Development of the projection from the nucleus of the brachium of the inferior colliculus to the superior colliculus in the ferret

Neurons in the deeper layers of the superior colliculus (SC) have spatially tuned receptive fields that are arranged to form a map of auditory space. The spatial tuning of these neurons emerges gradually in an experience-dependent manner after the onset of hearing, but the relative contributions of peripheral and central factors in this process of maturation are unknown. We have studied the postnatal development of the projection to the ferret SC from the nucleus of the brachium of the inferior colliculus (nBIC), its main source of auditory input, to determine whether the emergence of auditory map topography can be attributed to anatomical rewiring of this projection. The pattern of retrograde labeling produced by injections of fluorescent microspheres in the SC on postnatal day (P) 0 and just after the age of hearing onset (P29), showed that the nBIC-SC projection is topographically organized in the rostrocaudal axis, along which sound azimuth is represented, from birth. Injections of biotinylated dextran amine-fluorescein into the nBIC at different ages (P30, 60, and 90) labeled axons with numerous terminals and en passant boutons throughout the deeper layers of the SC. This labeling covered the entire mediolateral extent of the SC, but, in keeping with the pattern of retrograde labeling following microsphere injections in the SC, was more restricted rostrocaudally. No systematic changes were observed with age. The stability of the nBIC-SC projection over this period suggests that developmental changes in auditory spatial tuning involve other processes, rather than a gross refinement of the projection from the nBIC.     

The organization of the connections between the cortex and the claustrum in the monkey

The distribution of labelled cells and of extracellular granules in the claustrum has been studied after injections of horseradish peroxidase in several areas of the neocortex. The frontal and parietal lobes are related to the anterior and posterior halves respectively of the claustrum, and the occipital and temporal cortex to the posterior and inferior margins. Parts of the claustrum related to areas of the cortex in the frontal lobe overlap considerably in the antero-posterior dimension with parts related to widely separated but interconnected areas of the parieto-temporal cortex. Areas of cortex within one lobe which are interconnected are related to parts of the claustrum which overlap in the dorsoventral dimension.     

A projection to the striatum from the medial subdivision of the posterior group of the thalamus in the cat

Injections of wheat germ agglutinin-conjugated horseradish peroxidase in the lateral part of the caudate nucleus or the putamen of the cat result in retrograde thalamic cell-labeling in the rostral extension of the medial subdivision of the posterior group (POM). Autoradiography after [³H]amino acid injection of POM reveals a dense and discontinuous distribution of axons in the lateral half of the caudate and putamen concentrated at their middle rostrocaudal levels. This newly discovered thalamostriatal projection of POM may account for somatosensory activity observed in striatal cells.     

Sexual pheromones and the evolution of the reward system of the brain: the chemosensory function of the amygdala

The amygdala of all tetrapod vertebrates receives direct projections from the main and accessory olfactory bulbs, and the strong similarities in the organization of these projections suggest that they have undergone a very conservative evolution. However, current ideas about the function of the amygdala do not pay sufficient attention to its chemosensory role, but only view it as the core of the emotional brain. In this study, we propose that both roles of the amygdala are intimately linked since the amygdala is actually involved in mediating emotional responses to chemical signals. The amygdala is the only structure in the brain receiving pheromonal information directly from the accessory olfactory bulbs and we have shown in mice that males emit sexual pheromones that are innately attractive for females. In fact, sexual pheromones can be used as unconditioned stimuli to induce a conditioned attraction to previously neutral odorants as well as a conditioned place preference. Therefore, sexual pheromones should be regarded as natural reinforcers. Behavioural and pharmacological studies (reviewed here) have shown that the females' innate preference for sexual pheromones is not affected by lesions of the dopaminergic cells of the ventral tegmental area, and that the systemic administration of dopamine antagonists do not alter neither the attraction nor the reinforcing effects of these pheromones. Anatomical studies have shown that the vomeronasal amygdala gives rise to important projections to the olfactory tubercle and the islands of Calleja, suggesting that these amygdalo-striatal pathways might be involved in the reinforcing value of sexual pheromones.     

Evidence for the collateral innervation of the esophagus and the heart from neurons in the compact formation of the nucleus ambiguus of the rat

We investigated whether the heart receives collateral projections from the neurons which innervate the esophagus with a retrograde double-labeling method using two fluorescent tracers. Following injections of True Blue (TB) into the esophagus and Diamidino Yellow (DY) into the heart, about 21.9% of the labeled esophageal motoneurons in the compact formation of the nucleus ambiguus (AmC) were retrogradely double labeled. No single-labeled cardiac motoneurons were found in the AmC. The present results provide anatomical substrates for the esophagocardiac reflex.     

