Anticipation and frequency of feeding affect heart reactions in domestic pigs

Measuring heart reactions has become a widely used method for the assessment of emotions. Heart rate and its variability, which can quite easily be noninvasively recorded, reflect the inputs of the sympathetic and parasympathetic branches of the autonomous nervous system. We tested the hypothesis that frequent anticipation of a positive event results in an increased state of welfare in pigs, expressed as positive arousal in anticipation of announced feeding as well as lowered heart rate and augmented heart rate variability during resting periods. We used a controlled paradigm with 3 groups of young domestic pigs (Sus scrofa domestica). We compared frequent acoustic announcement of feed delivery (group 1: 3 feedings between 0730 h and 1030 h plus 3 feedings between 1200 h and 1530 h) with the same number of feedings as in group 1 but without a temporal relation to the sound (group 2) and with a fixed-schedule feeding (group 3: 2 feedings at 0600 h and 1500 h). Specific cardiac and behavioral reactions indicated short-term (1 min) anticipation in the conditioned group. In this group, heart rate increased (P < 0.001) mainly through vagal withdraw and behavior became more active (P < 0.001). Only the conditioned group displayed changing heart rate characteristics during the sound. Pigs in the frequent unpredictable feed group reacted to feed delivery with increased heart rates (P < 0.001), whereas the heart-rate characteristics of pigs with the fixed schedule were unchanged during the sound and while the other 2 treatment groups were feeding. Clear evidence for long-term anticipation (over the course of hours) was not present in the data. Comparisons between the 3 treatment groups suggested that in housing conditions where pigs cannot obtain feed by their actions but must wait for feed delivery, feeding at 2 fixed times would be preferred. Animals in this treatment group presented lower resting heart rates at the end of the experiment than animals in the other 2 groups (P < 0.01). Therefore, merely announcing a positive stimulus without giving control to its access is apparently not suitable for increasing welfare.

Altered Vocalization Rate During the Estrous Cycle in Dairy Cattle

Correct detection of estrus is a problem in dairy herds. In practice, several procedures exist for detection of estrus besides conventional visual observation by humans. These procedures deliver very different results regarding detection of estrus. It is known that the calls of female mammals can contain information about reproductive status. It is also suspected that the vocalizations of cattle contain information about age, sex, dominance status, and stage in the estrous cycle. In the present study, a methodology for the continuous automatic recording of vocalization of heifers during the periestrous period is presented. It was shown in 10 tethered heifers that the estrous climax results in an increase in vocalization rate. Vocalization rate of heifers increased approximately 84% from d -2 to 0 (related to observed estrus) and approximately 59% from d -1 to d 0. After d 0, vocalization rate decreased about 79%. Increased vocalization was correlated with the visual observation of estrus by humans. We also found 2 different structures in the vocalization of heifers. The harmonic structure showed regular frequency bands, whereas the nonharmonic structure was noisy. The hypothesis that the disharmonic structure increases near the estrous climax was confirmed. Hence, it seems possible to get information about stage of the estrous cycle of dairy cattle by means of monitoring vocalization. The presented method of automatically detecting the rate of cattle vocalization (patent pending) could be used solely or in combination with other automated systems for detecting estrus and could considerably increase current estrus detection rates once its applicability can be demonstrated in nontethered cattle.

Effects of attention and rewarded activity on immune parameters and wound healing in pigs

Challenging animals with a demanding situation they are able to cope with and where they are rewarded may be a source of positive emotions and possibly of increased welfare. In order to test if this results in changes of immunological parameters and wound healing, 56 pigs (7-20 weeks of age), housed in groups of 8 animals each, were successfully trained to recognize and localize an individual acoustic summons and to receive a small portion of feed as a reward. Immune reactions and the development of a standardized biopsy wound were compared to values of conventionally fed control groups of equal size and animal-to-feeding-place ratio (2:1). In the experimental animals a significantly higher concentration of IgG as well as an increased in vitro T-cell proliferation to ConA but a reduced LPS-induced proliferation of B-cells was found, while basal salivary cortisol concentrations were similar. Wound development was better in the experimental animals as measured by the area of the inflammatory corona. It decreased more rapidly in the experimental animals since the 5th day after biopsy and was significantly smaller than in the control groups. We conclude that environmental enrichment by equipment provoking attention and cognitive activity which is rewarded by feed may play a beneficial role for physical welfare of intensively housed pigs.

