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A behavioral bioassay is described that detected kairomonal activity in substances associated with the metatarsal glands of white-tailed deer, Odocoileus virginianus (Zimmermann). Dry and aqueous wipes or rubs of glandular areas elicited an arrestant response in adult blacklegged ticks, Ixodes scapularis Say.
A characteristic feature of associative conditioning is that learning a predictive relationship between two events can block later learning about an added event. It is not yet well established whether blocking occurs in the spatial domain or the circumstances in which it does. We now report, using rats trained to search for hidden food near landmarks in an open field arena, that blocking can occur in spatial learning. The animals noticed the added landmark at the start of the blocking phase and explored it, but either failed to incorporate it into their spatial map or developed a representation in which only some landmarks actually control behavior. Additionally, performance at asymptote was controlled by the shape of the landmark array rather than the individual landmarks comprising it, indicating that blocking in the spatial domain may represent a failure to alter the encoded geometry of a learned array.
To further elucidate the links among synaptic plasticity, hippocampal place cells, and spatial memory, place cells were recorded from wild-type mice and transgenic "R(AB)" mice with reduced forebrain protein kinase A (PKA) activity after introduction into a novel environment. Place cells in both strains were similar during the first exposure and were equally stable for recording sessions separated by 1 hr. Place cell stability in wild-type mice was unchanged for sessions separated by 24 hr but was reduced in R(AB) mice over the longer interval. This stability pattern parallels both the reduced late-phase long-term potentiation in hippocampal slices from R(AB) mice and the amnesia for context fear conditioning seen in R(AB) mice 24 but not 1 hr after training. The similar time courses of synaptic, network, and behavioral instability suggest that the genetic reduction of PKA activity is responsible for the defects at each level and support the idea that hippocampal synaptic plasticity is important in spatial memory.
On the basis of electrophysiological studies, the glossopharyngeal nerve (GL) is far more responsive to quinine than the chorda tympani (CT) or greater superficial petrosal (GSP) nerves. The licking behavior of water-deprived rats to quinine (0.03-3.0 mM) and distilled water (10-s trails) was tested before and after various nerve transections. GL+CT section caused a substantial reduction in responsiveness. GSP+CT section had a moderate effect, and GL section alone produced only marginal impairments. Control, partially desalivated, and CT-sectioned rats were unaffected. Thus, the GL is not necessary for normal unconditioned taste-guided appetitive responsiveness to quinine, but the collective input from the GSP and CT is necessary and most likely sufficient. These data suggest that the quinine-evoked input of the GL and CT converge centrally.
Morphological changes in the frontoparietal cortex were assessed in rats that exhibited deficits in a go/no go alternation task due to electrolytic lesion of the basal forebrain. Cortical area, laminar thickness, neuronal density, and soma area were examined in frontal, hindlimb, forelimb, and parietal areas of the cortex. Quantitative morphological analysis of the frontoparietal cortex in lesioned rats revealed a decrease in laminar thickness due to reduced soma size in particular cortical laminae. Neuronal density was not affected. These effects were present in all cortical areas examined and most pronounced in laminae II-III. Similar morphological changes were observed in the same cortical areas following lesions of the basal forebrain made with ibotenic acid, allowing a discrimination of lesion effects from those induced by damage to fibers of passage or differential behavioral testing. Lesions of the basal forebrain have previously been shown to produce both behavioral deficits and changes in cortical cholinergic activity. The cortical morphological changes observed in the present study following basal forebrain lesion provide further evidence for the importance of ascending cholinergic inputs to the cortex and their role in learning and memory.
Auditory brainstem response (ABR) and standard behavioral methods were compared by measuring in-air audiograms for an adult female harbor seal (Phoca vitulina). Behavioral audiograms were obtained using two techniques: the method of constant stimuli and the staircase method. Sensitivity was tested from 0.250 to 30 kHz. The seal showed good sensitivity from 6 to 12 kHz [best sensitivity 8.1 dB (re 20 microPa2 x s) RMS at 8 kHz]. The staircase method yielded thresholds that were lower by 10 dB on average than the method of constant stimuli. ABRs were recorded at 2, 4, 8, 16, and 22 kHz and showed a similar best range (8-16 kHz). ABR thresholds averaged 5.7 dB higher than behavioral thresholds at 2, 4, and 8 kHz. ABRs were at least 7 dB lower at 16 kHz, and approximately 3 dB higher at 22 kHz. The better sensitivity of ABRs at higher frequencies could have reflected differences in the seal's behavior during ABR testing and/or bandwidth characteristics of test stimuli. These results agree with comparisons of ABR and behavioral methods performed in other recent studies and indicate that ABR methods represent a good alternative for estimating hearing range and sensitivity in pinnipeds, particularly when time is a critical factor and animals are untrained.
