Inter-fastigial projections along the roof of the fourth ventricle.

The fastigial nucleus (FN) is a bilateral cerebellar integrative center for saccadic and vestibular control associated with non-motor functions such as feeding and cardiovascular regulation. In a previous study, we identified a tract of myelinated axons embedded in the subventricular zone (SVZ) that is located between the ependymal cells that form the dorsal wall of the ventricle and the glia limitans at the roof of the fourth ventricle González-González (Sci Rep 2017, 7:40768). Here, we show that this tract of axons, named subventricular axons or SVa, contains projection neurons that bilaterally interconnect both FNs. The approach consisted of the use of a battery of fluorescent neuronal tracers, transgenic mouse lines, and immunohistofluorescence. Our observations show that the SVa belong to a wide network of GABAergic projection neurons mainly located in the medial and caudal region of the FN. The SVa should be considered a part of a continuum of the cerebellar white matter that follows an alternative pathway through the SVZ, a region closely associated with the physiology of the fourth ventricle. This finding adds to our understanding of the complex organization of the FN; however, the function of the interconnection remains to be elucidated.

Nonreflecting Boundary Conditions for a CSF Model of Fourth Ventricle: Spinal SAS Dynamics.

In this paper, we introduce a one-dimensional model for analyzing the cerebrospinal fluid dynamics within the fourth ventricle and the spinal subarachnoid space (SSAS). The model has been derived starting from an original model of Linninger et al. and from the detailed mathematical analysis of two different reformulations. We show the steps of the modelization and the rigorous analysis of the first-order nonlinear hyperbolic system of equations which rules the new CSF model, whose conservative-law form and characteristic form are required for the boundary conditions treatment. By assuming sub-critical flows, for the particular dynamics we are dealing with, the most desirable option is to employ the nonreflecting boundary conditions, that allow the simple wave associated with the outgoing characteristic to exit the computational domain with no reflections. Finally, we carry out some numerical simulations related to different cerebral physiological conditions.

Glucagon-Like Peptide-1 Receptor Activation in the Ventral Tegmental Area Decreases the Reinforcing Efficacy of Cocaine.

Cocaine addiction continues to be a significant public health problem for which there are currently no effective FDA-approved treatments. Thus, there is a clear need to identify and develop novel pharmacotherapies for cocaine addiction. Recent evidence indicates that activation of glucagon-like peptide-1 (GLP-1) receptors in the ventral tegmental area (VTA) reduces intake of highly palatable food. As the neural circuits and neurobiological mechanisms underlying drug taking overlap to some degree with those regulating food intake, these findings suggest that activation of central GLP-1 receptors may also attenuate cocaine taking. Here, we show that intra-VTA administration of the GLP-1 receptor agonist exendin-4 (0.05 µg) significantly reduced cocaine, but not sucrose, self-administration in rats. We also demonstrate that cocaine taking is associated with elevated plasma corticosterone levels and that systemic infusion of cocaine activates GLP-1-expressing neurons in the nucleus tractus solitarius (NTS), a hindbrain nucleus that projects monosynaptically to the VTA. To determine the potential mechanisms by which cocaine activates NTS GLP-1-expressing neurons, we microinjected corticosterone (0.5 µg) directly into the hindbrain fourth ventricle. Intraventricular corticosterone attenuated cocaine self-administration and this effect was blocked in animals pretreated with the GLP-1 receptor antagonist exendin-(9-39) (10 µg) in the VTA. Finally, AAV-shRNA-mediated knockdown of VTA GLP-1 receptors was sufficient to augment cocaine self-administration. Taken together, these findings indicate that increased activation of NTS GLP-1-expressing neurons by corticosterone may represent a homeostatic response to cocaine taking, thereby reducing the reinforcing efficacy of cocaine. Therefore, central GLP-1 receptors may represent a novel target for cocaine addiction pharmacotherapies.