[Reaction of muscles to a stimulating environment--effects on the loin muscle (M. longissimus) of Landrace pigs]

The effects of an enriched environment on growth, meat quality, and muscle biological traits were investigated using 64 castrated pigs (age range 7 to 20 weeks). Positive emotional appraisal was induced by a system that acoustically frequently called individuals out of a group (n=32) to a feeding station, where they were rewarded with small portions of feed. The results were compared with traditional fed pigs (Control; n = 32). There was no environmental effect on live weight and lean muscle percentage. However, the stimulating keeping regime reduced the intramuscular fat content of the M. longissimus by 0.2 % and increased the protein content by 0.5 %. Moreover, the drip loss of M. longissimus was 1.1 % lower in the treatment group. The analysis of muscle fibre traits (biopsy samples of M. longissimus) showed a 7 % higher proportion of oxidative muscle fibres in the pigs reared in the enriched environment. This fibre type showed a tendency to increased fibre areas. These findings indicate a higher oxidative capacity of the muscle. However, the activity of the inarker enzyme citrate synthase (CS) was not influenced and the activity of lactate dehydrogenase (LDH) was even increased compared to the control animals.

Visual discrimination learning in dwarf goats and associated changes in heart rate and heart rate variability

We studied visual discrimination learning in a group of Nigerian dwarf goats using a computer-based learning device which was integrated in the animals' home pen. We conducted three consecutive learning tasks (T1, T2 and T3), each of which lasted for 13 days. In each task, a different set of four visual stimuli was presented on a computer screen in a four-choice design. Predefined sequences of stimulus combinations were presented in a pseudorandom order. Animals were rewarded with drinking water when they chose the positive stimulus by pressing a button next to it. Noninvasive measurements of goats' heartbeat intervals were carried out on the first and the last 2 days of each learning task. We analysed heart rate (HR) and heart rate variability (HRV) of resting animals to study sustained physiological effects related to general learning challenge rather than acute excitement during an actual learning session. The number of trials to reach the learning criterion was 1000 in T1, when visual stimuli were presented to the goats for the first time, but decreased to 210 in T2 and 240 in T3, respectively. A stable plateau of correct choices between 70% and 80% was reached on Day 10 in T1, on Day 8 in T2 and on Day 6 in T3. We found a significant influence of the task and of the interaction between task and day on learning success. Whereas HR increased throughout T1, this relationship was inverted in T2 and T3, indicating different effects on the HR depending on how familiar goats were with the learning task. We found a significant influence of the task and the interaction between task and time within the task on HRV parameters, indicating changes of vagal activity at the heart. The results suggest that changes in HR related to learning were predominantly caused by a withdrawal of vagal activity at the heart. With regard to nonlinear processes in heartbeat regulation, increased deterministic shares of HRV indicated that the animals did not really relax until the end of T3. Comparing changes of HR and HRV in T3 and in a subsequent postexperiment (PE), we assume a positive effect of such cognitive challenges once the task had been learned by the animals.

STREMODO, ein innovatives Verfahren zur kontinuierlichen Erfassung der Stressbelastung von Schweinen bei Haltung und Transport

Abstract. Title of the paper: STREMODO, an innovative technique for continuous stress assessment of pigs in housing and transport Vocal utterances of animals are the results of emotional states in specific situations. Therefore, distress calls of pigs can be used as indicators of impaired welfare. An automatic system was developed that responds selectively to stress vocalisations and that registrates and records their amount in the time domain. It can be applied in housing systems, during transports and in abattoirs. The patented technique is based on sequential records of the actual sound events in short time windows (92ms) and a parsimonious coding by 12 complex parameters (LPC-coefficients). A subsequent artificial neural network trained with respective parameters from porcine stress vocalisations is able to detect stress utterances with an error rate of less than 5 % even in noisy stables.

