A behavioral characterization of the effects of food deprivation on food and nonfood object interaction: an investigation of the information-gathering functions of exploratory behavior.

Previous research has shown that exploratory behavior serves not only to procure food, but also as a means of general information gathering. The purpose of this experiment was to investigate the function of exploratory behavior in rats by measuring behavior as they interacted with food and nonfood stimuli under different levels of food deprivation. Rats were food-deprived (0, 24, and 48 h), given free access to an open-field arena, and videotaped for a 20-min test session. The rats' behavior was assessed in a manner that isolated locomotor-, object-, and nonobject-related components. Deprivation did not affect locomotor activity levels; however, a decrease in rearing and propping against the test arena was shown. Rats distinguished between the food and nonfood objects because they attempted to ingest the food but not the nonfood object. Deprivation did result in increased contact with food objects; however, nonfood object interactions were maintained throughout the test session. These results suggest that exploratory behavior is separable from food seeking and functions in acquisition of information relating to multiple aspects of the environment.

arfI and arfII, two genes encoding alpha-L-arabinofuranosidases in Cytophaga xylanolytica.

arfI encoded the 57.7-kDa subunit of Cytophaga xylanolytica arabinofuranosidase I (ArfI). arfII encoded a 59.2-kDa subunit of ArfII. Products of both cloned genes liberated arabinose from arabinan and arabinoxylan. The deduced amino acid sequences of ArfI and ArfII revealed numerous regions that were identical to each other and to regions of homologous proteins from Bacteroides ovatus, Bacillus subtilis, and Clostridium stercorarium.

Purification and properties of ArfI, an alpha-L-arabinofuranosidase from Cytophaga xylanolytica.

An alpha-L-arabinofuranosidase (alpha-L-arabinofuranoside arabinofuranohydrolase [EC 3.2.1.55]; referred to below as ArfI) from Cytophaga xylanolytica XM3 was purified 85-fold by anion-exchange and hydrophobic interaction column chromatography. The native enzyme had a pI of 6.1 and an apparent molecular mass of 160 to 210 kDa, and it appeared to be a trimer or tetramer consisting of 56-kDa subunits. With p-nitrophenyl-alpha-L-arabinofuranoside as the substrate, the enzyme exhibited a K(m) of 0.504 mM and a Vmax of 319 mumol.min-1.mg of protein-1, and it had optimum activity at pH 5.8 and 45 degrees C. ArfI was relatively stable over a pH range of 4 to 10 and at temperatures up to 45 degrees C, and it retained nearly full activity when stored at 4 degrees C for periods as long as 24 months. The enzyme also released arabinose from 4-methylumbelliferyl-alpha-L-arabinofuranoside, as well as from rye, wheat, corn cob, and oat spelt arabinoxylans and sugar beet arabinan, but not from arabinogalactan. ArfI showed no hydrolytic activity toward a range of p-nitrophenyl- or 4-methylumbelliferyl-glycosides other than arabinoside, for which it was entirely specific for the alpha-L-furanoside configuration. ArfI interacted synergistically with three partially purified endoxylanase fractions from C. xylanolytica in hydrolyzing rye arabinoxylan. However, cell fractionation studies revealed that ArfI was largely, if not entirely, cytoplasmic, so its activity in vivo is probably most relevant to hydrolysis of arabinose-containing oligosaccharides small enough to pass through the cytoplasmic membrane. Antibodies prepared against purified ArfI also cross-reacted with arabinofuranosidases from other freshwater and marine strains of C. xylanolytica, as well as with some proteins that did not possess arabinofuranosidase activity. To our knowledge, this is the first alpha-L-arabinofuranosidase to be purified and characterized from any gliding bacterium.

Age and sex as factors influencing spontaneous exploration and object investigation by preadult rats (Rattus norvegicus).

This study examined developmental and sex differences in the exploratory and investigatory behaviors of Long-Evans rats (Rattus norvegicus). Littermate sextuplets were divided into sex-matched groups (at 30, 60, and 90 days of age) and were individually videotaped on 2 consecutive nights in an arena that contained stimulus objects. Multiple measures of locomotor exploration and object investigation increased significantly with age but were not influenced by sex. Older rats entered more quickly, were more active, spent more time in the arena, and spent more time investigating inanimate stimulus objects than did younger rats. Sex did not significantly affect most measures of open-field behavior; however, the data suggest that the sexes may begin to diverge by 90 days. These results suggest that preadult rats of both sexes are equipped early in development with similar strategies and repertoires for exploration and investigation.

The relationship between adrenal steroids and enrichment-induced brain growth.

The question of whether brain growth brought about by environmental enrichment is mediated by the adrenal cortex has not been answered. Accordingly, young male rats were either adrenalectomized (ADX) and infused with a constant maintenance dose of corticosterone (2 mg.kg-1.day-1) or sham-operated and implanted with a blank infusion device. Half of each surgical group was maintained in either impoverished (IC) or enriched conditions (EC). After 30 days, changes in forebrain growth and thickness of various cortical and subcortical regions were determined for each group. Enrichment and ADX independently increased forebrain weight and thickened cortical tissue at about the same anatomical sites. However, combined treatments were additive, not interactive. EC-induced brain growth is mimicked but not mediated by adrenalectomy.

Klebsiella aerogenes urease gene cluster: sequence of ureD and demonstration that four accessory genes (ureD, ureE, ureF, and ureG) are involved in nickel metallocenter biosynthesis.