Caudal fourth ventricular administration of the AMPK activator 5-aminoimidazole-4-carboxamide-riboside regulates glucose and counterregulatory hormone profiles, dorsal vagal complex metabolosensory neuron function, and hypothalamic Fos expression.

This study investigated the hypothesis that estrogen controls hindbrain AMP-activated protein kinase (AMPK) activity and regulation of blood glucose, counterregulatory hormone secretion, and hypothalamic nerve cell transcriptional status. Dorsal vagal complex A2 noradrenergic neurons were laser microdissected from estradiol benzoate (E)- or oil (O)-implanted ovariectomized female rats after caudal fourth ventricular (CV4) delivery of the AMPK activator 5-aminoimidazole-4-carboxamide-riboside (AICAR), for Western blot analysis. E advanced AICAR-induced increases in A2 phospho-AMPK (pAMPK) expression and in blood glucose levels and was required for augmentation of Fos, estrogen receptor-α (ERα), monocarboxylate transporter-2, and glucose transporter-3 protein in A2 neurons and enhancement of corticosterone secretion by this treatment paradigm. CV4 AICAR also resulted in site-specific modifications in Fos immunolabeling of hypothalamic metabolic structures, including the paraventricular, ventromedial, and arcuate nuclei. The current studies demonstrate that estrogen regulates AMPK activation in caudal hindbrain A2 noradrenergic neurons during pharmacological replication of energy shortage in this area of the brain, and that this sensor is involved in neural regulation of glucostasis, in part, through control of corticosterone secretion. The data provide unique evidence that A2 neurons express both ERα and -ß proteins and that AMPK upregulates cellular sensitivity to ERα-mediated signaling during simulated energy insufficiency. The results also imply that estrogen promotes glucose and lactate uptake by these cells under those conditions. Evidence for correlation between hindbrain AMPK and hypothalamic nerve cell genomic activation provides novel proof for functional connectivity between this hindbrain sensor and higher order metabolic brain loci while demonstrating a modulatory role for estrogen in this interaction.

Commissural nucleus of the solitary tract regulates the antihypertensive effects elicited by moxonidine.

The rostral ventrolateral medulla (RVLM) contains the presympathetic neurons involved in cardiovascular regulation that has been implicated as one of the most important central sites for the antihypertensive action of moxonidine (an α2-adrenergic and imidazoline agonist). Here, we sought to evaluate the cardiovascular effects produced by moxonidine injected into another important brainstem site, the commissural nucleus of the solitary tract (commNTS). Mean arterial pressure (MAP), heart rate (HR), splanchnic sympathetic nerve activity (sSNA) and activity of putative sympathoexcitatory vasomotor neurons of the RVLM were recorded in conscious or urethane-anesthetized, and artificial ventilated male Wistar rats. In conscious or anesthetized rats, moxonidine (2.5 and 5 nmol/50 nl) injected into the commNTS reduced MAP, HR and sSNA. The injection of moxonidine into the commNTS also elicited a reduction of 28% in the activity of sympathoexcitatory vasomotor neurons of the RVLM. To further assess the notion that moxonidine could act in another brainstem area to elicit the antihypertensive effects, a group with electrolytic lesions of the commNTS or sham and with stainless steel guide-cannulas implanted into the 4th V were used. In the sham group, moxonidine (20 nmol/1 µl) injected into 4th V decreased MAP and HR. The hypotension but not the bradycardia produced by moxonidine into the 4th V was reduced in acute (1 day) commNTS-lesioned rats. These data suggest that moxonidine can certainly act in other brainstem regions, such as commNTS to produce its beneficial therapeutic effects, such as hypotension and reduction in sympathetic nerve activity.

Median aperture of the fourth ventricle revisited.

