Afferents to the rostral olfactory bulb in sheep with special emphasis on the cholinergic, noradrenergic and serotonergic connections

The Onset of Maternal Behavior in Sheep and Goats: Endocrine, Sensory, Neural, and Experiential Mechanisms

In sheep and goats, the onset of maternal behavior at parturition is characterized by a first phase called maternal responsiveness during which the mother is attracted to any newborn. In a second phase, called maternal selectivity, the mother establishes a selective bond with her young so that she only accepts it at suckling. After a description of the behavioral expression of both phases, this chapter reviews the physiological, sensory, and neural mechanisms involved. These two behavioral processes are synchronized with parturition by the vaginocervical stimulation induced by the expulsion of the newborn. Olfactory cues provided by the neonate are involved in maternal responsiveness and selectivity. Oxytocin supported by estrogens is the key factor for maternal responsiveness. The neural network involved in maternal responsiveness is mainly hypothalamic and is different from the circuitry involved in selectivity, which mainly concerns olfactory processing regions. Visual and auditory cues are necessary for offspring recognition at a distance. This multisensory recognition suggests that mothers form a mental image of their young. Maternal experience renders mothers more responsive to maternally relevant physiology and to young-related sensory inputs.

Immunohistochemical study of the brainstem cholinergic system in the alpaca (<em>Lama pacos</em>) and colocalization with CGRP

Several cholinergic regions have been detected in the brainstem of mammals. In general, these regions are constant among different species, and the nuclear complement is maintained in animals belonging to the same order. The cholinergic system of the brainstem has been partially described in Cetartiodactyla, except for the medulla oblongata. In this work carried out in the alpaca, the description of the cholinergic regions in this order is completed by the immunohistochemical detection of the enzyme choline acetyltransferase (ChAT). In addition, using double immunostaining techniques, the relationship between the cholinergic system and the distribution of calcitonin gene-related peptide (CGRP) previously described is analysed. Although these two substances are found in several brainstem regions, the coexistence in the same cell bodies was observed only in the laterodorsal tegmental nucleus, the nucleus ambiguus and the reticular formation. These results suggest that the interaction between ChAT and CGRP may be important in the regulation of voluntary movements, the control of rapid eye movement sleep and states of wakefulness as well as in reward mechanisms. Comparing the present results with others previously obtained by our group regarding the catecholaminergic system in the alpaca brainstem, it seems that CGRP may be more functionally related to the latter system than to the cholinergic system.

Central olfactory structures

Axons from the olfactory bulb (OB) project to multiple central structures of the brain, many of which, in turn, send axons back into the OB and/or to one another. These secondary sensory regions underlie many aspects of odor representation, valence, and learning, as well as serving some nonolfactory functions, though many details remain unclear. We here describe the connectivity and essential structural and functional properties of these postbulbar olfactory regions in the mammalian brain.

Dopaminergic modulation of olfactory-evoked motor output in sea lampreys (Petromyzon marinus L.)

Detection of chemical cues is important to guide locomotion in association with feeding and sexual behavior. Two neural pathways responsible for odor-evoked locomotion have been characterized in the sea lamprey (Petromyzon marinus L.), a basal vertebrate. There is a medial pathway originating in the medial olfactory bulb (OB) and a lateral pathway originating from the rest of the OB. These olfactomotor pathways are present throughout the life cycle of lampreys, but olfactory-driven behaviors differ according to the developmental stage. Among possible mechanisms, dopaminergic (DA) modulation in the OB might explain the behavioral changes. Here, we examined DA modulation of olfactory transmission in lampreys. Immunofluorescence against DA revealed immunoreactivity in the OB that was denser in the medial part (medOB), where processes were observed close to primary olfactory afferents and projection neurons. Dopaminergic neurons labeled by tracer injections in the medOB were located in the OB, the posterior tuberculum, and the dorsal hypothalamic nucleus, suggesting the presence of both intrinsic and extrinsic DA innervation. Electrical stimulation of the olfactory nerve in an in vitro whole-brain preparation elicited synaptic responses in reticulospinal cells that were modulated by DA. Local injection of DA agonists in the medOB decreased the reticulospinal cell responses whereas the D2 receptor antagonist raclopride increased the response amplitude. These observations suggest that DA in the medOB could modulate odor-evoked locomotion. Altogether, these results show the presence of a DA innervation within the medOB that may play a role in modulating olfactory inputs to the motor command system of lampreys.