Effects of prenatal stress on corticosteroid receptors and monoamine concentrations in limbic areas of suckling piglets (Sus scrofa) at different ages

The present study was conducted in order to reveal the effects of prenatal stress on the central stress regulation in domestic pigs by measuring changes in corticosteroid receptor binding and monoamine concentrations in different limbic brain regions. Pregnant sows were subjected to a restraint stress for 5 min daily during the last 5 weeks of gestation. Maternal stress resulted in a significantly higher number of glucocorticoid receptors in the hippocampus, but decreased glucocorticoid receptors in the hypothalamus of the offspring at the first postnatal day. No alterations of hippocampal mineralocorticoid receptors were found. There was also no significant effect of prenatal stress on the brain monoamine concentrations. Prenatally stressed piglets showed lower basal plasma cortisol and increased corticosteroid binding globulin concentrations at the third postnatal day indicating decreased free cortisol concentrations after birth. Morbidity and mortality during the suckling period were significantly increased in prenatally stressed litters, as shown by a higher frequency of diseased and died piglets per litter. In conclusion, the results indicate that in pigs restraint stress during late gestation affects the ontogeny of the foetal neuroendocrine feedback system with consequences for the regulation of the hypothalamo-pituitary-adrenal function and the vitality of the offspring.

[Effects of muscle needle biopsy on parameters of humoral and cellular immunity in pigs]

The shot biopsy is a common experimental technique for the collection of samples to investigate muscle tissue characteristics or to determine meat quality features in pigs. Its application seems to be also possible in interdisciplinary research projects investigating animal stress, behaviour, and welfare. The present study on 12 group-housed pigs (age: 12 weeks, weight: 29.3 kg) shows the influence of this wound-causing technique on different humoral and cell-mediated parameters of the immune system at 1, 3, 5, and 9 days after biopsy compared to the initially investigated levels before. An enhancement of the blood sedimentation rate and both the IgG and the cellular immune response in vivo (leukocytes, lymphocytes) as well as in vitro (ConA) was observed. Furthermore, there were signs of a secondary wound infection 5 days after biopsies were taken possibly caused by mutual oral manipulation of the animals. We conclude that the muscle shot biopsy technique can be used on group-housed pigs as a method to investigate muscle physiological characteristics. The technique, however, induces immunological reactions which may interfere with stress-induced immune reactions.

A better welfare for nursing sows without increased piglet loss applying peri-parturition short term crating

Abstract. A housing for nursing sows is presented that allows the animals to move within the pen for most of the time until weaning of the piglets and thus increases welfare. Ten days before farrowing was expected the sows (n = 80) were stalled to Scan farrowing pens without restriction. They were allowed to move around and to get into contact with their neighbour animals. Three to five days before parturition the sows were confined to farrowing crates until 4–6 days after parturition. At that time the piglets (n = 4075 from 361 litters) reliably visited the heated and protected hiding area. Compared to conventional housing systems for nursing sows we observed no increased piglet loss by crushing. Hence, temporal confinement of the sows around farrowing offers a suitable method to increase well-being without impairing the economic achievement.

Central nervous regulation of the hypothalamic-pituitary-adrenal axis and its impact on fertility, immunity, metabolism and animal welfare – a review

Abstract. The paper reviews mechanisms of neuronal control of the hypothalamic-pituitary-adrenal (HPA) axis with a view on its impact on performance and welfare. The limbic hippocampal and amygdaloid input to the paraventricular hypothalamic nucleus constitutes the basic intracerebral axis by which emotional stimuli affect the stress response. This axis is the backbone of the HPA feedback loop where hippocampus and amygdala are plastic elements and add the ability of experience dependent adaptation and (emotional) learning. As a result large individual differences of the stress response may occur. The system mutually interacts with the immune system and with hypothalamic cell groups which control metabolism and fertility, explaining the influence of stress on these performance parameters. It is concluded that for the reliable assessment of emotional welfare in (farm-) animals a multitude of physiological and behavioral measures are needed which take into account the highly crosslinked nature of the system.

Linear prediction coding analysis and self-organizing feature map as tools to classify stress calls of domestic pigs (Sus scrofa)

It is assumed that calls may give information about the inner (emotional) state of an animal. Hence, in the last years sound analysis has become an increasingly important tool for the interpretation of the behavior, the health condition, and the well-being of animals. A procedure was developed that allows the characterization, classification, and visualization of the cluster structures of stress calls of domestic pigs (Sus scrofa). Based on the acoustic model of the sound production the extraction of features from calls was performed with linear prediction coding (LPC). A vector-based self-organizing neuronal network was trained with the determined LPC coefficients, resulting in a feature map. The cluster structure of the calls was then visualized with a unified matrix and the neurons were labeled for their input origin. The basic applicability of the procedure was tested by using two examples which were of special interest for a possible evaluation of the normal farming practice. The procedure worked well both in discriminating individual piglets by their scream characteristics and in classifying pig stress calls vs other calls and noise occurring under normal farming conditions.