BACKGROUND: The median aperture of Magendie is the largest of three openings of the fourth ventricle and thus it forms the main path for the outflow of the cerebrospinal fluid from the ventricle. The Magendie aperture connects the fourth ventricle with the cisterna magna and makes a natural corridor for neurosurgical approach and inspection of the ventricle and its floor. The purpose of this study was to give a contemporary anatomical view of this structure in the context of historical data. MATERIAL AND METHODS: The Magendie foramen was studied in 30 fixed specimens of human brainstems with cerebella. The microdissection technique was used. Measurements were taken with a microscope ocular ruler. RESULTS: The aperture is limited by the following structures: obex and gracile tubercles inferiorly, and tela choroidea with choroid plexus superolaterally. Obex tubercles usually have the form of a piece of neural tissue bridging two halves of the brainstem above the entrance to the central canal. Gracile tubercles together are 8.15 mm wide and the maximal width of the foramen is 6.53 mm. Tela choroidea attaches laterally at both sides to the inferior medullary velum. In most cases the right and left choroid plexus are connected to each other with a triangular membrane of tela choroidea, which protrudes through the median foramen and attaches to the vermis at a highly variable level. CONCLUSIONS: We hope that the presented description of anatomical relations around the Magendie aperture, with its new measurements, will be helpful for those operating in the area and will explain some of the inaccuracies found in literature.

Insight into the patterns of cerebrospinal fluid flow in the human ventricular system using MR velocity mapping.

The patterns of cerebrospinal fluid (CSF) flow within the human ventricular system are still not fully understood in all their complexity. Knowledge is based on either the interpretation of CSF flow curves or computational simulations. Both approaches only provide an incomplete insight into the spatial and temporal dynamics of CSF flow. Time-resolved three-dimensional magnetic resonance velocity mapping has previously been used to investigate normal and pathologic blood flow patterns in the human vascular system. Here we used this technique to study the spatial and temporal dynamics of CSF flow in the ventricular system of 40 normal volunteers. Classification of the patterns of CSF flow based on calculation of three-dimensional particle path lines over the cardiac cycle revealed one uniform flow pattern for the lateral ventricles, three categories for the third and two categories for the fourth ventricle. We found no significant aging effects on either the presence of a specific CSF flow pattern or on CSF flow velocities. Our results provide the first detailed demonstration of the patterns of CSF flow within the human ventricular system.

Synaptic responses in cochlear nucleus neurons evoked by activation of the olivocochlear system.

The action of olivocochlear collaterals to the cochlear nucleus is not fully established. Synaptic ultrastructure suggests an excitatory role. Extracellular recordings show spikes evoked by electrical stimulation of olivocochlear axons, but these spikes in the cochlear nucleus may be antidromic (activation of output axons) or orthodromic (synaptic input). We therefore recorded intracellular responses to shocks to olivocochlear axons in anaesthetized guinea pigs. In chopper and primary-like neurons shocks caused either no response or an inhibitory synaptic response (IPSP), but never an excitatory one (EPSP). In contrast, onset neurons never showed IPSPs but showed a variety of other responses; antidromic spikes, EPSPs, orthodromic spikes or no effect. The results agree with earlier extracellular observations in that olivocochlear collaterals provide excitatory input to onset neurons. Because some onset neurons are inhibitory they may be the source of the IPSPs observed in other cochlear nucleus neurons. The data also show that electrical stimulation at the floor of the IVth ventricle results in antidromic spikes as well. However, intracellular recording enabled the orthodromic action to be verified and the presumed olivocochlear action to be better understood. Our data support the hypothesis that olivocochlear collaterals initiate excitatory input onto onset-chopper neurons.

Forebrain melanocortin signaling enhances the hindbrain satiety response to CCK-8.

