelia and stroma of the rat mammary gland.

The importance of prolactin (PRL) in regulating growth and differentiation of the mammary gland is well known. However, it is not well established whether PRL acts solely on the mammary epithelia or if it can also directly affect the mammary stroma. To determine where PRL could exert its effects within the mammary gland, we investigated the levels of expression and the localization of the PRL receptor (PRLR) in the epithelia and stroma of the rat mammary gland at different physiological stages. For these studies, we isolated parenchymal-free 'cleared' fat pads and intact mammary glands from virgin, 18-day-pregnant and 6-day-lactating rats. In addition, intact mammary tissues were enzymatically digested to obtain epithelial cells, free of stroma. The mammary tissues, intact gland, stroma and isolated epithelia, were then used for immunocytochemistry, protein extraction and isolation of total RNA. PRLR protein was detected in tissues using specific polyclonal antisera (PRLR-l) by immunocytochemistry and Western blot analysis. Messenger RNA for PRLR was measured by ribonuclease protection assay. Immunocytochemistry and Western blots with the PRLR-1 antisera detected PRLR in wild-type rat and mouse tissues, whereas the receptor protein was absent in tissues from PRLR gene-deficient mice. PRLR was found to be present both in the epithelia and stroma of mammary glands from virgin, pregnant and lactating rats, as determined by immunocytochemistry and Western blotting. Western blots revealed the predominance of three bands migrating at 88, 90 and 92 kDa in each of the rat mammary samples. These represent the long form of the PRLR. During pregnancy and lactation, PRLR protein increased in the epithelial compartment of the mammary gland but did not change within the stromal compartment at any physiological stage examined. We also found PRLR mRNA in both the epithelia and stroma of the mammary gland. Again, the stroma contained lower levels of PRLR mRNA compared with the epithelia at all physiological stages examined. Also, the PRLR mRNA levels within the stroma did not change significantly during pregnancy or lactation, whereas PRLR mRNA within the epithelia increased twofold during pregnancy and fourfold during lactation when compared with virgin rats. We conclude from this study that PRLR is expressed both in the stromal and epithelial compartment of the mammary gland. This finding suggests PRL may have a direct affect on the mammary stroma and by that route affect mammary gland development.

Red nucleus stimulation inhibits within the inferior olive.

Red nucleus stimulation inhibits within the inferior olive. J. Neurophysiol. 80: 3127-3136, 1998. In the anesthetized cat, electrical stimulation of the magnocellular red nucleus (RNm) inhibits responses of rostral dorsal accessory olive (rDAO) neurons to cutaneous stimulation. We tested the hypothesis that RNm-mediated inhibition occurs within the inferior olive by using stimulation of the ventral funiculus (VF) of the spinal cord in place of cutaneous stimulation of the hindlimb. Fibers in the VF terminate on hindlimb rDAO neurons, so inhibition of this input would have to occur within the olive. rDAO responses elicited by VF stimulation were inhibited by prior stimulation of the RNm, indicating that inhibition occurs within the olive. In contrast, evoked potentials recorded from the VF or dorsal columns following hindlimb stimulation were not affected by prior stimulation of RNm, indicating that stimulation of the RNm does not inhibit olivary afferents at spinal levels. RNm stimulation that inhibited rDAO responses had little effect on evoked somatosensory responses in thalamus, indicating that inhibition generated by activity in RNm may be specific to rDAO. To test limb specificity of RNm-mediated inhibition, conditioning stimulation was applied to the dorsolateral funiculus at thoracic levels, which selectively activates RNm neurons projecting to the lumbar cord. Stimulation at thoracic levels inhibited evoked responses from hindlimb but not forelimb regions of rDAO, suggesting that inhibitory effects of RNm activity are limb specific. Several studies have reported that olivary neurons have reduced sensitivity to peripheral stimulation during movement; it is likely that RNm-mediated inhibition occurring within the olive contributes to this reduction of sensitivity. Inhibition of rDAO responses by descending motor pathways appears to be a salient feature of olivary function.

Construction of a reach-to-grasp.

