P-653 The impact of clinical factors on the number of MII oocytes

Study question

What is the impact of clinical factors on number of MII oocytes retrieved after ovarian stimulation?

Summary answer

Using selected clinical factors, Machine Learning models are capable of accurately predicting the number of MII oocytes.

What is known already

There are well known clinical factors that correlate with the number of MII oocytes that can be harvested as a result of ovarian stimulation. When deciding on an appropriate stimulation protocol and gonadotropin doses, gynecologist mainly take into consideration patient’s age and selected markers of ovarian reserve. The choice of protocol and dosage itself influences the outcome of the stimulation. What is still debated is to what extent each of the aforementioned factors influences the final outcome of the stimulation. Recent progress in Machine Learning now allows to develop predictive model that address this question.

Study design, size, duration

In the retrospective study, data collected between Nov 2014 and Jan 2021 was analyzed. Dataset consisted of 8428 ovarian stimulations undergone by 5692 patients at the Invicta Fertility Clinics. Eight clinical factors chosen by gynecologists were used in the modelling phase. Study’s inclusion criteria set boundaries on age (between 24 and 46 years), Anti-Müllerian hormone (AMH) (lower than 15 ng/ml) and the number of MII oocytes retrieved as a result of stimulation (fewer than 20).

Participants/materials, setting, methods

For MII oocytes prediction a Machine Learning model based on gradient boosting technique was created. The model contains 500 decision trees with 16 leaves and maximal depth of 64 nodes. Model’s performance was evaluated with median of absolute error and root mean square error (RMSE) metrics. To validate the model, a k-fold cross validation was used with 5 separate folds. Importance of aforementioned clinical factor in the model was assessed with Shapley values.

Main results and the role of chance

To predict the number of MII oocytes, following factors were included: AMH, antral follicle count on the start of stimulation (AFC), patient age, number of MII oocytes retrieved in the last stimulation (available for 37% of IVF cycles), daily gonadotropin dose in days 1-3 and 4-7, type of IVF protocol and the presence of Polycystic Ovary Syndrome (PCOS). Model achieved an RMSE of 3.38 and a median absolute error of 2.09. AMH was proved to have the greatest impact on the predicted number of MII, with an average impact on the model’s output magnitude (SHAP) equal to 1.40. AFC was identified as the second most important variable (SHAP=0.78). The number of MII oocytes from last stimulation (SHAP=0.21), daily gonadotropin dose used in days 1-3 of stimulation (SHAP=0.18), patient age (SHAP=0.17), daily gonadotropin dose days 4-7 of stimulation (SHAP=0.08), type of protocol (SHAP=0.06) and PCOS (SHAP=0.01) were far less significant to the prediction outcomes. Our model suggests that AMH is over 8 times more important for the prediction of number of retrieved MII than age. The algorithm found that 300 IU dose of gonadotropin administered on days 4-7 of stimulation actually lowered the number of retrieved MII oocytes.

Limitations, reasons for caution

Only 5% of study patients had PCOS, which might contribute to low importance of this factor in the model.

Wider implications of the findings

Research shows that AMH and AFC are the most impactful factors in MII oocytes prediction by a large margin and should be considered in a first place by gynecologists while choosing gonadotropin dose. To grow more MII oocytes, clinicians should use higher gonadotropin dose in days 1-3.

Trial registration number

Not applicable

P-666 Detecting gene variants correlated with MII oocytes developed during ovarian stimulation

Study question

Is it possible to identify genetic factors influencing the number of MII oocytes produced in the course of ovarian stimulation?

Summary answer

Applying data exploration techniques made it possible to identify gene variants that markedly improved ability to predict the number of MII oocytes to be retrieved.

What is known already

There are well known clinical factors that correlate with the number of MII oocytes that can be retrieved as a result of ovarian stimulation. When deciding on an appropriate stimulation protocol and gonadotropin doses, clinicians mainly take into consideration patient’s age and selected markers of ovarian reserve. The choice of protocol and dosage itself influences the outcome of the stimulation. Certain genes have been shown to participate in the regulation of the expression of FSH, LG and HCG receptors although direct influence of genetic background on the number of MII oocytes still need to be elucidated.