Melanocortin 4 receptors (MC4R) are hypothesized to mediate the central nervous system actions of leptin to enhance the satiety effects of cholecystokinin (CCK). To further elucidate this mechanism, we confirmed that peripheral administration of CCK-8 is less effective in producing this effect in MC4R-deficient mice (MC4R(-/-)). Whereas intraperitoneal (ip) CCK-8 at 0.75 nmol/kg lean body mass (lbm) suppressed food intake in wild-type mice, CCK-8 doses of 7.5 nmol/kg lbm were required to attenuate food intake in MC4R(-/-) mice. To determine whether melanocortin signaling in the hypothalamic paraventricular nucleus (PVN) participates in regulating this CCK satiety response, we administered the MC3/MC4R antagonist, SHU9119, into the PVN of rats before ip CCK-8 administration. PVN administration of SHU9119 attenuated the ability of CCK-8 to reduce 30-min food intake by 20%. To determine whether MC4R are expressed by PVN neurons that project directly to hindbrain nuclei involved in the satiety response to ip CCK-8, the retrograde tracer fluorescent cholera toxin subunit B was injected into the nucleus tractus solitarius (NTS) of the hindbrain. After 4 days, labeled PVN neurons were collected by laser capture microdissection and found to express MC4R mRNA by quantitative RT-PCR analysis. These data provide evidence for a neuroanatomical link between hypothalamic melanocortin signaling in the PVN and NTS neurons that regulate food intake. These findings highlight the contribution of melanocortin signaling in the PVN toward regulating the satiety effects of CCK-8 while acknowledging that melanocortin-dependent pathways in other brain regions and/or melanocortin-independent mechanisms are also important in this mechanism.

Three-dimensional computational modeling of subject-specific cerebrospinal fluid flow in the subarachnoid space.

This study aims at investigating three-dimensional subject-specific cerebrospinal fluid (CSF) dynamics in the inferior cranial space, the superior spinal subarachnoid space (SAS), and the fourth cerebral ventricle using a combination of a finite-volume computational fluid dynamics (CFD) approach and magnetic resonance imaging (MRI) experiments. An anatomically accurate 3D model of the entire SAS of a healthy volunteer was reconstructed from high resolution T2 weighted MRI data. Subject-specific pulsatile velocity boundary conditions were imposed at planes in the pontine cistern, cerebellomedullary cistern, and in the spinal subarachnoid space. Velocimetric MRI was used to measure the velocity field at these boundaries. A constant pressure boundary condition was imposed at the interface between the aqueduct of Sylvius and the fourth ventricle. The morphology of the SAS with its complex trabecula structures was taken into account through a novel porous media model with anisotropic permeability. The governing equations were solved using finite-volume CFD. We observed a total pressure variation from -42 Pa to 40 Pa within one cardiac cycle in the investigated domain. Maximum CSF velocities of about 15 cms occurred in the inferior section of the aqueduct, 14 cms in the left foramen of Luschka, and 9 cms in the foramen of Magendie. Flow velocities in the right foramen of Luschka were found to be significantly lower than in the left, indicating three-dimensional brain asymmetries. The flow in the cerebellomedullary cistern was found to be relatively diffusive with a peak Reynolds number (Re)=72, while the flow in the pontine cistern was primarily convective with a peak Re=386. The net volumetric flow rate in the spinal canal was found to be negligible despite CSF oscillation with substantial amplitude with a maximum volumetric flow rate of 109 mlmin. The observed transient flow patterns indicate a compliant behavior of the cranial subarachnoid space. Still, the estimated deformations were small owing to the large parenchymal surface. We have integrated anatomic and velocimetric MRI data with computational fluid dynamics incorporating the porous SAS morphology for the subject-specific reconstruction of cerebrospinal fluid flow in the subarachnoid space. This model can be used as a basis for the development of computational tools, e.g., for the optimization of intrathecal drug delivery and computer-aided evaluation of cerebral pathologies such as syrinx development in syringomelia.

Selective blockade of the rat brain aqueduct with thermogelling hydrogel nanoparticle dispersion.