Die Wirkung von psychischem Streß auf das Immunsystem. Ein weiterer Grund für tiergerechte Haltung (Übersichtsreferat)

Abstract. Title of the paper: The effect of psycho stress on the immune System. Another reason for pursuing animal welfare (Review) Stress can be seen as the body's most important and complex reaction to ensure survival. Thus, stress must be considered a fundamentally positive type of adaptive reaction and concepts of stress have to be integral parts in considering animal well-being. It is widely recognized that acute and chronic stress have an impact on the neuroendocrine and immune system, the latter being of special interest with respect to health and welfare of animals. This review intends to provide an integrative approach to the complex relationships between stress, behaviour, neuroendocrine and immune system of farm animals. Physiological mechanisms that mediate the effects of stress on immune function including basic mechanisms of neuroendocrine-immune network and principles of immuno-modulation are presented and discussed in consideration of their practical impact for livestock production.

Effects of weaning and restraint stress on glucocorticoid receptor binding capacity in limbic areas of domestic pigs

Changes in glucocorticoid receptor (GR) binding in different brain areas were investigated in neonatal and adult pigs exposed to psychological stress (weaning) and a physical stressor (repeated snaring). The GR binding was significantly decreased 4 days after weaning in both the hippocampus and the amygdala, but there were no changes in the hypothalamus. Repeated snaring of adult pigs resulted in a significant diminished GR binding only in the hippocampus.

An automated training device for pattern discrimination learning of group-housed gerbils

The setup, designed for the rodent Meriones unguiculatus (gerbil), allows flexible stimulus presentations and rewarding as well as on-line data registration. It consists of a spacious housing where the animals have free access to water. Food is supplied exclusively in the y-maze training compartment and serves as a reinforcer in an operant conditioning paradigm.

A model of the saccadic sensorimotor system of salamanders

A model of the saccadic system of salamanders on the basis of electrophysiological and anatomical results is presented. The model includes centers found to be significant for the guidance of saccades in these comparatively simple vertebrates. In particular, these are the optic tectum, the bulbar reticular formation and the motor system. The latter consists of two pairs of neck-muscles, an epaxial and a hypaxial one driven by their respective motoneurons. The model includes a visual, a sensori-motor, and a motor level. At the sensory level, the retinal coordinates are transferred to the optic tectum to establish an orthogonal map of visual angles. A secondary visual map of the ipsilateral eye with a pointsymmetrical organization exists in addition. The premotor system of the tectum was modelled according to an ensemble-coding principle. Thus, local activation of the visual map results in recruitment of an appropriate number of tectal premotor units. Simulation of the model reproduces correct metric properties of salamander saccades under varying stimulus presentations.

Quantitative distribution of descending tectal efferent cells in salamanders

In salamanders of the species Salamandra salamandra, Pleurodeles waltl, and Plethodon jordani, tectal efferent neurons projecting to the bulbar reticular formation show a stereotyped distribution as revealed by the horseradish peroxidase (HRP) method. The density of these cells increases toward caudal tectal levels reaching its maximum at the isthmic region. Neurons with ipsilaterally descending axons constitute 60-87% and are concentrated in the dorsomedial and ventrolateral sector of the tectal hemisphere, with only few neurons in the intermediate part. The contralaterally descending neurons are concentrated in the lateral sector. This pattern is assumed to reflect a motor map in the coordinates of the salamander neck muscle system.

Configuration-sensitive visual responses in the superior colliculus of the house mouse (Mus musculus domesticus)

In order to compare visual pattern discrimination by tectal neurons in distantly related vertebrate groups, collicular cells of mice were examined for their responses to each of three simple configurational stimuli commonly used in studies of amphibians. The stimuli consisted of a large square, a horizontal bar and a vertical bar moved at various velocities. Of the recorded units (n = 51), 30-50% significantly preferred the square to the other stimuli at medium (10 degrees/s) and high (67 degrees/s) velocities. Approximately 10% preferred the horizontal bar at these velocities. A significant discrimination between the horizontal and the vertical bar was found in 39% of the units at a velocity of 10 degrees/s, and in 61% at a velocity of 67 degrees/s. These response types are very similar to those found in amphibians; therefore, it is concluded that tectal configurational sensitivity may be a plesiomorphic tetrapod character resulting from basic properties of tectal neuronal circuitry.

