Rabbit Forebrain Research Articles

Hyaluronidase and Hyaluronan Oligosaccharides Promote Neurological Recovery after Intraventricular Hemorrhage.

Intraventricular hemorrhage (IVH) in premature infants results in inflammation, arrested oligodendrocyte progenitor cell (OPC) maturation, and reduced myelination of the white matter. Hyaluronan (HA) inhibits OPC maturation and complexes with the heavy chain (HC) of glycoprotein inter-α-inhibitor to form pathological HA (HC-HA complex), which exacerbates inflammation. Therefore, we hypothesized that IVH would result in accumulation of HA, and that either degradation of HA by hyaluronidase treatment or elimination of HCs from pathological HA by HA oligosaccharide administration would restore OPC maturation, myelination, and neurological function in survivors with IVH. To test these hypotheses, we used the preterm rabbit model of glycerol-induced IVH and analyzed autopsy samples from premature infants. We found that total HA levels were comparable in both preterm rabbit pups and human infants with and without IVH, but HA receptors--CD44, TLR2, TLR4--were elevated in the forebrain of both humans and rabbits with IVH. Hyaluronidase treatment of rabbits with IVH reduced CD44 and TLR4 expression, proinflammatory cytokine levels, and microglia infiltration. It also promoted OPC maturation, myelination, and neurological recovery. HC-HA and tumor necrosis factor-stimulated gene-6 were elevated in newborns with IVH; and depletion of HC-HA levels by HA oligosaccharide treatment reduced inflammation and enhanced myelination and neurological recovery in rabbits with IVH. Hence, hyaluronidase or HA oligosaccharide treatment represses inflammation, promotes OPC maturation, and restores myelination and neurological function in rabbits with IVH. These therapeutic strategies might improve the neurological outcome of premature infants with IVH. Significance statement: Approximately 12,000 premature infants develop IVH every year in the United States, and a large number of survivors with IVH develop cerebral palsy and cognitive deficits. The onset of IVH induces inflammation of the periventricular white matter, which results in arrested maturation of OPCs and myelination failure. HA is a major component of the extracellular matrix of the brain, which regulates inflammation through CD44 and TLR2/4 receptors. Here, we show two mechanism-based strategies that effectively enhanced myelination and neurological recovery in preterm rabbit model of IVH. First, degrading HA by hyaluronidase treatment reduced CD44 and TLR4 expression, proinflammatory cytokines, and microglial infiltration, as well as promoted oligodendrocyte maturation and myelination. Second, intraventricular injection of HA oligosaccharide reduced inflammation and enhanced myelination, conceivably by depleting HC-HA levels.

Neuroanatomical distribution of oxytocin receptor binding in the female rabbit forebrain: Variations across the reproductive cycle

Oxytocin receptors (OTR) have been characterized in the brains of several mammals, including rodents, carnivores, and primates. Their species-specific distribution in the brain has been associated with species differences in social organization, including mating strategy and parenting behavior. In several species, the density of OTR binding in specific brain regions varies according to reproductive condition, including ovarian cycle, pregnancy and lactation. Rabbits are induced ovulators, polygamous, and monoparental but their distribution and regulation of brain OTR has not been described. Here we used receptor autoradiography to quantitatively characterize OTR binding in the brains of estrous, ovariectomized, late pregnant, and lactating does. Intense binding occurred in the prefrontal cortex (PFC), preoptic area (POA), lateral septum (LS; dorsal and ventral), hippocampus, and medial amygdala. Variations among the experimental groups were seen only in PFC, POA, LS. Ovariectomy increased OTR density in PFC but had the opposite effect in POA. Lactating does had significantly reduced OTR density, relative to late pregnancy, in PFC and POA. Our results are consistent with a possible role of OT in modulating social and maternal behavior in rabbits since the brain regions sensitive to OT have been implicated in social interaction, learning and memory, olfactory processing and maternal behavior.