The size of the hippocampus has been previously shown to reflect species differences and sex differences in reliance on spatial memory to locate ecologically important resources, such as food and mates. Black-capped chickadees (Parus atricapillus) cached more food than did either Mexican chickadees (P. sclateri) or bridled titmice (P. wollweberi) in two tests of food storing, one conducted in an aviary and another in smaller home cages. Black-capped chickadees were also found to have a larger hippocampus, relative to the size of the telencephalon, than the other two species. Differences in the frequency of food storing behavior among the three species have probably produced differences in the use of hippocampus-dependent memory and spatial information processing to recover stored food, resulting in graded selection for size of the hippocampus.
Five experiments addressed the issue of how pigeons learn to discriminate the relative frequency of stimuli. During a sampling period, three different stimuli (keylights) were presented serially, in mixed order, and with different frequencies. During a choice period, the stimuli were presented simultaneously, and reinforcement was arranged for choosing the stimulus that was presented the least number of times during the sample. The results showed that (a) the overall proportion of correct choices was always above chance levels; (b) the likelihood of a correct choice decreased with the serial position of the correct stimulus, a negative recency effect; (c) when the last three stimuli of the sample were constrained to be one of each kind, the negative recency effect decreased but errors became more likely when the correct stimulus occurred early in the sample, a negative primacy effect; (d) accurate performance generalized to new and larger samples; and (e) under some conditions the probability of a correct choice was independent of the serial position of the correct stimulus. The serial position curves suggest that in a least frequent discrimination task, two processes determine how the least frequent stimulus controls behavior: a passive decay process (the stimulus loses its effectiveness with time since its last occurrence), and a residual salience process (when the stimulus occurs in the first position it may decay to a higher asymptote than when it occurs in later positions.
Monkeys exposed to low doses of the dopamine neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) develop cognitive deficits in the absence of gross motor dysfunction. Attentional deficits and task impersistence are now also described in these animals. The task impersistence correlated with no-response errors (i.e. errors of omission) on a delayed response task and improved with dopamine agonist therapy. In parallel studies, it was observed that there were significant differences in the ability of normal monkeys to learn to perform cognitive tasks. We found that monkeys classified as poor learners had similar deficits in task persistence as did MPTP-exposed monkeys, suggesting a relationship between poor cognitive performance and task impersistence in untreated as well as MPTP-treated monkeys. The possible significance of these results for two clinical disorders, early Parkinson's disease and attention deficit hyperactivity disorder is discussed. Cognitive and behavioral similarities between chronic low dose MPTP-treated monkeys, early Parkinson's disease patients and people with attention deficit hyperactivity disorder may suggest the existence of related pathophysiological mechanisms in these disorders.
Anatomical and pharmacological evidence suggests that excitatory amino acids (EAA's) may function as neurotransmitters within the median raphe nucleus (MR). Previous studies have shown that injections of EAA antagonists into the MR result in marked hyperactivity. The current report extends these findings by demonstrating that intra-raphe injections of two EAA antagonists, kynurenic acid and 2-amino-5-phosphonovaleric acid, result in dose-dependent increases in food and water intake in nondeprived rats. These results suggest that EAA's within the MR may play a role in the control of appetitively motivated behaviors.
Experiments were performed on dogs with bilateral electrolytic damage of dorso-medial amygdala. Before the operation dogs were trained in alimentary-social reward differentiation. It consisted in conditioning of instrumental responses of either right or left foreleg to two different tones respectively. Chlorpromazine was injected intramuscularly in 1.5 mg/kg dose during four consecutive days, beginning at third to fifth week after the operation. Amygdala damage produced significant deterioration of the instrumental performance both reinforced by food and by social-sensory rewards. Chlorpromazine produced further dramatic decrease of performance of both responses. It was concluded that chlorpromazine exerts a suppressing effect on motivated behavior reinforced by positive rewards in amygdala dogs. As the effect of chlorpromazine and medial amygdalar damage are summated it may be suggested that the deficit of medial amygdala neurons impairs similar neurochemical mechanisms, (probably dopaminergic and alpha-adrenergic transmission) as does chlorpromazine.
