Experimental and immunohistochemical studies concerning the major origins of the substance P-containing fibers in the lateral lemniscus and lateral parabrachial area of the rat, including the fiber pathways

Comparative distribution of NK1, NK2, and NK3 receptors in the rat brainstem auditory nuclei

While the distribution of substance P in the auditory system is well illustrated, the localization of its receptors has not yet been documented. The goal of our study was to characterize the distribution of the tachykinin receptors NK1-R, NK2-R and NK3-R in the brainstem auditory nuclei of the adult rat using immunohistochemical techniques. The immunoreactivity of the neurokinin receptors was found to be widely distributed in most neurons of the cochlear nucleus (CN), the lateral superior olive (LSO), the medial nucleus of the trapezoid body (MNTB) and in the inferior colliculus (IC). Immunoreactivity was generally confined to post-synaptic targets (neuronal cell body and proximal or primary dendrites) in all auditory nuclei. However, unlike brainstem nuclei, the IC showed, in addition to neuronal cell body staining, a positive axonal immunolabeling (axons and pre-synaptic terminals) with the anti-NK1-R antibody. This axonal staining, revealing a pre-synaptic expression of NK1-R, is in good agreement with the known presence of substance P in the IC neurons. The absence of axonal staining in the superior olivary complex nuclei which projects afferent to the IC indicated that the NK1-R labeled axons are rather intrinsic IC fibers or descending thalamic projections to the IC. Overall, the wide distribution of the three types of tachykinin receptors observed in the present study argues for an important role of tachykinin neuropeptides in the central auditory system.

Distribution and possible functional roles of some neuroactive peptides in the mammalian superior olivary complex

The mammalian superior olivary complex (SOC) is innervated by neuronal systems that contain a variety of neuroactive peptides. Conversely, neurones of the SOC form peptidergic projections to other targets. In this review, the peptides substance P, calcitonin-gene-related peptide, enkephalins and dynorphins, cholecystokinin and somatostatin are considered. Their distribution in fibres and cell bodies of the SOC are considered, with particular attention to differences between the SOC subdivisions. Evidence for the functional effects of these peptides is also reviewed and some brief speculations are offered about their possible functional role in hearing.

Substance P is involved in the sensitization of the acoustic startle response by footshocks in rats

The acoustic startle response (ASR) can be enhanced by administration of footshocks (sensitization). The neural mechanisms underlying this effect are largely unknown. A previous electrophysiological study (Kungel et al., Brain Res., 643 (1994) 29-39) has shown that the neuropeptide substance P (SP) increases the responsiveness to acoustic stimuli of neurons in the caudal pontine reticular nucleus (PnC). Since the PnC is an important part of the primary acoustic startle circuit, we hypothesized that SP is involved in the enhancement of the ASR by electric footshocks. We tested this hypothesis in different experiments by locally injecting SP and SP-antagonists into the PnC of freely moving rats. The present data show that SP (0.5 pmol-1 nmol) locally injected into the PnC dose-dependently increases the amplitude of the ASR in rats. This effect was antagonized by pretreatment with the SP-antagonist CP-96,345. Furthermore, we show that the sensitization of the ASR by 0.6 mA-footshocks can be blocked by local microinjections of the SP-antagonists CP-96,345 (5 pmol-10 nmol) or CP-99,994 (0.5 nmol-100 nmol) into the PnC. Possible pathways relevant for the sensitization of the ASR are discussed.

Substance P and other putative transmitters modulate the activity of reticular pontine neurons: an electrophysiological and immunohistochemical study

