The use of tactile and olfactory cues in neonatal orientation and localization of the nipple

Development of multisensory processing in ferret parietal cortex

It is well known that the nervous system adjusts itself to its environment during development. Although a great deal of effort has been directed towards understanding the developmental processes of the individual sensory systems (e.g., vision, hearing, etc.), only one major study has examined the maturation of multisensory processing in cortical neurons. Therefore, the present investigation sought to evaluate multisensory development in a different cortical region and species. Using multiple single-unit recordings in anaesthetised ferrets (n = 18) of different ages (from postnatal day 80 to 300), we studied the responses of neurons from the rostral posterior parietal (PPr) area to presentations of visual, tactile and combined visual-tactile stimulation. The results showed that multisensory neurons were infrequent at the youngest ages (pre-pubertal) and progressively increased through the later ages. Significant response changes that result from multisensory stimulation (defined as multisensory integration [MSI]) were observed in post-pubertal adolescent animals, and the magnitude of these integrated responses also increased across this age group. Furthermore, non-significant multisensory response changes were progressively increased in adolescent animals. Collectively, at the population level, MSI was observed to shift from primarily suppressive levels in infants to increasingly higher levels in later stages. These data indicate that, like the unisensory systems from which it is derived, multisensory processing shows developmental changes whose specific time course may be regionally and species-dependent.

Vitality in Newborn Farm Animals: Adverse Factors, Physiological Responses, Pharmacological Therapies, and Physical Methods to Increase Neonate Vigor

Vitality is the vigor newborn animals exhibit during the first hours of life. It can be assessed by a numerical score, in which variables, such as heart rate, respiratory rate, mucous membranes' coloration, time the offspring took to stand up, and meconium staining, are monitored. Vitality can be affected by several factors, and therapies are used to increase it. This manuscript aims to review and analyze pharmacological and physical therapies used to increase vitality in newborn farm animals, as well as to understand the factors affecting this vitality, such as hypoxia, depletion of glycogen, birth weight, dystocia, neurodevelopment, hypothermia, and finally, the physiological mechanism to achieve thermostability. It has been concluded that assessing vitality immediately after birth is essential to determine the newborn's health and identify those that need medical intervention to minimize the deleterious effect of intrapartum asphyxia. Vitality assessment should be conducted by trained personnel and adequate equipment. Evaluating vitality could reduce long-term neonatal morbidity and mortality in domestic animals, even if it is sometimes difficult with the current organization of some farms. This review highlights the importance of increasing the number of stock people during the expected days of parturitions to reduce long-term neonatal morbidity and mortality, and thus, improve the farm's performance.

The effects of olfactory bulb removal on single-pellet skilled reaching task in rats

We focused on how the rat uses olfactory cues in a single-pellet reaching task, which is composed of three successive learned responses, Orient, Transport, and Withdrawal. Orient comprised: front wall detection, slot localisation, and nose poke until reach start. High-speed video-recording enabled us to describe the temporal features of this sequence in controls vs. 3-5 and 12-14 days after bilateral bulbectomy in trials with (P trial) vs. without (no-P trial) pellet. In controls, the full sequence was complete in P trials, while it was interrupted after Orient in no P-trials. After bulbectomy, the full sequence was seen in both P and no-P trials at days 3-5 and 12-14 and there was an increase in Orient duration due to the increased time in slot/shelf localisation. Unlike in controls, in anosmic rats, the first nose contact with the front wall took place below the slot/shelf level, and the number of nose touches together with the number of whisker cycles was significantly higher at 3-5 but not at 12-14 days. The relationship between nose touches and whisker cycles was linear in all experimental conditions. Bulbectomy resulted in no changes in the Transport duration or the time the paw spent out of the slot. These findings suggest that olfaction allows the animal to orient itself in pellet localisation, and offers insight into the contribution of olfaction during different stages of natural behaviour in skilled reaching task.

The effect of premature maternal separation on distress vocalizations and activity in kittens (Felis catus) during a brief nest separation

It is unknown how premature maternal separation affects the responses of kittens to potentially stressful events. In the United States, thousands of kittens are orphaned each year due to death of the queen, neglect, or accidental separation by humans. Neonatal mammals emit distress calls and increase locomotion when socially isolated, suggesting that being separated from the nest is a stressful event. Increased vocalization and activity of isolated neonates may aid maternal retrieval or relocation of the nest. In the current study, we assessed the effects of early maternal separation on later vocalizations and activity of 49 kittens (28 orphaned, 21 mother-reared; 23 female, 26 male) from 11 litters (5 mothered, 6 orphaned) during an open field test when the kittens were one and three weeks of age. We conducted a total of 79 trials. Each kitten was placed individually in a 1-meter diameter pen away from the rest of the litter and/or mother for two minutes. The number of calls emitted and total activity (in seconds) were recorded for each kitten on every trial. We assessed the effects of age, sex, orphan status, and interactions between orphan status with sex and age on activity and vocalizations. Orphaned kittens were more active than mother-reared kittens at both times (t(46) = 4.62, p < 0.001), with an interaction between age and orphan status (t(28) = -2.84, p = 0.008). Orphaned kittens emitted more vocalizations at both times (Z = 2.38, p = 0.018), with an interaction between age and orphan status (Z = -3.18, p = 0.001). Orphaned kittens showed increased activity and vocalizations in response to a brief nest separation compared to mother-reared kittens. This effect was still present after over two weeks of maternal separation, suggesting that maternal separation may lead to long-term changes in stress responses. Future research should explore if such effects of maternal separation are present in older kittens or adult cats.