Topographic relationships of ipsi- and contralateral visual inputs to the rostral tectum opticum in the salamander Plethodon jordani indicate the presence of a horopter

Topographies of ipsilateral and contralateral retinal inputs to the optic tectum were studied by means of electrophysiological multi-unit recordings from the superficial layers. It was found that the nasotemporal coordinate of the visual field is represented along a rostrocaudal axis on the contralateral tectal map and along a caudorostral axis on the ipsilateral map. Electrical stimulation of one tectal hemisphere and recording of the response in the other hemisphere revealed that the ipsilateral map is most probably established by an intertectal pathway. In one tectal hemisphere, inputs from the ipsilateral eye match those from the contralateral eye if stimuli are located at a certain distance at arbitrary horizontal angles within the binocular field. This distance varied from 11.8 to 29.5 mm between the 5 individuals examined.

Origins of descending projections to the medulla oblongata and rostral medulla spinalis in the urodele Salamandra salamandra (amphibia)

Descending projections to the medulla oblongata and rostral medulla spinalis have been examined in the urodele Salamandra salamandra with retrograde horseradish peroxidase tracing. Ipsilateral projections originate from the striatum and the nucleus ventrolateralis thalami and reach the medulla oblongata. The ipsilateral nucleus praeopticus magnocellularis reaches the medulla spinalis. The rostral part of the nucleus tuberculi posterioris projects to the ipsilateral medulla oblongata; its caudal part projects further caudally. Tectal efferents and the efferents of the nucleus praetectalis profundus project bilaterally, the nucleus praetectalis superficialis, nucleus mesencephalicus nervi trigemini, torus semicircularis, nucleus Darkschewitsch, and nucleus fasciculi longitudinalis medialis project ipsilaterally to the medulla oblongata. The nucleus mesencephalicus nervi trigemini, nucleus fasciculi longitudinalis medialis, and tectal efferents reach the rostral medulla spinalis. The nucleus ruber projects mainly via the contralateral dorsolateral funiculus to the medulla spinalis. A largely crossed medullary projection arises in the nucleus dorsalis tegmenti pars anterior, a bilateral projection arises in the nucleus dorsalis tegmenti pars posterior, and an ipsilateral projection arises in the nucleus ventralis tegmenti pars anterior. Cerebellar and statoacoustic efferents descend to the medulla spinalis. The nucleus reticularis isthmi, superior, medius and inferior as well as the nucleus raphes exhibit spinal trajectories. The nucleus vestibularis magnocellularis projects bilaterally, the nucleus vestibularis medialis projects ipsilaterally spinalward. The supposed nucleus descendens nervi trigemini descends mainly contralaterally. A small spinal projection arises in the nucleus tractus solitarii. The results indicate that salamander brains display elaborate descending connections which are similar to those in other vertebrates despite their scarcely differentiated neuronal cytoarchitecture.

On the presence of nucleus ruber in the urodele Salamandra salamandra and the caecilian Ichthyophis kohtaoensis

The presence of nucleus ruber in urodeles and caecilians (amphibia) was investigated. For that purpose, horseradish peroxidase was applied to the rostral spinal cord, the medulla oblongata at various levels and the dorsolateral funiculus. Whereas Salamandra salamandra possesses a rubrospinal tract, it is absent in the limbless caecilian Ichthyophis kohtaoensis.

Binocular afferents to the salamander pretectum mediate rotation sensitivity of cells selective for visual background motions

The majority (85%) of background motion-sensitive pretectal cells in salamanders was found to be binocularly driven. In 70% of the units the binocularity establishes a rotation selectivity with respect to background pattern-movements. This results in a considerable augmentation of the discharge rate when pattern movement is perceived simultaneously in the temporonasal direction by the contralateral eye and nasotemporally by the ipsilateral eye. The response is depressed when the pattern movement is seen in the same direction by both eyes. It is concluded that the rotation-sensitive cells are mainly excited by contralateral retinal afferents selective for temporonasal movements and inhibited by direct or indirect ipsilateral afferents with the same type of direction selectivity.

