Removal Of Vibrissae Research Articles

By a whisker: the sensory role of vibrissae in hovering flight in nectarivorous bats.

Whiskers are important tactile structures widely used across mammals for a variety of sensory functions, but it is not known how bats-representing about a fifth of all extant mammal species-use them. Nectar-eating bats typically have long vibrissae (long, stiff hairs) arranged in a forward-facing brush-like formation that is not present in most non-nectarivorous bats. They also commonly use a unique flight strategy to access their food-hovering flight. Here we investigated whether these species use their vibrissae to optimize their feeding by assisting fine flight control. We used behavioural experiments to test if bats' flight trajectory into the flower changed after vibrissa removal, and phylogenetic comparative methods to test whether vibrissa length is related to nectarivory. We found that bat flight trajectory was altered after vibrissae removal and that nectarivorous bats possess longer vibrissae than non-nectivorous species, providing evidence of an additional source of information in bats' diverse sensory toolkit.

On the Pullout Strength of Human Nasal Hair (Vibrissae)

This study investigates nasal vibrissae-to-dermis detachment in humans, quantifying the pullout force required in adult males. While many studies have investigated the behavior and function of mammalian vibrissae, little is known concerning the mechanical properties of human nasal vibrissae or the strength of the vibrissae-to-dermis attachment. Improved understanding of nasal vibrissae pullout in humans could aid nasal packing design, contaminate removal procedures, and even aid certain cosmetic procedures where vibrissae removal via pullout is the objective. In this study, pullout behavior of human nasal vibrissae is investigated using sensitive force-measuring equipment and advanced scanning electron microscopy. Twenty five vibrissae samples are collected from two human subjects representing a total of 50 pullout measurements. Results indicate that vibrissae thickness (diameter) is unrelated to required pullout force, and that the follicle-width-to-vibrissae-diameter ratio is a good indicator of the resulting vibrissae pullout strength. Larger follicle ratios generally correspond to larger required pullout forces. Vibrissae pullout strength from the combined 50 samples tested varied between 0.071N and 0.726N with a mean pullout strength of 0.379N.

Effects of early sensory deprivation on spatial learning in adult rats

Following vibrissae removal in early ontogenesis from P1 (post-natal day 1) to P30, three-month old rats were trained to run for food in an 8-arm radial maze. Training started at the age of three months. Adult rats demonstrated ability to perform the behavioral task; however, their performance was not as good as in the control group. Our findings revealed the differences in the rats exploratory strategy and key behavioral tactics of entering the maze arms at a certain angle. The results show that active vibrissae sensing plays an important role in shaping rat behavioral tactics during spatial learning in the 8-arm radial maze.

Non-invasive stimulation of the vibrissal pad improves recovery of whisking function after simultaneous lesion of the facial and infraorbital nerves in rats

We have recently shown that manual stimulation of target muscles promotes functional recovery after transection and surgical repair to pure motor nerves (facial: whisking and blink reflex; hypoglossal: tongue position). However, following facial nerve repair, manual stimulation is detrimental if sensory afferent input is eliminated by, e.g., infraorbital nerve extirpation. To further understand the interplay between sensory input and motor recovery, we performed simultaneous cut-and-suture lesions on both the facial and the infraorbital nerves and examined whether stimulation of the sensory afferents from the vibrissae by a forced use would improve motor recovery. The efficacy of 3 treatment paradigms was assessed: removal of the contralateral vibrissae to ensure a maximal use of the ipsilateral ones (vibrissal stimulation; Group 2), manual stimulation of the ipsilateral vibrissal muscles (Group 3), and vibrissal stimulation followed by manual stimulation (Group 4). Data were compared to controls which underwent surgery but did not receive any treatment (Group 1). Four months after surgery, all three treatments significantly improved the amplitude of vibrissal whisking to 30° versus 11° in the controls of Group 1. The three treatments also reduced the degree of polyneuronal innervation of target muscle fibers to 37% versus 58% in Group 1. These findings indicate that forced vibrissal use and manual stimulation, either alone or sequentially, reduce target muscle polyinnervation and improve recovery of whisking function when both the sensory and the motor components of the trigemino-facial system regenerate.