A survey-based assessment of risk factors for cross-sucking behaviors in neonatal kittens, Felis catus

Cross-sucking, or non-nutritive sucking on the bodies of littermates, is commonly observed in early-weaned animals. This behavior has been well-documented in production animals, which are often separated from their mothers before weaning. The behavior is less well-understood in other domestic species, such as cats (Felis catus), that can be orphaned due to neglect, maternal death, or accidental separation. Anecdotally, cross-sucking can cause injuries in kittens, sometimes severe enough to warrant euthanasia. To our knowledge, this is the first detailed study of this behavior in domestic cats. We conducted a survey of caretakers (N = 407) of kittens (< 60 days old) with the goal of identifying characteristics of individual kittens, litters, the environment, and husbandry that might be associated with the presence of cross-sucking. The final data set, representing 1358 kittens, was comprised of 301 litters experiencing sucking and 106 litters not experiencing sucking behaviors. Almost all of the kittens represented in the survey (91%) were orphaned. Results suggested that being orphaned (X 2(1) = 42.64, p < 0.001), bottle-fed (X 2(2) = 40.32, p < 0.001), younger (t(405) = 3.48 p < 0.001), separated earlier from the mother (t(376) = 3.10, p = 0.002), and being in an all-male litter (X 2(2) = 7.13, p = 0.03) increased the risks of cross-sucking. Male kittens also were more likely to be recipients of sucking behavior (X 2(1) = 32.30, p < 0.001). No clear associations between the environment or husbandry practices and the presence of sucking behavior were identified. Interruption and separation were the most frequently reported management strategies, but most kittens returned to sucking behavior when reunited. Cross-sucking is a frequently reported behavior problem in orphaned kittens that may indicate distress or poor welfare. Future research should focus on a better understanding of prevention and management strategies, and determination of the effects, if any, of cross-sucking as a kitten on adult cat outcomes or behavior.

Preparing for Life After Birth: Introducing the Concepts of Intrauterine and Extrauterine Sensory Entrainment in Mammalian Young

Presented is an updated understanding of the development of sensory systems in the offspring of a wide range of terrestrial mammals, the prenatal exposure of those systems to salient stimuli, and the mechanisms by which that exposure can embed particular sensory capabilities that prepare newborns to respond appropriately to similar stimuli they may encounter after birth. Taken together, these are the constituents of the phenomenon of "trans-natal sensory continuity" where the embedded sensory capabilities are considered to have been "learnt" and, when accessed subsequently, they are said to have been "remembered". An alternative explanation of trans-natal sensory continuity is provided here in order to focus on the mechanisms of "embedding" and "accessing" instead of the potentially more subjectively conceived outcomes of "learning" and "memory". Thus, the mechanistic concept of "intrauterine sensory entrainment" has been introduced, its foundation being the well-established neuroplastic capability of nervous systems to respond to sensory inputs by reorganising their neural structures, functions, and connections. Five conditions need to be met before "trans-natal sensory continuity" can occur. They are (1) sufficient neurological maturity to support minimal functional activity in specific sensory receptor systems in utero; (2) the presence of sensory stimuli that activate their aligned receptors before birth; (3) the neurological capability for entrained functions within specific sensory modalities to be retained beyond birth; (4) specific sensory stimuli that are effective both before and after birth; and (5) a capability to detect those stimuli when or if they are presented after birth in ways that differ (e.g., in air) from their presentation via fluid media before birth. Numerous beneficial outcomes of this process have been reported for mammalian newborns, but the range of benefits depends on how many of the full set of sensory modalities are functional at the time of birth. Thus, the breadth of sensory capabilities may be extensive, somewhat restricted, or minimal in offspring that are, respectively, neurologically mature, moderately immature, or exceptionally immature at birth. It is noted that birth marks a transition from intrauterine sensory entrainment to extrauterine sensory entrainment in all mammalian young. Depending on their neurological maturity, extrauterine entrainment contributes to the continuing maturation of the different sensory systems that are operational at birth, the later development and maturation of the systems that are absent at birth, and the combined impact of those factors on the behaviour of newborn and young mammals. Intrauterine sensory entrainment helps to prepare mammalian young for life immediately after birth, and extrauterine sensory entrainment continues this process until all sensory modalities develop full functionality. It is apparent that, overall, extrauterine sensory entrainment and its aligned neuroplastic responses underlie numerous postnatal learning and memory events which contribute to the maturation of all sensory capabilities that eventually enable mammalian young to live autonomously.

