Flavor preferences,food intake,and weight gain in baboons (Papio sp.)

To evaluate the influence of flavor on ad lib consumption and on associated changes in body weight, female baboons, 7–15 years of age, served in two experiments with seven monkey chows which were identical except for flavor: lemon, orange, apple, sugar, fruit punch, chocolate, and unflavored. In the first experiment, two groups of animals (n=7 and 4) received five of the seven flavors, presented in daily pair-wise combinations. Analysis of quantities consumed demonstrated marked and consistent flavor preferences in individual baboons. Although specific preference varied between animals, total amounts consumed of the various flavors differed significantly, with rank ordering clearly evident. Overall food intake and body weights increased significantly over baseline values obtained with a standard, unflavored chow. In the second experiment, three baboons received chow of a preferred flavor for nine weeks. Amounts consumed and body weights increased significantly over baseline. These results indicate that flavored chows may be useful for producing a nonhuman primate behavioral model of obesity and for inducing animals to eat otherwise unpalatable diets.     

Pre‐conditioning activates adenosine utilization in a cost‐effective way during myocardial ischaemia

During pre‐conditioning the interstitial concentration of adenosine, in contrast to lactate, presents a die‐away curve‐pattern for every successive episode of ischaemia. This die‐away pattern might not necessarily be attributed to diminished adenosine production. The present study was undertaken to investigate whether pre‐conditioning alters the metabolic turnover of adenosine as observed by the lactate production during ischaemia. Interstitial levels of metabolites in pre‐conditioned (n=21) and non‐preconditioned (n=21) porcine hearts were monitored with microdialysis probes inserted in both ischaemic and non‐ischaemic tissue in an open chest heart model. Three subgroups perturbated with either plain microdialysis buffer (control), buffer containing adenosine (375 μM ), or buffer containing deoxyadenosine (375 μM ) were studied. All animals were subjected to 90 min of equilibrium microdialysis before 40 min of regional myocardial ischaemia and 120 min of reperfusion. Pre‐conditioning consisted of four repetitive episodes of 10 min of ischaemia and 20 min of reperfusion. Significantly higher levels of inosine and lactate were found in the ischaemic tissue of the pre‐conditioned subgroup receiving adenosine (P < 0.05) compared with the other two subgroups receiving deoxyadenosine and plain buffer, respectively. This difference was only valid for pre‐conditioned ischaemic myocardium, and hence equal amounts of inosine and lactate were produced in the non‐preconditioned ischaemic myocardium regardless of the presence of adenosine or deoxyadenosine. In the non‐ischaemic myocardium baseline levels of metabolites were measured in all subgroups. Pre‐conditioning favoured degradation of exogenous adenosine to inosine successively ending up in enhanced lactate production. This was probably because of the involvement of the hexose monophosphate pathway in the pre‐conditioned ischaemic myocardium. This route may therefore be supplementary in energy metabolism as a metabolic flow can be started by adenosine ending up in lactate without initial adenosine 5′‐triphosphate (ATP) investment. Utilization of adenosine in this way may also explain the successive die‐away pattern of adenosine seen in consecutive pre‐conditioning cycles.     

Cerebellar cortex and eyeblink conditioning: bilateral regulation of conditioned responses

We examined the role of the cerebellum in classical conditioning of the nictitating membrane response (NMR) of rabbits by comparing the effects of unilateral and bilateral cerebellar cortical lesions. Using extended preoperative conditioning to ensure high levels of learning, we confirmed that unilateral lesions of lobules HVI and ansiform lobe impaired conditioned responses (CRs) previously established to an auditory conditioned stimulus, but did not prevent some relearning with post-operative retraining. Bilateral lesions of HVI and ansiform lobe produced similar impairments of CRs, but also prevented subsequent relearning. Unilateral cortical lesions produced significant enhancement of unconditioned response (UR) amplitudes to periorbital electrical stimulation. Bilateral cortical lesions enhanced UR amplitudes to a lesser extent. Because there was no correlation between the degree of CR impairment and UR enhancement across the unilateral and bilateral lesion groups, the suggestion that the lesions impaired CRs due to general effects upon performance, rather than due to losses of learning, is not supported. Both sides of the cerebellar cortex contribute towards learning a unilaterally trained CR. This finding is important for the re-interpretation of unilateral, reversible inactivation studies that have found no involvement of the cerebellar deep nuclei in the acquisition of NMR conditioning. In addition, we found conditioning-dependent modifications of unconditioned responses that were particularly apparent at low intensities of periorbital electrical stimulation. This finding is important for the re-interpretation of studies that have found apparent changes in the UR of conditioned subjects after cerebellar lesions.     

Greater Resistance to Extinction of Electrodermal Responses Conditioned to Potentially Phobic CSs: A Noncognitive Process?

Previous results have suggested that electrodermal responses classically conditioned to potentially phobic CSs (e.g., pictures of snakes or spiders) are highly resistant to extinction and occur largely independently of cognitive expectancies. In order to test stringently for these possibilities, 144 college student subjects were administered differential classical conditioning acquisition and extinction paradigms while expectancies of the shock UCS were closely monitored. Half the subjects had potentially phobic CSs, whereas the other half had neutral CSs. Regardless of type of CS, during acquisition no evidence of electrodermal conditioning was found among subjects unaware of the CS?UCS contingency, nor was conditioning found on the pre-aware trials of subjects who became aware. During extinction, there was significantly greater resistance to extinction of electrodermal responses conditioned to potentially phobic CSs as well as a similar trend with expectancies of the UCS. However, when expectancies were equated, there was no greater resistance to extinction of electrodermal responses conditioned to potentially phobic CSs. Thus, while electrodermal responses conditioned to potentially phobic CSs did exhibit greater resistance to extinction, this conditioning was no more independent of expectancies than is conditioning with neutral CSs.     