Neonatal sensory deprivation promotes development of absence seizures in adult rats with genetic predisposition to epilepsy

Absence epilepsy has age-related onset. In a WAG/Rij rat genetic model, absence seizures appear after puberty and they are increased with age. It is known that (1) epileptic activity in WAG/Rij rats is initiated at the perioral area in the somatosensory cortex; (2) sensory deprivation, i.e., whisker trimming during the critical period of development, could enhance excitatory activity in the somatosensory cortex. It is hypothesized that the cortex may become more excitable after neonatal vibrissae removal, and this may precipitate absence seizures in adult rats. We found that whisker trimming during the first postnatal weeks caused more rapid development of EEG seizure activity in adult WAG/Rij rats. Epileptic discharges in the trimmed rats were more numerous (vs control), showed longer duration and often appeared in desynchronized and drowsy EEG. The number of absence-like spindle-shaped EEG events (spike–wave spindles) in the whisker-trimmed rats was higher than in control, especially during the intermediate sleep state. An age-dependent increase of intermediate sleep state was found in the trimmed rats, but not in the intact animals. We discuss epigenetic factors that can modulate absence epilepsy in genetically prone subjects.

Lasting facilitatory effects of neonatal vibrissae removal on the propagation of cortical spreading depression: an electrophysiological study in well-nourished and early-malnourished adult rats

Early malnutrition interferes with the formation of somatosensory pathways and reduced sensory input activity during brain development can induce morphological and physiological changes in the cerebral cortex, altering their response properties in the long-term. Here, we investigated cortical spreading depression (CSD) propagation in male adult rats submitted to unilateral vibrissae removal, at postnatal days 2–3, and malnourished during lactation followed by nutritional recovery until adulthood (90–120 days), when CSD was recorded. Compared to nutrition-matched non-lesioned controls, CSD-propagation was increased in the hemisphere contralateral to the vibrissae removal. The findings indicate that vibrissae removal during brain development enhances CSD-propagation, and early malnutrition did not modify this effect. Considering that CSD-facilitation persisted until adulthood, we suggest that this effect is permanent. The data might contribute to the understanding of the mechanisms by which sensory input deprivation-induced plasticity modifies cerebral electrophysiological responses in the developing brain.

Early vibrissae removal facilitates cortical spreading depression propagation in the brain of well-nourished and malnourished developing rats

Reduced sensory input activity during brain development can induce morphological and physiological changes in the cerebral cortex, altering their response properties. Malnutrition delays the formation of somatosensory pathways. Here we used cortical spreading depression as a neurophysiological parameter to investigate electrophysiological changes after vibrissae removal in well-nourished and malnourished rats. Male Wistar rat pups had the right mystacial vibrissae-removed at postnatal days 2–3, and were submitted to spreading depression recording at 30–40 days of life. In both nutritional conditions, spreading depression velocities were increased in the hemisphere contralateral to the vibrissae removal, as compared to age- and nutrition-matched non-lesioned controls, in which no inter-hemispheric differences were found. In contrast to the well-nourished rats, in the vibrissae-removed malnourished animals the spreading depression propagation in the ipsilateral hemisphere decreased as compared to the corresponding hemisphere of the non-lesioned malnourished rats. It is concluded that deprivation of sensory input from whiskers during brain development facilitates spreading depression propagation, and early malnutrition seems to influence this effect. Since the effect persisted until 40 days, it is tempting to suggest that it is permanent, or at least long-lasting. Data might contribute to the understanding of sensory input deprivation-induced plasticity mechanisms underlying cerebral electrophysiological changes in the developing brain.

Enhanced Plasticity in Zincergic, Cortical Circuits after Exposure to Enriched Environments

Despite the plethora of reports that demonstrate plasticity in the mammalian cerebral cortex, the characterization of the cellular mechanisms that mediate it is sparse. Here, we show that the magnitude of the experience-dependent regulation of vesicular zinc is significantly increased through enriched-environment housing. Mice were reared either in a deprived environment and subsequently housed in deprived, minimally enriched, or enriched conditions after the removal of the c-row of vibrissae or reared in an enriched environment before and after vibrissae removal. Levels of vesicular zinc were assessed in deprived and nondeprived barrels 6 h to 14 d after vibrissae removal. We found that housing in enriched environmental conditions resulted in a greater change in vesicular zinc levels than did other housing conditions; however, this effect was dependent on both the magnitude and duration of enrichment. Our data indicate that enriched-environment housing has profound effects on the regulation of vesicular zinc that occurs concurrently with experience-dependent plasticity, suggesting a role for zinc in the multitude of cortical modifications associated with enriched environments.