Role of the paraventricular nucleus in the projection from the nucleus of the solitary tract to the olfactory bulb

Electrophysiological experiments were performed on anesthetized rats to determine the effects of lesions of the paraventricular nucleus on the amplitude of evoked potentials recorded in the periglomerular layer of the olfactory bulb after nucleus of the solitary tract electrical stimulation. Lesions of the paraventricular nucleus enhance the amplitude of both the positive and negative components of the evoked potential in the olfactory bulb. The pathway from the paraventricular nucleus to the olfactory bulb seems to exert a suppressive influence over the projection from the nucleus of the solitary tract to the olfactory bulb under these conditions.     

On the origin of the serotonergic input to the intermediate lobe of the rat pituitary

Single stimulations of the vagina and cervix were performed between proestrus and the first day of diestrus with a stimulator designed to grade the intravaginal penetration of a rod. The percent incidence of pseudopregnancy after this stimulation was exponentially related to the extent of intravaginal penetration and was also affected by the stage of the cycle at which the stimulation was performed. At 10.00 h on proestrus, an exponential increase in the incidence of pseudopregnancy was observed with shallow penetrations, while an exponential decrease was found when deeper penetrations were applied. Such negative exponential correlation had disappeared at 22.00 h on proestrus. At that time, also, some responses were elicited by very shallow penetrations (17 mm) and all the animals responded to penetrations of 20 mm or more. Sensitivity to cervicovaginal stimulation at 10.00 h on estrus was lower than that at 22.00 h on proestrus and it was even lower at 10.00 h on the first day of diestrus. The response to 18 mm of penetration was studied every 3 h between 10.00 h on proestrus and 10.00 h on estrus, and then every 12 h until 10.00 h on the first day of diestrus. This stimulation was usually ineffective to induce pseudopregnancy, except for a brief period encompassing the night between proestrus and estrus, when a peak in the incidence of responses was reached. This peak sensitivity could be advanced following the s.c. administration of 250 and 500 ng of LH-RH at 11.00 h on proestrus. Other doses were ineffective. The peptide (500 ng) was unable to induce pseudopregnancy in rats that received no cervicovaginal stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

On the development of the stratification of the inner plexiform layer in the chick retina

This study investigated the development of the subdivision of the chick inner plexiform layer (IPL). The approach included an immunohistological analysis of the temporal and spatial expressions of choline acetyltransferase, of the neural-glial-related and neural-glial cell adhesion molecules (NrCAM and NgCAM, respectively) and axonin-1, and of inwardly rectifying potassium (Kir) channels in 5- to 19-day-old (E5-E19) embryos. Ultrastructural investigations evaluated whether synaptogenesis accompanies the onset of differentiation of the IPL. We found that the differentiation of the IPL started at E9. Distinct cholinergic strata appeared, NrCAM immunoreactivity showed a poorly defined stratification, and Kir3.2 was expressed in the IPL and in the inner nuclear layer. From E10 until late E14, NgCAM- and axonin-1-immunoreactive strata emerged in an alternating sequence from the outer to the inner IPL. During this period, the NrCAM pattern sharpened, and eventually five bands of weaker and stronger immunoreactivity were found. Conventional synapses formed at the beginning of E9, and stratification of the IPL also began on the same day at the same location. Synaptogenesis and stratification followed a gradient from the central to the peripheral retina. The topographic course of differentiation of the IPL generally corresponded to the course of maturation of ganglion and amacrine cells. Synaptogenesis and the expression of G-protein-gated Kir3.2 channels accompanied the onset of stratification. These events coincide with the occurrence of robust and rhythmic spontaneous neuronal activity. The subsequent differentiation of the IPL seemed to be orchestrated by several mechanisms.     

Projections from the five divisions of the orbital cortex to the thalamus in the rat

The orbital cortex (ORB) of the rat consists of five divisions: the medial (MO), ventral (VO), ventrolateral (VLO), lateral (LO), and dorsolateral (DLO) orbital cortices. No previous report has comprehensively examined and compared projections from each division of the ORB to the thalamus. Using the anterograde anatomical tracer, Phaseolus vulgaris leucoagglutinin, we describe the efferent projections from the five divisions of the ORB to the thalamus in the rat. We demonstrated that, with some overlap, each division of the ORB distributed in a distinct (and unique) manner to nuclei of the thalamus. Overall, ORB projected to a relatively restricted number of sites in the thalamus, and strikingly distributed entirely to structures of the medial/midline thalamus, while completely avoiding lateral regions or principal nuclei of the thalamus. The main termination sites in the thalamus were the paratenial nucleus (PT) and nucleus reuniens (RE) of the midline thalamus, the medial (MDm) and central (MDc) divisions of the mediodorsal nucleus, the intermediodorsal nucleus, the central lateral, paracentral, and central medial nuclei of the rostral intralaminar complex and the submedial nucleus (SM). With some exceptions, medial divisions of the ORB (MO, VO) mainly targeted “limbic-associated” nuclei such as PT, RE, and MDm, whereas lateral division (VLO, LO, DLO) primarily distributed to “sensorimotor-associated” nuclei including MDc, SM, and the rostral intralaminar complex. As discussed herein, the medial/midline thalamus may represent an important link (or bridge) between the orbital cortex and the hippocampus and between the ORB and medial prefrontal cortex. In summary, the present results demonstrate that each division of the orbital cortex projects in a distinct manner to nuclei of the thalamus which suggests unique functions for each division of the orbital cortex.     