Differential effects of oxytocin on olfactory, hippocampal and hypothalamic neurogenesis in adult sheep

New neurons are continuously added in the dentate gyrus of the hippocampus, the olfactory bulb and the hypothalamus of mammalian brain. In sheep, while the control of adult neurogenesis by the social environment or the photoperiod has been the subject of several studies, its regulation by intrinsic factors, like hormones or neurotransmitters is less documented. We addressed this question by investigating the effects of central oxytocin administration on hippocampal, olfactory and hypothalamic neurogenesis. Endogenous markers, Ki67, Sox2 and DCX were used to assess cell proliferation, progenitor cells density and cell survival respectively in non-gestant ewes receiving a steroid treatment followed by intracerebroventricular injections of either oxytocin or saline. The results showed that oxytocin treatment significantly decreases the density of neuroblasts in the olfactory bulb, increases the density of neuroblasts in the ventromedian nucleus of the hypothalamus while no change is observed in both ventral and dorsal dentate gyrus. In addition, no change in the density of progenitor cells is found in the three neurogenic niches. These findings show for the first time that in females, oxytocin can regulate adult neurogenesis by acting on neuroblasts but not on progenitor cells and that this regulation is region specific.

Aversive learning-induced plasticity throughout the adult mammalian olfactory system: insights across development

Experiences, such as sensory learning, are known to induce plasticity in mammalian sensory systems. In recent years aversive olfactory learning-induced plasticity has been identified at all stages of the adult olfactory pathway; however, the underlying mechanisms have yet to be identified. Much of the work regarding mechanisms of olfactory associative learning comes from neonates, a time point before which the brain or olfactory system is fully developed. In addition, pups and adults often express different behavioral outcomes when subjected to the same olfactory aversive conditioning paradigm, making it difficult to directly attribute pup mechanisms of plasticity to adults. Despite the differences, there is evidence of similarities between pups and adults in terms of learning-induced changes in the olfactory system, suggesting at least some conserved mechanisms. Identifying these conserved mechanisms of plasticity would dramatically increase our understanding of how the brain is able to alter encoding and consolidation of salient olfactory information even at the earliest stages following aversive learning. The focus of this review is to systematically examine literature regarding olfactory associative learning across developmental stages and search for similarities in order to build testable hypotheses that will inform future studies of aversive learning-induced sensory plasticity in adults.

First evidence of neuronal connections between specific parts of the periaqueductal gray (PAG) and the rest of the brain in sheep: placing the sheep PAG in the circuit of emotion

The periaqueductal gray (PAG) is a mesencephalic brain structure organised in subdivisions with specific anatomical connections with the rest of the brain. These connections support the different PAG functions and especially its role in emotion. Mainly described in territorial and predatory mammals, examination of the PAG connections suggests an opposite role of the ventral and the dorsal/lateral PAG in passive and active coping style, respectively. In mammals, the organisation of PAG connections may reflect the coping style of each species. Based on this hypothesis, we investigated the anatomical connections of the PAG in sheep, a gregarious and prey species. Since emotional responses expressed by sheep are typical of active coping style, we focused our interest on the dorsal and lateral parts of the PAG. After injection of fluorogold and fluororuby, the most numerous connections occurred with the anterior cingulate gyrus, the anterior hypothalamic region, the ventromedial hypothalamic nucleus and the PAG itself. Our observations show that the sheep PAG belongs to the neuronal circuit of emotion and has specific parts as in other mammals. However, unlike other mammals, we observed very few connections between PAG and either the thalamic or the amygdalar nuclei. Interestingly, when comparing across species, the PAG connections of sheep were noticeably more like those previously described in other social species, rabbits and squirrel monkeys, than those in territorial species, rats or cats.