Study design, size, duration

In the retrospective study, data collected between 05/08/2013 and 28/10/2020 was analyzed. The dataset consisted of 516 ovarian stimulations undergone by 264 patients as well as and 605 unique changes found in sequence data for 14 genomes (AMH, AMHR2, FSHB, FSHR, LHB, LHCGR, PRL, PRLR, AR, ESR1, ESR2, GDF9, BMP15, SOX3). Inclusion criteria set boundaries on women’s age (between 24 and 46 years) and Anti-Müllerian hormone results (AMH) (lower than 15).

Participants/materials, setting, methods

Neural Network model based on 7 statistically important clinical factors was trained to predict the number of MII oocytes and used as a benchmark for model including genetic factors. A model’s performance was evaluated with median of absolute error metric and validated on the test subset. Feature importance in the model was assessed using Shapley values. Important gene variants were selected using grouping algorithm Self Organizing Map and haplotype block generation algorithm Four Gamete Rule.

Main results and the role of chance

In the benchmark model, following clinical factors were included: AMH, antral follicle count on the first stimulation day (AFC), patient age, number of MII oocytes and denuded cumuluses obtained in the previous cycle (available for 37% of IVF processes), IVF protocol type and the presence of Polycystic ovary syndrome (PCOS). The trained model obtained median absolute error equal to 1,62. Out of all genetic data, 3 important variant combinations (haplotypes IV40-8, IV22-2 and a group of 6 variants labeled IV8-6) included in table 1 were identified. The addition of those 3 factors to the model resulted in a decrease in the median absolute error by 0.19 (12%). The average impact on the model output magnitude (mean SHAP) of genetic factors was greater than the impact of the chosen IVF protocol or the presence of PCOS. The presence of haplotypes IV40-8 and IV22-2 increased the expected number of MII oocytes, whereas the grater the number of variants grouped as IV8-6 found in the patient the lower the predicted number of MII oocytes. Additionally, if the patient’s previous cycle results were not given, the impact of genetic factors on the model magnitude was comparable to AFC on the first day of stimulation.

Limitations, reasons for caution

Considering the number of gene variants found (605) And the sample size of the study a broader study allowing for a better understanding of the influence of less frequently observed variants would be beneficial.

Wider implications of the findings

Research shows including gene factors in MII oocytes prediction could substantially increase the precision of MII oocyte predictions for patients and especially for patients undergoing ovarian stimulation for the first time. Knowing the expected MII oocytes count could help clinicians with deciding on gonadotropin dosing.

Trial registration number

Not applicable

Application of a user-friendly comprehensive circulatory model for estimation of hemodynamic and ventricular variables

Purpose

Application of a comprehensive, user-friendly, digital computer circulatory model to estimate hemodynamic and ventricular variables.

Methods

The closed-loop lumped parameter circulatory model represents the circulation at the level of large vessels. A variable elastance model reproduces ventricular ejection. The circulatory model has been modified embedding an algorithm able to adjust the model parameters reproducing specific circulatory conditions. The algorithm reads input variables: heart rate, aortic pressure, cardiac output, and left atrial pressure. After a preliminary estimate of circulatory parameters and ventricular elastance, it adjusts the amount of circulating blood, the value of the systemic peripheral resistance, left ventricular elastance, and ventricular rest volume. Input variables and the corresponding calculated variables are recursively compared: the procedure is stopped if the difference between input and calculated variables is within the set tolerance. At the procedure end, the model produces an estimate of ventricular volumes and Emaxl along with systemic and pulmonary pressures (output variables). The procedure has been tested using 4 sets of experimental data including left ventricular assist device assistance.

Results

The algorithm allows the reproduction of the circulatory conditions defined by all input variable sets, giving as well an estimate of output variables.

Conclusions

The algorithm permits application of the model in environments where the simplicity of use and velocity of execution are of primary importance. Due to its modular structure, the model can be modified adding new circulatory districts or changing the existing ones. The model could also be applied in educational applications.

[Stereotactic biopsy and brachytherapy in the diagnostics and treatment of brain tumors--preliminary report]

Promising results have been obtained using brachytherapy in the treatment of brain tumors. Between November 99 and August 2000, 28 patients with brain tumors (15 newly diagnosed gliomas, 11 recurrent gliomas, 2 metastases) underwent implantation of temporary iridium 192 sources with stereotactic technique. This group received external beam radiation therapy (45 Gy) following implantation. Patients were followed-up with CT scans every 3 months. Serious complications occurred in two patients (postradiation brain oedema). Median survival has not been assessed due to short follow-up period and small number of patients. Further clinical assessment is required especially long-term follow-up. Brachytherapy appears to be a useful technique for the treatment of selected brain tumors.

