Fourth Ventricle Of Rats Research Articles

AGOUTI-RELATED PEPTIDE AMELIORATES LONG-TERM SUPPRESSION OF FOOD INTAKE FOLLOWING INTERLEUKIN-1β ADMINISTRATION TO THE BRAINSTEM.

Cachexia involves an anorexic response to proinflammatory diseases such as cancer, acquired immune deficiency syndrome (AIDS), and cystic fibrosis. Prior experiments have implicated the involvement of hypothalamic neurons producing pro-opiomelanocortin (POMC) that release α-melanocyte stimulating hormone, which then acts on melanocortin-4 receptors (MC4R) to produce a decrease in appetite. The nucleus of the solitary tract (NTS) in the brainstem-which also contains POMC neurons and is involved in many autonomic responses, such as gastric motility and response to taste-is likely to be involved in producing some of the symptoms of cachexia. Its response to inflammation, however, is not currently known. We hypothesized that administration of interleukin (IL)-1β to the fourth ventricle overlying the NTS would result in short-term anorexia, which would be blocked via the use of agouti-related peptide (AgRP), a natural antagonist of the MC4R. We placed intracerebroventricular (ICV) cannulas in the fourth ventricle of rats. One hour prior to lights-out, we administered artificial cerebrospinal fluid (aCSF) or AgRP. Then just prior to lights-out, we injected aCSF or IL-1β and measured 3-hour and 12-hour food intake in these animals. In a separate experiment, we sacrificed and perfused three groups of rats: those who had received two injections of aCSF, those who had received an injection of aCSF prior to IL-1β 1 hour prior to sacrifice, and those who received AgRP followed by IL-1β prior to sacrifice. We performed double-label immunohistochemistry using fluorescent tracers to identify neurons expressing tyrosine hydroxylase and c-fos, a marker of neuronal activation. Rats who received injections of IL-1β exhibited a decrease in 3-hour and 12-hour food intake compared with rats treated with aCSF alone (−73% vs control at 3 hours [p .05]). Rats treated with AgRP followed by aCSF did not differ in food intake from the control animals. Immunohistochemistry showed no significant difference in c-fos activation of neurons expressing tyrosine-hydroxylase immunoreactivity, although there was a trend toward a significant increase in activation in TH neurons (47% for control vs 59% for TH [p = .055]). IL-1β administration to the fourth ventricle produces anorexia, which is ameliorated by preadministration of AgRP. This may involve activation of neurons expressing tyrosine hydroxylase, although further experiments are needed to establish their role in the process.

Choroid plexus ependymal cells host neural progenitor cells in the rat

We previously demonstrated that choroid plexus epithelial (modified ependymal) cells (CPECs) differentiated into astrocytes after grafting into the spinal cord. In the present study, we examined whether CPECs from rats at postnatal 1 day (P1), 7 day (P7), and 8 weeks (P8W) can function as neural progenitor cells that give rise to neurons and glial cells. Cell spheres were produced in cultures of whole tissue of the choroid plexus from the fourth ventricle of rats at each postnatal period. beta-tubulin class III (Tuj-1), glial fibrillary acid protein (GFAP)-, and O4-positive cells differentiated from cell spheres in the differentiation medium. We produced a monoclonal antibody 3E6 specifically labeling microvilli of CPECs. Using this monoclonal antibody, CPECs were isolated from the choroid plexus of P8W rats by cell sorter (FACS). Immunocytochemistry confirmed that there was no contamination from fibroblasts, endothelial cells, macrophages, or Schwann cells in the FACS-isolated 3E6-labeled cells. Cell spheres formed in the cultures of these 3E6-labeled CPECs. After expansion, these cell spheres gave rise to Tuj-1- (5%), GFAP- (45%), and O4-positive cells (0.16%). The remaining cells (45%) were unlabeled neural or glial markers. Some CPECs of the P8W rat were immunohistochemically stained with lineage-associated markers of Musashi-1 and epidermal growth factor-receptor (EGF-R). In addition, infusion of EGF or fibroblast growth factor-2 (FGF2) into the ventricle increased the number of bromodeoxyuridine (BrdU)-positive cells among CPECs from 0.03% (untreated) to 1.14% (38-fold, EGF) and 1.03% (35-fold, FGF2), respectively. These findings indicate that neural progenitor cells exist among CPECs in the rat.