Effects of bilateral vibrissotomy on the expression of focused stereotypy (FS) induced by amphetamine in Sprague Dawley (SD) or Fischer 344 (F344) rats

Above doses of about 2.5 mg/kg in SD rats, amphetamine produces FS, a syndrome characterized by a complete lack of locomotion accompanied by rapid, rhythmic head movements. During these movements, the rat’s vibrissae are stimulated by accelerations of the head and by contact with the floor and walls of the cage. Given that previous reports have linked removal of vibrissae with changes in brain dopamine systems and given amphetamine’s dopamine releasing effects in vivo, we hypothesized that bilateral removal of the vibrissae would alter the FS response to amphetamine. Of additional interest was the question of rat strain differences in response to amphetamine. Accordingly, in a between-groups dosing design male SD and male F344 rats were treated with 0, 1.25, 2.5 and 5.0 mg/kg d-amphetamine sulfate every 4th day for a total of 7 injections, and on the 7th day, amphetamine treatment was accompanied by bilateral vibrissotomy. Behavior was recorded continuously in 4-hr sessions with a force-plate actometer, a new type of technology that permits quantitation of FS without human observers. Vibrissotomy did not alter the basic style of FS for either rat strain where style was assessed by the power spectra of the vertical force component of the head movements. Area-under-the-curve analyses of FS scores showed vibrissotomy increased the intensity of the head movements in the F344 rats but not in the SD rats. Indexes of spatial confinement were not significantly affected. These data suggest that the rhythmic, rapid head movements of FS are probably not sustained by, nor appreciably modulated by sensory feedback from the vibrissae. Supported by MH43429 and HD002528.

Effects of vibrissae removal on search accuracy in the water maze

In two experiments, the vibrissae were clipped on either the left, the right, or both sides, and the rats were trained to find a submerged platform in the Morris water maze. In both experiments, animals without vibrissae on both sides or on the left consistently spent significantly more time in the "counter" area twice the platform diameter in size, surrounding the submerged platform, than intact controls. Counter preference was not as consistent across experiments in rats with right vibrissae removed. These results suggest that the vibrissae are required for proprioceptive location of the platform itself, but not for proximal search accuracy. Since ischemic damage to hippocampal CA1 pyramidal cells has also been reported to prolong counter search during training, the results support the suggestion that impaired hippocampal processing of proprioceptive information from the vibrissae may contribute to the increased latency to find the platform shown by ischemic rats.

Effects of vibrissae removal on methamphetamine-induced damage to rat somatosensory cortical neurons.

Repeated methamphetamine (mAMPH) damages forebrain monoamine terminals and causes degeneration of nonmonoaminergic cell bodies in rat primary somatosensory cortex (S1). These degenerating cortical neurons can be labeled with the fluorochrome dye Fluoro-Jade (FJ) and are found almost exclusively in layers II/III and IV of the vibrissae representation in S1. Within S1, layer IV is organized into discrete, anatomically identifiable units termed barrels, each of which receives information from a single whisker. We previously reported that mAMPH-damaged neurons in S1 were located within the whisker barrels, suggesting that the prolonged mAMPH-induced whisking contributes to S1 neuronal injury. Here, we investigate effects of vibrissae removal on mAMPH-induced damage to S1 neurons. Rats were anesthetized and vibrissae were trimmed from either the left, right, or neither side of the snout. The next day they were given four injections of either saline (1 ml/kg, s.c.) or mAMPH (4 mg/kg, s.c.) at 2-h intervals. Three days later, cortical sections were processed for FJ histochemistry. The hemivibrissotomy produces a hemispheric asymmetry in FJ-positive neurons in barrel cortex, with fewer damaged neurons contralateral than ipsilateral to whisker removal. Taken together with the demonstration that acute injection of this dose of mAMPH induces the immediate early gene zif/268 and Fos protein in barrel cortex, these data suggest that the prolonged behavioral activity involving the vibrissae contributes to the mAMPH-induced damage to S1 neurons. Thus, some of the injurious effects of drugs may depend on afferent activity occurring as a result of the abnormal behaviors evoked by their administration.