[The case of giant pleomorphic adenoma of the parotid gland with the malignancy features]

The aim of the study was showed the case of patient aged 41 years, treated in the Otolaryngology Department of Military Medical Academy because of giant pleomorphic adenoma of the parotid gland with the malignancy features. After performed of the BAC of tumour, the CT of neck and the scintigraphy of salivary glands the patient qualified for operation. The tumour resected with capsule and the superficial lobe of the left parotid gland, conservating of function of the facial nerve. The histopathologic examination proved the mucoepidermoid carcinoma in the pleomorphic adenoma didn't infiltrate of capsule. After oncologic consultation the patient had not of complementary radiotherapy, because the operation was radical and the carcinoma had a low radiosensitivity. The above mentioned case confirms of the reports, that the pleomorphic adenoma can undergo of malignancy changes, however the gigantic tumour doesn't write off possibility of operating success.

[Clinical and immunohistoenzymatic investigations in patients with vasomotor and perennial allergic rhinitis]

The aim of our study was evaluation of the results of clinical examination in patients with vasomotor and perennial allergic rhinitis and assessment of number of blood vessels, nerve fibres and mast cells on the basis of immunohistoenzymatic examination. There were 42 patients examined aged from 18 to 50 and divided into three groups: I--16 patients with vasomotor rhinitis and II--14 patients with perennial allergic rhinitis and III--12 patients (control) with nasal septum deviation. On the basis of the patient's history data, clinical otorhinolaryngologic examination and active anterior rhinomanometry the patients were qualified to bilateral inferior turbinectomy. The nasal mucosa removed during surgery underwent immunohistoenzymatic examination using the monoclonal antibody against the tryptase of mast cells (MCT company, DAKO), the endothelin of blood vessels (EC - DAKO) and the neurospecific enolase (NSE - DAKO). In examined groups of patients with vasomotor and perennial allergic rhinitis and control group similar escalation of clinical symptoms expressed by means of points index were stated. In immunohistoenzymatic studies the differences in mean number of blood vessels and nerve fibres between examined groups were not statistically significant, however statistically significant difference concerned higher number of mast cells patients with vasomotor rhinitis in comparison to perennial allergic rhinitis.

[Delay inhibition of the active avoidance reflex and intertrial responses in rats in the shuttle box]

A diminished probability of avoidance response in early phases of a warning signal was revealed with salient signals given after short intertrial intervals. The inhibition of the delay in avoidance response is due to an interaction of the safety state conditioning and the excitation elicited by onset of warning signal.

Escape from shock versus escape from shock accompanied by a visual stimulus in rats

Two groups of 15 rats each were trained in a shuttle box to escape foot-shock either unsignalled or presented in compound with a visual cue: darkness. The visual cue presented in shock compartment amplifies the behavioral tendency actually prevailing in the response repertory of the rat. During the 1st session the compound enhanced the species-specific flight resulting in shortening of the rat's escape latency. Thereafter, during subsequent sessions, darkness exaggerated resistance to enter the other compartment; thus escape latencies were longer under compounded than under unsignalled procedure. The darkness cue reduces the intertrial response rate relative to the unsignalled group. This latter finding supports the discrimination model of the effect, since the compound helps the animals to discriminate the illuminated "safe" period between trials from the aversive shock period. Our data seem to suggest that the darkness presented synchronously with escapable grid-shock acquires aversive properties.

How do rats cope with the two-way escape problem in a homogeneous shuttle box?

The behavior of 25 rats trained in a homogeneous shuttle box to escape unsignalled grid-shock was analyzed. Three categories of escape were distinguished: (1) species-specific fly away from the charged grid, (2) long-latency crossing preceded and accompanied by other behaviors that compete with the escape response, and (3) short-latency escape which followed an anticipatory postural pose. The animals displayed species-specific fly away only during the initial trials of a session. Subsequently long-latency crossings develops, reflecting a resistance to enter the opposite compartment. A measure based on a comparison of escape latency distributions in the two halves of the 1st session discriminates between good and poor learners. Subgroups of good and poor learners differed in performance efficiency in all five training sessions. Good learners were able to overcome the resistance to enter the opposite compartment and recall the learned short-latency escape.