Biostimulation and nursing modify mating-induced c-FOS immunoreactivity in the female rabbit forebrain

Mating in rabbits lasts only 3–5s but profoundly changes the female׳s physiology and behavior (e.g., inhibition of scent-marking and ambulation, changes in EEG, and release of GnRH). The behavioral responsiveness to copulation is reduced in lactating rabbits, relative to estrous does, but is enhanced after suppressing a single nursing bout (“biostimulation”). Little is known about the mechanisms mediating the differential responsiveness to mating among estrous, lactating, and biostimulated rabbits. To begin addressing this issue we quantified the number of c-FOS-immunoreactive (IR) cells in the preoptic area (POA), dorsomedial hypothalamus (DMH), ventromedial hypothalamus (VMH), infundibular nucleus (INF), paraventricular nucleus (PVN), supraoptic nucleus (SON), and lateral septum (LS) in mated and unmated does from the above three reproductive conditions. Mating increased c-FOS-IR cells in the POA and PVN relative to unmated estrous does. Biostimulation increased c-FOS-IR cells in the PVN, relative to lactating does, regardless of mating. Lactation reduced the responsiveness of the LS and INF to copulation but increased it in the DMH. No differences were found in the VMH. Conclusions: a) copulation activates forebrain nuclei that regulate scent-marking (POA), ovulation (INF), and post-coital oxytocin release (PVN); b) lactation and suppression of one nursing bout modulate the magnitude of such changes.

Novel organotypic in vitro slice culture model for intraventricular hemorrhage of premature infants

Mechanisms of brain injury in intraventricular hemorrhage (IVH) of premature infants are elusive, and no therapeutic strategy exists to prevent brain damage in these infants. Therefore, we developed an in vitro organotypic forebrain slice culture model to advance mechanistic studies and therapeutic developments for this disorder. We cultured forebrain slices from E29 rabbit pups and treated the cultured slices (CS) with moderate (50 μl) or large (100 μl) amounts of autologous blood to mimic moderate and severe IVH. Blood-induced damage to CS was evaluated by propidium iodide staining, lactate dehydrogenase (LDH) levels, microglial density, neuronal degeneration, myelination, and gliosis over 2 weeks after the initiation of culture. CS were viable for at least 14 days in vitro (DIV). The application of blood induced significant neural cell degeneration. Degenerating cells were more abundant and LDH levels were elevated in a dose-dependent manner in CS treated with 50 versus 100 μl of blood compared with untreated controls. Microglial density was higher in blood-treated CS compared with controls at both 7 and 14 days posttreatment, and myelination was reduced and gliosis enhanced. Selective application of blood fractions revealed that CS treated with plasma displayed more hypomyelination and gliosis compared with erythrocyte-treated slices. This study develops and characterizes a novel rabbit forebrain slice culture model of IVH that exhibits neuropatholgical changes similar to those in human infants with IVH. Importantly, plasma appears to induce greater white matter damage than erythrocytes in IVH,indicating plasma as a source of neurotoxic components.

Motherhood and nursing stimulate c-FOS expression in the rabbit forebrain.

Mother rabbits nurse once daily with circadian periodicity. The authors investigated brain structures involved in regulating this activity by quantifying c-FOS-immunoreactive (IR) cells in the forebrain of: (1) mothers killed on postpartum Day 1 (PPD 1) after nursing (Group 1) or not given pups (Group 2); (2) mothers killed on PPD 7 after nursing (Group 3) or not given pups on such day (Group 4); (3) unmated virgins (Group 5). Groups 1 through 4 showed similar numbers of c-FOS-IR cells in the preoptic area, an amount around three to fourfold larger than that found in virgins. Nursing increased, on PPD 1 and 7, c-FOS-IR cell number in the lateral septum and paraventricular and supraoptic nuclei. No differences were seen among Groups 1 through 5 in the suprachiasmatic nucleus. In the ventromedial hypothalamus virgins had more c-FOS-IR cells compared with Groups 1 and 2. Results suggest that specific forebrain structures participate in regulating particular aspects of rabbit maternal behavior: the POA and LS seem associated with the establishment of motherhood and the magnocellular nuclei with the occurrence of milk letdown.

Progesterone receptor mRNA expression and distribution in the female rabbit brain

Progesterone regulates diverse functions in the rabbit brain through the interaction with its nuclear receptor (PR). Although PR protein has been detected in some regions of the rabbit forebrain, PR mRNA expression and distribution in the rabbit brain are unknown. Hence, we investigated these issues by in situ hybridization. New Zealand adult female rabbits were ovariectomized and treated with vehicle or estradiol (5 μg/(kg day)) for 3 days. The results show an extended distribution of PR mRNA expression in the rabbit brain. The highest expression was detected in preoptic area and hypothalamic anterior nuclei such as paraventricular, periventricular and arcuate nuclei. A high expression was also detected in thalamic and telencephalic areas, including hippocampus and cerebral cortex. Estradiol treatment induced an increase in PR mRNA expression in many brain areas, particularly in the hippocampus and the hypothalamic and preoptic area regions. The wide distribution of PR mRNA in the rabbit brain suggests that progesterone through PR activation is involved in several functions apart from reproductive behavior in rabbits, and that PR expression is up-regulated by estradiol in the rabbit brain.