Vibrissal sense is not the main sensory modality in rat exploratory behavior in the elevated plus-maze

Four groups of male Wistar rats were submitted to acute bilateral removal of mystacial vibrissae at different lengths from the follicle. Each group was divided into two subgroups, tested under high (150 Lux) and low environmental illumination (2 Lux). All the subjects were allowed to freely explore an elevated plus-maze for 5 min. Results indicated that rats tested under low illumination tended to explore the open arms more frequently and longer then rats tested under high illumination. When tested under low illumination, rats in the group that suffered whole vibrissa removal stayed longer in the open arms than those in the other groups but did not differ in the number of entries. The average increase in the length of open arm entries, rather than a decrease in aversion to the open arms, may be due to the need of more time to obtain information about the environment since there is no light and the vibrissae were removed. This effect was not seen with rats tested under high illumination, possibly because vision could be used to obtain relevant information.

Modular distribution of vasoactive intestinal polypeptide in the rat barrel cortex: changes induced by neonatal removal of vibrissae

The distribution of vasoactive intestinal polypeptide-immunoreactive neuronal structures in the barrel cortex (posteromedial barrel subfield) of adult rats was analysed after unilateral removal of the vibrissal follicles of row C in neonatal rats. The hypothesis was tested whether the distribution of vasoactive intestinal polypeptide-immunoreactive structures depends on the normal anatomical organization of the specific sensory input. After three months survival the distribution of the vasoactive intestinal polypeptide-immunoreactive structures was morphometrically evaluated. This approach revealed alterations in the contralateral posteromedial barrel subfield, where the disappearance of barrel row C and a substantial increase in size mainly of barrel row D, but also of other rows could be detected. Increase in row D included both barrels and the interspace (septal segments between barrels in one row). As vasoactive intestinal polypeptide immunoreactivity of the barrel field was found previously to be localized in synaptic boutons involved in symmetric synapses, our present findings suggest that (i) the interspace is enriched in inhibitory vasoactive intestinal polypeptide-immunoreactive synapses as opposed to the excitatory thalamocortical input reaching the barrel hollow, (ii) the spatial distribution of the vasoactive intestinal polypeptide system in the barrel cortex is closely associated with the neuronal organization of the sensory input and reacts with a considerable plasticity to lesion-induced changes of the input, and (iii) the compensatory barrel hypertrophy in a row neighbouring the deafferented row involves an increasing number of vasoactive intestinal polypeptide-immunoreactive synapses per barrel.

The tuberomammillary nucleus projections in the control of learning, memory and reinforcement processes: evidence for an inhibitory role

The tuberomammillary nucleus (TM), a cluster of magnocellular cells in the posterior hypothalamus, is the main source of neuronal histamine in the brain. Although this nucleus is well described in terms of anatomy and neurochemistry, only little is known about its function. Our earlier work showed that the TM projection system may be involved in behavioral asymmetries and behavioral recovery after unilateral manipulations of the brain. Using horseradish peroxidase (HRP) labeling we found an increase in strength (structure and/or activity) in the crossed and uncrossed tuberomammillary-striatal projections in the course of recovery from behavioral asymmetries produced by unilateral removal of the rats' vibrissae, which were in the same direction as the asymmetries found in projections from the substantia nigra to the striatum. Experiments performed with unilateral lesions of the TM region provide evidence for an involvement of the TM system in reinforcement mechanisms. Unilateral destruction of the TM with direct current (DC) or ibotenic acid was found to increase the rate of lateral hypothalamic self-stimulation ipsilateral to the lesion site, suggesting that the TM (particularly the E2 subgroup in its rostra] part: may function as a reinforcement inhibiting neural substrate. Experiments performed with bilateral DC or ibotenic acid lesions of the TM region suggest a role of the nucleus in learning and mnemonic processes. A bilateral electrolytic or neurotoxic lesion of the TM region was found to facilitate the performance of adult and behaviorally impaired aged rats in a variety of learning tasks, including a habituation paradigm, aversively motivated learning tasks and water mazes. Examination of the site of the neurotoxic lesion in the TM region with immunohistochemical techniques revealed a marked decline of histamine-staining neurons mainly in the rostral part of the TM nucleus, suggesting that the facilitatory effects on reinforcement and mnemonic processes might be related to the destruction of TM intrinsic histaminergic cells. In summary, the present results indicate that the TM nucleus is involved in neural plasticity and functional recovery following damage to the CNS and may function as an inhibitory neural substrate in the control of reinforcement and mnemonic processes.

Neonatal sensory deprivation induces selective changes in the quantitative distribution of GABA-immunoreactive neurons in the rat barrel field cortex.