Morphological analysis of regenerated bulbar fibers in relation to neonatal olfaction

It was revealed that regeneration of the lateral olfactory tract (LOT) occurred in developing rats and the regenerated olfactory system was functional 4 weeks after transection. The aim of this study was to determine the earliest onset of functional recovery in LOT-injured rats and to quantify regenerated nerve components with functional correlation. Neonatal rats on postnatal day (P) 2 were subjected to unilateral transection of the left LOT and underwent unilateral removal of the right olfactory bulb on P11. Functional recovery of the tract injury was assessed by the suckling capability, which can be achieved by olfaction. Suckling capability was observed on P12 in most neonatally LOT-transected pups. Rat pups were subjected to unilateral transection of the left LOT on P2, and received injections of biotinylated dextran amine (BDA) into the bilateral olfactory bulb on P5 to quantify normal and regenerated nerve components in the olfactory cortices at the level of the olfactory tubercle. BDA(+) areas and density indices of the olfactory cortices in the neonatally LOT-transected P12 pups were 11.05×10⁵μm² and 0.35 on the normal right side and 4.34×10⁵μm² and 0.21 on the transected left side. We concluded that functional recovery of the LOT-transected neonatal rats occurred as early as 10days after tract transection and that areas and densities of regenerated nerve components essential for functional recovery were approximately 40% and 60% of the age-matched normal values in the olfactory cortices at the level of the olfactory tubercle.

Survival implications of the development of behavioural responsiveness and awareness in different groups of mammalian young

This paper focuses on the development of behaviours that are critical for the survival of newborn and juvenile mammals of veterinary and wider biological interest. It provides an updated, integrated and comparative analysis of how postnatal maturation of sensory, motor and perceptual capacities support and constrain behavioural interactions between mammalian young and the mother, any littermates and the environment. Young that are neurologically exceptionally immature, moderately immature and mature at birth are compared, and include, for example, marsupial joeys, rodent pups and ruminant offspring. Mothers in these three groups exhibit distinctive patterns of birthing and postnatal care behaviours. To secure survival of the young, maternal care must compensate for behavioural inadequacies imposed by the limited sensory capacities the young possess at each stage. These sensory capacities develop in a predictable sequence in most mammals such that before birth the sequence progresses to an extent that parallels the degree of neurological maturity reached at birth. The extent of neurological maturity is likewise reflected in how long it takes after birth for the necessary brain circuit connectivity to develop sufficiently to support cortically based cognitive modulation of behaviour. This takes several months, days-to-weeks or minutes-to-hours in young that are, respectively, neurologically exceptionally immature, moderately immature, or mature at birth. Once achieved, cognitive awareness confers a high degree of behavioural flexibility that allows the young to respond more effectively to the unpredictability of their postnatal environments. It is shown that the onset of this cognitively based flexibility in the young of each group coincides with their first exposure to a variable environment that requires such behavioural flexibility.

Development of multisensory integration from the perspective of the individual neuron

The ability to use cues from multiple senses in concert is a fundamental aspect of brain function. It maximizes the brain’s use of the information available to it at any given moment and enhances the physiological salience of external events. Because each sense conveys a unique perspective of the external world, synthesizing information across senses affords computational benefits that cannot otherwise be achieved. Multisensory integration not only has substantial survival value but can also create unique experiences that emerge when signals from different sensory channels are bound together. However, neurons in a newborn’s brain are not capable of multisensory integration, and studies in the midbrain have shown that the development of this process is not predetermined. Rather, its emergence and maturation critically depend on cross-modal experiences that alter the underlying neural circuit in such a way that optimizes multisensory integrative capabilities for the environment in which the animal will function.

The development of suckling behavior of neonatal mice is regulated by birth

Background

Although the function of the sensory system rapidly develops soon after birth in newborn pups, little is known about the mechanisms triggering this functional development of the sensory system.

Results

Here we show that the birth of pups plays an active role in the functional development of the sensory system. We first optimized the experimental procedure for suckling behavior using neonatal mouse pups. Using this procedure, we found that preterm birth selectively accelerated the development of suckling behavior in neonatal pups, but not that of motor performance, suggesting that the birth of pups regulates the functional development of the sensory system soon after birth.

Conclusions

Taken together with our recent findings that birth itself regulates the initiation of sensory map formation in the somatosensory and visual systems, these results support the idea that the birth of pups actively regulates the anatomical and functional development of the sensory system.

Organization and plasticity in multisensory integration: early and late experience affects its governing principles

Neurons in the midbrain superior colliculus (SC) have the ability to integrate information from different senses to profoundly increase their sensitivity to external events. This not only enhances an organism's ability to detect and localize these events, but to program appropriate motor responses to them. The survival value of this process of multisensory integration is self-evident, and its physiological and behavioral manifestations have been studied extensively in adult and developing cats and monkeys. These studies have revealed, that contrary to expectations based on some developmental theories this process is not present in the newborn's brain. The data show that is acquired only gradually during postnatal life as a consequence of at least two factors: the maturation of cooperative interactions between association cortex and the SC, and extensive experience with cross-modal cues. Using these factors, the brain is able to craft the underlying neural circuits and the fundamental principles that govern multisensory integration so that they are adapted to the ecological circumstances in which they will be used.

Olfactory guidance of nipple attachment and suckling in kittens of the domestic cat: Inborn and learned responses

In 60 kittens (11 litters) from free-ranging domestic cats we investigated the role of chemical cues in facilitating nipple attachment and suckling during the first month of postnatal life when kittens are totally dependent on the mother's milk. Kittens were tested both together and individually on sedated females in different reproductive states. We found (1) that newborn kittens with no suckling experience responded to the ventrum of lactating but not to the ventrum of nonlactating females with search behavior and attached to nipples within minutes; (2) that even in older kittens, nipple attachment depended on females' reproductive state, with virtually no attachments on nonreproducing females, some on pregnant females, the greatest number on early-lactating females, followed by a decline on late-lactating females; and (3) that kittens could locate their particular, most used nipple on their mother but not on a female of similar lactational age, even after eye opening. We suggest that kittens respond from birth with efficient nipple-search behavior to inborn olfactory cues on the mother's ventrum, that emission of these is under hormonal control, but that kittens also quickly learn olfactory cues specific to their own mother and to their own particular nipples.