Immunocytochemical detection of progesterone receptor in the female rabbit forebrain: distribution and regulation by oestradiol and progesterone.

There is no information on the neuroanatomical distribution of the progesterone receptor (PR) in the rabbit. Therefore, we mapped the distribution of PR-immunoreactive cells in the forebrain of ovariectomized female rabbits. Vehicle-injected ovariectomized rabbits showed PR-immunoreactive cells only in the infundibular nucleus (IN) and nucleus X (lateral to the ventromedial hypothalamic nucleus). The injection of oestradiol benzoate (EB; 5 micro g/day for 5 days) increased the number of PR-immunoreactive cells in the IN and in three nuclei of the preoptic region (periventricular, medial, and principal). Abundant PR were also found in the paraventricular nucleus and nucleus X. Administration of progesterone (10 mg/day) for 3 days to EB-treated rabbits (a treatment that induces digging behaviour for the maternal nest and suppresses sexual receptivity and scent-marking) eliminated PR-immunoreactivity from all brain areas analysed except the IN. Thus, one-third of the number of cells seen in the ovariectomized + EB condition persisted in this region despite progesterone injections. Withdrawal of progesterone (and continuation of EB) for 5 (but not for 2) days (in a schedule similar to the one that induces straw-carrying and hair-pulling for the maternal nest) increased the number of PR-immunoreactive cells in all regions analysed. These results show that restricted regions of the female rabbit forebrain express abundant PR which are either: (i). up-regulated by oestradiol and down-regulated by progesterone; (ii). oestradiol-insensitive and down-regulated by progesterone; or (iii). insensitive to both oestradiol and progesterone.

Rabbit forebrain cholinergic system: morphological characterization of nuclei and distribution of cholinergic terminals in the cerebral cortex and hippocampus.

Although the rabbit brain, in particular the basal forebrain cholinergic system, has become a common model for neuropathological changes associated with Alzheimer's disease, detailed neuroanatomical studies on the morphological organization of basal forebrain cholinergic nuclei and on their output pathways are still awaited. Therefore, we performed quantitative choline acetyltransferase (ChAT) immunocytochemistry to localize major cholinergic nuclei and to determine the number of respective cholinergic neurons in the rabbit forebrain. The density of ChAT-immunoreactive terminals in layer V of distinct neocortical territories and in hippocampal subfields was also measured. Another cholinergic marker, the low-affinity neurotrophin receptor (p75(NTR)), was also employed to identify subsets of cholinergic neurons. Double-immunofluorescence labeling of ChAT and p75(NTR), calbindin D-28k (CB), parvalbumin, calretinin, neuronal nitric oxide synthase (nNOS), tyrosine hydroxylase, or substance P was used to elucidate the neuroanatomical borders of cholinergic nuclei and to analyze the neurochemical complexity of cholinergic cell populations. Cholinergic projection neurons with heterogeneous densities were found in the medial septum, vertical and horizontal diagonal bands of Broca, ventral pallidum, and magnocellular nucleus basalis (MBN)/substantia innominata (SI) complex; cholinergic interneurons were observed in the caudate nucleus, putamen, accumbens nucleus, and olfactory tubercule, whereas the globus pallidus was devoid of cholinergic nerve cells. Cholinergic interneurons were frequently present in the hippocampus and to a lesser extent in cerebral cortex. Cholinergic projection neurons, except those localized in SI, abundantly expressed p75(NTR), and a subset of cholinergic neurons in posterior MBN was immunoreactive for CB and nNOS. A strict laminar distribution pattern of cholinergic terminals was recorded both in the cerebral cortex and in CA1-CA3 and dentate gyrus of the hippocampus. In summary, the structural organization and chemoarchitecture of rabbit basal forebrain may be considered as a transition between that of rodents and that of primates.