In this study we investigated the effects of possible modulatory transmitters on acoustically responsive neurons of the caudal pontine reticular nucleus (PnC). From previous work in our laboratory it has been suggested that the acoustically responsive giant neurons of this nucleus are the sensorimotor interface mediating the acoustic startle response. Furthermore they are the site of some of the modulatory influence impinging on this response. Besides a possibly glutamatergic excitation from the amygdala a cholinergic input from the midbrain has been described which may use substance P as cotransmitter. Therefore we used electrophysiological and histochemical methods to study this possible modulatory influence in the caudal pontine reticular nucleus. In the first part of this study we recorded extracellularly from single units in the PnC in vivo and studied the effects of iontophoretically applied transmitters. Substance P elicited a long lasting excitation. This excitatory effect of SP was potentiated by acetyl-beta-methylcholine (AMCh, an acetylcholine agonist), whereas single application of AMCh showed no uniform response. Glutamate elicited a potent brief excitation, while application of GABA showed a potent brief inhibition of PnC neurons. In the second part of this study we employed immunoperoxidase staining for substance P, which revealed a fairly dense network of substance P-immunoreactive (SP-ir) fibers in the lateral and ventral aspects of the PnC. Combining retrograde tracing and immunocytochemistry for substance P, we demonstrated that the SP-ir axons in the PnC originate mainly in the laterodorsal tegmental nucleus. We therefore conclude that activation of the laterodorsal tegmental nucleus may facilitate the acoustic startle response by a long lasting excitation of neurons in the caudal pontine reticular nucleus.

Substance P opens cation channels and closes potassium channels in rat locus coeruleus neurons

Whole-cell recordings were made from neurons of the rat locus coeruleus in a tissue slice removed from rat brain. Substance P caused an inward current in cells voltage-clamped at -60 mV. The effect of substance P was concentration-dependent (30 nM-3 microM) and was mimicked by similar concentrations of substance K and neuromedin K. The inward current resulted predominantly from an increase in membrane cation conductance; in potassium-free solutions it reversed polarity at about 12 mV. Substance P also reduced the conductance of an inwardly rectifying potassium current; this action was studied with low external sodium concentration. It is concluded that substance P excites rat locus coeruleus neurons by activating an intracellular transduction pathway leading to both cation conductance increase and potassium conductance decrease.

Immunohistochemical study on the distribution of neuropeptides within the pontine tegmentum--particularly the parabrachial nuclei and the locus coeruleus of the human brain

The topographical distribution of neuropeptide-containing cell bodies, fibers and terminals was studied in human parabrachial nuclei and the pontine tegmentum with immunohistochemical stainings. Brains of seven adult human subjects of 35-72 years were fixed within 2 h post mortem. Serial sections were immunostained by antisera of 14 different neuropeptides--oxytocin, vasopressin, thyrotropin-releasing hormone, angiotensin II, calcitonin gene-related peptide, beta-endorphin, dynorphin A, dynorphin B, leucine-enkephalin, alpha-melanocyte stimulating hormone, substance P, neuropeptide Y, cholecystokinin and galanin--alternately. All of these peptides were found to be present in nerve fibers and terminals, but only two, angiotensin II and dynorphin B, in cell bodies of the parabrachial nuclei. Calcitonin gene-related peptide-, neuropeptide Y-, cholecystokinin- and galanin-immunoreactive cells were present in other areas of the pontine tegmentum, like the motor trigeminal nucleus, locus coeruleus, periventricular gray matter but not in the parabrachial nuclei. Peptidergic fibers were distributed unevenly throughout the pontine tegmentum having unique, individual distribution patterns. In the parabrachial nuclei, substance P, neuropeptide Y, cholecystokinin and galanin showed the highest density of immunoreactive neuronal networks. Moderate to low concentrations of immunoreactive processes were detected by calcitonin gene-related peptide, alpha-melanocyte stimulating hormone, dynorphin B, thyrotropin releasing hormone, leucine-enkephalin, dynorphin A, angiotensin II, beta-endorphin, vasopressin and oxytocin antisera, respectively. Other pontine tegmental areas, like the locus coeruleus, dorsal tegmental, pontine raphe and motor trigeminal nuclei as well as the central gray of the tegmental region exhibited a varying assortment of neuropeptides with distinct, individual localization patterns. Their detailed topographical distributions are mapped and given in coronal sections.

Distribution and morphology of substance P-immunoreactive structures in the olfactory bulb and olfactory peduncle of the common marmoset (Callithrix jacchus), a primate species

The present study describes the morphology and distribution of substance P-immunoreactive (SP-ir) elements in the olfactory bulb (OB) and olfactory peduncle (OP) of the common marmoset (Callithrix jacchus), a primate species. SP-ir neurons are very abundant in the OB and belong to two types. External tufted cells are present in the glomerular layer (GL), whereas granule cells are found in the deeper layers, especially in the granule cell layer (GRL), but also scattered in the OP. SP-ir fibers, putatively of central origin, were identified in the OP. They ascend into the bulbar layers. The SP-chemoarchitecture of the marmoset OB and OP does not differ more from rat, guinea pig and cat, than the SP-chemoarchitecture of these species varies among one another.