A new dopaminergic nigro-olfactory projection

Parkinson disease (PD) is a neurodegenerative disorder characterized by massive loss of midbrain dopaminergic neurons. Whereas onset of motor impairments reflects a rather advanced stage of the disorder, hyposmia often marks the beginning of the disease. Little is known about the role of the nigro-striatal system in olfaction under physiological conditions and the anatomical basis of hyposmia in PD. Yet, the early occurrence of olfactory dysfunction implies that pathogens such as environmental toxins could incite the disease via the olfactory system. In the present study, we demonstrate a dopaminergic innervation from neurons in the substantia nigra to the olfactory bulb by axonal tracing studies. Injection of two dopaminergic neurotoxins-1-methyl-4-phenylpyridinium and 6-hydroxydopamine-into the olfactory bulb induced a decrease in the number of dopaminergic neurons in the substantia nigra. In turn, ablation of the nigral projection led to impaired olfactory perception. Hyposmia following dopaminergic deafferentation was reversed by treatment with the D1/D2/D3 dopamine receptor agonist rotigotine. Hence, we demonstrate for the first time the existence of a direct dopaminergic projection into the olfactory bulb and identify its origin in the substantia nigra in rats. These observations may provide a neuroanatomical basis for invasion of environmental toxins into the basal ganglia and for hyposmia as frequent symptom in PD.

Gestational naltrexone ameliorates fetal ethanol exposures enhancing effect on the postnatal behavioral and neural response to ethanol

The association between gestational exposure to ethanol and adolescent ethanol abuse is well established. Recent animal studies support the role of fetal ethanol experience-induced chemosensory plasticity as contributing to this observation. Previously, we established that fetal ethanol exposure, delivered through a dam's diet throughout gestation, tuned the neural response of the peripheral olfactory system of early postnatal rats to the odor of ethanol. This occurred in conjunction with a loss of responsiveness to other odorants. The instinctive behavioral response to the odor of ethanol was also enhanced. Importantly, there was a significant contributory link between the altered response to the odor of ethanol and increased ethanol avidity when assessed in the same animals. Here, we tested whether the neural and behavioral olfactory plasticity, and their relationship to enhanced ethanol intake, is a result of the mere exposure to ethanol or whether it requires the animal to associate ethanol's reinforcing properties with its odor attributes. In this later respect, the opioid system is important in the mediation (or modulation) of the reinforcing aspects of ethanol. To block endogenous opiates during prenatal life, pregnant rats received daily intraperitoneal administration of the opiate antagonist naltrexone from gestational day 6-21 jointly with ethanol delivered via diet. Relative to control progeny, we found that gestational exposure to naltrexone ameliorated the enhanced postnatal behavioral response to the odor of ethanol and postnatal drug avidity. Our findings support the proposition that in utero ethanol-induced olfactory plasticity (and its relationship to postnatal intake) requires, at least in part, the associative pairing between ethanol's odor quality and its reinforcing aspects. We also found suggestive evidence that fetal naltrexone ameliorated the untoward effects of gestational ethanol exposure on the neural response to non-fetal-exposure odorants. Thus, gestational naltrexone may also have a neuroprotective and/or neuroproliferative impact on olfactory development.

The main but not the accessory olfactory system is involved in the processing of socially relevant chemosignals in ungulates

Ungulates like sheep and goats have, like many other mammalian species, two complementary olfactory systems. The relative role played by these two systems has long been of interest regarding the sensory control of social behavior. The study of ungulate social behavior could represent a complimentary alternative to rodent studies because they live in a more natural environment and their social behaviors depend heavily on olfaction. In addition, the relative size of the main olfactory bulb (MOB) [in comparison to the accessory olfactory bulb (AOB)] is more developed than in many other lissencephalic species like rodents. In this review, we present data showing a clear involvement of the main olfactory system in two well-characterized social situations under olfactory control in ungulates, namely maternal behavior and offspring recognition at birth and the reactivation of the gonadotropic axis of females exposed to males during the anestrous season. In conclusion, we discuss the apparent discrepancy between the absence of evidence for a role of the vomeronasal system in ungulate social behavior and the existence of a developed accessory olfactory system in these species.