Development of multisensory convergence in the Xenopus optic tectum

The adult Xenopus optic tectum receives and integrates visual and nonvisual sensory information. Nonvisual inputs include mechanosensory inputs from the lateral line, auditory, somatosensory, and vestibular systems. While much is known about the development of visual inputs in this species, almost nothing is known about the development of mechanosensory inputs to the tectum. In this study, we investigated mechanosensory inputs to the tectum during critical developmental stages (stages 42-49) in which the retinotectal map is being established. Tract-tracing studies using lipophilic dyes revealed a large projection between the hindbrain and the tectum as early as stage 42; this projection carries information from the Vth, VIIth, and VIIIth nerves. By directly stimulating hindbrain and visual inputs using an isolated whole-brain preparation, we found that all tectal cells studied received both visual and hindbrain input during these early developmental stages. Pharmacological data indicated that the hindbrain-tectal projection is glutamatergic and that there are no direct inhibitory hindbrain-tectal ascending projections. We found that unlike visual inputs, hindbrain inputs do not show a decrease in paired-pulse facilitation over this developmental period. Interestingly, over this developmental period, hindbrain inputs show a transient increase followed by a significant decrease in the alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionate (AMPA)/N-methyl-D-aspartate (NMDA) ratio and show no change in quantal size, both in contrast to visual inputs. Our data support a model by which fibers are added to the hindbrain-tectal projection across development. Nascent fibers form new synapses with tectal neurons and primarily activate NMDA receptors. At a time when retinal ganglion cells and their tectal synapses mature, hindbrain-tectal synapses are still undergoing a period of rapid synaptogenesis. This study supports the idea that immature tectal cells receive converging visual and mechanosensory information and indicates that the Xenopus tectum might be an ideal preparation to study the early development of potential multisensory interactions at the cellular level.

The neural basis of multisensory integration in the midbrain: its organization and maturation

Multisensory integration describes a process by which information from different sensory systems is combined to influence perception, decisions, and overt behavior. Despite a widespread appreciation of its utility in the adult, its developmental antecedents have received relatively little attention. Here we review what is known about the development of multisensory integration, with a focus on the circuitry and experiential antecedents of its development in the model system of the multisensory (i.e., deep) layers of the superior colliculus. Of particular interest here are two sets of experimental observations: (1) cortical influences appear essential for multisensory integration in the SC, and (2) postnatal experience guides its maturation. The current belief is that the experience normally gained during early life is instantiated in the cortico-SC projection, and that this is the primary route by which ecological pressures adapt SC multisensory integration to the particular environment in which it will be used.

Postnatal experiences influence how the brain integrates information from different senses

Sensory processing disorder (SPD) is characterized by anomalous reactions to, and integration of, sensory cues. Although the underlying etiology of SPD is unknown, one brain region likely to reflect these sensory and behavioral anomalies is the superior colliculus (SC), a structure involved in the synthesis of information from multiple sensory modalities and the control of overt orientation responses. In the present review we describe normal functional properties of this structure, the manner in which its individual neurons integrate cues from different senses, and the overt SC-mediated behaviors that are believed to manifest this “multisensory integration.” Of particular interest here is how SC neurons develop their capacity to engage in multisensory integration during early postnatal life as a consequence of early sensory experience, and the intimate communication between cortex and the midbrain that makes this developmental process possible.

Determination of functionally essential neuronal population of the olfactory epithelium for nipple search and subsequent suckling behavior in newborn rats

Neuronal population of the olfactory epithelium required for nipple search and subsequent suckling behavior was examined in newborn rats. After unilateral ablation of the olfactory bulb, different concentrations of ZnSO(4) were contralaterally injected into the nasal cavity to produce varying degrees of neuronal degeneration in the olfactory epithelium. The ZnSO(4)-treatment resulted in two populations of pups. One exhibited suckling while the other did not, and intact olfactory receptor neurons were quantified immunohistochemically using an antibody for olfactory marker protein (OMP), a marker protein for olfactory receptor neurons. The total numbers of the OMP (+) cells in the ZnSO(4)-treated pups with suckling capability ranged between 2457 and 4615, whereas those in the ZnSO(4)-treated pups without suckling capability ranged between 112 and 2398. With the mean value (4969) of the total numbers of the OMP (+) cells of the normal/control pups assumed to represent 100%, the total numbers of the OMP (+) cells accounted for 49-93% in the suckling (+) group and 2-48% in the suckling (-) group. From these findings, we conclude that approximately 50% of neuronal population of the olfactory epithelium is a critical value to distinguish between the two groups with and without suckling capability in the unilateral olfactory system of newborn rats.

Huntingtin associated protein 1 and its functions

Huntington disease (HD) is caused by a polyglutamine expansion in the protein huntingtin (Htt). Several studies suggest that Htt and huntingtin associated protein 1 (HAP1) participate in intracellular trafficking and that polyglutamine expansion affects vesicular transport. Understanding the function of HAP1 and its related proteins could help elucidate the pathogenesis of HD. The present review focuses on HAP1, which has proved to be involved in intracellular trafficking. Unlike huntingtin, which is expressed ubiquitously throughout the brain and body, HAP1 is enriched in neurons, suggesting that its dysfunction could contribute to the selective neuropathology in HD. We discuss recent evidence for the involvement of HAP1 and its binding proteins in potential functions.