Substance P- and opioid-immunoreactive structures in olfactory centers of the cat: adult pattern and postnatal development

Substance P (SP)-ir and opioid-ir structures were studied in the cat main olfactory bulb (MOB), accessory olfactory bulb (AOB), and olfactory peduncle. In the MOB, the opioid-ir and the majority of the SP-ir neurons belong to the granule cell type. SP-ir granule cells reside in the deeper granule cell layer, whereas opioid-ir granule cells reside in the superficial granule cell layer, internal plexiform, and mitral cell layer. Many granule cells are observed in the external plexiform and glomerular layer. Other granule cells were found in the bulbar/peduncular white matter, the taenia tecta, and the genu of the corpus callosum. A new substance P-ir cell type was identified in the glomerular layer. This cell type was also identified by using the technique of intracellular injection of Lucifer Yellow. The cell type corresponds neither to the external tufted type nor to the short axon cell types described so far. The AOB resembles the MOB with respect to large numbers of SP-ir and opioid-ir granule cells. In addition, a few opioid-ir neurons, probably superficial mitral cells, were found in the glomerular layer. The AOB is surrounded by islands of immunoreactive granule cells, which connect to the granule cell layer by extremely long processes. Opioid-ir and SP-ir beaded axons pass through the olfactory peduncle terminating on granule cells, and ascend as far as the glomerular layer. All subdivisions of the anterior olfactory nucleus (AON) contain immunoreactive terminal fields. Afferent fibers and terminal plexuses derive from a population of immunoreactive neurons located predominantly in the region of the septo-olfactory junction. They have large somata. Their axons form recurrent collaterals, some of which run rostrally in the peduncular white matter. Others ascend caudally towards the septal region. The fibers seem to remain ipsilaterally, since the olfactory limb of the anterior commissure and the commissure proper are devoid of SP-ir and opioid-ir fibers. During development SP and opioid immunoreactivity were found only in differentiated granule cells. The peptides were not detectable in migrating or immature granule cells, as identified in Golgi-impregnated material. The granule cell population largely develops during postnatal life. The number of opioid-ir granule cells increases slowly and continuously, reaching the adult level not before the sixth postnatal month. Strikingly, SP-ir granule cell number increases fast and reaches a transient peak during the second month. Thereafter it declines (40% decrease) to the adult density, which is similar to that of opioid-ir granule cells.

Enkephalin-immunoreactive neurons in the nucleus tractus solitarius project to the parabrachial nucleus of the cat

Enkephalin immunoreactive neurons within the nucleus tractus solitarius (NTS) were found to project to the parabrachial nucleus of the cat with the use of a combination of immunohistochemistry and retrograde transport of horseradish peroxidase. Double labelled neurons were located in the medial, parvocellular and commissural subdivisions of the NTS and were present predominantly ipsilateral to the injection site within the parabrachial nucleus. Only a few double labelled neurons were found in the contralateral NTS. The presence of neurons containing enkephalin immunoreactivity suggests that the role of enkephalin in the regulation of autonomic functions may be, in part, by circuits between the NTS and the parabrachial nucleus.

Neuropeptide and monoamine components of the parabrachial pontine complex

The present investigation examined the distributions of immunoreactive neurotensin (NT), cholecystokinin octapeptide (CCK), substance P (SP), methionine enkephalin (ENK), vasoactive intestinal polypeptide (VIP), somatostatin (SS), rat neurophysin II (RNP II), vasopressin (VP), oxytocin (OXY), tyrosine hydroxylase (TH), and serotonin in the parabrachial nuclear complex (PB) of the rat. All of these substances were localized to the PB and they appeared to be chemoarchitecturally organized within the complex. The lateral subdivision (PBL) was organized medial-lateral and ventral-dorsal. Specifically NT, CCK, and SP immunoreactive fibers were found to be the most dense in the ventral aspect of the PBL. The distribution of NT-containing fibers was similar to the pattern of CCK-containing fibers and these were localized primarily to the central zone of the PBL. Immunoreactive SP fibers and cells were found in the external and internal zones ventrally and surrounding the dorsal and dorsolateral nuclei in the PBL. Somatostatin, ENK and VIP were found to be the most dense in the dorsal PBL. Serotonin- and TH-containing cells and fibers were found in both the PBL and PBM. These results, coupled with the observations of neuronal connections of the PB and the known functions of this region, underscore the potential involvement for these neuropeptides and monoamines in limbic-brainstem mechanisms of autonomic control.

