Regeneration of fungiform taste buds: temporal and spatial characteristics.

The gross morphology of the tongue of the Mongolian gerbil Meriones unguiculatus), the location of papillae and taste buds, and the normal innervation pattern of the tongue and taste buds were determined. The chorda tympani nerve was interrupted to produce degeneration of fungiform taste buds. Regenerating chorda tympani axons followed the original nerve pathways in the tongue en route to the fungiform papillae in the epithelium where they initiated the regeneration of taste buds. The spatial distribution of reinnervated fungiform papillae and reformed taste buds was examined 7 to 19 days following surgery. Beginning at eight days following chorda tympani interruption there was a progressive increase, first, in the proportion of fungiform papillae that were reinnervated, and later in the number of reformed taste buds. On the basis of these measures it was concluded that a taste bud is reformed one to two days after reinnervation of its papilla. From the time course of reinnervation of the fungiform papillae it was calculated that some fibers regenerated at rates in excess of 2 mm/day. Regeneration was precise and systematic. The regenerating chorda tympani fibers accurately returned to the fungiform papillae; they did not follow the pathways of lingual nerve axons. In the initial stages of recovery both reinnervated papillae and reformed taste buds were preferentially located toward the front of the tongue; the reinnervation of posterior fungiform papillae was delayed.

Taste fiber responses during reinnervation of fungiform papillae.

Crushing or transecting the chorda tympani nerve of the gerbil (Meriones unguiculatus) caused ipsilateral degeneration of taste buds in the fungiform papillae. In less than two weeks some taste fibers regenerated into the tongue and formed new taste buds and receptor cells. The recovery process was evaluated electrophysiologically in 53 gerbils by acute recording proximal to the nerve injury site. Initially the chorda tympani was electrically silent. In gerbils tested at later times spontaneous activity appeared. This was followed by responses to pressure on the tongue. Taste responses returned as early as day 11. The receptive field of regenerated taste fibers was limited to a small number of fungiform papillae. Taste responses were always associated with the presence of one or more taste buds in the receptive field. Taste buds identified as responsive to chemicals contained some fusiform cells. We found that the taste responses of single fiber, few-fiber and multi-unit preparations reflected the diversity of responses found in normal taste axons as determined by recording from 26 normal single fibers and 27 normal whole nerves. The early emergence of a variety of fiber types and responses to many chemicals in regeneration is inconsistent with the proposition that the relative chemical responsiveness of a receptor cell is strictly a function of its age; the response of a given young taste receptor is not necessarily limited to a few of the standard taste stimulants.

L-Dopa and piribedil alter different components of attentional behavior dependent on dose.

L-Dopa (3, 10, 30, 100 mg/kg) given SC after carbidopa, and piribedil (10, 30, 100, 300 mg/kg) had biphasic effects on investigation of a novel cup. Gerbils given a low dose of L-Dopa (10 mg/kg) or piribedil (10 or 30 mg/kg) investigated the cup more than did vehicle-injected gerbils, whereas those gerbils given a high dose of L-Dopa (100 mg/kg) or piribedil (300 mg/kg) investigated it less. L-Dopa, but not piribedil, also had biphasic effects on investigation of conspecific odors. The increase in duration with no increase in frequency of investigation suggested an inability to shift attention normally. High-dose attenuation of investigation is considered nonspecific, as many other drugs have the same effect. Locomotor activity scores showed no concomitant increase following low doses, but only a dose-dependent decrease. In addition, L-Dopa (100 mg/kg), but not piribedil at any dose tested, prevented the normal decrement in response to the cup 24 h after injection. As a high response is normally only shown when the stimulus is novel, the data suggest that L-Dopa at the high dose, but not piribedil, interfered with selective attention. Thus, the different dopamine agonists affected different aspects of attention. The data are discussed in relation to neural effects of the drugs as reported in the literature.

Differential effects of haloperidol and clozapine on attention.

Haloperidol (0, 0.1, 0.3, or 1.0 mg/kg), the typical butyrophenone neuroleptic, decreased investigation of novel objects by gerbils following systemic injections. When given prior to apomorphine (1 or 3 mg/kg), haloperidol blocked apomorphine-induced disruption of selective attention in a dose-dependent manner. Thus, haloperidol acts like pimozide in this paradigm. In contrast, clozapine (0, 0.03, 0.1, 0.3, 1.0, or 3.0 mg/kg), the atypical dibenzodiazepine neuroleptic, increased frequency of investigation both soon after injection and 24h later, suggesting interference with maintenance of attention. When given with apomorphine (1.0 mg/kg), clozapine did not block apomorphine effects on selective attention. The results are related to differential effects of these neuroleptics on other behaviors and to their individual pharmacological profiles.