Birth and hatching: Key events in the onset of awareness in the lamb and chick

The neuroanatomical and neurophysiological development of the embryo and fetus and unique features of the physiological environment of the fetal brain, features which are lost at birth, support recent conclusions that under normal circumstances awareness (or consciousness) is probably not exhibited by the ovine embryo-fetus before birth and that it appears for the first time only after birth. However, there has apparently been no evaluation of whether or not similar mechanisms modulate awareness-related functions in domestic chicks before and after hatching. This comparative review, in seeking to rectify this, arrived at the following conclusions. First, the neural apparatus of both lambs and chicks appears to be too immature to support any states resembling awareness during at least the first half of pregnancy or incubation. Second, electroencephalographic (EEG) activity, which evolves subsequently, shows that states of sleep-like unconsciousness are likely to be continuously present in lambs until after birth, and that such states at least predominate in chicks until after hatching. Third, as in fetal lambs, epochs of so-called 'wakefulness' previously reported in chick embryos do not seem likely to represent short periods of awareness in ovo. Fourth, several neurosuppressive mechanisms, with some unique features, also operate or have the potential to operate in chicks before hatching, but a dearth of published information currently hinders a full comparison with those demonstrated to operate in fetal lambs. Fifth, contradicting the intuitive perception that vocalisation pre-hatching by the chick indicates the presence of awareness, published evidence suggests that vocalisation before and during hatching occurs mostly during EEG states indicating sleep-like unconsciousness. Sixth, as seems to be the case for newborn lambs after birth, it is possible that demonstrable awareness may appear for the first time only after hatching in chicks, presumably through waning neurosuppression and burgeoning neuroactivation, but such awareness seems to take longer to manifest itself. However, additional research in chicks is recommended to further assess this suggestion. Particular attention should be given to the status of vocal interactions between hen and chick which begin several days before hatching, and to the operation of neurosuppressive and neuroactivating mechanisms throughout the last 40% of incubation and during and after hatching.

Functional role of lingual nerve in breastfeeding

Functional role of lingual nerve in breastfeeding was investigated in rat pups during the suckling period. DiI, a postmortem neuronal tracer, was used to confirm the immature lingual nerve (LN) responsible for tongue sensation and resulted in successful fiber labeling anterogradely to the tongue, which showed different distribution patterns from fiber labeling derived from the hypoglossal nerve. Unilaterally LN-injured pups did not show suckling disturbance with absence of any shortening (P11 pups: 559+/-16s; 105% of the control value) in nipple attachment time and the survival rate remained high (P11: 100%). Bilaterally LN-injured pups showed suckling disturbance with marked shortening (P11 pups: 220+/-54 s; 42% of the control value) in nipple attachment time and a low survival rate (P1: 33%; P11: 41%). Bilaterally infraorbital nerve-injured or bilaterally bulbectomized pups did not show any nipple attachment at all and there were no survivors, confirming the crucial roles of upper lip sensation and olfaction in suckling. Based on these findings, we conclude that tongue sensation is very important, but not essential for suckling.

The development of cortical multisensory integration

Although there are many perceptual theories that posit particular maturational profiles in higher-order (i.e., cortical) multisensory regions, our knowledge of multisensory development is primarily derived from studies of a midbrain structure, the superior colliculus. Therefore, the present study examined the maturation of multisensory processes in an area of cat association cortex [i.e., the anterior ectosylvian sulcus (AES)] and found that these processes are rudimentary during early postnatal life and develop only gradually thereafter. The AES comprises separate visual, auditory, and somatosensory regions, along with many multisensory neurons at the intervening borders between them. During early life, sensory responsiveness in AES appears in an orderly sequence. Somatosensory neurons are present at 4 weeks of age and are followed by auditory and multisensory (somatosensory-auditory) neurons. Visual neurons and visually responsive multisensory neurons are first seen at 12 weeks of age. The earliest multisensory neurons are strikingly immature, lacking the ability to synthesize the cross-modal information they receive. With postnatal development, multisensory integrative capacity matures. The delayed maturation of multisensory neurons and multisensory integration in AES suggests that the higher-order processes dependent on these circuits appear comparatively late in ontogeny.

The development of spatial capacity in piloting and dead reckoning by infant rats: Use of the huddle as a home base for spatial navigation

Two forms of spatial navigation, piloting using external cues and dead reckoning using self-movement cues, are manifest in the outward and homeward trips of adult rats exploring from a home base. Here, the development of these two forms of spatial behavior are described for rats aged 14-65 days using a new paradigm in which a huddle of pups or an artificial huddle, a small heat pad, served as a home base on an open circular table that the rats could explore. When moving away from both home bases, the travel distance, path complexity, and number of stops of outward trips from the home base increased progressively with age from postnatal day 16 through 22. When returning to the home bases, the return trips to the home base were always more direct and had high travel velocities even though travel distance increased with age for the longest trips. The results are discussed in relation to the ideas that: (1) the pups pilot on the outward portion of their excursion and dead reckon on the homeward portion of their excursion, and (2) the two forms of navigation and associated spatial capacity are interdependent and develop in parallel and in close association with locomotor skill.