This study examined the effects of ethanol (EtOH) and toluene on fixed-ratio (FR) responding in mice selectively bred for sensitivity to the effects of EtOH on sleep time. Although the more sensitive long sleep (LS) mice showed greater EtOH-induced impairment in a motor performance task than did the less sensitive short sleep (SS) mice, changes in FR performance in the two lines did not differ in response to EtOH, regardless of route (oral or intraperitoneal) or time (40 vs. 60 min pre-session) of administration. These results emphasize the importance of considering task variables in determination of the behavior of different genotypes. In contrast to results with EtOH, the volatile inhalant toluene produced different effects on FR responding in the selected lines, with SS mice being more sensitive than LS mice.
Rats (n = 11) with bilateral kainate lesions of the caudate nucleus and subsequent unilateral transplantation of embryonic striatal tissue into the damaged area preferred 4 months later to reach for food with the forepaw contralateral to the graft. No such asymmetry was observed in lesioned, nontransplanted (n = 8) or unoperated (n = 5) control rats. Good integration of the graft with the host brain was indicated by the finding that cortical spreading depression did not enter the lesioned caudate nucleus but did penetrate into the lesioned caudate with the graft almost as regularly as in intact rats. Behavioral asymmetry produced by unilateral grafts in bilaterally lesioned animals reveals the effects of transplantation with more sensitivity than the graft-induced compensation of the asymmetries caused by unilateral lesions.
Previous studies have shown that those food-storing birds of the order Passeriformes that remember the locations of their caches have relatively larger hippocampal complexes than do non-storing passerines. Woodpeckers constitute a different avian order (Piciformes), which also includes some food-storing species. We compared hippocampal volume, relative to the volume of the rest of the telencephalon, across four species of woodpeckers with disparate caching behavior. Red-bellied woodpeckers (Melanerpes carolinus) are "scatter hoarders'. During the fall and winter they cache acorns or beechnuts in dispersed sites throughout a large territory. Red-headed woodpeckers (Melanerpes erythrocephalus) also store nuts but in central "larders' on their small territories which they fiercely defend. Caching is absent or much reduced in hairy woodpeckers (Picoides villosus) and downy woodpeckers (Picoides pubescens), both of which forage on a variety of foods within large winter home ranges. The relative volume of the hippocampal complex in the scatter hoarder was larger than in the larder hoarder, suggesting that red-bellied woodpeckers, like passerine scatter hoarders, rely on memory to recover their caches. Surprisingly, the relative hippocampal volumes in the two non-storing Picoides woodpeckers were most similar to the scatter hoarder of the other genus. In passerine birds, hippocampal volume and telencephalon volume are highly correlated in storing species but not in non-storers. We found that the volumes of these two brain areas were highly correlated in both Melanerpes species, uncorrelated in the hairy woodpeckers, and more weakly correlated in the downy woodpeckers. The unexpectedly large hippocampal complexes in the Picoides species suggests they may engage in some behavior, other than food-storing, that selects for this trait. Conversely, our results concerning the relationship between hippocampal and telencephalon volumes may indicate that a weak correlation is associated with a less specialized hippocampus, independent of its relative volume.
Operant responding on a progressive ratio (PR) schedule for intravenous cocaine as well as sucrose reinforcement was examined in female rats throughout the reproductive process. Self-administration sessions began before mating, and continued throughout pregnancy and until lactational Day 8; following parturition, litters were present with dams during operant sessions. Physiological changes associated with the reproductive process dramatically altered PR responding for cocaine, while PR responding for sucrose was relatively stable throughout pregnancy and lactation. Female animals exhibited the highest number of responses/session for cocaine during estrus and the 1st trimester of pregnancy and the lowest responding near parturition, with levels only partially recovering during lactation. Dams self-administering cocaine exhibited notably different patterns of maternal behavior in the operant chambers than dams responding for sucrose. Thus, cocaine's reinforcing efficacy may be influenced by (a) the changing physiological profile associated with the reproductive process and (b) competition from the reinforcing properties of offspring during lactation.