Experimental methods targeting molecules or drugs to specific neuronal tissue(s) can be important in determining function. In this study we focused on blockade of the small channel or aqueduct connecting the third and fourth ventricles of the rat brain. A cannula was placed into the aqueduct between the third and fourth ventricle. A second cannula was placed into the third or fourth ventricle. An aqueous dispersion of hydrogel nanoparticles, that maintains a liquid state at temperatures below 33 degrees C and solidifies near body temperature (35 degrees C), was infused into the aqueduct. Two interpenetrating polymer networks (IPN) of hydrogel nanoparticles with polymer concentrations at 2% by weight and 3% by weight were separately infused into the aqueduct to block cerebrospinal fluid (CSF) flow. Following infusion of hydrogel CSF was isolated to a particular ventricle as shown by the lack of dye movement between the ventricles. In addition, stress hormone, corticosterone, feeding behavior and blood glucose levels were measured. Results show upon reaching the aqueduct the hydrogel dispersion solidified and restricted the flow of CSF. A higher concentration of dispersion (3% wt.) was more effective in blocking the aqueduct and isolating the third from the fourth ventricle. Over the period of measurement, infusion of the dispersion had no measurable detrimental physiological effects on the animal. We conclude that isolation of ventricles in the brain can be completed for 48-h by using dispersions of hydrogel nanoparticles and the effects of drugs on certain brain tissues can be determined with this method.

The circumventricular organs: an atlas of comparative anatomy and vascularization.

The circumventricular organs are small sized structures lining the cavity of the third ventricle (neurohypophysis, vascular organ of the lamina terminalis, subfornical organ, pineal gland and subcommissural organ) and of the fourth ventricle (area postrema). Their particular location in relation to the ventricular cavities is to be noted: the subfornical organ, the subcommissural organ and the area postrema are situated at the confluence between ventricles while the neurohypophysis, the vascular organ of the lamina terminalis and the pineal gland line ventricular recesses. The main object of this work is to study the specific characteristics of the vascular architecture of these organs: their capillaries have a wall devoid of blood-brain barrier, as opposed to central capillaries. This particular arrangement allows direct exchange between the blood and the nervous tissue of these organs. This work is based on a unique set of histological preparations from 12 species of mammals and 5 species of birds, and is taking the form of an atlas.

Glucose does not activate nonadrenergic, noncholinergic inhibitory neurons in the rat stomach.

We reported previously that intravenously administered d-glucose acts in the central nervous system to inhibit gastric motility induced by hypoglycemia in anesthetized rats. The purpose of this study was to determine whether this effect is due to inhibition of dorsal motor nucleus of the vagus (DMV) cholinergic motoneurons, which synapse with postganglionic cholinergic neurons, or to excitation of DMV cholinergic neurons, which synapse with postganglionic nonadrenergic, noncholinergic (NANC) neurons, particularly nitrergic neurons. Three approaches were employed: 1) assessment of the efficacy of d-glucose-induced inhibition of gastric motility in hypoglycemic rats with and without inhibition of nitric oxide synthase [10 mg/kg iv nitro-l-arginine methyl ester (l-NAME)], 2) assessment of the efficacy of intravenous bethanechol (30 mug.kg(-1).min(-1)) to stimulate gastric motility in hypoglycemic rats during the time of d-glucose-induced inhibition of gastric motility, and 3) determination of c-Fos expression in DMV neurons after intravenous d-glucose was administered to normoglycemic rats. Results obtained demonstrated that l-NAME treatment had no effect on d-glucose-induced inhibition of gastric motility; there was no reduction in the efficacy of intravenous bethanechol to increase gastric motility, and c-Fos expression was not induced by d-glucose in DMV neurons that project to the stomach. These findings indicate that excitation of DMV cholinergic motoneurons that synapse with postganglionic NANC neurons is not a significant contributing component of d-glucose-induced inhibition of gastric motility.

Mechanisms underlying the cardioinhibitory and pressor responses elicited from the medullary neurons in the gigantocellular tegmental field of cats.