Lesion of posterior parietal cortex in rats does not disrupt place avoidance based on either distal or proximal orienting cues

A current topic in neurobiology is the study of the role of various brain structures in processing of spatial information. The present study was aimed at elucidating the role of the rat posterior parietal cortex in performing a place avoidance task. Two variants of the task were used: an arena frame task, in which animals were trained to avoid a sector defined by local cues bound to the surface of a rotating arena, and the room frame task, in which the shock sector was defined with respect to distal room landmarks. The results showed that both control and lesioned rats were able to efficiently solve both tasks, while locomotion was not altered. These results suggest that the posterior parietal cortex is not crucial for the processing of either proximal or distal cues in place avoidance.     

Adrenaline turnover rates in the medial preoptic area and mediobasal hypothalamus in relation to the release of luteinizing hormone in female rats

The turnover rates of adrenaline in the medial preoptic area and mediobasal hypothalamus, areas which, respectively, include the cell bodies and terminals of luteinizing hormone-releasing hormone neurons, have been measured in female rats on pro-oestrus, the day of the preovulatory surge of luteinizing hormone, and on dioestrus, the preceding day. A rise in the rate of turnover was found in the medial preoptic area coinciding with the surge of luteinizing hormone in the late afternoon of pro-oestrus; the rate of turnover at this time was higher than at the same time on dioestrus. No changes in turnover rate were found in the mediobasal hypothalamus within either of these days.The results indicate that the adrenaline-containing projections to the preoptic area may be actively involved in the production of the spontaneous preovulatory surge of luteinizing hormone in rats.     

Operant Conditioning of Heart Rate: Somatic Correlates

The relationships between heart rate (HR) and several parameters of somatic activity were evaluated in human subjects when shuck avoidance was made contingent on either increases or decreases in HR. In order to depict any influence of the contingency specific 10 HR, somatic activity was controlled to varying degrees by instructions and the use of non-contingent control groups. When increases in HR were reinforced, the contingency we found to influence somatic activity but an effect specific to HR was also observed. When decreases in HR were reinforced, there was no evidence that HR were influenced independently of somatic activity. The result are discussed with respect to several current issues.     

Effects of signaled and unsignaled stressor on ECG T-wave amplitude

Thirty-six human subjects were exposed to noise (noxious US) under one of the following signal (CS) conditions: signaled stressor (SS), unsignaled stressor (NS) and a truly random control group (RS). Changes in ECG T-wave amplitude were used to index the stress response and the greatest change in amplitude occurred in the SS group. T-wave amplitude change was compared to HR change as an index of sympathetic stimulation and the former proved the more sensitive. The increased sympathetic responding in the SS condition suggests that a reliable signal may serve a physiologically adaptive purpose.     

Temporal discrimination in the cerebellar cortex during conditioned eyelid responses

Little is known about mechanisms used by the nervous system to encode time. In light of recent evidence, cerebellar cortex involvement in the learned timing of conditioned eyelid responses shows promise as an area of investigation into neural timing mechanisms. Lesion studies indicate that the cerebellar cortex is necessary for response timing, but do not rule out the possibility that response timing is encoded afferent to the cerebellum. To differentiate between precerebellar and cerebellar cortical timing mechanisms, rabbits were trained by pairing direct stimulation of mossy fibers in the cerebellum as the conditioned stimulus (CS) with an eyeshock unconditioned stimulus (US). We find that individual animals can produce diffently timed conditioned responses when trained with a mossy fiber CS that has been paired with the US at various interstimulus intervals. The fact that differently timed responses can be conditioned using constant-frequency stimulation of an invariant subset of mossy fibers as the CS suggests that timing information in the afferent input to the cerebellum is not essential. Two rabbits trained with single-pulse stimulation in the cerebellum as the CS also learned differently timed conditioned responses; suggesting that fiber recruitment during a stimulus train does not convey the necessary temporal coding to the cerebellar cortex. Together with the lesion data, these findings suggest that the learned timing of conditioned eyelid responses occurs in the cerebellar cortex. Received: 25 August 1997 / Accepted: 12 January 1998     

RESPONSE CONTINGENCY AND HUMAN GASTRIC ACIDITY

The purpose of this study was to investigate the relationship between avoidance behavior of human subjects and gastric acid changes. An intragastric radio transmitter was employed to record stomach acid secretion rates. The subjects were divided into two groups. The members of the Response-Contingent (RC) group were led to believe that they would be able to avoid a strong electric shock during the Test phase of their session. In the No-Response (NR) group, subjects were correctly told that they would be without means of avoiding shock. The results demonstrated that (a) subjects could not be differentiated according to gastric acid secretion rate strictly on the basis of whether or not they made an avoidance response to an aversive stimulus; (b) a non-significant majority of subjects in both groups exhibited decreased gastric acid secretion rates during the Test phase; and (c) both groups showed a significantly faster rate of gastric acid secretion during the Post-Test phase than during the Test condition.