Connections of the terminal nerve and the olfactory system in two galeomorph sharks: an experimental study using a carbocyanine dye

In elasmobranchs the terminal nerve courses separately from the olfactory nerve. This characteristic makes elasmobranchs excellent models to study the anatomy and function of these two systems. Here we study the neural connections of the terminal nerve and olfactory system in two sharks by experimental tracing methods using carbocyanine dyes. The main projections from the terminal nerve system (consisting of three ganglia in Scyliorhinus canicula) course ipsilaterally to the medial septal nucleus and bilaterally to the ventromedial telencephalic pallial region. Minor terminal nerve projections were also traced ipsilaterally to diencephalic and mesencephalic levels. With regard to the olfactory connections, our results show that in sharks, unlike ray-finned fishes, the primary olfactory projections are mainly restricted to the olfactory bulb. We also performed tracer application to the olfactory bulb in order to analyze the possible central neuroanatomical relationship between the projections of the terminal nerve and the olfactory bulb. In these experiments labeled neurons and fibers were observed from telencephalic to caudal mesencephalic regions. However, we observe almost no overlap between the two systems at central levels. The afferent and the putatively efferent connections of the dogfish olfactory bulb are compared with those previously reported in other elasmobranchs. The significance of the extratelencephalic secondary olfactory projections is also discussed in a comparative context.

Ingestion of amniotic fluid enhances the facilitative effect of VTA morphine on the onset of maternal behavior in virgin rats

Previous research has shown that injection of morphine into the ventral tegmental area (VTA) facilitates the onset of maternal behavior in virgin female rats, and injection of the opioid antagonist naltrexone into the VTA disrupts the onset of maternal behavior in parturient rats. Placentophagia -- ingestion of placenta and amniotic fluid, usually at parturition -- modifies central opioid processes. Ingestion of the active substance in placenta and amniotic fluid, Placental Opioid-Enhancing Factor (POEF), enhances the hypoalgesic effect of centrally administered morphine, and more specifically, enhances delta- and kappa-opioid-receptor-mediated hypoalgesia and attenuates mu-opioid-receptor-mediated hypoalgesia. POEF (in placenta or amniotic fluid) ingestion does not, by itself, produce hypoalgesia. In the present study, we tested the hypothesis that ingestion of amniotic fluid enhances the facilitative effect of opioid activity (unilateral morphine injection) in the VTA on the rate of onset of maternal behavior. Virgin female Long-Evans rats were given one intra-VTA injection of morphine sulfate (0.0, 0.01, or 0.03 microg, in saline) and an orogastric infusion of 0.25 ml amniotic fluid or saline once each day of the first three days of the 10-day testing period. Subjects were continuously exposed to foster pups that were replaced every 12 h; replacement of pups was followed by a 15-min observation period. Maternal behavior latency was determined by the first of two consecutive tests wherein the subject displayed pup retrieval, pup licking in the nest, and crouching over all foster pups, during the 15-min observation. We confirmed the previous finding that the VTA injection, alone, of 0.03 microg morphine shortened the latency to show maternal behavior and that 0.0 microg and 0.01 microg morphine did not. Ingestion of amniotic fluid (and therefore POEF) facilitated the onset of maternal behavior in rats receiving an intra-VTA microinjection of an otherwise subthreshold dose of morphine (0.01 microg).

Olfactory system gamma oscillations: the physiological dissection of a cognitive neural system

Oscillatory phenomena have been a focus of dynamical systems research since the time of the classical studies on the pendulum by Galileo. Fast cortical oscillations also have a long and storied history in neurophysiology, and olfactory oscillations have led the way with a depth of explanation not present in the literature of most other cortical systems. From the earliest studies of odor-evoked oscillations by Adrian, many reports have focused on mechanisms and functional associations of these oscillations, in particular for the so-called gamma oscillations. As a result, much information is now available regarding the biophysical mechanisms that underlie the oscillations in the mammalian olfactory system. Recent studies have expanded on these and addressed functionality directly in mammals and in the analogous insect system. Sub-bands within the rodent gamma oscillatory band associated with specific behavioral and cognitive states have also been identified. All this makes oscillatory neuronal networks a unique interdisciplinary platform from which to study neurocognitive and dynamical phenomena in intact, freely behaving animals. We present here a summary of what has been learned about the functional role and mechanisms of gamma oscillations in the olfactory system as a guide for similar studies in other cortical systems.

