Consummatory responses to taste stimuli in the hedgehog (Erinaceus europaeus)

Consummatory responses of hedgehogs to several concentrations of five chemical stimuli (sucrose, sodium chloride, sodium saccharin, quinine hydrochloride and formic acid) were investigated using the 24 hr two-bottle preference test. Hedgehogs distinguished between water and at least some concentrations of each stimulus tested by regulating their intake from each bottle, according to preference and water balance needs. Compared to other mammals, hedgehogs did not fall at either extreme of the sensitivity scale for preference or rejection, although they were placed with the group most tolerant to sodium chloride. When percentage preference was used as the indicator, an overall view placed hedgehogs and opossums as most similar in taste profiles and their similarities and differences to each other and to other insectivores are discussed. An argument is made for the need for standardization of preference data recorded as a ratio of intake (ml) to body weight (g) for each animal's daily consumption of water and solutions to be available in raw form to all investigators.     

Early weight gain and behavioral responsivity as predictors of dietary obesity in rats

Variance in diet-induced weight gain was examined for possible relationships with variations in early weight gain and three tests of behavioral responsivity. Female Sprague-Dawley rats were reared in litters of 4, 8, or 20. When animals reached adulthood, each animal's acoustic startle reflex, tail-pinch feeding responses and activity in an open field containing a palatable food were assessed. After completing these behavioral tests, rats were exposed to either palatable foods or a control diet for 59 days, following which all subjects were maintained on the control diet for 66 days. Body weights, food intakes, and naso-anal lengths were measured. Preweaning body weight gain for all rats correlated positively with later diet-induced weight gain. Rats reared in litters of 4 or 20 both gained less weight after exposure to palatable foods than did rats reared in litters of 8. Diet-induced weight gain correlated positively with magnitude of acoustic startle reflex and with latency to eat in response to tail pinch. These results tentatively identify specific predictive factors which may be useful in future studies of dietary obesity.     

Reactivity to different saccharin concentrations as a function of testing procedure and alterations in body weight of intact and oophorectomized female rats

Two studies compared saccharin preference in oophorectomized and intact rats. Using a one bottle test, reliable preference difference between surgical groups were found at 0.1%, 0.4% and 0.75% saccharin concentrations. Using a two bottle test, reliable preference differences were found at the 0.4% and 0.75% concentrations. Although several differences were weight related, neither Marks' nor Zucker's hypotheses were supported.     

Mobile apparatus for rapid cooling of a caged animal

A mobile apparatus for rapid cooling of a laboratory animal such as the caged rat or cat or a monkey confined to a primate restraining chair is described. Air is circulated through convoluted copper heat exchangers immersed in a mixture of ethanol and solid CO₂ with a temperature of ?60° ± 5°C. The cooled air is then blown into the animal's cage or chamber. The ambient temperature in the chamber of a primate restraining chair can be lowered from 25–26°C to 4°C within 2 to 4 min. When this cooling apparatus is coupled to a temperature controller, the temperature inside the animal's chamber can be maintained easily and accurately at a low level for an extended period of time. Applications for studies of physiological and behavioral thermoregulation are discussed.     

Rostral medial preoptic area lesions' influence on female estrous processes and LHRH distribution

The effect of bilateral electrolytic lesions placed in the rostral medial preoptic area (MPOA) of the 26 day old rats was observed on each animal's onset of puberty, vaginal cyclicity, sexual receptivity and LHRH distribution. Lesions located in the lower two-thirds of the rostral MPOA induced persistent vaginal cornification and polyfollicular ovaries. Lesions limited to the dorsal third of the periventricular region of the rostral MPOA were associated with repetitive pseudopregnancy as indicated by repeated series of diestrous smears separated by one or two proestrous or estrous smears and ovaries dominated by corpora lutea. The age of onset of puberty was not altered by any of these lesions. Receptivity induced by estrogen alone or by estrogen followed by a low dosage of progesterone was lower in ovariectomized females with lesions than in control animals. Immunocytochemical identification of LHRH containing neurons using Sternberger's peroxidase-antiperoxidase method revealed LHRH reactive fibers in the MPOA in both lesioned and control animals. A greater reduction in immunopositive LHRH fibers was seen on the same side of the median eminence at the level of the tuberoinfundibular sulcus as that containing the larger damage in the MPOA.     