Directional selectivities of visual afferents to the pretectal neuropil in the fire salamander

Single-unit recordings from visual afferents in the pretectal neuropil of Salamandra salamandra were performed to characterize the properties of direction specific units which are probably involved in the optokinetic reflex. It was shown that afferents from the contralateral eye were more sharply tuned than those from the ipsilateral eye. However, the majority of both were selective for temporonasal movements.

Localization of motoneurons innervating the extraocular muscles in Salamandra salamandra L. (Amphibia, Urodela)

The central innervation patterns of the extraocular muscles were investigated in the European fire salamander Salamandra salamandra L. by means of the horseradish peroxidase method. The ipsilateral portion of the nucleus nervi oculomotorii, which is located in the rostral ventral tegmentum mesencephali, supplies the musculi recti inferior and medialis and the musculus obliquus inferior without a clear somatotopic representation of the motoneurons. The musculus rectus superior is innervated mainly by a contralateral portion of this nucleus. A definite nucleus Edinger-Westphal could not be recognized. The nucleus nervi trochlearis, which rostrally joins the nucleus nervi oculomotorii with a gap of only about 40 micron between the nuclei, is situated completely contralateral to the musculus obliquus superior supplied by it. The nucleus nervi abducentis, innervating the musculus rectus lateralis, and the nucleus accessorius nervi abducentis, supplying the musculus retractor bulbi, are found in the ipsilateral medulla oblongata and exhibit a large rostrocaudal extension from the eighth cranial nerve to the first root of the vagus nerve. Dendrites of the nucleus nervi oculumotorii and of the nucleus accessorius nervi abducentis extend into neuropil areas receiving primary sensory afferents.

Amphibian optokinetic after nystagmus: properties and comparative analysis in various species

Optokinetic nystagmus and after nystagmus were studied in six amphibian species, three urodeles and three anurans. It was demonstrated that two of the urodeles, Hydromantes italicus and Salamandra salamandra, display a relatively well-developed optokinetic after nystagmus, which is less pronounced in Bombina variegata and nearly absent in Bufo bufo, Rana temporaria, and Tylototriton verrucosus. These results indicate a certain degree of velocity storage in the optokinetic reflex of some amphibians.

Retinal projections in the caecilian Ichthyophis kohtaoensis (Amphibia, Gymnophiona)

The retinal projections of the caecilian Ichthyophis kohtaoensis were investigated by anterograde transport of HRP. The optic tract forms two bundles in the diencephalon, a narrow medial bundle in the optic tectum, and a basal optic tract consisting of few fibres. Terminal fields are in the thalamus, pretectum, tectum, and as a circumscribed basal optic neuropile in the tegmentum. Thalamic, pretectal and tectal projections are contralateral as well as ipsilateral. The reduced but existing visual projection corresponds to a reduced but existing visually guided behaviour.

Monocular and binocular optic inputs to salamander pretectal neurons: intracellular recording and HRP labelling study

Intracellular recordings and horseradish peroxidase injections were performed in the pretectum and adjacent tegmentum of Salamandra salamandra, while both optic nerves were electrically stimulated. In approximately half of the recorded units no spikes could be evoked but rather graded postsynaptic potentials. The latter type morphologically showed features of interneurons. From a total of 48 recorded units, nearly 60% were excited only by the contralateral optic nerve, whereas approximately 40% were binocular. For the most part (10/19) the binocular cells were excited by the contralateral and inhibited by the ipsilateral optic nerve. Fewer neurons (7/19) received excitatory inputs from both optic nerves. The latency distribution of the monocular cells shows a maximum of 20-30 ms. The same maximum exists for the contralateral inputs to the binocular cells, whereas the ipsilateral inputs to these units were nearly as frequent with latencies of 20-30 and 40-50 ms. Since neurons with the short ipsilateral latencies always had parts of their dendrites within the ipsilateral ocular projection field, a feature which was lacking in the cells with long ipsilateral latencies, it is possible that the longer latencies are due to indirect ipsilateral inputs. Efferents of labelled dorsal pretectal cells reach the contralateral pretectum via the posterior commissure, the basal optic neuropil of the accessory optic system and the tegmental white substance. More ventrally located cells often reach the pretectal and the basal optic neuropil with their dendrites. Axons of this type descend to the medulla oblongata via the medial longitudinal fasciculus.