[Macroscopic estimation of the placenta using a morphometric grid. Part I: pre-pregnancy and post-pregnancy diabetes mellitus]

Kurt Benirschke has once written that the placenta provides the most accurate records of prenatal history of foetus. Our study included 104 placentas obtained from pregnancy complicated by diabetes. An obstetrician did the planimetric estimation directly after delivery. A measurement of lesions was conducted with using a special own idea's morphometric grid that allowed us to evaluate a placental surface and a relative size of change statement in a very quick and convenient way. Our method is very useful for making a quantitative estimation of pathological changes in the chorionic plate of placenta.

[Macroscopic assessment of the placenta using a morphometric grid. Part III: preterm delivery]

Kurt Benirschke has once written that the placenta provides the most accurate records of prenatal history of foetus. Our study included 198 placentas obtained from pregnancy complicated by preterm delivery. An obstetrician did the planimetric estimation directly after delivery. A measurement of lesions was conducted with using a special own idea's morphometric gird that allowed us to evaluate a placental surface and a relative size of change statement in a very quick and convenient way. Our method is very useful for making a quantitative estimation of pathological changes in the chorionic plate of placenta.

[Macroscopic assessment of the placenta using a morphometric grid. Part II: other selected pathologies]

Kurt Benirschke has once written that the placenta provides the most accurate records of prenatal history of foetus. Our study included 2498 placentas obtained from pregnancy complicated by pregnancy-induced hypertension (PIH), intrauterine growth retardation (IUGR) and epilepsy. An obstetrician did the planimetric estimation directly after delivery. A measurement of lesions was conducted with using a special own idea's morphometric grid that allowed us to evaluate a placental surface and a relative size of change statement in a very quick and convenient way. Our method is very useful for making a quantitative estimation of pathological changes in the chorionic plate of placenta.

Effects of octreotide on propylotiouracil-induced goiter in rats: a quantitative evaluation

To evaluate the possible antigoitrogenic effect of somatostatin, the influence of long-acting somatostatin analog--octreotide--on experimental goiter developed in rats treated with propylthiouracil was examined. Goiter formation was assessed by measurement of the main histological compartments of the thyroid as well as by morphometric analysis of the vascularization and blood supply of the gland. Although treatment with octreotide did not prevent the goiter formation, it clearly reduced blood supply and vascularization of the thyroid and counteracted propylthiouracil-induced increase in the relative volume of follicular epithelium. To conclude, the somatostatin analog--octreotide--is effective in reduction of goiter vascularisation. This finding provides a rationale for the clinical trials of the treatment of hypervascular goiter by somatostatin analogs.

CS modality transfer of two-way avoidance in rats with central and basolateral amygdala lesions

Post-lesion acquisition of two-way avoidance and subsequent transfer to two warning signals (conditioned stimulus, CS) of different modality were investigated in 60 rats. In Experiment I the animals were originally trained with less salient (darkness) CS, then transferred to more salient compound (darkness and white noise), and finally to white noise CS. The opposite arrangement of the conditioned stimuli (CSi) during the subsequent stages was employed in Experiment II. In control animals, avoidance acquisition was faster and the intertrial responding (ITR) rate lower with the auditory than with the visual CS. Lesioned rats learned avoidance responses more slowly, independently of CS modality. The transfer to other CSi revealed dramatic between-group difference in the level and consistency of avoidance response, shuttle-box latencies and ITR rate. In control animals, transfer to more salient CSi enhanced avoidance performance, whereas change to less salient CS decreased it. Rather small changes in shuttle-box performance and consistency of avoidance response due to CS modality were seen in rats with the basolateral lesions. In contrast, central nucleus injury caused a strong deterioration in the avoidance transfer, especially when the visual CS followed the acoustic one. The results indicate differential involvement of the basolateral and central amygdala nuclei in stimulus-processing mechanisms of instrumental defensive behavior.

[The study of individual differences as a method for dividing into stages the acquisition of a complex reflex]

Two-way active avoidance learning is a complex task characterized by a high level of interindividual variability. We have demonstrated in our previous paper that rats with different rate of learning vary in expression of freezing responses, which reflects a conflict tendency not to re-enter the previous chock compartment [4]. In the present work we analyzed as main indices the proportions of avoidance, rapid escape, and freezing responses and their distribution within a session. Sequences of occurrence of these three types of responses were examined in groups of rats with different success of avoidance learning. The obtained results confirmed a hypothesis that overcoming the conflict tendency was a separate stage of learning which preceded avoidance response appearance and subsequent stabilization. Only in rats which failed to learn and develop avoidance responses within the first session, freezing responses were observed in successive session being indicative of reappearance of the conflict tendency. The intensity of the conflict tendency did not depend on the type of the first response of an animal (fleeing or freezing) to an unexpected aversive stimulus.