CCK,endogenous insulin condition and satiety in free-fed rats

Cholecystokinin (CCK) has been shown to elicit insulin secretion and increased insulin availability has been shown to correlate with increased satiety attributed to reduced size of spontaneously occurring meals. The present experiment, however, clearly showed that CCK was effective in suppressing food ingestion in free-fed rats independent of the animal's level of insulin. Rats were tested with 1, 2 and 4 μg/kg of CCK-octapeptide (Sincalide, Squibb) during a baseline (pancreatic-normal) period, an insulin-poor state (streptozotocin diabetic) and an insulin clamped condition (diabetic treated by a minipump). CCK produced a highly significant (p<0.01) reduction of food intake compared to saline, control injections regardless of the insulin conditions of the animals. Higher doses of CCK were more effective than lower doses during all three periods of study. CCK and hyperinsulinemia function independently if they produce satiety or reductions in food intake.     

The multiplicity of biological oscillators in the control of circadian running activity in the rat

The purpose of this experiment was to determine the degree to which a circadian running activity could be controlled by multiple biological oscillators within a single organism. Twelve male rats, housed in running wheels, had access to food from noon to 1 p.m. daily. In addition to this noon or fixed feeding, the rats received a moving feeding during which they had access to food for 1 hr every 25 hr. These two circadian feedings had a continually shifting phase relationship to each other. The animals responded to this regime by displaying separate bursts of running activity which were in relative coordination. Each animal's behavior shifted between the three following general patterns: (1) one cycle of activity, either before the fixed or the moving feed; (2) two bursts of activity, one before the fixed feeding and one preceding the moving feeding or (3) a burst of activity not entrained to either one of the feedings but rather free running between the two. When the animals were subsequently offered continuous access to food, 10 of the 12 rats maintained two bursts of activity.     

Interactions between dopamine and γ-aminobutyrate in the substantia nigra: Implications for the striatonigral output hypothesis

Experiments employing a rodent circling model were conducted to test the predictive capacity of the theory which states that striatonigral γ-aminobutyrate neurones transmit striatal information influencing the animal's locomotion and orientation. In agreement with this proposal, blocking nerve conduction in one substantia nigra with procaine, or nigral γ-aminobutyrate receptors with bicuculline administered stereotaxically, frequently forced rats to move ipsiversively to systemic apomorphine, as though the treatment had impaired striatonigral transmission on that side of the brain. Attempts to reverse the direction of apomorphine circling by stimulating γ-aminobutyrate receptors with muscimol, by facilitating the amino acid's action with flurazepam, or by increasing its synaptic concentration either with a breakdown inhibitor (ethanolamine O-sulphate or 4-amino-hex-5-enoic acid) or an uptake blocker (cis-1,3-aminocyclohexane carboxylic acid) in one nigra, proved unsuccessful. In fact, ethanolamine O-sulphate, flurazepam and muscimol all gave the appearance of hindering rather than enhancing the passage of striatal-derived motor information through the nigra. Broadly speaking, these drugs gave predictable behavioral responses from the ventromedial thalamus, suggesting they were acting in accordance with known mechanisms.The anomalous behaviour with ethanolamine O-sulphate may be attributed to its elevating γ-aminobutyrate levels in other brain areas, since similar ipsiversive rotations occurred if γ-aminobutyrate catabolism was prevented at a wide variety of extranigral sites. A simple explanation for the paradoxical ipsiversive behaviours produced by intranigral flurazepam or muscimol in combination with systemic or intracerebral injection of dopamine agonists, is that they act via presynaptic receptors to inhibit the release of endogenous γ-aminobutyrate and thereby impede striatonigral outflow ipsilaterally.     

Effects of ovariectomy and subsequent estradiol replacement on intake of sweet solutions

Neither ovariectomy nor subsequent estradiol replacement has any effect on the female rat's ingestion of saccharine solutions of varied concentrations. This holds whether or not the animal has had experience with the sweetener prior to ovariectomy. Removal of the ovaries enhances intake of glucose solutions while replacement of estradiol reduces the glucose intake of ovariectomized rats. Modifications of glucose ingestion by ovarian hormone manipulation may reflect the influence of these hormones on mechanisms controlling food ingestion rather than any separate effect of estrogens on preference for or ingestion of sweet solutions.     

Psychophysical mapping of reward system operating characteristics: Utility transforms of stimulation duration

By applying signal detection theory to the utility scaling of rewarding brain stimulation, we have obtained a psychophysical function which maps duration of medial forebrain bundle (MFB) stimulation to reward value. Six 120 day-old Charles River rats, implanted with bipolar electrodes directed at the MFB, were trained to discriminate between high and low frequency tones for brain stimulation durations which ranged from .2 sec to 8.5 sec. The ratios of manipulated reward durations formed between the two types of correct response produced changes in the animal's response bias, as measured by beta, which were used to derive utility transforms of brain stimulation duration. We propose an optimizing differential equation system, based on the derived utility function, which models the total utility of rewarding electrical stimulation as subject to its marginal utility. Our results suggest that the brain scales activity in the reward pathway as a stimulus falling on a prothetic continuum, thereby allowing fine distinctions to be made between motivational stimuli across a wide range of stimulation.     