Ultrastructural localization and afferent sources of substance P in the rat parabrachial region

The ultrastructural morphology and afferent sources of terminals containing substance P-like immunoreactivity were examined in the rat parabrachial region. In the first portion of the study, a polyclonal antiserum to substance P was localized in the ventrolateral parabrachial region using the peroxidase-antiperoxidase labeling technique combined with electron microscopy. The antiserum was tested for cross-reaction with substance P, physalaemin, substance K and neuromedins B, C and K. Cross-reactivity was most intense with substance P. However, substance K, neuromedin K and physalaemin also exhibited limited cross-reactions with the antiserum. In the ventrolateral parabrachial region of untreated adult animals, substance P-like immunoreactivity was localized in axon terminals containing numerous small (40-60 nm) clear vesicle and 1-3 large (90-120 nm) dense-core vesicles. At least 54% of the labeled terminals formed asymmetric synapses with unlabeled dendrites; and at least 30% of the recipient dendrites received more than one labeled axon terminal. In addition, the labeled terminals were associated less frequently with other unlabeled soma, axon terminals and blood vessels. In the second part of the study, we examined whether or not perikarya in various extrinsic regions contributed to the substance P-like immunoreactivity in axon terminals in the parabrachial region. Wheat-germ agglutinin conjugated horseradish peroxidase was injected unilaterally into the parabrachial region of adult rats two days prior to being killed and one day prior to intraventricular injection of colchicine (100 micrograms in 7.5 microliter saline) which enhanced the detection of immunoreactivity in perikarya. Sections were first processed by a tetramethylbenzidine reaction stabilized with cobalt-diaminobenzidine for demonstration of the transported peroxidase then were immunocytochemically labeled for substance P. Perikarya containing both the black granular retrograde labeling and brown peroxidase-immunoreactivity were found in the nuclei of the solitary tracts, the caudal ventrolateral reticular formation, the lateral dorsal tegmental nucleus and the paraventricular, dorsomedial and lateral hypothalamic nuclei. The projections were largely, but not exclusively, from perikarya located on the same side as the parabrachial injection. We conclude that substance P, or a closely related tachykinin, is a putative transmitter or modulator within a number of pathways to the parabrachial region and that these afferents act primarily through axodendritic synapses with intrinsic neurons.

Substance P, neurotensin, enkephalin, and catecholamine-synthesizing enzymes: light microscopic localizations compared with autoradiographic label in solitary efferents to the rat parabrachial region

The immunocytochemical localizations of substance P, neurotensin, enkephalin and the catecholamine-synthesizing enzymes tyrosine hydroxylase and dopamine-beta-hydroxylase were examined in the rat parabrachial region. The immunoreactivity for each marker was compared with the distribution of superimposed autoradiographic labeling of parabrachial afferents after unilateral injection of 3H-amino acids into the caudal portion of the medial nucleus of the solitary tract (m-NTS). Substance-P- and neurotensinlike immunoreactivity (SPLI and NTLI, respectively) were localized primarily in varicose processes in the ventrolateral quadrant of the parabrachial region. The SPLI and NTLI were differentially localized with respect to each other; however, both peptides were detected in regions of the parabrachial containing dense autoradiographic label. In contrast, enkephalinlike immunoreactivity (ELI), tyrosine hydroxylase, and dopamine-beta-hydroxylase were detected in processes and a few perikarya located outside the ventrolateral parabrachial region. The ELI was primarily in the dorsolateral, and the catecholamine-synthesizing enzymes were primarily in the medial parabrachial regions which contained sparse autoradiographic labeling of transported amino acids. We conclude that in the rat parabrachial region, SPLI and NTLI are contained within two distinct populations of afferents which may originate from perikarya in the caudal m-NTS, whereas ELI and the catecholamines are more likely to be found in other afferents or possibly in intrinsic neurons.