Immunocytochemical Detection of Estrogen Receptor-α in the Female Rabbit Forebrain: Topography and Regulation by Estradiol

Two antibodies (H222 and Zymed) directed towards different sites of the estrogen receptor-α (ERα) were used for the following objectives: (1) to map the ERα in the forebrain of ovariectomized (ovx) rabbits by immunocytochemistry and (2) to determine the effect of endogenous (intact non-pregnant animals) and exogenous (ovx, estrogen-treated animals) estradiol (E2) on the population of ERα in the forebrain. Similar results were obtained with both antibodies used: dense aggregations of ERα-immunoreactive (IR) neurons were found in the infundibular nucleus (IN), the medial preoptic area (POA), the bed nucleus of the stria terminalis (BNST), and some nuclei of the amygdala. By contrast, no ERα-IR neurons were present in the ventromedial hypothalamic nucleus (VMN), but a dense aggregation of ERα-IR neurons occurred lateral to it in nucleus X. Numerous ERα-IR neurons were observed in the paraventricular hypothalamic nucleus, but not in the supraoptic or suprachiasmatic nuclei. The hippocampus proper lacked ERα-IR neurons, but the ventral subiculum in the hippocampal formation had a dense group of such cells. Intact non-pregnant rabbits showed less ERα-IR neurons in all regions tested than ovx animals. This difference was particularly clear in the medial POA, amygdala and BNST, while the IN showed only a marginal decrease. The dorsal, but much less the ventral, part of nucleus X also showed a decrease in the number of ERα-IR neurons compared with ovx animals. E2 benzoate (5 µg/day for 5 days) reduced even further the number of ERα-IR neurons in all regions except in a circumscribed area of the IN and the ventral part of nucleus X. These results show the existence of both sensitive and insensitive neurons to the down-regulatory effect of E2 on the presence of ERα. Sensitive neurons are located in the telencephalon, POA and several hypothalamic nuclei (PVN), while insensitive neurons are mainly restricted to the IN and the ventral part of nucleus X in the basal hypothalamus.

Aminoacyl-histidine dipeptides in the glial cells of the adult rabbit forebrain☆ ,1

The mammalian nervous system contains high amounts of the aminoacyl-histidine dipeptides carnosine and homocarnosine. In the brain, they prevalently occur mainly in glial and ependymal cells, their role(s) still remaining obscure. In vitro studies indicate that these molecules exert diverse protective effects, and in vivo they are frequently associated with extracellular fluid compartments. Recently, carnosine-like immunoreactivity has been found in the subependymal layer (SEL) of adult rodents, a region endowed with persistent cell proliferation and migration. Unlike rodents, the SEL of the rabbit has a persistent olfactory ventricle. We show here that the morphologic organization of the SEL is different in these species, with particular reference to the glial/non glial cell compartments. The distribution of carnosine-like immunoreactivity in the rabbit displays some differences only within the SEL, which could be linked to its arrangement and compartmentalization.

Differential induction of heat shock mRNA in oligodendrocytes, microglia, and astrocytes following hyperthermia.

A time course analysis of hsp70 mRNA induction in response to a physiologically relevant increase in body temperature of 2.6 degrees C was performed in the rabbit forebrain. A protocol that combined in situ hybridization and cytochemistry on the same tissue section was employed to identify reactive glial cell types. Cytochemical markers for astrocytes, microglia, and oligodendrocytes were utilized in combination with a DIG-labelled hsp70 riboprobe, which permitted mRNA localization at high resolution. Four glial cell body-enriched regions of the rabbit forebrain were examined, namely, cortical layer 1, hippocampal fissure, corpus callosum, and fimbria. Maximal hsp70 mRNA induction was observed in 2 and 3 h hyperthermic animals. The colocalization analysis demonstrated that hsp70 mRNA was induced in oligodendrocytes and microglia, but not in forebrain GFAP positive astrocytes. In addition, cell counts were performed which showed that almost all oligodendrocytes induced hsp70 mRNA while a subpopulation of microglial cells responded. These data are consistent with the notion that oligodendrocytes, microglia, and astrocytes exhibit distinct thresholds for activation of the heat shock response following a physiologically relevant increase in body temperature.