Origins of the sympathetic innervation of the cervical end of the uterus in the rat

A retrograde neuronal tracer (Fast Blue) was injected in the cervical end of the uterine horn of virgin rats. The majority of the retrogradely labeled post-ganglionic sympathetic neurons were found in the sympathetic chain (74%). The superior mesenteric ganglia, inferior mesenteric ganglia and suprarenal ganglia accounted for 22, 3 and <1%, respectively. The distribution of neurons in the sympathetic chain labeled from the uterus resembles that described for other pelvic organs.     

Organization of projections from the mediodorsal nucleus of the thalamus to the basolateral complex of the amygdala in the rat

Mediodorsal thalamic (MD) projections to the basolateral amygdaloid complex of the rat were investigated with the anterograde neuronal tracer, Phaseolus vulgaris-leucoagglutinin. Iontophoretic injections were made in distinct subdivisions of the rostral and caudal part of the MD. Both the medial and lateral division of the MD showed a projection to the basolateral complex and there appears to be a topographical organization of the innervation in the rostrocaudal direction: the rostral and caudal part of the MD project to respectively the mid-rostrocaudal and rostral part of the basolateral complex.     

An electrophysiological characterization of the projection from the central nucleus of the amygdala to the periaqueductal gray of the rat: the role of opioid receptors

The midbrain periaqueductal gray (PAG) and the central nucleus of the amygdala (CNA) are both known to be involved in fear and anxiety, analgesia, vocalization, cardiovascular and respiratory changes, and freezing. Anatomical studies have shown that a connection between these two regions exists but little is known about the physiology or the neurochemical constituents of this pathway. The goals of this study were to characterize the projection from the CNA to the PAG using electrophysiological techniques and to determine whether μ- and/or δ-opioid receptors, which play a large role in a majority of the functions of the PAG, are involved in this pathway. Of the 38 PAG cells tested with single shock stimulation of the CNA, 44% responded; of those, 46% were excited and 54% were inhibited. The latency to onset of response for the inhibitory cells (12.71 ± 6.61 ms) was shorter than that of the excitatory cells (22.33 ± 4.04 ms). Forty-six percent of the 129 PAG cells tested with train electrical stimulation of the CNA responded; 44% were excited and 56% were inhibited. Chemical stimulation of the CNA (10 mMd,l-homocysteic acid) produced similar results; 48% (62/128) of PAG cells responded; 45% of cells were excited and 55% were inhibited. The baseline firing rate of the inhibitory cells was significantly higher compared to the excitatory cells. Chemical stimulation of the CNA produced an increase in blood pressure in 12 animals, a decrease in two animals, and had no effect on the blood pressure of 68 animals. The blood pressure changes ranged between 8.5 and 26.3 mmHg with a mean of 16.2 ± 2.2 mmHg. The effect of naloxone (given either on site in the PAG or systemically) on the response to CNA stimulation was tested in 21 cells. Twenty-five percent of the excitatory cells (2/8) and 77% (10/13) of the inhibitory cells were blocked by naloxone with the majority of the blocked cells located in the ventrolateral PAG. It is concluded that: (1) Approximately 50% of cells in the lateral and ventrolateral columns of the PAG respond to CNA stimulation; (2) the inhibitory response is mediated by a faster conducting or a more direct pathway than the pathway that mediates the excitatory response; (3) neurons that are inhibited by CNA stimulation have a significantly higher baseline firing rate than neurons that are excited, suggesting that they may be tonically active interneurons; and (4) at least one link in the CNA-PAG pathway utilizes μ- or δ-opioid receptors.     