Reaching out to grasp an object requires the coordinated action of many different areas of the brain. Each area probably makes a unique contribution to the control of limb movement. We have studied the discharge of interpositus, the output nucleus of intermediate cerebellum, and magnocellular red nucleus, which connects interpositus to the spinal cord. The neurons in these areas discharge at high rates only if a hand movement is included with the reach, and discharge pattern is similar regardless of reach direction. Therefore, interpositus and magnocellular red nucleus are involved primarily in grasp control during the reach-to-grasp; other areas must be controlling the reach. Several other areas of the brain, including the reticular formation, rostral mesencephalon, superior colliculus and motor cortex, are active during reaching. The output from these descending systems converges on interneurons at spinal level C1 and C2 which, in turn, project to level C6, where motor neurons innervating shoulder muscles are located. We hypothesize that reach control is achieved by the convergence of multiple descending pathways onto a complex spinal interneuronal system.

Reduction of rostral dorsal accessory olive responses during reaching.

1. Rostral dorsal accessory olive (rDAO) neurons are sensitive to light touch but have little or no discharge during active movement. We hypothesize that sensitivity of the rDAO is reduced during movement. To test this hypothesis, we evaluated sensitivity of rDAO neurons as cats reached out and retrieved a handle. On selected trials, mechanical or electrical perturbations to the forelimb were presented, and responses of rDAO neurons to the disturbances were recorded. 2. All rDAO units were highly sensitive to somatosensory stimuli during periods of stance. The cells responded to stimuli such as touch to hairs or light taps to the platform on which the cat was standing. 3. Discharges of rDAO neurons showed little or no synchronization to any aspect of the reaching task. rDAO neurons failed to fire to mechanical perturbations of the food handle during retrieval or hold phases of the task, even when their receptive fields included the surface of the paw in contact with the handle. 4. Electrical stimulation of the skin produced the greatest evoked response at all rDAO recording sites when the cats were at stance. Stimulation at any time during the reaching task, including periods of holding and licking, produced lower-amplitude evoked responses. The reduction in evoked response could be large and was restricted to the limb performing the task. 5. The data support the hypothesis that the cutaneous sensitivity of the rDAO is reduced during behavior. However, the inhibition does not appear to be tailored to specific times during the task or to neurons with specific receptive field locations on the actively moving limb. The reduction in sensitivity is as likely to be dependent on limb posture as on movement. We conclude that the rDAO discharge provides the cerebellum with information about vibration or contact during stance; it does not provide reliable information about undisturbed or disturbed movement. Climbing fiber input from rDAO might be useful in the preparation to make a movement, but it is probably not useful for correction of movement errors.

Activity of interpositus neurons during a visually guided reach.

Neurons in the cerebellar interpositus nucleus greatly increase their discharge rates when a monkey reaches out to grasp an object. However, when the monkey is required to track a target on a screen by moving a manipulandum, the increase in discharge rate is relatively small or nonexistent. Moving the hand directly to a target is a visuomotor task that may be fundamentally different from a remote tracking task. We hypothesize that the interpositus nucleus is specialized for direct visual guidance of the limb or, alternatively, interpositus is specialized for controlling hand movements required to grasp an object. A monkey was trained to hold a sensor and move it directly over a visual target to obtain water reward. Small drawers were mounted next to two of the targets; on some trials a drawer would open so that the monkey would reach out and retrieve a raisin that had been placed in it. Interpositus neurons discharged strongly during reach to grasp the raisin but not when the monkey was positioning the sensor over the target. For individual cells, discharge pattern and amplitude were largely independent of the size and direction of the reach to grasp, suggesting that interpositus does not control direction or amplitude of the reach. The results are consistent with the hypothesis that neurons in forelimb regions of interpositus participate in the control of hand movements used in grasping, but they are not consistent with the hypothesis that interpositus neurons participate in direct visual guidance of the limb.

The importance of hand use to discharge of interpositus neurones of the monkey.