Evidence of limited capacity and noise reduction with single-element displays in the location-cuing paradigm.

Precuing a location facilitates accuracy of identification of a target at that location and reduces noise from other nontarget characters in a multicharacter field. In 5 experiments, evidence for facilitation included higher accuracy with long precue-target intervals than with short intervals and higher accuracy when a precue indicated the correct location than with short intervals and higher accuracy when a precue indicated the correct location than when it indicated the wrong location. These results were found for each target-mask condition used (1 target with 1 mask, 1 target with 4 masks, or 1 target and 3 nontargets with 4 masks) in experienced and inexperienced observers. Evidence for noise reduction was found because accuracy was higher in the 1 target-1 mask condition than in the other conditions on correctly cued trials with short-cue-target intervals and on incorrectly cued trials. Data are related to methodological factors that are important to obtaining these effects and to capacity and noise reduction models.

Environmental enrichment facilitates foraging behavior.

Mongolian gerbils (Meriones unguiculatus) were tested at 24 months of age after having experienced an outdoor desert environment for one hour each month after weaning, or at 8 months of age after being reared from birth in outsize cages in the laboratory. Both groups of enriched gerbils found food more rapidly than did 24-month-old handled controls, 8-month-old naive gerbils, or 8-month-old gerbils reared in small cages. There were no differences in locomotor activity, in latency to emerge from a small box, or in attention to novel objects or conspecific odors. Efficiency in finding food was not associated with types of food chosen, and the foods selected were not directly related to types of food eaten previously.

Attention and habituation: separation of specific components in development.

In four experiments using habituation procedures, it was shown that selective investigation of stimuli that are novel gradually developed between 13 and 28 days of age in gerbil pups. The youngest pups investigated the stimuli, but were highly variable in their responses to an object or to odors of conspecifics. Habituation could, but did not reliably, occur. By 21 days of age, investigation of a cup attenuated in a series of 5 one-minute trials and responses increased after the cup was moved to a new location. By 28 days of age, reliable habituation was shown 24 hours after a one-minute exposure to a cup. The data were used to infer how an immature process of selective attention may be responsible for variability in expression of habituation during development.

Taste responses of the chorda tympani nerve in the mouse.

Electrophysiological taste responses were obtained from the chorda tympani nerve of the mouse by using a technique whereby a 50 microns nichrome wire electrode was placed against the nerve where it passes through the middle ear.

Brief periods of environmental enrichment facilitate adolescent development of gerbils.

In a lifespan study, measures of motor behavior and somatic growth were recorded monthly from 31 male and 31 female gerbils. Each month, after measures were recorded, the gerbils were placed in a large, outdoor environment, or in a small indoor control cage for one hour. The enrichment experience for one hour a month had no effect on motor behavior between 2 and 7 months of age, but facilitated adolescent development. Area of the ventral gland increased more rapidly in gerbils given environmental enrichment. In male gerbils, the hindlimb was longer in those given environmental enrichment, but the opposite was true in female gerbils. More female gerbils had seizures than did male gerbils after 3 months of age, and enrichment had no significant effect on seizures in female gerbils. In male gerbils, however, more of the gerbils given enrichment experience had seizures from 2 to 4 months of age and fewer had seizures at 5 and 6 months of age than did controls.

Perseveration of attention to conspecific odors and novel objects in castrated gerbils.

Castrated male and female gerbils were tested for odor preference and for attention to conspecific odors and a novel object. Castrated gerbils housed with sham-operates preferred home odors, discriminated between two groups of male gerbils by olfactory cues, and perseverated in attention to odors of male gerbils and to a novel object. Similar perseveration to male conspecific odors was shown in gerbils given injections of L-DOPA (30 mg/kg). Combined treatment (castration and L-DOPA) resulted in additive effects on perseveration. This research challenges two general hypotheses of gonadal hormone function. The first, that changes in odor preference after castration are due to a loss in testicular androgen, is insufficient, because (1) female as well as male gerbils showed similar perseveration to odors, (2) there was a significant correlation between LH and duration of investigation of male conspecific odors, and (3) L-DOPA, the dopamine precurser, also caused perseveration to conspecific odors. The second, that gonadal hormones are responsible for persistence of attention, cannot be broadly generalized, because castration with resultant elevation of LH and regression of ventral glands resulted in perseveration of attention in male and female gerbils.