Plasma catecholamines: Exaggerated elevation is associated with stress susceptibility

The ability to survive acute stress differs markedly between individual rats. In order to determine whether ability to survive stress is correlated with aberrations of the sympathoad-renomedullary response, we measured plasma and tissue catecholamines (CA's) and blood glucose before, during, and for 5 hr after footshock stress. Splenic weights and liver glycogen were measured at sacrifice. Rats that survived the post-stress period (survivors) were compared to rats that did not survive (lethalities). Our results revealed a malignant rise of plasma CA's in lethalities beginning at stress onset and continuing until death. Plasma CA's in lethalities during stress were over 200% of those in survivors, whereas tissue CA's were reduced in both groups. Paradoxically, responses to circulating and neuronal CA's appeared to be diminsished in lethalities. Lethalities, but not survivors, became profoundly hypoglycemic after stress, in spite of their elevated plasma CA's. Likewise, evidence of significant splenic contraction was absent in lethalities. Thus, elevated plasma CA concentrations and reduced target organ responsiveness are associated with stress-induced lethality.     

System for instrumental motor conditioning in cats and temporal parameters computation

A conditioning system for training cats to carry out typical prehension movements which exhibit the highest degree of reproducibility is described. It is composed of the following: (a) a cage which is furnished with a particular foot-board to check the starting position of the forelimbs; (b) an electropneumatic machine for transporting a food pellet and (c) an electronic device for controlling the right animal's starting position, randomizing the time of nourishment, and quantifying the temporal data of the forelimb movement—the reaction time (RT) and the execution time (ET).     

Choices by rats between water and solutions of GABA or other amino acids

Responses differed widely when rats were offered choices between water and solutions of GABA, its isomers alpha-aminobutyric acid (AABA) and alpha-aminoisobutyric acid (AIB), or of another 4-carbon amino acid, threonine. They preferred solutions of threonine and AABA starting at concentrations of about 30 mM; preference for threonine declined when its concentration was 330 mM or above. Rats never preferred GABA or AIB, but instead avoided these amino acids when concentrations were approximately 100 mM or above. Control rats showed strong preferences for drinking from a given location. Limited studies with humans showed variations in the concentrations at which they could detect GABA; the mean was about 0.06 mM, a concentration far below that at which rats began to avoid this amino acid. The ability of dietary GABA to depress food intake of rats (as shown in earlier studies) does not seem related to a uniquely high sensitivity to its gustatory qualities.     

Effects of eating,meal cues and ventromedial hypothalamic lesions on serum corticosterone,glucose and free fatty acid concentrations

Male hooded rats were fed once daily for 14 days with 1-hr access to food mash and water to establish the stimuli of the experimenter's entrance into the animal quarters (Experiment 1) or placement of the rat's cage into a chamber (Experiment 2) as cues for a meal. Rats without brain lesions failed to exhibit changes in serum concentrations of glucose or free fatty acids (FFA) to meal cues while exhibiting declines in serum corticosterone concentration. In response to meal consumption, these rats exhibited robust increases in glucose and decreases in FFA and corticosterone levels. VMH lesions (Experiment 2) accentuated glucose declines and diminished corticosterone declines in response to meal consumption or a meal cue. The results suggest a role of the VMH in pituitary-adrenal inhibition, but also indicate the importance of considering the roles of anticipatory metabolic activity and emotional reaction in the regulation of metabolic substrates and pituitary-adrenal activity.     

Involvement of hippocampal serotonergic activity in age-related changes in exploratory behavior

The effect of aging on exploratory behavior was investigated in adult (5 month) and aged (28 month) CB6F₁ mice. During the first 10 minutes of the test session, aged mice made fewer head dip responses and spent less time exploring the novel stimuli. Because the aged mice were observed to subsequently increase their duration of exploration, it was suggested that the initial differences in exploration reflected a suppression of exploratory behavior by the aged mice. Immediately after behavioral testing, mice were sacrificed and hippocampal serotonin (5HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were determined. While 5HT concentrations were not found to be significantly altered with age, significant increases in 5-HIAA concentrations and in the ratio of 5-HIAA/5HT were observed in the aged mice. Further, the elevation in the 5-HIAA/5HT ratio was found to be significantly correlated with age-related differences in the duration, but not the frequency, of head dip responses. In view of this finding, it was suggested that alterations in serotonergic function with age may selectively affect specific aspects of an animal's response to novel stimuli.     