Modified activity of the rat vibrissae from birth to adulthood induces profound alterations of the responsiveness and selectivity of neurons in the contralateral somatosensory barrel field cortex of adult rats. Because these functional properties are under the control of the intracortical inhibitory mechanisms, we investigated the effects of unilateral removal of face pad vibrissae on the quantitative distribution of intracortical gamma-aminobutyric acid (GABA)-immunoreactive neurons in the rat contralateral and ipsilateral barrel field cortices. This distribution was then compared to a population of control animals. For the entire cortical depth, no significant changes in the density (7,700/mm3 vs. 7,400/mm3), proportion (13.6% vs. 14.4%), or size (11.7 microns vs. 12.5 microns) of GABA-immunoreactive neurons were found in the left contralateral vs. the right ipsilateral barrel field cortex. However, in cortical layer IV, contralateral to the deprivation, the density and proportion of GABA-immunoreactive neurons were lower (6,300/mm3 vs. 13,900/mm3, 6.0% vs. 13.6%; P < 0.01), and these neurons were larger (mean projected height of 15.1 microns vs. 10.8 microns; P < 0.01) than in the ipsilateral barrel field cortex, suggesting a specific loss of GABA expression in a subpopulation of small intracortical neurons. In addition to changes in the contralateral layer IV, GABA-immunoreactive neurons located in the ipsilateral granular layer were also affected. Indeed, their numerical density (13,900/mm3) and proportion (13.6%) were higher (P < 0.01) than in both hemispheres of control animals (average of 10,050/mm3 and 9.4%). On the other hand, GABA-immunoreactive neurons in the ipsilateral layer V were less numerous (5,600/mm3, 15.0%) than in both sides of the controls (average of 10,300/mm3, 22.0%; P < 0.01). Thus, our results show that a unilateral sensory deprivation induces highly selective changes in the intracortical GABA inhibitory circuitry of both hemispheres. These changes are located directly at the input of thalamic afferents and at an output layer of corticofugal and commissural axons and could result in a profound reorganization of the excitatory and inhibitory drives of both sides of the sensory-deprived barrel field cortex.

Effect of vibrissae deprivation on follicle innervation, neuropeptide synthesis in the trigeminal ganglion, and S1 barrel cortex plasticity

Deprivation of vibrissae from an early age causes plasticity in S1 barrel cortex. This method of deprivation is most likely to induce plasticity by altering the balance of primary afferent activity from the deprived and spared vibrissae. To study whether or not induction or expression of this type of plasticity might be affected by follicle nerve injury caused by the deprivation technique, three different methods of detecting nerve injury were used: counting axon numbers in the distal follicle nerve, quantifying morphological changes in axons, and measuring neuropeptide expression in the trigeminal ganglion cells. First, nerves innervating follicles chronically deprived of vibrissae from birth had the same number of myelinated and unmyelinated axons as nerves from normally reared animals. Second, axons innervating deprived follicles showed no morphological changes in myelination or mitochondria characteristic of damaged nerves. Third, the corresponding nerve cell bodies in the trigeminal ganglion did not show upregulation of galanin or neuropeptide Y expression. In contrast, animals receiving mild injury of the follicle nerve endings (by cauterization of the follicle) showed profound changes in axonal myelination and mitochondria and increases in neuropeptide expression. These results imply that vibrissae deprivation does not act by inducing injury of the follicular nerve, suggesting that changes in the balance of follicle nerve activity are the cause of cortical plasticity. Consistent with this notion, a fourth experiment demonstrated that trimming the vibrissae induces cortical plasticity comparable to that induced by complete vibrissae removal.

Tactile sensory input regulates basal and apomorphine-induced immediate-early gene expression in rat barrel cortex.

Clipping of mystacial vibrissae on one side of the rat's snout results in sensorimotor asymmetries in normal behavior and in behavior induced by the dopamine receptor agonist, apomorphine. Immediate-early gene expression, a marker for short-term changes in neuron function, was used to examine whether this sensory deprivation leads to functional changes in the somatosensory barrel cortex under experimental conditions which reveal behavioral asymmetries. The expression of c-fos and zif268 immediate-early genes was assessed with in situ hybridization histochemistry. Four hours after unilateral clipping of the mystacial vibrissae, the level of zif268 mRNA was reduced in the corresponding part of the contralateral barrel field. Injection of apomorphine (5 mg/kg) resulted in increased expression of both c-fos and zif268 immediate-early genes in cortex and striatum. This apomorphine-induced increase was blocked in the sensory-deprived somatosensory cortex. Laminar analysis of gene regulation showed that vibrissae removal affected immediate-early gene expression in all layers of the barrel cortex. These results demonstrate that: (1) basal zif268 gene expression in neurons of the somatosensory cortex is dependent on sensory input, (2) cortical immediate-early gene expression is increased after dopamine receptor activation, and (3) in the barrel cortex, this increase is also dependent on sensory input. We suggest that the observed reduction in gene expression after vibrissae removal reflects decreased activation of neurons in the barrel column by removal of sensory input.