Huntingtin-associated protein 1 (Hap1) mutant mice bypassing the early postnatal lethality are neuroanatomically normal and fertile but display growth retardation

Huntingtin-associated protein 1 (Hap1) is the first huntingtin interacting protein identified in a yeast two-hybrid screen. Although Hap1 expression has been demonstrated in neuronal and non-neuronal tissues, its molecular role is poorly understood. Recently, it has been shown that targeted disruption of Hap1 in mice results in early postnatal death as a result of depressed feeding behavior. Although this result clearly demonstrates an essential role of Hap1 in postnatal feeding, the mechanisms leading to this deficiency, as well as the role of Hap1 in adults, remain unclear. Here we show that Hap1 null mutants display suckling defects and die within the first days after birth due to starvation. Upon reduction of the litter size, some mutants survive into adulthood and display growth retardation with no apparent brain or behavioral abnormalities, suggesting that Hap1 function is essential only for early postnatal feeding behavior. Using a conditional gene repair strategy, we also show that the early lethality can be rescued if Hap1 expression is restored in neuronal cells before birth. Furthermore, no synergism was observed between Hap1 and huntingtin mutation during mouse development. Our results demonstrate that Hap1 has a fundamental role in regulating postnatal feeding in the first 2 weeks after birth and a non-essential role in the adult mouse.

Animal welfare implications of neonatal mortality and morbidity in farm animals

Much has been learnt during the last 50 years about the causes of neonatal mortality and morbidity and about practical means for minimising them in newborn lambs, kids, bovine calves, deer calves, foals and piglets. The major causes of problems in these newborns are outlined briefly and include hypothermia due to excessive heat loss or to hypoxia-induced, starvation-induced or other forms of inhibited heat production. They also include maternal undernutrition, mismothering, infection and injury. The published literature reveals that the scientific investigations which clarified these causes and led to practical means for minimising the problems, involved iterative successions of self-reinforcing laboratory and field or clinical investigations conducted over many years. These studies focused largely on solutions to the problems, not on the suffering that the newborn might experience, so that an analysis of the associated welfare insults had not apparently been conducted until now. The present assessment focuses on potentially noxious subjective experiences the newborn may have. The account of the causes of neonatal mortality and morbidity outlined early in this review indicates that the key subjective experiences which require analysis in animal welfare terms are breathlessness, hypothermia, hunger, sickness and pain. Reference to documented responses of farm animals and, where appropriate, to human experience, suggests that breathlessness and hypothermia usually represent less severe neonatal welfare insults than do hunger, sickness and pain. Major science-based improvements in the management of pregnancy and birth have markedly reduced the overall amount of welfare compromise experienced by newborn farm animals and further improvements may be expected as knowledge is refined and extended in the future.

Characterizing the functional significance of the neonatal rat vibrissae prior to the onset of whisking

The present series of experiments assessed how information from the whiskers controls and modulates infant rat behavior during early learning and attachment. Passive vibrissal stimulation can elicit behavioral activity in pups throughout the first two postnatal weeks, although orienting to the source of stimulation is evident only after ontogenetic emergence of whisking. In addition, while pups were capable of demonstrating learning in a classical conditioning paradigm pairing vibrissa stimulation with electric shock, no corresponding changes were detected in the anatomy of the barrel cortex as determined by cytochrome oxidase (CO) staining. Finally, the role of whiskers in a more naturalistic setting was determined in postnatal day (PN)3-5 and PN11-12 pups. Our results showed that both nipple attachment and huddling were disrupted in whisker-clipped PN3-5 pups but only marginally altered in PN1I 1-12 pups. Together, these results suggest that the neonatal whisker system is behaviorally functional and relevant for normal mother-infant interactions, though it lacks the sophistication of a mature whisker system that evokes very specific and directed responses.

Nonvisual influences on visual-information processing in the superior colliculus

Although visually responsive neurons predominate in the deep layers of the superior colliculus (SC), the majority of them also receive sensory inputs from nonvisual sources (i.e. auditory and/or somatosensory). Most of these 'multisensory' neurons are able to synthesize their cross-modal inputs and, as a consequence, their responses to visual stimuli can be profoundly enhanced or depressed in the presence of a nonvisual cue. Whether response enhancement or response depression is produced by this multisensory interaction is predictable based on several factors. These include: the organization of a neuron's visual and nonvisual receptive fields; the relative spatial relationships of the different stimuli (to their respective receptive fields and to one another); and whether or not the neuron is innervated by a select population of cortical neurons. The response enhancement or depression of SC neurons via multisensory integration has significant survival value via its profound impact on overt attentive/orientation behaviors. Nevertheless, these multisensory processes are not present at birth, and require an extensive period of postnatal maturation. It seems likely that the sensory experiences obtained during this period play an important role in crafting the processes underlying these multisensory interactions.