A fully automated open-field apparatus incorporating rearing detection

An open-field instrument is described utilising a versatile rsistance detection system for measuring ambulation in mice and rats. The ambulation detector may sense horizontal and vertical ambulation or horizontal, vertical and diagonal ambulation in the ground plane, depending on mode selection. In addition, it can respond to an animal's presence on particular plates or areas in a ‘touch toggle’ fashion. A separate circuit records height selected rears by way of capacitance effects. The rearing detection surface consists of a moveable perforated metal grid above the open-field. The complete open-field system is controlled by a process-timer and facilities for ‘real time’ recording are incorporated. Details of accuracy, reliability and mode of use are reported.     

Salt preference in rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain)

Brattleboro rats are homozygous for diabetes insipidus (HO-DI), lacking the ability to synthesize vasopressin. Besides increasing water consumption, HO-DI rats may compensate for their excessive renal water loss by reducing their intake of and preference for substances that elevate plasma osmolarity. In two experiments we assessed this possibility. In Experiment 1, salt preference of HO-DI and control Long-Evans (LE) rats was measured by presenting the rats with two tubes: one filled with water and the other with NaCl. In the first part of the experiment, 18 NaCl concentrations were presented in increasing order (from 6 to 300 mM). In the second part, other groups of HO-DI and LE rats were presented with 6 concentrations of NaCl, ranging from 6 to 450 mM in either increasing or decreasing order of concentrations. In Experiment 2, preference for 6 concentrations of citric acid ranging from 0.1 to 6 mM was assessed. With NaCl concentrations greater than 100 mM, intake and preference declined rapidly for the HO-DI group but very gradually for the LE group. In contrast, the HO-DI rats preferred all citric acid solutions more than LE rats. The results suggest that HO-DI rats compensate for their inability to concentrate urine not only by increasing water consumption, but also by decreasing consumption of and preference for salty solutions.     

Maternal and paternal pheromones in gerbils

Mongolian gerbil pups are attracted to maternal and parental nest odors. They approach these odors in preference to the odors of either virgin females or clean bedding. The pups do not distinguish between maternal or parental odors and odors of unfamiliar lactating females. Thus lactating female gerbils produce a maternal pheromone similar to that of rats and other rodents. Attraction to the pheromone develops by two weeks of age and persists for at least three weeks. The primary source of the pheromone is the mother's enlarged ventral scent gland. Removing this gland eliminates maternal attractiveness. Development of attraction to maternal scent gland odors depends on prior exposure to them. Pups raised by mothers lacking scent glands do not approach lactating females that have scent glands. The father's presence during development alters the responses of gerbil pups to odors of other males. Pups raised by both parents avoid odors of other pairs with young, whereas pups raised by their mothers only do not. Pups are not attracted to their father's odors.     

Loss of place specificity in hippocampal complex spike cells of senescent rat

Firing characteristics of “place” cells in dorsal CA1 of hippocampus were recorded from 5 young (10–14 months) and 5 old (25–29 months) Fischer-344 rats. Animals were trained to obtain food reward on a radial 8-arm maze. Entry to the arms was controlled by the experimenter so that all 8-arm were visited in random sequence from trial to trial. For each cell, 8 such trials were given (64 arm choices) in order that statistical reliabilty could be obtained for firing rates over the maze surface. Single unit activity and the animal's position on the maze were continuously monitored by digital computer. Twenty-seven cells from each age group were studied in this way. No statistically significant differences were found between age groups in unit spike height, width or firing rates. A large, statistically significant difference, however, was found in both spatial specificity and reliability of firing patterns from trial to trial. These results are discussed in terms of a possible deficit in spatial information processing in the older animals.     

Does the Race/Ethnicity or Gender of a Physician's Name Impact Patient Selection of the Physician?

This study's objective was to examine the extent to which individuals exhibit a preference for physicians based upon the race/ethnicity and gender of a physician's name. We conducted an online survey of 915 adults, who viewed a comparative display of four physicians' quality performance. We randomized the name of one physician, whose quality performance was equal to that of one physician and better than two other physicians, to be either typically African American male, African American female, white male, white female, or Middle Eastern (gender ambiguous). In regression models, participants more frequently selected the physician with the randomized name when displayed with a white male name, compared to when presented with an African American male, African American female, or Middle Eastern name (ORs ranging from .59 to .64). White and male study participants exhibited this pattern, while racial/ethnic minority participants did not. If the hypothetical choice bias observed here translates to people's actual selection of physicians, it could be a contributing factor for why women and racial/ethnic minority physicians have lower incomes than white male physicians.