Effects of Sinoaortic Denervation on Fos Expression in the Brain Evoked by Hypertension and Hypotension in Conscious Rabbits

We have previously shown [Li and Dampney (1994) Neuroscience 61, 613–634] that periods of sustained hypertension and hypotension each induces a distinctive and reproducible pattern of neuronal expression of Fos (a marker of neuronal activation) in specific regions of the brainstem and forebrain of conscious rabbits. The aim of this study was to determine the contribution of afferent inputs from arterial baroreceptors to the activation of neurons in these various brain regions that is caused by a sustained change in arterial pressure. Experiments were carried out on rabbits in which the carotid sinus and aortic depressor nerves were cut in a preliminary operation. Following a recovery period of seven to 10 days, a moderate hypertension or hypotension (increase or decrease in arterial pressure of 20–30 mmHg) was induced in conscious barodenervated rabbits for 60 min by the continuous infusion of phenylephrine or sodium nitroprusside, respectively. In control experiments, barodenervated rabbits were subjected to the identical procedures except that they were infused with the vehicle solution alone. Compared with the effects seen in barointact rabbits, [Li and Dampney (1994) Neuroscience 61, 613–634] the number of neurons that expressed Fos in response to hypertension was reduced by approximately 90% in the nucleus of the solitary tract and in the caudal and intermediate parts of the ventrolateral medulla. In supramedullary regions, baroreceptor denervation resulted in a reduction of approximately 60% in hypertension-induced Fos expression in the central nucleus of the amygdala and in the bed nucleus of the stria terminalis, but no significant reduction in the parabrachial complex in the pons. Following hypotension, the number of neurons that expressed Fos in barodenervated rabbits, compared with barointact rabbits, [Li and Dampney (1994) Neuroscience 61, 613–634] was reduced by approximately 90% in the nucleus of the solitary tract, area postrema, and caudal, intermediate and rostral parts of the ventrolateral medulla. Baroreceptor denervation also resulted in a similar large reduction in hypotension-induced Fos expression in many supramedullary regions (locus coeruleus, midbrain periaqueductal grey, hypothalamic paraventricular nucleus, and in the central nucleus of the amygdala and the bed nucleus of the stria terminalis in the basal forebrain). In the supraoptic nucleus, hypotension-induced Fos expression in barodenervated rabbits was reduced by 75% compared to barointact animals, but was still significantly greater than in control animals. There was also a high level of Fos expression, much greater than in control animals, in the circumventricular organs surrounding the third ventricle (subfornical organ and organum vasculosum lamina terminalis). The results indicate that in conscious rabbits the activation of neurons that occurs in several discrete regions at all levels of the brain following a sustained change in arterial pressure is largely dependent upon inputs from arterial baroreceptors, with the exception of neurons in the circumventricular organs surrounding the third ventricle that are activated by sustained hypotension. The latter group of neurons are known to project to vasopressin-secreting neurons in the supraoptic nucleus, and may therefore via this pathway trigger the hypotension-induced release of vasopressin that occurs in the absence of baroreceptor inputs.

Basal expression of stress-inducible hsp70 mRNA detected in hippocampal and cortical neurons of normal rabbit brain

In response to stresses, such as elevated temperature, cells increase synthesis of a group of highly conserved proteins known as heat shock proteins (hsps). Here, we report detection of basal expression of the stress- inducible hsp70 mRNA species in neurons of the normal rabbit brain. By regional Northern blot analysis, basal levels of hsp70 mRNA were observed in control hippocampus, cortical layers, thalamus, and kidney. Using radioactive in situ hybridization, similar patterns of expression were noted for constitutive hsc70 mRNA and hsp70 mRNA in the unstressed rabbit forebrain. Non-radioactive (DIG) in situ hybridization allowed localization of both heat shock mRNA species to hippocampal neurons. In addition, a dual in situ hybridization protocol, which allowed colocalization of two mRNAs to a single cell, demonstrated that hsp70 and hsc70 mRNAs are expressed in the same hippocampal and cortical neurons.

3H]‐idazoxan binding to rabbit cerebral cortex recognises multiple imidazoline I2‐type receptors: pharmacological characterization and relationship to monoamine oxidase