Vibrissae-evoked behavior and conditioning before functional ontogeny of the somatosensory vibrissae cortex

The following experiments determined that the somatosensory whisker system is functional and capable of experience-dependent behavioral plasticity in the neonate before functional maturation of the somatosensory whisker cortex. First, unilateral whisker stimulation caused increased behavioral activity in both postnatal day (P) 3-4 and P8 pups, whereas stimulation-evoked cortical activity (14C 2-deoxyglucose autoradiography) was detectable only in P8 pups. Second, neonatal rat pups are capable of forming associations between whisker stimulation and a reinforcer. A classical conditioning paradigm (P3-P4) showed that the learning groups (paired whisker stimulation-shock or paired whisker stimulation-warm air stream) exhibited significantly higher behavioral responsiveness to whisker stimulation than controls. Finally, stimulus-evoked somatosensory cortical activity during testing [P8; using 14C 2-deoxyglucose (2-DG) autoradiography] was assessed after somatosensory conditioning from P1-P8. No learning-associated differences in stimulus-evoked cortical activity were detected between learning and nonlearning control groups. Together, these experiments demonstrate that the whisker system is functional in neonates and capable of experience-dependent behavioral plasticity. Furthermore, in contrast to adult somatosensory classical conditioning, these data suggest that the cortex is not required for associative somatosensory learning in neonates.

Development of multisensory neurons and multisensory integration in cat superior colliculus

The development of multisensory neurons and multisensory integration was examined in the deep layers of the superior colliculus of kittens ranging in age from 3 to 135 d postnatal (dpn). Despite the high proportion of multisensory neurons in adult animals, no such neurons were found during the first 10 d of postnatal life. Rather, all sensory-responsive neurons were unimodal. The first multisensory neurons (somatosensory-auditory) were found at 12 dpn, and visually responsive multisensory neurons were not found until 20 dpn. Early multisensory neurons responded weakly to sensory stimuli, had long latencies, large receptive fields, and poorly developed response selectivities. Most surprising, however, was their inability to integrate combinations of sensory cues to produce significant response enhancement (or depression), a characteristic feature of the adult. Responses to combinations of sensory cues differed little from responses to their modality-specific components. At 28 dpn an abrupt physiological change was noted. Some multisensory neurons now integrated combinations of cross-modality cues and exhibited significant response enhancements when these cues were spatially coincident and response depressions when the cues were spatially disparate. During the next 2 months the incidence of multisensory neurons, and the proportion of these neurons capable of adult-like multisensory integration, gradually increased. Once multisensory integration appeared in a given neuron, its properties changed little with development. Even the youngest integrating neurons showed superadditive enhancements and spatial characteristics of multisensory integration that were indistinguishable from the adult. Nevertheless, neonatal and adult multisensory neurons differed in the manner in which they integrated temporally asynchronous stimuli, a distribution that may reflect the very different behavioral requirements at different ages. The possible maturational role of corticotectal projections in the abrupt gating of multisensory integration is discussed.

Sensory systems and nipple attachment behavior in neonatal pigs

The influence of piglet sensory systems and the role of odors from the sow's ventrum on piglet nipple attachment were investigated. In Experiment 1, four sows had their ventrum washed with organic solvents and four were unwashed control sows. Piglets were given one of four treatments shortly after birth: nares that were mechanically blocked (B), a lidocaine flush of the olfactory system (LFO), a saline flush of the olfactory system (SFO) or nontreated controls (C). Time to attach to a nipple, up to a maximum of 600 sec, was recorded. On unwashed sows, nipple attachment was affected (p less than 0.01) by piglet treatment. Piglets have B or LFO treatments took longer to attach to a nipple than SFO or C piglets. Piglets of all treatments took longer to attach to washed sows than to unwashed controls. Seven unwashed sows and their litters were used in Experiment 2. Piglets were tested after birth with one of the following treatments: an olfactory system flushed with lidocaine, lidocaine on nose (LN), lidocaine applied to the tongue (LT) or nontreated controls. All lidocaine-treated piglets took more time to attach than C piglets. Nipple attachment latencies were intermediate for LN or LT piglets. In Experiment 3, three unwashed sows and their litters were used. Treatments were: lidocaine applied to both the nose and the tongue (LNT), an olfactory system flushed with lidocaine or nontreated controls. LFO piglets had an increased latency to attachment compared to controls while LNT piglets were intermediate in latency to attach. Piglet olfaction, gustation and tactile sensory modalities as well as odors on the sow's ventrum influenced nipple attachment.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticothalamic and corticotectal somatosensory projections from the anterior ectosylvian sulcus (SIV cortex) in neonatal cats: an anatomical demonstration with HRP and 3H-leucine

Corticothalamic and corticotectal projections from the anterior ectosylvian sulcus (AES) in neonatal cats were studied with anterograde and retrograde neuroanatomical techniques. When the injection site was relatively restricted to the sulcal walls and fundus of the rostral AES (i.e., the SIV cortex), heavy ipsilateral thalamic label was observed in the medial subdivision of the posterior group, in the suprageniculate nucleus, and in the external medullary lamina. No terminal label was seen in the contralateral thalamus although the contralateral homotopic cortex was heavily labeled. Within the ventrobasal complex (VB), dense axonal label was observed in fascicles that traversed VB, but only light terminal label was observed within VB itself. However, in cases where the tracer spread into adjacent SII, terminal label in VB was pronounced. Similarly, when the injection site extended into auditory cortex, terminal label was observed in the lateral and intermediate subdivisions of the posterior group. Rostral AES injections produced distinct, predominantly ipsilateral, terminal label in the superior colliculus that was distributed in two tiers: a discontinuous band in the stratum griseum intermedium and a more diffuse band in stratum griseum profundum. Caudally, dense terminal label was seen in the intercollicular zone and dorsolateral periaqueductal gray. When the injection site did not include rostral AES, no label was observed in the superior colliculus. Horseradish peroxidase injections into the superior colliculus of neonates produced retrogradely labeled neurons throughout the AES, but none was found on the crown of the gyrus where SII is located. Thus, the neonatal corticotectal somatosensory projection arises exclusively from AES and parallels that found in adults. These data indicate that the elaboration of a major descending somatosensory pathway from AES to the thalamus and midbrain is largely a prenatal event. The in utero anatomical maturation of the corticofugal projections from SIV cortex to the superior colliculus contrasts with the protracted postnatal development of the corticotrigeminal projections from SI cortex but is consistent with the mature anatomical state of ascending trigeminotectal projections.