Behavioral and neurochemical asymmetries following unilateral trephination of the rat skull: Is this control operation always appropriate?

The present results are from rats that were intended as sham-operated controls in a study of unilateral lesion of the cortical barrel fields. These animals received a trephime hole through the skull, centered over the barrel fields of one hemisphere. Unexpectedly, they showed time-dependent behavioral and neurochemical asymmetries: 1 + 4 days after unilateral skull trephination they scanned an open field mainly with the contralateral vibrissae. Thereafter (days 7 + 14), scanning recovered to symmetry; however, an ipsilateral asymmetry was induced now by challenge with the dopamine receptor agonist apomorphine. At the same time period after skull trephination, an asymmetry of thigmotactic swimming had developed, with more thigmotactic swimming ipsilateral to the side of skull trephination. Neurochemically, there were indications for changes in neostriatal dopamine metabolism because the tissue levels of dopamine and dihydroxyphenylacetic acid were lower on the ipsilateral side in animals killed 6–16 days after trephination. The time courses of behavioral and neurochemical asymmetries after unilateral skull trephination paralleled those seen following unilateral barrel cortex lesion or unilateral removal of the corresponding contralateral vibrissae; however, without exception, the asymmetries after trephination were in the opposite direction than after cortex lesion or vibrissae removal. The possible mechanisms by which skull trephination might have affected behavior and neurochemistry are discussed, especially with respect to the vibrissae-barrel cortex system and the basal ganglia. Because trephination of the skull is routinely employed, both as a control procedure and for CNS manipulation, these results may have important implications for the design of future experiments.

Unilateral stimulation or removal of rat vibrissae: Analysis of nerve growth factor and tyrosine hydroxylase mRNA in the brain

Previous work has shown that unilateral manipulation of vibrissae in the rat can lead to behavioral asymmetries and to neuronal changes in the basal ganglia: in brief, vibrissae stimulation led to increases in neostriatal dopamine release, whereas unilateral removal of vibrissae led to asymmetries in striatal afferents and to bilateral changes in mesencephalic dopamine mechanisms which were related to the occurrence of behavioral asymmetries and the later recovery therefrom. In the present study, the analysis of neuronal mechanisms possibly affected by vibrissae manipulation was extended to the nerve growth factor and the expression of tyrosine hydroxylase mRNA. Unilateral stimulation or removal of the vibrissae did not lead to significant changes in tissue levels of nerve growth factor in the neostriatum, parietal cortex (including the barrel cortex) or the hippocampus. In contrast, tyrosine hydroxylase mRNA in the substantia nigra and ventral tegmental area was affected by vibrissae removal but not by stimulation, as a bilateral increase in labeling was observed on the level of individual neurons. This effect was only observed in animals tested 4 h after vibrissae removal but not after 10 days. The results are discussed with respect to the interaction of vibrissae function with the basal ganglia, the neurotransmitter dopamine and mechanism of functional recovery.

Whisker trimming behaviour in A2G mice is not prevented by offering means of withdrawal from it.

In group-housed laboratory mice whisker trimming (removal of vibrissae) occurs occasionally, but in the A2G strain it is seen almost invariably. We have tested the hypothesis that whisker trimming in A2G mice is not prevented by offering the possibility to withdraw from it. Pairs of male or female mice showing absence of whiskers and/or absence of nasal fur were separated by placing in their cage either one or two wire screens with a 10 mm mesh. Unlike the single screen, the two screens, which were 10 mm apart from each other, excluded nose to mouth contact. After five weeks, whiskers had regrown in mice separated by the double screen, whereas in the pairs separated by the single screen whiskers remained in part absent. This suggests that 2 mice involved in whisker trimming, either actively or passively, co-operate in this behaviour.