[The dependence of learning an active avoidance reaction on overcoming a problem-solving situation in a shuttle box]

The two-way avoidance procedure dramatically differs from the one-way procedure in rate of learning. The present study was conducted to prove that retardation of the two-way avoidance acquisition resulted from development of the behavioral conflict tendency not to reenter the previous shock compartment. Cluster analysis of avoidance response indices divided rats into three distinctive classes. The occurrence of avoidance, escape, and freezing responses in the first session was analyzed in these three groups. Freezing during the shock action reflected the conflict tendency and showed a negative correlation with avoidance response indices. Only the rats which overcame the conflict and performed at least one avoidance reaction toward the end of the first session significantly improved their avoidance score in the following session. Discriminant analysis of indices of the three reaction types in the first session revealed sufficiency of these indices for prediction of the success in avoidance learning in subsequent sessions. Our results proved the hypothesis formulated previously that the conflict situation inherent to the two-way shuttle box procedure retarded the active avoidance acquisition. A number of trials have to be reserved in the first session for solving the conflict situation (direct effect on the rate of learning). The conflict intensity which directly effects the avoidance performance in the first session, presumably, influences learning in subsequent sessions (secondary effect on learning).

The effect of somatostatin analog octreotide on diethylstilbestrol-induced prolactin secretion, cell proliferation and vascular changes in the rat anterior pituitary gland

The effects of diethylstilbestrol (DES) and of long-acting somatostatin analog, octreotide (SMS) on the rat anterior pituitary microvasculature have been studied by means of computer-assisted image analysis. Additionally, the effects of DES and SMS on prolactin secretion and anterior pituitary cell proliferation have been studied, as well. The vascularization was visualized using Selye's method modified by Poely et al. (1964). The prolactin serum levels were estimated by radio-immunoassay. The proliferation indices were assessed using bromodeoxyuridine incorporation assay. As expected, it was found that DES sharply increased serum prolactin levels and enhanced cell proliferation in the anterior pituitary gland. DES also induced changes in parameters of vascularization. Simultaneous treatment of rats with SMS inhibited the DES-induced elevation of prolactin levels and pituitary cell proliferation. It also suppressed some but not all DES-induced changes in the anterior pituitary vascularization. These data suggest that the angio-inhibitory activity of SMS might be involved in its anti-tumor action on pituitary adenomas, but not as a sole or principal mechanism.

Changes of intertrial response rate with elapse of time after two-way avoidance trial in rats

The changes of intertrial response (ITR) rate along the intertrial interval duration were examined in 30 rats trained in two-way avoidance. The lowest ITR rate was observed just after a cross-through response terminating a trial. Rats trained with a warning signal of darkness showed over-all higher ITR rates and shorter periods of post-trial reduction of ITR rate than rats trained with a more salient noise warning signal. The period of post-trial low ITR rate lengthened in consecutive sessions indicating the gradual development of a safety state.

The effect of angiotensin II receptor antagonists on diethylstilbestrol-induced vascular changes in the rat anterior pituitary gland: a quantitative evaluation

The effects if diethylstilbestrol (DES) and of angiotensin II (Ang II) receptor antagonists, such as losartan (selective AT1 receptor antagonist) or PD 123319 (selective AT2 receptor antagonist) on the anterior pituitary microvasculature were studied by means of computer-assisted image analysis. The vascularization was visualized using Selye's method modified by Poely et al. (1964). It was found that DES induced a sharp increase in vessel area, mean vessel diameter and perimeter, whereas mean vessel number was reduced. These DES-induced changes were inhibited by simultaneous administration of losartan. On the other hand, PD 123319 was less effective. These findings suggest an involvement of Ang II, acting mainly via AT1 receptors, in the mechanism of estrogen-induced vascular changes in the rat anterior pituitary gland.