Electrophysiology and anatomy of direction-specific pretectal units in Salamandra salamandra

Pretectal cells of the European fire salamander were recorded extracellularly during binocular and monocular horizontal optokinetic stimulations. The locations of the individual units within the pretectal nucleus were verified with Alcian blue injections. The particular anatomical properties of single cells were demonstrated after single-unit recordings by means of horseradish peroxidase preparations. Direction selective pretectal cells were found to be predominantly (2/3) sensitive to temporo-nasal movements in the visual field of the contralateral eye. They usually possessed large receptive fields centered on the visual equator with restricted diameters in the dorso-ventral axis. Their resting discharge was low, and in some cells no spontaneous discharges were observed. The cells preferred low stimulus velocities, most of them being optimally stimulated with velocities of 1 to 10 deg/s. A group of units was exclusively sensitive to accelerated movements. A subclass of them was transiently responsive when the stimulus stopped. In the anterior and most dorsal part of the pretectal nucleus, binocularly influenced units were found. These cells responded best with binocular optokinetic stimulations and less vigorously or with less pronounced direction selectivity if only the contralateral eye was stimulated. With ipsilateral stimulations alone no response could be elicited. This response type could be explained by inhibitory inputs from the ipsilateral eye via direct ipsilateral projections or crossing pretectal fibers. The responses of these cells are well correlated to behavioral results showing that OKN performance in salamanders, as in some other vertebrates, is different with binocular as compared to monocular stimulations. The direction-sensitive pretectal cells usually possess extensive dendritic arborizations within the ipsilateral pretectal neuropil. Most of the cell bodies were scattered in the white substance or in the superficial layers of the periventricular gray. In the cases where the efferent fiber of a particular cell could be clearly recognized, the axon projected to the basal optic neuropil of the accessory optic system, the contralateral pretectum or, in two cases, to the medulla oblongata into a region which might be homologous to the inferior olive of higher vertebrates.

Quantitative analysis of salamander horizontal head nystagmus

The horizontal optokinetic head nystagmus of salamanders (Salamandra salamandra) was investigated at various constant and sinusoidally modulated velocities. With constant velocities the best compensation (head velocity/stimulus velocity) measured was 0.6 at a stimulus velocity of 3 deg/s. With slow stimuli up to 5 deg/s, small oscillations in the slow phase of the nystagmus occurred. The nystagmus started with a delay of 1.1 s after onset of stimulus with an acceleration period of up to 6 s. After the stimulus terminated, the head was decelerated within (on average) 5 s, indicating a weak velocity storage element. The nystagmus frequency, the acceleration time, and the deceleration time were in correlation with the head velocity during the slow phase. With sinusoidal stimuli, nonlinearities were displayed: the gain was amplitude-dependent, and distortions of the sinusoidal head movements occurred with higher frequencies.

A 'physiological' model for the salamander horizontal optokinetic reflex

The salamander optokinetic head nystagmus can be explained by a comparatively simple negative feedback loop with few operational units within the loop. These units may easily be represented by properties of neural elements. In particular, the retinal slip velocity is transformed into an internal excitation by a velocity transfer function derived from pretectal recordings. A velocity storage element with input-output comparator is proposed as a recurrent inhibition network. A threshold element sums up the neuronal thresholds of the units involved. An internal gain factor may be interpreted as the transformation of the neural signal to a motor output. This output occurs with a stimulus-independent delay of 1 s, which is considered to be the sum of all conduction delays in the system. The model produces an output that is in excellent conformity with the optokinetic behavior. Additionally, the model predicts behavioral responses to optokinetic stimulation with extended stimulus ranges or with central lesions.

The accessory optic system in the newt, Triturus cristatus: unitary response properties from the basal optic neuropil

Recordings from the basal optic neuropil (BON) demonstrated directional sensitivity. These directional sensitivities were different in different units, however, most of them displayed a strong vertical component. Inhibition in the non-preferred direction did not occur, only a lower activation than in the preferred direction was found. The identified velocity functions correlate well with the velocity dependence of the nystagmus frequency demonstrated in the behavior. The units responded well to moving large-area stimuli and exhibited horizontally elongated receptive fields with diameters up to 120 degrees. Additionally, bimodal recordings were observed in the BON which were probably due to input from the otoliths. As the recordings are likely to be presynaptic, the BON receives types of input which establish its function in the control of visuomotor behavior.