Attention and habituation: catecholamine interactions and sex differences.

Norepinephrine (NE)-dopamine (DA) interactions in mediation of long-term habituation were tested using the stimulus-elicited investigation paradigm. Systemic injections of clonidine hydrochloride (CLON), an alpha-adrenergic receptor agonist, given before apomorphine (APO) (1 mg/kg SC), a DA receptor agonist, prevented APO-induced disruption of the duration measure of habituation 25-hr later. A lower dose was effective in female gerbils than that required for male gerbils, suggesting that females are more sensitive to the effects of clonidine. In addition, apomorphine, with or without CLON (0.01 mg/kg), increased locomotor activity in male gerbils but reduced activity in female gerbils. The same dose of CLON that prevented APO-induced disruption of 24-hr habituation did not reverse APO-induced reduction of investigation of an object or an odor, or APO-induced changes in activity. Neither CLON nor desmethylimipramine, a blocker of NE reuptake, had any selective effects on investigation of novel stimuli or short-term habituation showing that relative NE-DA activity can be disrupted without interfering with the behavior, However, CLON interfered with the frequency measure of long-term habituation in male gerbils but not in female gerbils at any dose used (0.0100.3 mg/kg). THe data suggest important sex dependent NE-DA interactions in mediation of long-term habituation.

Understanding Diverse Effects of Visual Attention with the VAP-Filters Metaphor

The Variable and Permeable Filters (VAP-Filters) metaphor is presented with an explanation of its advantages over other popular metaphors in accounting for attention effects in many different research paradigms. Research from laboratories of the author and others are discussed briefly and shown to result in diverse facilitatory and inhibitory attention effects on visual perception. All of these effects are consistent with the VAP-Filters metaphor.

Facilitatory or Inhibitory Nontarget Effects in the Location-Cuing Paradigm

The effect of nontargets on the identification of targets in the location-cuing paradigm was investigated in order to determine whether observers consistently allocate their attention to a validly cued location and whether the effect of nontargets is to facilitate or to inhibit performance. In four experiments, the effects of a single matching nontarget or a single nonmatching nontarget were compared. In each experiment, it was shown that observers consistently allocate their attention to a cued location when a precue appears and that performance is inhibited more by nonmatching nontargets in the display than it is facilitated by matching nontargets.

Implications for multiple transmitter mediation of amphetamine-induced stereotypies.

Gerbils were pretreated with the dopamine (DA) receptor blocker, pimozide, prior to stereotypy-inducing injections of d-amphetamine. Some of the stereotypies induced with amphetamine were blocked, but some were not, supporting the hypothesis that multiple neurotransmitters are involved in the mediation of amphetamine-induced stereotypy. In addition, when apomorphine hydrochloride was injected, different stereotypic motor behaviors were induced than were induced with amphetamine. The behavioral changes following amphetamine treatment could be classified into four groups: (1) those that are probably DA related, based on the fact that they were induced with either amphetamine or apomorphine, and amphetamine induction was blocked with pimozide; (2) those that are probably not DA related because they were not induced by apomorphine, and amphetamine induction was not blocked by pimozide; (3) those behaviors that may be incompatible with stereotypic behaviors, were reduced with either amphetamine or apomorphine, but were not maintained with pimozide; and (4) circling, which was induced with amphetamine, blocked with pimozide, but not induced with apomorphine.

Importance of precue location in directing attention.

In location-precuing experiments, accuracy in discrimination of T-like characters improves with increasing time between the precue and the target. In this experiment, two central and two peripheral cue locations were examined using 13 different cue-target intervals from 0 to 234 msec. Accuracy was the same when trials were cued from the two peripheral locations (two thirds distance between fixation and target or distal to the target location). Centrally cued trials (cues at fixation or next to fixation) resulted in slower onset of attentional effects than peripherally cued trials, but there was greater accuracy at long cue-target intervals for central than for peripheral cues. Data are compared to previously published research.

Benefits from attention depend on the target type in location-precued discrimination.