The region located immediately upstream from the Klebsiella aerogenes urease structural genes was sequenced and shown to possess an open reading frame capable of encoding a 29.8-kDa peptide. Deletions were generated in this gene, denoted ureD, and in each of the genes (ureE, ureF, and ureG) located immediately downstream of the three structural genes. Transformation of the mutated plasmids into Escherichia coli resulted in high levels of urease expression, but the enzyme was inactive (deletions in ureD, ureF, or ureG) or only partially active (deletions in ureE). Ureases were purified from the recombinant cells and shown to be identical to control enzyme when analyzed by gel filtration chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis; however, in every case the activity levels correlated to nickel contents as analyzed by atomic absorption analysis. UreD, UreE, UreF, and UreG peptides were tentatively identified by gel electrophoretic comparison of mutant and control cell extracts, by in vivo expression of separately cloned genes, or by in vitro transcription-translation analyses; the assignments were confirmed for UreE and UreG by amino-terminal sequencing. The latter peptides (apparent M(r)s, 23,900 and 28,500) were present at high levels comparable to those of the urease subunits, whereas the amounts of UreF (apparent M(r), 27,000) and UreD (apparent M(r), 29,300) were greatly reduced, perhaps because of the lack of good ribosome binding sites in the regions upstream of these open reading frames. These results demonstrate that all four accessory genes are necessary for the functional incorporation of the urease metallocenter.

Scopolamine suppresses both locomotion and object contact in a free-exploration situation.

It was recently reported by Buhot et al. that presession cholinergic disruption with scopolamine decreases time spent in proximity to novel objects while increasing locomotor behavior. Male Long-Evans rats (Rattus norvegicus, 80 days old) were given low-light access to an arena containing objects but were not forced to remain in the arena. On day 1, each subject was injected with saline (SAL). This session was used for familiarization with the apparatus and procedure. On days 2 and 3, four groups were given saline (SAL) or scopolamine (SCO, 1 mg/kg or 0.25 mg/kg), resulting in SAL-SAL, SAL-SCO, SCO-SAL, and SCO-SCO groups. Videotapes of these sessions were scored according to a standard protocol that allows separate quantification of locomotion, general activity, and object interaction behaviors. Scopolamine suppressed object investigation (both gross contact measures and indices of interaction character) whenever present. In contrast to Buhot et al. (using a forced-exploration situation), in this free-exploration context SCO also suppressed locomotor behavior. This study supports the conclusion that anticholinergics impair information gathering instead of affecting memory directly, which calls into question memory-related explanations of cholinergic treatments.

Molar characteristics of exploratory and investigatory behavior in the rat (Rattus norvegicus).

Despite clear functional significance, understanding of exploratory behavior is hampered by the lack of a careful descriptive account. This article reports extensive descriptions of rats' behavior in a stable environment and after environmental change. For 7 nights, 12 male Long-Evans rats (Rattus norvegicus) were given access to a large arena. Subjects budgeted session time differently across days, spending less time in the home cage and more time interacting with objects. Locomotion and general activities were typically unchanged over days. Several measures of object interaction showed systematic changes across sessions for the nonmanipulable object but not for the manipulable object. Finally, exploratory and spatial locomotor patterns were modified in response to the addition or removal of objects. These results indicate that exploratory and investigatory behaviors are lawful and orderly expressions of spontaneous behavioral organization.

The golden-mantled ground squirrel (Spermophilus lateralis) as a model for the effects of environmental enrichment in solitary animals.

It has been proposed that the brain effects induced by laboratory environmental enrichment may be a product of the social stimulation inherent in the standard enriched environment. This experiment was conducted in order to study the suitability of the golden-mantled ground squirrel Spermophilus lateralis (a solitary-living species) for studies attempting to dissociate social factors from other effects in brain and behavioral effects of environmental enrichment. Juvenile Spermophilus lateralis, born in the laboratory of mothers wild-caught while pregnant, were assigned singly to individual enriched conditions (I-EC) or impoverished (IC) conditions at 55-62 days (an age at which wild individuals would disperse from the natal burrow and live alone). After 30 days, the subjects were videotaped in two 10-min opportunities for exploration; following this, they were sacrificed and their brains dissected. Multiple indications of isolation stress were observed, including unusual difficulty in handling, stereotyped pacing behavior, and escape behaviors in the exploration arena. Comparisons between I-EC and IC showed no differences in whole-brain weight or weights of several brain regions. These results indicate that S. lateralis is not suitable for this type of study; in addition, this species' reported nonsociality is questioned, based on these subjects' reactions to isolation housing and field observations of social interactions in this species.

Social interactions among rats housed in grouped and enriched conditions.

Two experiments examine the hypothesis that brain differences found in environmental enrichment are due to differences in social interaction. Both experiments compare enriched versus group housed rats using videotape records of home cage activity, scored with a protocol developed by the authors. Experiment 1 examines social interactions in group and enriched housed rats in the first 30 days postweaning; In Experiment 2 rats were housed in the differential environments from 90 to 120 days of age, an age at which rats have been reported no longer to engage in play; in addition, weights of sections of the brain were obtained at sacrifice and these showed typical patterns of differences among rats from differential environments. Neither experiment revealed any consistent pattern of differences in social interaction, either by chi-square comparisons of overall profiles of social activity or by discriminant analysis applied to behavioral observations. No evidence was found in support of the hypothesis that play is responsible for the effects of environmental enrichment.