Perinatal visceral events and brain mechanisms involved in the development of mother-young bonding in sheep

In sheep the onset of maternal responsiveness and the development of the mutual mother-young bond are under the combined influence of hormonal and visceral somatosensory stimulations. These stimuli are provided in the mother by parturition (via steroids and vaginocervical stimulation) and in the neonate by the first suckling episodes (via cholecystokinin and oro-gastro-intestinal stimulation). In addition, each partner relies on specific chemosensory stimulation for reciprocal attraction: amniotic fluids for the mother, colostrum for the young. In the ewe parturition activates several brain structures to respond specifically to sensory cues emanating from the young. The main olfactory bulbs undergo profound neurophysiological changes when exposed to offspring odors at parturition. Additional activations in the hypothalamus - preoptic area - and the amygdala - medial and cortical nuclei - also contribute to maternal responsiveness and memorization of lamb odors. In the neonate, post-ingestive stimulations activate the brain stem via vagal afferents. Like in the ewe, several regions of the hypothalamus and the amygdala respond to colostrum ingestion suggesting common ground for the integrative neural processes involved in early learning and bonding. This leads to rapid visual and auditory recognition in both partners although olfaction remains important in the ewe to display selective nursing. It is concluded that the biological basis for the development of maternal and filial bonding in sheep presents striking similarities.

A map of the major nuclei of the fetal sheep brainstem

The fetal sheep has been used to investigate a wide range of developmental and pathological processes such as the effect of severe hypoxia, asphyxia, or intrauterine infection on the brain but, until now, there has been no complete description of the normal anatomical organisation of neuronal groups to facilitate interpretation of these studies. In this paper, we describe the major nuclei of the fetal sheep brainstem based on a study of 5 fetal sheep at 140 days of gestation (G140: term is G147). Nuclei were identified with the aid of brain atlases available for other species, and from the previously published, partial descriptions available for the sheep. Fifty-five distinct nuclei were identified after Nissl (thionin) staining, and their caudal and rostral margins were defined. This paper provides an easy reference to the position of the major nuclei within the fetal sheep brainstem, and can be used as a guide for future studies examining the organisation of neuronal populations under normal and pathological conditions in this animal model.

An argument for an olfactory thalamus

The mammalian olfactory system is unique in that sensory receptors synapse directly into the olfactory bulb of the forebrain without the thalamic relay that is common to all other sensory pathways. We argue that the olfactory bulb has an equivalent role to the thalamus, because the two regions have very similar structures and functions. Both the thalamus and the olfactory bulb are the final stage in sensory processing before reaching target cortical regions, at which there is a massive increase in neuron and synapse numbers. Thus, both structures act as a bottleneck that is a target for various modulatory inputs, and this arrangement enables efficient control of information flow before cortical processing occurs.

Topography and connections of the telencephalon in a chondrostean,Acipenser baeri: An experimental study

Sturgeons belong to an ancient group of the extant actinopterygian fishes. Accordingly, the study of their brain connections is important to understand brain evolution in the line leading to teleosts. We examined the topography and connections of the various telencephalic regions of the Siberian sturgeon (Acipenser baeri). The telencephalic regions were characterized on the basis of acetylcholinesterase histochemistry and calbindin-D28k and calretinin immunohistochemistry. The telencephalic connections were investigated by using the fluorescent dye DiI (1,1'-dioctadecyl 3,3,3',3'-tetramethylindocarbocyanine perchlorate) in fixed brains. Application of DiI to different areas of the pallial (dorsal) regions of the telencephalic lobes showed that they have mostly intratelencephalic connections. A posterior pallial region is characterized by its similar hodology to that of the posterior zone of the teleosts dorsal telencephalon and those described in other ancient groups. Extratelencephalic connections of the pallium are scarce, although a few afferent and efferent connections with the diencephalon, mesencephalon, and rostral rhombencephalon were observed. DiI application to subpallial regions showed both intratelencephalic connections and connections with different brain regions. Afferents to the subpallium originate from the olfactory bulbs, preoptic area, thalamus, posterior tuberculum, hypothalamus, secondary gustatory nucleus, and raphe nuclei. Some of these connections are quite similar to those described for other vertebrates.