Intermittent nicotine administration modulates food intake in rats by acting on nicotine receptors localized to the brainstem

Previous studies have shown nicotine (NIC) administration leads to decreased food intake, while other investigations have reported that NIC stimulates c-Fos expression in the brainstem. Whether there is a causal relationship between NIC effects on ingestion and its effect on brainstem neurons is uncertain, however we hypothesized that blocking NIC action in the brainstem would prevent, to some extent, the hypophagic effects of NIC. In the present study, cannulas were placed in the fourth ventricle of rats. A dose of NIC or saline was injected i.p. in four equal injections during the dark phase for four days. At the start of the second day of injections the NIC receptor antagonist mecamylamine (MEC) or artificial cerebrospinal fluid (a-CSF) was infused intracerebroventricularly (i.c.v.). Thus, four experimental groups were examined: a-CSF + SAL; a-CSF + NIC; MEC + SAL; MEC + NIC. Meal patterns were recorded using a computerized system and water intake and body weight were measured daily. Peripheral NIC injections suppressed food intake by decreasing meal size, whereas infusion of the NIC receptor antagonist MEC (4 μg) into the fourth ventricle blocked the NIC suppression of food intake. Moreover, the MEC effect was due primarily to an increase in dark phase meal size, which suggests neurons localized to the brainstem transmit NIC signals that regulate feeding behavior by affecting meal size.

Locomotor activity after nicotine infusions into the fourth ventricle of rats

Microinjections of nicotine into the fourth ventricle of rats were reported previously to produce a characteristic prostration syndrome; similar microinjections have been investigated for effects of locomotor activity. It was confirmed that nicotine (4 μg) administered into the fourth ventricle of rats produced prostration which was also manifested on a second challenge with the drug. Increasing doses of nicotine produced increasing magnitudes of prostration and dose-related decreases in locomotor activity. In rats pretreated with nicotine (0.4 mg/kg SC) for 10 days, no tolerance was seen to either the prostration response or the locomotor depression. Mecamylamine (1.0 mg/kg SC) completely prevented the prostration response produced by 4 μg of nicotine, but the locomotor depression was still evident. The locomotor changes following intraventricular administration of nicotine appeared to be different from the locomotor depression seen following systemic administration because the posture of the animals was different and the latter effects showed tolerance with repeated exposures to nicotine and were fully blocked by mecamylamine. These findings suggested that the prostration response and the locomotor depression were mediated by different mechanisms.

Cardiovascular effects of microinjections of adenosine analogs into the fourth ventricle of rats

Rats were implanted with chronic indwelling cannulae into the posterior region of the fourth ventricle. After recovery from surgery, acute experiments on blood pressure were conducted under urethane anesthesia. The blood pressure and heart rate responses following administration of two adenosine analogs, NECA and L-PIA were examined. Microinjections of both analogs produced dose-dependent reductions in blood pressure and heart rate. NECA was appoximately 20-fold more potent than L-PIA in reducing blood pressure and depressing heart rate. The cardiovascular effects of both analogs were antagonized by parenteral injections of caffeine. These findings show that microinjections of analogs of adenosine into the fourth ventricle can influence areas of the central nervous system involved in cardiovascular control.

Reaction of periventricular tissue in the rat fourth ventricle to chronically placed shunt tubing implants.

The reaction of periventricular tissue to shunt tubing chronically implanted in the fourth ventricle of the rat was investigated by correlative scanning and transmission electron microscopy. Sterile silicone tubing with four 0.4 mm diameter holes was inserted into the fourth ventricle of adult Sprague-Dawley rats through an incision in the atlantooccipital membrane and the animals were killed at postoperative intervals of 5 and 8 weeks. Reactive changes that could be correlated with the extent of contact with the implant occurred in the periventricular tissue. The ependyma lining the ventricle underwent a progressive loss of cilia and microvilli, became attenuated and, in circumscribed areas, was lost entirely. A significant subependymal gliosis accompanied these changes. In regions denuded of ependyma, neurons and glia were exposed directly to the cerebrospinal fluid. Eruptions of periventricular tissue corresponding precisely to the location of holes in the implanted tubing were observed on both the vermal surface of the cerebellum and the floor of the ventricle. Evaginations from the surface of the inferior vermis and the floor of the ventricle were most prevalent at 5 and greatest at 8 weeks postimplantation, respectively. Gliosis combined with mechanical factors are believed to be responsible for development of these periventricular tissue evaginations, which may be a factor in the pathogenesis of cerebrospinal fluid shunt obstruction in treated human hydrocephalus.

Central vasopressin in the modulation of catecholamine release in conscious rats.

Neurons containing arginine vasopressin (AVP) have been shown to project from the paraventricular nucleus of the hypothalamus to the nucleus tractus solitarius (NTS) in the medulla. We investigated whether AVP acts in brain stem regions to influence sympathoadrenal outflow. Cannulae were implanted into the fourth ventricle of rats 7 days prior to the experiment. The effects of intracerebroventricular (icv) injections of AVP, the vehicle, and AVP antagonist, d(CH2)5Tyr(Me)AVP, on mean arterial pressure (MAP) and plasma noradrenaline (NA) and adrenaline (A) levels were determined in conscious unrestrained rats. Injections of AVP (icv, 23 and 73 ng/kg) but not the vehicle increased MAP and plasma NA and A levels. In contrast, iv injection of AVP increased MAP but decreased plasma concentrations of A and NA. The pressor response to icv injection of AVP was abolished by prior icv injection of AVP antagonist. Injection of AVP antagonist (icv, 0.5 and 1.5 microgram/kg) had no effect on MAP or plasma NA or A levels. These results show that centrally injected AVP activates sympathoadrenal outflow, possibly via an inhibition of baroreceptor reflexes. Since centrally administered AVP antagonist did not influence MAP or plasma NA or A levels, it appears that endogenously released AVP does not have a tonic influence on central cardiovascular reflex system in conscious, unrestrained rats.