Topographic organization of the projections from the interstitial system of the spinal trigeminal tract to the parabrachial nucleus in the rat

Neurons in the paratrigeminal nucleus are known to project to the parabrachial region, but both these areas are heterogeneous, and the subnuclei that account for these connections are not known. To characterize better these projections, we injected small amounts of fluorogold or latex beads labeled with rhodamine or fluorescein into the parabrachial area in the rat and evaluated the retrograde transport of tracer to the paratrigeminal nucleus and neighboring regions. The results show that the rostral part of the paratrigeminal nucleus projects to the medial subnucleus of the parabrachial nucleus. The intermediary part of the paratrigeminal nucleus projects to both the external lateral and to the external medial subnuclei of the parabrachial nucleus. The caudal part of the paratrigeminal nucleus projects to the ventral lateral subnucleus of the parabrachial nucleus. The dorsal paramarginal nucleus projects to the external lateral and the extreme lateral subnuclei of the parabrachial nucleus. Lamina I and II of the spinal trigeminal nucleus also project to the external lateral and the extreme lateral subnuclei of the parabrachial nucleus. In conclusion, the rostral, intermediate, and caudal parts of the paratrigeminal nucleus and the dorsal paramarginal nucleus each have clearly different projection patterns and presumably have different functions.     

Projections from the parvocellular part of the posteromedial ventral nucleus of the thalamus to the lateral amygdaloid nucleus in the cat

It was shown in the cat by anterograde and retrograde WGA-HRP methods that the medial portion of the parvocellular part of the posteromedial ventral nucleus of the thalamus (VPMpc-m) sent fibers ipisilaterally to the rostrodorsal part of the lateral amygdaloid nucleus (Al-rd). The regions of the orbital gyrus (OG), which connected reciprocally with the VPMpc-m, were also observed to send fibers to the Al-rd. Thus the VPMpc-m was assumed to project to the Al-rd directly, and indirectly via the OG.     

Direct projections from the globus pallidus to the paraventricular nucleus of the thalamus in the rat

After injecting horseradish peroxidase into the thalamic regions around the paraventricular thalamic nucleus (Pv) in the rat, small neurons in the globus pallidus (GP) were labeled retrogradely with the ezyme. After injecting [³H]leucine into the GP, terminal labeling was autoradiographically observed in the Pv bilaterally with an ipsilateral dominance. These terminals in the Pv were shown by electron microscopic autoradiography to make asymmetrical synaptic contacts upon small dendrites of Pv neurons.     

Ontogeny of the projections from the anteroventral periventricular nucleus of the hypothalamus in the female rat

Neurons in the anteroventral periventricular nucleus of the hypothalamus (AVPV) mediate a variety of autonomic functions. In adults they primarily innervate neuroendocrine nuclei in the periventricular zone of the hypothalamus, including the paraventricular and arcuate nuclei (PVH, ARH). Ascending projections from the AVPV also provide inputs to the ventrolateral septum (LSv) and the principal division of the bed nuclei of the stria terminalis (BSTp). Consistent with a role in regulating preovulatory luteinizing hormone secretion, rostral projections from the AVPV contact gonadotropin-releasing hormone (GnRH) neurons surrounding the vascular organ of the lamina terminalis (OVLT). To study the development of these pathways, we placed implants of the lipophilic tracers DiI and CMDiI into the AVPV of female rats ranging in age from embryonic day 19 (E19) through adulthood. The earliest projections targeted a population of GnRH neurons, with apparent contacts from labeled fibers observed as early as E19. These connections appeared to be fully developed before birth, as similar numbers of appositions from AVPV projections onto the GnRH-immunoreactive cells were observed at all ages examined. Caudal projections were delayed relative to projections to the OVLT. Labeled AVPV fibers reached the PVH during the first postnatal week, and fibers targeting the BSTp and LSv were not observed until the second and third postnatal weeks, respectively. Labeled AVPV fibers were not seen in the ARH of animals at any age. Our results demonstrate that projections from the AVPV develop with both spatial and temporal specificity, innervating each target with a unique developmental profile.     

Organization and origin of the connection from the inferior to the superior colliculi in the rat

The inferior colliculus (IC) is the main ascending auditory relay station prior to the superior colliculus (SC). The morphology and origin of the connection from inferior to superior colliculus (I-SC) was analyzed both by anterograde and retrograde tracing. Irrespective of the subregion of the IC in which they originate, the terminal fields of these connections formed two main tiers in the SC. While the dorsal one primarily involved the stratum opticum and the stratum griseum intermediale, the ventral one innervated the deep strata, although some fibers did connect these tiers. While the dorsal tier occupied almost the whole extension of the SC, the ventral one was mostly confined to its caudomedial quadrant. The fiber density in these tiers decreased gradually in a rostral gradient and the terminal fields became denser as the anterograde tracer at the injection site was distributed more externally in the cortex of the IC. Retrograde tracing confirmed this result, although it did not reveal any topographic ordering for the I-SC pathway. Most presynaptic boutons of the I-SC terminal field were located either inside or close to the patches of acetylcholinesterase activity. Together with previous anatomical and physiological studies, our results indicate that the I-SC connection relays behaviorally relevant information for sensory-motor processing. Our observation that this pathway terminates in regions of the superior colliculus, where neurons involved in fear-like responses are located, reinforce previous suggestions of a role for the IC in generating motor stereotypes that occur during audiogenic seizures.