In a laboratory simulation of foraging conditions, pigeons maintained ad lib weight by treadle pressing for lengthy periods of access to grain in a 24-hr live-in environment. Localized visual signals produced by treadle pressing evoked approach and pecking behavior if they signaled impending food presentation (Pavlovian first-order conditioning) or the presentation of an established signal for food (Pavlovian second-order conditioning). These findings imply a role for associative mechanisms in the control of foraging.
We have previously shown that lesions of the sensorimotor cortex induced by either thermocoagulation or aspiration produce different effects on axonal plasticity. We have now investigated whether these methods of lesion also influence the behavioral outcome. The behavioral effects of unilateral and bilateral lesions of the sensorimotor cortex induced by either aspiration or by thermocoagulation of pial blood vessels were examined in adult Sprague-Dawley rats. Rats were tested to determine limb use asymmetry by analyzing (1) coordinated forelimb placement and (2) paw use preference when rearing. Their responsiveness to somatosensory stimulation was tested by analyzing (1) the latency to remove sticky tape on the ventral surface of the paw, and (2) vibrissae-stimulated forelimb placing. Behavioral tests were performed prior to surgery and on day 4, 8, 12, 16, and 20 after surgery. Both unilateral lesions resulted in an over-reliance on the nonimpaired forelimb as early as 4 days after the surgery; functional recovery occurred after 16 days. Animals with bilateral lesions did not use either forelimb for support in postural support behaviors. However, this effect was more apparent in the animals with a thermocoagulatory lesion and, in contrast to the animals with an aspiration lesion, these animals did not show functional recovery. Animals with a unilateral aspiration, but not a thermocoagulatory lesion, showed a slowed response to tactile stimulation applied to the contralateral forelimb. After bilateral lesions, animals showed a slowed response to tactile stimulation applied to either forelimb at early time points after the lesion and recovery of function at later time points. These data indicate that, for the most part, lesions of the sensorimotor cortex by aspiration or thermocoagulation produce very similar effects on the behaviors examined in this study. However, unexpectedly, thermocoagulatory lesions induced a more severe (unilateral lesion) or prolonged (bilateral lesion) deficit in forelimb use than aspiration lesions. Conversely, the effect on tactile stimulation is more prominent after unilateral aspiration than thermocoagulatory lesions.
This study compared the effects of transection of the lateral olfactory tracts (LOT) and the accessory olfactory tracts (AOT) in male hamsters on nest building, food piling, and sexual behavior. Autoradiographic tracing of amino acids injected into the olfactory bulbs allowed accurate determination of the location and extent of the transections. Animals with complete bilateral transection of the projections to the amygdaloid targets of the accessory olfactory bulbs and to the main olfactory targets posterior to the olfactory tubercle showed no sexual behavior postoperatively; they did not exhibit extensive genital investigation and did not mount females. In contrast, most of the animals with partial sparing of accessory olfactory bulb efferents to the amygdala did exhibit investigatory and copulatory behaviors postoperatively, although half of the animals with this partial sparing developed delayed deficits in these sexual behaviors. Almost all animals without detectable main olfactory bulb efferents to posterior targets showed delayed deficits in nest building and food piling. This was true whether or not there was partial sparing of accessory olfactory bulb efferents to the amygdala. The animals with LOT transections typically built nests and piled food during the first postoperative week, but stopped building nests and piling food by the fourth postoperative week. Cold stress enhanced these two behaviors in control animals but did not obviate the deficits in experimental animals. Caudally placed transections, which spared a larger portion of the main olfactory projections than rostally placed transections, did not spare more behavior. In fact, the caudally placed transections produced shorter delays in the appearance of deficits in nest building and food piling. These results indicate that the accessory olfactory bulb efferents to the amygdala are more important for sexual behavior than for nest building and food piling in male hamsters. Nest building and food piling are not directly dependent on normal ongoing or sensory evoked activity in the main or accessory olfactory bulb efferents which project through the LOT and AOT. The deficits in nest building and food piling may represent a deterioration in the ability of the animals to organize their living space. The observed delays in the appearance of deficits in behavior may also reflect slow degenerative processes or humoral changes associated with loss of input from the main olfactory bulbs to posterior olfactory target areas, and possibly with interruptions of projections to targets of the accessory olfactory system.