Conditioning of fear and conditioning of safety in rats

In separate groups of rats forward and backward procedures for classical defensive conditioning were superimposed on on-going bar pressing for food. The forward conditioned stimulus elicited suppression of bar presses, indicating acquisition of fear. The backward stimulus paired with identical shock elicited behaviour typical for rats in a condition of safety and caused an increase of bar press rate. Enhancement of bar presses acquired in the course of backward conditioning was stable, immune to influences from unsignalled shocks presented in the same experimental context, and resistant to extinction when all shocks were discontinued. Properties of the employed variety of the backward conditioning procedure are discussed. When a brief shock overshadowed the onset of a backward stimulus, the remaining portion of the stimulus became a signal of safety.

Effects of partial lesion of dorsal hippocampal afferent and GM1 ganglioside treatment on conditioned emotional response and hippocampal afferent markers in rats

Acquisition of the conditioned emotional response (CER) in 32 male hooded rats previously learned to press a bar for food and divided into four groups was studied. Two groups received electrolytic lesions of the dorsal hippocampal afferent and were thereafter injected either with GM1 ganglioside (30 mg/kg daily) or with buffer. Two remaining groups were sham operated and similarly injected. The partial hippocampal deafferentation evoked immediate enhancement of bar presses rate which persisted during the 2-week period of testing. CER training undertaken 2 days after surgical procedures appeared unsuccessful, whereas similar training with a cue of different modality initiated a week later resulted in acquisition of conditioned suppression of bar presses in all groups. Toward the end of training the conditioned suppression was more pronounced in lesioned than in control rats. The GM1 injections attenuated the conditioned suppression in control rats, presumably due to an antinociceptive role of ganglioside treatment. Behavioural training did not change the normal distribution pattern in cholinergic and serotonergic hippocampal afferent markers showing dorso-ventral gradient along longitudinal axis. The lesion-induced decrease pattern was also not affected. However, in contrast to previous findings in non-trained animals, the GM1 treatment was not effective in protecting against degenerative changes in the hippocampus of trained rats.

Do amygdaloid nucleus centralis and nucleus lateralis serve similar functions in defensive responding in cats?

Bar pressing escape response has been trained, extinguished, retrained and then transformed into avoidance response in cats subjected to electrocoagulation of either the dorsolateral part of the central nucleus (Group CE) ox the lateral nucleus (Group L) of amygdala. In comparison with normal carts Group L was deficient in acquisition of the short latency escape responses and Group CE was handicapped in reacquisition of the escape response after the extinction procedure. Both lesioned groups were unable to acquire avoidance responding. Group CE was marked by gradual decrease of the sensitivity to shock in the course of learning, whereas Group L was less sensitive to changes in experimental procedures than the other two groups. However, most of the observed group differences were related to a decrease of sensitivity to shock and to a lowered general emotionality produced by lesions in both amygdaloid nuclei.

Science in Poland. The Nencki Institute of Experimental Biology

The Nencki Institute in Warsaw was founded in 1918 to honor one of Poland's most distinguished biochemists, Marceli Nencki. Since its inception, the institute has evolved from a confederation of privately supported laboratories to a center of research productivity intimately associated with the Polish Academy of Sciences. Early relations with Pavlov's laboratory laid the foundation for the emergence of a Polish School of Neurophysiology under the leadership of Jersy Konorski. The impact of Konorski and his colleagues has transformed the interpretation of conditioning to include a systematic physiologic basis that more adequately considers the psychology of learning processes. The prestige of the Nencki Institute within contemporary Eastern European and Soviet science was achieved despite the economic pressures on a new nation and its total devastation of World War II. Moreover, the more than 60 years of scientific work in an independent Poland have provided a critical transition between Eastern and Western research efforts, and the Nencki Institute has filled a leading role in facilitating communication among scientists.

The role of conditioned stimulus termination in short-latency avoidance responding in cats

The behavioral effects of two procedures for bar-pressing avoidance training in cats were studied. In one procedure conditioned stimulus (CS) termination was response-contingent on both shock and non-shock trials; in the other the minimal duration of the CS was equal to the CS-US (unconditioned stimulus) interval. When avoidance responses did not terminate the CS short-latency avoidance responses were not acquired, the cats made more intertrial responses, and removal of the proreal and orbital gyri interfered more with avoidance responding than was observed in the other group. Abolition of shock application and introduction of a fixed duration of the CS resulted in extinction of the avoidance responses, which was more rapid in cats trained under the response contingent CS termination procedure. The data suggest that responses performed during the CS-US interval should be divided into two subclasses: short-latency responses which not only avoid pain but also avoid fear conditioned to the CS, and long-latency responses which avoid pain and escape from the fear state.