In previous research, we found that precuing of attention to a target location greatly improved discrimination of targets that differed in line arrangement, but had little effect on discrimination of targets that differed in line orientation. In the present research, a number of other targets that represent various feature differences were used. The new data are consistent with and extend our earlier findings by showing that (1) there is some effect of precuing with all targets tested, and (2) the size of precuing effects varies in a complex way with the nature of the target. Moreover, the difficulty of the discrimination cannot explain the size of the precuing effects. A framework for understanding the events occurring during trials in the location-cuing paradigm is presented and applied to these results.

Lifespan ontogeny of breeding and reproductive success in Mongolian gerbils.

An analysis was made of demographic data collected from a colony of Mongolian gerbils (Meriones unguiculatus). The data on births of over 3800 gerbils provide evidence on several aspects of development and fecundity. Approximately 4% more females than males survived to weaning. Mean number of pups per dam per year was estimated to be 48.3, greater reproductive success than reported previously. The shortest period of gestation resulting in viable pups was 25 days. Implantation was delayed by the presence of suckling pups. When gestation was prolonged, there was a direct relationship between the number of pups being suckled concurrently and the length of the delay. Length of gestation did not affect the size of the subsequent litter. Female gerbils gave birth as early as 72 days of age. Gerbils continued to reproduce until after 2 years of age in some cases. There were fewer pups per litter born to older females, fewer pups per litter with increasing parity, and longer intervals between litters with increasing age.

Time course of attention effects with abrupt-onset and offset single- and multiple-element precues.

Large differences between the time course of attentional responsiveness to onset single-element precues (onset singles) and to onset multiple-element precues (onset multiples) have suggested differences in the way attention is controlled. In five experiments here, singles presented as offsets produced rapid attention buildup, attentional decay across longer precue-to-target delays, and attentional capture, as do onset singles, suggesting exogenous attentional control; both offset and onset multiples produced gradual onset of attentional effects without subsequent attentional decay, suggesting endogenous attentional control; and onset and offset singles produced higher accuracy than onset and offset multiples. Thus, the dynamic quality of a sudden onset is not sufficient explanation for the exogenous attentional control produced by a single-element peripheral precue.

Inhibition of return: support for generality of the phenomenon.

Inhibition of return (IOR), first described in 1984, was considered to be a general phenomenon for ensuring that attention would be allocated to successive stimuli in the environment. In the present research, IOR was expressed in forced-choice identification tasks with either reaction time or accuracy as the dependent measure. Thus, the generality of IOR was supported, because response inhibition cannot explain IOR found with accuracy measures. Concepts from the variable and permeable filters metaphor are used to suggest how changes in attention can change expression of IOR by rapid variation in perceptual threshold.

Allocation of visual attention depends on type of precue.

To distinguish between theoretical concepts of how attention is allocated, participants were presented with different types of precues in 6 experiments. In 1 condition with 100% valid precues (Experiments 1 and 2), the time course of attention effects revealed that (a) higher accuracy was obtained with dynamic multiple-element precues (MEPs in which the unique element was defined by apparent motion) than with static MEPs, in which the elements did not move once they were presented (Cheal & Chastain, 1998); (b) a longer precue-target interval (stimulus-onset asynchrony; SOA) was needed to reach asymptote accuracy with dynamic MEPs than with dynamic single-element precues (SEPs); and (c) all dynamic precues (both MEPs and SEPs) resulted in a decline in accuracy at long SOAs. These results suggest that static and dynamic MEPs result in delayed engagement of attention relative to SEPs. Further, a decline in accuracy at long intervals is associated with static and dynamic SEPs and dynamic MEPs, but not with static MEPs. With irrelevant precues (Experiments 3 to 5), there was capture by precues in which the unique element moved briskly, smoothly, or abruptly, or simply flashed on and off, although there were differences in the amount of capture. The strongest capture occurred with smooth movement in static background elements and the weakest with smooth movement in abruptly moving background elements. It was shown in Experiment 6 that a static MEP will not capture attention if one element changes to a unique brightness near the time of precue onset, but if the element changes after 1,000 ms, it will capture attention. The authors suggest that different types of precues result in unequal influence of endogenous and exogenous components of attention, even when the same targets are used. In addition, they show that neither singleton detection mode nor contingent involuntary orienting is necessary for the capture of attention.