A stimulation of the gigantocellular tegmental field (FTG) in the medulla oblongata often increases systemic arterial blood pressure (SAP) and decreases heart rate (HR). We investigated if the cardioinhibitory/depressor areas, including the nucleus ambiguus (NA), the dorsal motor nucleus of vagus (DMV) and the caudal ventrolateral medulla (CVLM), underlied the functional expression of FTG neurons in regulating cardiovascular responses. In 73 chloralose-urethane anesthetized cats, the HR, SAP and vertebral nerve activity (VNA) were recorded. Neurons in the FTG, NA, DMV and CVLM were stimulated by microinjection of sodium glutamate (25 mM Glu, 70 nl). To study if the NA, DMV, and CVLM relayed the cardioinhibitory messages from the FTG, 24 mM kainic acid (KA, 100 nl) was used as an excitotoxic agent to lesion neurons in the NA, DMV or CVLM. We found that the cardioinhibition induced by FTG stimulation was significantly reduced by KA lesioning of the ipsilateral NA or DMV. Subsequently, a bilateral KA lesion of NA or DMV abolished the cardioinhibitory responses of FTG. Compared to the consequence of KA lesion of the DMV, only a smaller bradycardia was induced by FTG stimulation after KA lesion of the NA. The pressor response induced by Glu stimulation of the FTG was reduced by the KA lesion of the CVLM. Such an effect was dominant ipsilaterally. Our findings suggested that both NA and DMV mediated the cardioinhibitory responses of FTG. The pressor message from the FTG neurons might be partly working via a disinhibitory mechanism through the depressor neurons located in the CVLM.

Implantation of neural stem cells via cerebrospinal fluid into the injured root.

In avulsion injury of the dorsal root, regenerating axons cannot extend through the entry zone, i.e. the transition zone between peripheral and central nervous systems, due to the discontinuity between Schwann cells and astrocytes. We infused neural stem cells through the 4th ventricle in an attempt to enhance axonal growth in injured dorsal roots. Infused stem cells were attached to, and integrated into, the lesion of the root and became associated with axons in the same manner as Schwann cells or perineurial sheath cells in the peripheral nerve, and as astrocytes in the central nerve area. These findings suggest that neural stem cells integrated by infusion through CSF might have a beneficial effect on nerve regeneration by inducing a continuity of Schwann cells and astrocytes at the transition zone.

Cannabinoid1 receptor in the dorsal vagal complex modulates lower oesophageal sphincter relaxation in ferrets.

Delta9-tetrahydrocannabinol (delta9-THC) is an effective anti-emetic; however, other potential gastrointestinal therapeutic effects of delta9-THC are less well-known. Here, we report a role of delta9-THC in a vago-vagal reflex that can result in gastro-oesophageal reflux, that is, gastric distension-evoked lower oesophageal sphincter (LOS) relaxation. Oesophageal, LOS and gastric pressures were measured using a miniaturized, manometric assembly in decerebrate, unanaesthetized ferrets.Gastric distension (30 ml) evoked LOS relaxation (70 +/- 8% decrease from baseline). Delta9-THC administered systemically (0.2 mg kg-1, iv.) or directly to the dorsal hindbrain surface (0.002 mg),significantly attenuated the nadir of the gastric distention-evoked LOS relaxation, and time to reach maximal response. Similar increases to maximal effect were observed after treatment with the cannabinoid receptor agonist WIN 55,212-2 (0.2 mg kg-1 iv.). The effect of systemic delta9-THC on gastric distention-evoked LOS relaxation was reversed by a selective cannabinoid1 (CBI) receptor antagonist, SR141617A (1 mg kg-1 i.v.). Since this reflex is vagally mediated, we used a CB1 receptor antiserum and immunocytochemistry to determine its distribution in ferret vagal circuitry. CBI receptor staining was present in cell bodies within the area postrema, nucleus tractus solitarius (NTS) and nodose ganglion. Intense terminal-like staining was noted within the NTS and dorsal motor vagal nucleus (DMN). Neither nodose ganglionectomy nor vagotomy altered the CB1 receptor terminal-like staining in the dorsal vagal complex. Retrogradely labelled gastric- or LOS-projecting DMN neurones did not express CBI receptors within their soma. Therefore, CBI receptor staining in the NTS and DMN is not due to primary vagal afferents or preganglionic neurones. These novel findings suggest that delta9-THC can modulate reflex LOS function and that the most likely site of action is via the CBI receptor within the NTS. This effect of delta9-THC may have implications in treatment of gastro-oesophageal reflux and other upper gut disorders.