A field guide to the anterior olfactory nucleus (cortex)

While portions of the mammalian olfactory system have been studied extensively, the anterior olfactory nucleus (AON) has been relatively ignored. Furthermore, the existing research is dispersed and obscured by many different nomenclatures and approaches. The present review collects and assembles the relatively sparse literature regarding the portion of the brain situated between the olfactory bulb and primary olfactory (piriform) cortex. Included is an overview of the area's organization, the functional, morphological and neurochemical characteristics of its cells and a comprehensive appraisal of its efferent and afferent fiber systems. Available evidence suggests the existence of subdivisions within the AON and demonstrates that the structure influences ongoing activity in many other olfactory areas. We conclude with a discussion of the AON's mysterious but complex role in olfactory information processing.

5-hydroxytryptamine action in the rat olfactory bulb: In vitro electrophysiological patch-clamp recordings of juxtaglomerular and mitral cells

The olfactory bulb, first relay of olfactory pathways, is densely innervated by serotoninergic centrifugal fibers originating from the raphe nuclei. Although serotonin innervation was reported to be involved in olfactory learning in mammals, the action of this neurotransmitter on its putative cellular targets has been never described through unitary recordings. This lack of data initiated the present study where the effects of 5HT on juxtaglomerular and mitral cells are analyzed using whole-cell recordings on olfactory bulb slices. Serotonin depolarizes 34% of 525 JG cells. A multivariate statistical analysis of juxtaglomerular cells characteristics shows that the serotonin responsive cell group can be individualized regarding their tonic discharge-mode in response to a direct current injection, their lower expression of hyperpolarization-activated cation current and their low membrane capacities. The use of ion channel blockers and ramp voltage protocol indicate that serotoninergic depolarization of juxtaglomerular cells may be due to a nonselective cation current with a reversal potential of -44 mV. Pharmacological tests with serotonin receptor antagonists and agonists reveal that 5HT action on juxtaglomerular cells would be mainly mediated by 5HT2C receptors. In mitral cells, serotonin acts on 49.1% of the 242 tested cells, inducing two types of responses. A first subset of mitral cells (26.8%, n=65) were hyperpolarized by serotonin. This response would be indirect and mediated by action of GABA on GABAA receptors since it was antagonized by bicuculline. The involved GABAergic neurons are hypothesized to be juxtaglomerular and granular cells, on which serotonin would act mainly via 5HT2C and via 5HT2A receptors respectively. The second subset of mitral cells (22.3%, n=54) were directly depolarized by serotonin acting through 5HT2A receptors. Our data on serotonin action on juxtaglomerular cells and mitral cells reveal a part of functional mechanisms whereby serotonin can act on olfactory bulb network. This is expected to enrich the understanding of its determining role in olfactory learning.

Nutritional and environmental effects on reproduction in small ruminants

Animals live in environments that are both complex and continually changing, so they have to respond to short- and long-term variations in a wide range of factors, such as photoperiod, nutrition and sociosexual signals. Before they were domesticated, animals developed reproductive strategies that coped with these changes and often took advantage of them. The physiological processes that implement these strategies have been modified to some extent during several millennia of controlled breeding, but most persist. Thus, many genotypes still exhibit profound responses to external inputs, such as the induction of ovulation by sociosexual signals and the doubling of litter size by a change in nutrition. The complexity in these responses is now becoming clearer. For example, with sociosexual signals, we now need to consider the stimulatory effects of males on females, of females on males and of females on females. Similarly, the impact of nutrition has been extended beyond the control of puberty and the production of gametes to include phenomena such as ‘fetal programming’, with its potentially profound effects on the life-long performance of the animals. Fortunately, our capacity to research these phenomena has been greatly enhanced by technical improvements in hormone assays, molecular and cellular biology, and real-time ultrasound. This has brought us a better understanding of several of the environmental influences on reproduction, including: the cellular processes within ovarian follicles that mediate the effect of nutrition on ovulation rate; the neuroendocrine pathways through which nutritional inputs affect the brain centres that control appetite and reproduction; and the intracerebral pathways through which sociosexual signals (olfactory and non-olfactory) stimulate the reproductive axis. Importantly, we are now beginning to realise that, as well as considering interactions between environmental inputs and genotype, we need to take into account interactions between the environmental factors themselves, just as the animals do. We still have a long way to go for a complete understanding, but we are nevertheless in a position where we can begin to use this information to develop new management systems for our animals to improve their productivity.