Studies on the Role of Central Histamine in the Acquisition of a Radiation-Induced Conditioned Taste Aversion

The experiments described in this report were designed to test two hypotheses about how exposure to low-level radiation can affect the behavior of an organism: first, tht radiation effects on behavior are mediated by a radiation-induced release of histamine; and second, that this radiation-induced histamine release can exert relatively direct effects on the central nervous system. The results of the first experiment showed that microinjection of histamine directly into the fourth ventricle of rats produced a taste aversion to a novel sucrose solution. Pretreating rats with intraventricular H/sub 1/ or H/sub 2/ blockers was not effective in preventing the acquisition of the radiation-induced aversion, although the H/sub 1/ blocker did prevent the acquisition of a histamine-induced taste aversion. It also was not possible to establish a cross-tolerance between centrally administered histamine and radiation. The results are interpreted as not supporting the hypothesis that a radiation-induced release of central histamine mediates the acquisition of a conditioned taste aversion following exposure to low-level radiation.

ACTH 1–24 blocks opiate - induced analgesia in the rat

Samples of 1 μl containing 15 μg of morphine sulfate with or without 1 μg of synthetic ACTH were injected into the fourth ventricle of rats. The inclusion of ACTH eliminated the analgesic effect of morphine as evaluated by the tail-flick test, both in restrained and in unrestrained, lightly sedated animals. The same result was obtained when β-endorphin was used to bring about analgesia. Since the effect of the peptides was shown to be mediated by central actions alone, the results are discussed in light of the brain ACTH/β-endorphin system.

Hyperinnervation of arrested granule cells produced by the transplantation of monoamine-containing neurons into the fourth ventricle of rat.

An attempt to learn whether chemically specific neurons affect the sequence of cerebellar development was made by transplanting ectopic tissues rich in monoamines adjacent to the early developing cerebellum of neonatal rat. Three types of brainstem grafts were used: (1) ventral midline raphe region, (2) inferior olivary region, (3) locus coeruleus region. When transplanted into the fourth ventricle of host animals, neurons from the transplant sprout axons into the host cerebellar parenchyma producing changes in cerebellar cytoarchitecture. The changes produced by the three types of brain grafts were investigated with conventional light and electron microscopy. Autoradiography with tritiated serotonin (3H-5HT) and norepinephrine (3H-NE) and immunocytochemistry using antibodies raised against serotonin allowed identification of the chemical specificity of the process. The three fundamental changes caused by the transplants were folial malformation, arrest of migration of external granule cells, and disruption of the Purkinje cell monolayer. By intraventricular infusion of 3H-5HT and immunocytochemistry with antibodies raised against serotonin, an extraordinarily rich serotonin innervation was detected within or around the foci of arrested granule cells after transplantation with raphe-rich tissue. In addition to an increase in the number of parallel fibers that accumulate 3H-5HT, numerous glomerulus-like structures were observed within the foci. After transplantation with locus coeruleus fragments, intraventricular infusion of 3H-NE demonstrated some increase of labeled fibers inside the foci of arrested granule cells, but the extent of the increase of NE fibers was less marked than the increase in 5-HT fibers. Conventional electron microscopic study revealed numerous synaptic formations within the arrested granule cell foci. Terminals containing large granular vesicles were seen, which resemble serotonin nerve terminals previously described (Chan-Palay, 1975, 1977).

Synthesis of nuclear RNA in nerve and glial cells.

Abstract—Tritium‐labelled RNA precursors were injected at 30 min intervals into the fourth ventricle of rats or rabbits. After 4 h the nuclei from neurones, astrocytes, and other glial cells were isolated and RNA extracted. Investigations were performed in order to establish optimum conditions for RNA extraction from this particular material.The sedimentation patterns obtained in sucrose gradients were similar to those of nuclear RNA from other mammalian tissues and showed the presence of RNA species with high specific activities in the region of the gradient between 10S and 16S and above 28S. All three types of nuclei contained a 45S and a 38S RNA. Moreover, a 32S component could be identified in astrocytic nuclei, a 35S fraction in neuronal nuclei, and both a 32S and 35S RNA in nuclei from glial cells. The nuclei from the various cell types also differ with respect to the rate of incorporation of the label into the nuclear RNA, being four times higher in astrocytic and neuronal nuclei than in those derived from the other glial cells.