Viscerotopic representation of the subdiaphragmatic tracts of the digestive apparatus within the vagus complex in the sheep.

The distribution in the brainstem and cervical spinal cord of neurons supplying the reticulum and the reticular groove, the rumen, the omasum, the abomasum, and the small and large intestine was investigated in the sheep using the fluorescent retrograde tracer technique. Only the reticulum and reticular groove were represented in the dorsal motor nucleus of the vagus nerve (DMNX), in the nucleus ambiguus (NA), and in the nucleus retroambigualis (NRA). The other forestomach, the abomasum and the small intestine were supplied by the DMNX only, with the exception of the rumen which was also innervated by the NRA. Some reticular formation neurons were found labeled after the injection of the tracer into the reticulum, the reticular groove, and the rumen. We present evidence that the reticular groove is the part of the forestomach having the widest representation, and also the richest innervation.

CART in the dorsal vagal complex: sources of immunoreactivity and effects on Fos expression and food intake.

CART-peptide (CARTp) has been shown to suppress food intake, particularly when injected into the 4th ventricle of rats, and the presence of CART in nodose ganglia suggested a role in satiation. Based on retrograde tracing from the DVC combined with CART immunohistochemistry and supranodose vagotomy, we found that CART immunoreactivity in varicose fibers of the dorsal vagal complex originates from vagal afferents, sparse projections from the medullary reticular formation and the arcuate/retrochiasmatic nucleus of the hypothalamus, and most likely also from local CART neurons in the area postrema and NTS. In the nodose ganglia, 17% of neurons with projections to the stomach and 41% to the duodenum express CART-IR. CART-IR vagal afferents significantly contribute to the rich fiber plexus in mainly the commissural NTS and the adjacent area postrema. Injections of CARTp into the 4th ventricle strongly suppressed sucrose drinking and stimulated expression of c-Fos in the NTS. Injections of CARTp directly into various subnuclei of the NTS were less effective in suppressing food intake. The findings suggest that the critical site for CART's suppression of food intake is not in the termination zone of CART-containing vagal afferents in the commissural NTS, and that CART release from vagal afferent terminals plays a minor role in satiation. The functional role of CART in vagal afferents and the site of food intake suppression by 4th ventricular CARTp remain to be determined.

Dual action of olivocochlear collaterals in the guinea pig cochlear nucleus.

Axons of olivocochlear neurones in the superior olivary complex terminate on hair cells of the cochlea, reducing the sensitivity to sound. These axons also have collateral branches to neurones in the cochlear nucleus, the first processing centre in the brainstem. Anatomical data show that these collaterals terminate mainly in the granule cell area but their precise neuronal targets and the effects they might have are unknown. We have studied the effects of these collaterals in guinea pigs, by electrically stimulating the olivocochlear axons at the floor of the IVth ventricle while recording single neurone responses in the cochlear nucleus. We eliminated the peripheral effects of olivocochlear stimulation either by destruction of the target receptor cells using chronic administration of kanamycin, or by acute perfusion of the cochlea with strychnine, a specific blocker of the postsynaptic receptors. Electrical stimulation of the olivocochlear axons in normal animals caused a variety of effects on cochlear nucleus neurones. In some neurones, there was suppression of spontaneous firing and a reduction in sensitivity to sound, while in others there was an excitatory effect of olivocochlear axon stimulation. When the peripheral olivocochlear action was eliminated, we still found both inhibition and excitation in the cochlear nucleus. These results show that the effects of olivocochlear stimulation on cochlear nucleus responses are not a simple passive reflection of peripheral changes but are a result of complex interactions between peripheral suppression of afferent input and collateral-mediated excitation and possibly also inhibition.