Mapping the Neural Substrates Involved in Maternal Responsiveness and Lamb Olfactory Memory in Parturient Ewes Using Fos Imaging

In sheep, recognition of the familiar lamb by the mother depends on the learning of its olfactory signature after parturition. The authors quantified Fos changes in order to identify brain regions activated during lamb odor memory formation. Brain activation was compared with those measured in anosmic ewes displaying maternal behavior but not individual lamb recognition. In intact ewes, parturition induced significant increase in Fos expression in olfactory cortical regions and in cortical amygdala, whereas in anosmic mothers, Fos expression was very low. In contrast, no difference was observed between intact and anosmic ewes in hypothalamic areas and medial amygdala, suggesting a differentiation between the neural network controlling maternal responsiveness and that involved in olfactory lamb memory.

Extensive immunolesions of basal forebrain cholinergic system impair offspring recognition in sheep

The involvement of the basal forebrain cholinergic system has been extensively investigated in instrumental learning but little is known of its participation in social memory, especially in the memorization of individual traits of a conspecific. The present study tested in sheep its contribution to both instrumental learning and individual offspring recognition. Six weeks before parturition, ewes received injections of a specific cholinergic immunotoxin (ME20.4 IgG-saporin) into the lateral ventricles (150 microg) and in some cases additional immunotoxin injections into the nucleus basalis (11 microg/side). After 3 weeks of recovery, ewes were trained on a classical instrumental visual discrimination task known to be sensitive to cholinergic deficits. The formation of memory of offspring was assessed through both olfactory and visual/auditory recognition tasks. Olfactory recognition was tested by presenting at suckling successively an alien and the familiar lamb at 2 and 4 h after parturition. Visual/auditory recognition of the lamb was performed using a non-olfactory discrimination test between the familiar and an alien lamb after 12 h of mother-young contact. The lesion extent was assessed by counting choline acetyltransferase-immunopositive neurons in the basal forebrain and measuring the density of acetylcholinesterase fibers in different target areas. Results showed that immunotoxic lesions delayed acquisition of the instrumental visual discrimination. Moreover, olfactory recognition of the lamb was severely impaired while visual/auditory lamb recognition was marginally altered. There was no evidence for sensorimotor or motivational deficits. Importantly, impairment was observed in animals for which loss of basal forebrain cholinergic neurons and their efferent fibers was higher than 75%, while striatal cholinergic neurons and Purkinje cells were unaffected. This study provides evidence that the basal forebrain cholinergic system contributes not only to instrumental but also to social learning. In addition, the cholinergic modulation seems of importance for processing visual and olfactory modalities. However, since only extensive lesions affect performance, this indicates that the basal forebrain cholinergic system possesses substantial reserve capacity to sustain cognitive functions.

Distribution and co-localization of choline acetyltransferase and p75 neurotrophin receptors in the sheep basal forebrain: implications for the use of a specific cholinergic immunotoxin

The basal forebrain cholinergic system is involved in different forms of memory. To study its role in social memory in sheep, an immunotoxin, ME20.4 immunoglobulin G (IgG)-saporin, was developed that is specific to basal forebrain cholinergic neurons bearing the p75 neurotrophin receptor. The distribution of sheep cholinergic neurons was mapped with an antibody against choline acetyltransferase. To assess the localization of the p75 receptor on basal forebrain cholinergic neurons, the distribution of p75 receptor-immunoreactive neurons with ME20.4 IgG was examined, and a double-labeling study with antibodies against choline acetyltransferase and p75 receptor was undertaken. The loss of basal forebrain cholinergic neurons and acetylcholinesterase fibers in basal forebrain projection areas was assessed in ewes that had received intracerebroventricular injections of the immunotoxin (50, 100 or 150 microg) alone, as well as, in some of the ewes treated with the highest dose, with bilateral immunotoxin injections in the nucleus basalis (11 microg/side). Results indicated that choline acetyltransferase- and p75 receptor-immunoreactive cells had similar distributions in the medial septum, the vertical and horizontal limbs of the band of Broca, and the nucleus basalis. The double-labeling procedure revealed that 100% of the cholinergic neurons are also p75 receptor positive in the medial septum and in the vertical and horizontal limbs of the band of Broca, and 82% in the nucleus basalis. Moreover, 100% of the p75 receptor-immunoreactive cells of these four nuclei were cholinergic. Combined immunotoxin injections into ventricles and the nucleus basalis produced a near complete loss (80-95%) of basal forebrain cholinergic neurons and acetylcholinesterase-positive fibers in the hippocampus, olfactory bulb and entorhinal cortex. This study provides the first anatomical data concerning the basal forebrain cholinergic system in ungulates. The availability of a selective cholinergic immunotoxin effective in sheep provides a new tool to probe the involvement of basal forebrain cholinergic neurons in cognitive processes in this species.