1. Monkey interpositus neurones show large discharge modulations during reaching to grasp, however, the same neurones show little or no modulation during operation of devices that exercise individual forelimb joints. We tested the hypothesis that grasping during the reach-to-grasp is necessary for eliciting high discharge modulation. 2. Three monkeys (Macaca mulatta) moved an articulated lever between low and high target zones. While in the lower zone the monkey's hand was at its waist, in the upper zone its hand was in a position that required forelimb extension at right-angles to the body axis. Small drawers adjacent to the target zones contained raisins, and the drawers could be remotely opened. Thus, we could elicit two types of reaches having similar trajectories: one reach involved limb transport while holding the lever handle, and the other involved limb transport while forming the hand to grasp a raisin. 3. Eighty-one neurones from two monkeys, mostly from interpositus with some from adjacent regions of dentate, were tested during device use and reaching to grasp: 93% of the neurones discharged at high rates during at least one of the tasks. Of these, about half increased discharge rate solely during reaching to grasp; the other half showed some increase during device use but only discharged strongly during reaching to grasp. Overall, discharge modulations during the reach-to-grasp averaged twice as high as during the corresponding device movement (112 versus 56 impulses s-1). 4. Individual neurones consistently discharged with characteristic patterns during the reach-to-grasp with rates often exceeding 300 impulses s-1. Discharge during the reach-to-grasp was independent of reach trajectory: discharge patterns and amplitudes were similar when reaching from either the lower or upper target zone to the upper raisin drawer as when reaching from the upper target zone to the upper raisin drawer. Reach direction also made little difference: reaches from the upper target zone to the lower drawer typically elicited similar discharge modulation as those from the lower target zone to the upper drawer. 5. High discharge rates associated with grasping were independent of the item being grasped: typically, grasping the device handle elicited as high discharge rates as grasping a raisin. 6. The hypothesis was confirmed that grasping is critical for eliciting high discharge modulation in interpositus during reaching to grasp. Discharge pattern and modulation do not vary with reach direction or amplitude of the reach and, therefore, it is unlikely that intermediate cerebellum controls these features of the reach-to-grasp.(ABSTRACT TRUNCATED AT 400 WORDS)

Deficits in speed discrimination following lesions of the lateral suprasylvian cortex in the cat.

We examined the role of the lateral suprasylvian (LS) cortex in motion perception by testing the ability of three cats to detect moving targets and to discriminate differences in stimulus direction and speed before and after making bilateral ibotenic acid lesions in LS. The lesions had little or no effect on contrast sensitivity for detecting moving sinusoidal gratings. Moreover, we found no deficits in discriminating opposite directions of motion: the cats discriminated grating directions at threshold contrasts. All three cats, however, showed permanent deficits in discriminating differences in speed and in flicker rate. The deficits were most pronounced at higher temporal and spatial frequencies and at lower contrasts. This result suggests that LS plays an important role in the analysis of stimulus speed. It appears that information needed for discriminating opposite directions of motion may be signalled by visual areas outside LS.

Origin of butyrylcholinesterase in the lateral geniculate nucleus of tree shrew.

We examined the distribution and possible origins of pseudocholinesterase activity within the lateral geniculate nucleus (LGN) of the tree shrew. Butyrylcholinesterase (BuChE) activity was spread diffusely throughout the LGN and not localized to neuronal perikaryon. Lesions of the LGN eliminated this BuChE activity while not affecting acetylcholinesterase (AChE) activity; however, removal of retinal input by unilateral ocular enucleations failed to affect the BuChE activity within the denervated layers of the LGN. This lack of effect suggests that, unlike the macaque monkey, retinal terminals within the LGN of tree shrew are not the source of BuChE. Thus, in the tree shrew LGN it appears that BuChE is not metabolically related to or dependent upon AChE nor does it originate from retinal sources, but rather BuChE appears to represent an enzyme that is endogenous to the LGN.

Kainic acid-induced terminal degeneration in the dorsal lateral geniculate of tree shrew.

The dorsal lateral geniculate nucleus of tree shrews is very susceptible to the neurotoxic effects of kainic acid. In addition to neuronal loss, there is a profound loss of retinal terminals that is manifested through a disruption of anterograde transport of WGA/HRP from the retina to the kainic acid-lesioned area of the geniculate nucleus. The actions of kainic acid upon both the presynaptic terminals and geniculate neurons may be mediated by a glutamatergic pathway and questions the hypothesis that kainic acid is solely neuron-specific in its toxic action.

Intratympanic injection of sodium arsanilate (atoxyl) solution results in postural changes consistent with changes described for labyrinthectomized rats.

Intratympanic injections of sodium arsanilate (atoxyl) have been shown to produce vestibular dysfunction in the rat. Unilateral and bilateral dysfunction can be distinguished by changes in the animals' postures. These changes are consistent with changes described for unilateral or bilateral labyrinthectomized rats. The intratympanic injection technique offers a simple yet effective alternative to labyrinthectomy.

Visual modulation of neuronal activity within the rat vestibular nuclei.

Sixty-two of 95 units within the vestibular nuclei of 24 hooded, Long-Evans rats were found to respond to both linear accelerations on a parallel swing and to linear movements of the visual field. The addition of visual clues during periods of linear accelerations produced a phase shift in the majority of the units towards the maximal acceleration of the animal, and an increase in the peak activity during the periods of maximal acceleration. Conflicting visual-vestibular stimulation resulted in reduced directional sensitivity and lower rates of firing in visually sensitive units.