Sensory determinants of nipple-attachment behavior in 2-4-day-old kittens

Fourteen kittens, 2-4 days of age, were studied on their anesthetized dams for nipple attachment behavior. In agreement with a previous report (Larson, M. A., & Stein, B. E., 1984, Dev. Psychobiol., 17: 423-436) we find that olfaction contributed rather little to nipple attachment in kittens. The major determinants appear to be tactile, centering in the mouth and trigeminal projection field. The behavior of kittens with temporary oral and/or trigeminal deafferentation is described in detail to provide some understanding of the contribution of each of those areas to nipple attachment in kittens.

Trigeminotectal and other trigeminofugal projections in neonatal kittens: an anatomical demonstration with horseradish peroxidase and tritiated leucine

The trigeminal projection to the superior colliculus in neonatal kittens was studied by using both anterograde and retrograde neuroanatomical tracing techniques. Trigeminothalamic observations also were made. In the first series of experiments, horseradish peroxidase was injected into the superior colliculus in kittens on the day of parturition and in adult cats. Retrogradely labeled cells were found throughout the contralateral sensory trigeminal complex: the greatest numbers of cells were concentrated in pars oralis, with fewer in the principal nucleus, and fewer still in pars interpolaris and pars caudalis. Thus, the distribution pattern of trigeminotectal cells in neonates is similar to that in adult animals. In the second series of experiments, we injected tritiated leucine into the rostral portion of the spinal trigeminal nucleus in neonatal kittens and adult cats and compared the laminar and spatial distribution of anterogradely transported label in the superior colliculus and thalamus. Terminal label was observed in both structures in animals as young as 1-2 days postpartum. The label in the superior colliculus was overwhelmingly contralateral and formed a tier of discontinuous patches in the stratum griseum intermediale and, in a more diffuse manner, in the stratum griseum profundum. Most of the patches were located in the rostral 80% of the superior colliculus and were 60-280 micron in width. Although the size of the patches was smaller in the neonates, their distribution was similar to that in adult cats. Thus, with the exception of the difference in patch size, the terminal pattern of trigeminotectal projections is essentially adultlike at birth. The dense pattern of contralateral terminal label in the arcuate division of the ventrobasal complex also was similar to that of the adult cat, as was the trigeminal projection to the supraoculomotor gray. These data indicate that the development of the spatial organization of a major ascending somatosensory pathway to the superior colliculus (and to the thalamus) is largely a prenatal event. It is likely that the further maturation of these systems during postnatal life is limited to fine changes in axonal terminals and synaptic formation within prenatally determined terminal territories. The in utero maturation of these trigeminofugal projections is necessary to enable the newborn kitten to utilize the perioral tactile cues necessary for early orientation and suckling behaviors.

The contribution of the olfactory and tactile modalities to the nipple-search behaviour of newborn rabbits

By performing uni- and bilateral olfactory bulb lesions and uni- and bilateral transsections of the infraorbital branches of the trigeminal nerves in 2-day-old rabbits, it could be shown that: Both the olfactory and tactile modalities are essential for the successful performance of nipple-search behaviour. While bilateral bulbectomy completely eliminates searching, and hence suckling, unilateral bulbectomy has relatively little effect. Bilateral denervation of the muzzle does not eliminate searching, but pups are unable to suckle as they fail to show the mouth-opening component necessary for nipple attachment. In contrast to unilateral bulbectomy, unilateral denervation of the muzzle results in a lateralization of head movements during searching, nipple grasping and nipple release.

Cardiac orienting and habituation to auditory and vibrotactile stimuli in the infant decerebrate rat

Phasic changes in heart rate were used to evaluate sensory reactivity and habituation in 5- and 12-day-old normal and decerebrate rats. Twenty-four and forty-eight hours after thalamic transection, temporally paired auditory or vibrotactile stimuli were repeatedly presented in a sensory disparity paradigm. While tone stimuli failed to evoke consistent cardiac change, vibrotactile stimuli produced cardiac decelerations, characteristic of the orienting response, in all subject groups. The magnitude of this response was comparable in both normal and decerebrate subjects at 5 days of age, but demonstrated a more notable increase with age in the normal subjects. Habituation of the cardiac response was apparent in all groups, and was not significantly different in the normal and decerebrate subjects. No consistent responses were apparent in any group to the unexpected omission of the second stimulus of the pair. Results indicate that orienting and habituation processes can persist in the absence of the cerebral hemispheres and support the view that lower levels of the neuraxis are capable of mediating a range of adaptive functions.