Oligosynaptic pathways possibly relaying visceral and/or gustatory information to the olfactory bulb in the hedgehog tenrec

Using anterograde and retrograde transport of wheat germ agglutinin we showed that the parabrachial nucleus, known to receive second order visceral and gustatory afferents, might project directly to the anterior olfactory nucleus which is connected with the olfactory bulb (OfB). Only a small bulbar region is targeted directly by parabrachial fibers. This region is located immediately adjacent to the accessory OfB and may be closely related to, if not identical with the modified glomerular complex. To further substantiate the presence of true parabrachio-bulbar projections thyrosine hydroxylase immunohistochemistry was employed. The absence of immunoreactive neurons in the parabrachial nucleus and the different distribution patterns of immunoreactive fibers and axons labeled with wheat germ agglutinin conjugated to horseradish peroxidase in the target areas make it unlikely that catecholaminergic fibers were involved in the projections shown.

Effects of dopamine receptor antagonists on ongoing maternal behavior in rats

The effects of different peripheral doses of four dopamine (DA) receptor antagonists on general activity and maternal behavior were examined in lactating female rats. Administration of the classic D1-like and D2-like DA receptor blocker haloperidol (0.1 and 0.05 mg/kg) disrupted pup retrieval and nest-building behaviors and reduced motor activity. Pimozide (0.5 and 0.2 mg/kg), which has more affinity for DA D2-like receptors, mildly disrupted pup retrieval while showing no significant influence on open-field behaviors. The putative DA D(4) receptor blocker, clozapine (1.5 and 1.0 mg/kg) reduced motor activity significantly, while only 1.0 mg/kg dose significantly decreased percent of rats displaying nest building. The DA D1-like receptor blocker SKF-83566 (0.2 and 0.1 mg/kg) significantly reduced pup retrieval, nest building and motor activity. These results suggest a role for DA receptors in ongoing maternal behavior that correlates directly with general activity.

Basal telencephalic regions connected with the olfactory bulb in a Madagascan hedgehog tenrec

In an attempt to gain insight into the organization and evolution of the basal forebrain, the region was analysed cytoarchitecturally, chemoarchitecturally, and hodologically in a lower placental mammal, the lesser hedgehog tenrec. Particular emphasis was laid on the subdivision of the olfactory tubercle, the nuclear complex of the diagonal band, and the cortical amygdala. The proper tubercule and the rostrolateral tubercular seam differed from each other with regard to their immunoreactivity to calbindin and calretinin, as well as their afferents from the piriform cortex. Interestingly, the tubercular seam showed similar properties to the dwarf cell compartment, located immediately adjacent to the islands of Calleja. The most prominent input to the olfactory bulb (OfB) originated from the diagonal nuclear complex. This projection was ipsilateral, whereas the bulbar afferents from the hypothalamus and the mesopontine tegmentum were bilateral. The amygdala projected only sparsely to the OfB, but received a prominent bulbar projection. An exception was the nucleus of the lateral olfactory tract, which was poorly connected with the OfB. Unlike other species with an accessory OfB, the projections from the tenrec's main OfB did not show a topographic organization upon the lateral and medial olfactory amygdala. However, there was an accessory amygdala, which could be differentiated from the lateral nuclei by its intense reaction to NADPh-diaphorase. This reaction was poor in the diagonal nuclear complex as in monkey but unlike in rat. The variability of cell populations and olfactory bulb connections shown here may help to clarify both phylogenetic relationships and the significance of individual basal telencephalic subdivisions.