1. In rabbit cerebral cortical homogenates, saturation analysis of [3H]-idazoxan, an alpha 2-adrenoceptor antagonist, revealed high affinity binding to a single site with high density. Competition experiments demonstrated that the [3H]-idazoxan recognition site was insensitive to the catecholamines, adrenaline and noradrenaline and possessed a low affinity for the alpha 2- and alpha 1-adrenoceptor antagonists, rauwolscine, yohimbine and prazosin, suggesting that the site was not an adrenoceptor. Mapping [3H]-idazoxan binding sites in the forebrain of rabbits by autoradiography, showed high densities of I2 sites in the medial preoptic area and in the stria terminalis. Moderate binding was found in caudate nucleus, putamen, cerebral cortex and hippocampus. 2. The imidazolines cirazoline, naphazoline, guanabenz and BRL44408 along with amiloride, which is structurally related to the imidazolines, all had high affinity for the [3H]-idazoxan site, suggesting that the site was related to the I2 imidazoline-recognition site described by other groups. However, the imidazolines, clonidine and UK-14,304 and the structurally related rilmenidine all had a low affinity for the binding site, showing that [3H]-idazoxan was not binding to the I1 imidazoline-recognition site found in rat, bovine and human medulla oblongata. 3. Naphazoline, guanabenz, clonidine and amiloride competition studies had Hill slopes which were significantly different from unity (P < 0.01) and computer analysis showed that the [3H]-idazoxan binding data could be best fitted to a model which considers binding to two sites (P < 0.01). One site has a high affinity for idazoxan, cirazoline, naphazoline, guanabenz and amiloride and a moderate affinity for BRL44408 and clonidine (70% of binding) and the second site (30% of binding) has a high affinity for idazoxan and cirazoline, but a lower affinity for naphazoline, guanabenz, amiloride,BRL44408 and clonidine.4. Experiments using [3H]-RX821002, in contrast to [3H]-idazoxan, clearly demonstrated the presence ofa single type of alpha2-adrenoceptor in rabbit cortex with a pharmacological profile which is similar to the alpha2A-adrenoceptor possessing a high affinity for yohimbine, rauwolscine, BRL44408 and oxymetazoline,but a lower affinity for prazosin.5. The monoamine oxidase inhibitors, clorgyline, pargyline and deprenyl had at least a ten fold lower affinity at the rabbirt cortex I2 site as compared to their known affinity at monoamine oxidase suggesting that the I2 site is not related to the active site of the enzyme, monoamine oxidase. In addition, the peripheral benzodiazepine ligands, PK-11195 or Ro 5-4864 both had very low affinities at the I2 site in rabbit cortex suggesting that the [3H]-idazoxan binding was not to the peripheral benzodiazepine binding site.

Imidazole binding sites in rabbit kidney and forebrain membranes

1. The binding of [3H]-clonidine, [3H]-idazoxan and [3H]-yohimbine to rabbit forebrain and kidney membranes was compared. 2. Yohimbine bound exclusively to adrenergic sites, idazoxan to non-adrenergic sites and clonidine to both non-adrenergic and adrenergic sites. 3. Differences were observed between the ligands not only in binding at adrenergic and non-adrenergic sites but also between the non-adrenergic binding of [3H]-clonidine and [3H]-idazoxan. 4. However, no tissue specific differences were found.

Substance P receptor binding sites are expressed by glia in vivo after neuronal injury.

In vitro studies have demonstrated that glia can express functional receptors for a variety of neurotransmitters. To determine whether similar neurotransmitter receptors are also expressed by glia in vivo, we examined the glial scar in the transected optic nerve of the albino rabbit by quantitative receptor autoradiography. Receptor binding sites for radiolabeled calcitonin gene-related peptide, cholecystokinin, galanin, glutamate, somatostatin, substance P, and vasoactive intestinal peptide were examined. Specific receptor binding sites for each of these neurotransmitters were identified in the rabbit forebrain but were not detected in the normal optic nerve or tract. In the transected optic nerve and tract, only receptor binding sites for substance P were expressed at detectable levels. The density of substance P receptor binding sites observed in this glial scar is among the highest observed in the rabbit forebrain. Ligand displacement and saturation experiments indicate that the substance P receptor binding site expressed by the glial scar has pharmacological characteristics similar to those of substance P receptors in the rabbit striatum, rat brain, and rat and canine gut. The present study demonstrates that glial cells in vivo express high concentrations of substance P receptor binding sites after transection of retinal ganglion cell axons. Because substance P has been shown to regulate inflammatory and immune responses in peripheral tissues, substance P may also, by analogy, be involved in regulating the glial response to injury in the central nervous system.

3H]yohimbine and [ 3H]idazoxan bind to different sites on rabbit forebrain and kidney membranes

The binding of the α 2-adrenoceptor ligands [ 3H]yohimbine and [ 3H]idazoxan to rabbit kidney and forebrain membranes was compared. The maximum number of [ 3H]yohimbine sites was higher than the number of [ 3H]idazoxan binding sites in forebrain and lower in kidney. Large differences were observed in the ability of noradrenaline, adrenaline, idazoxan, rauwolscine, yohimbine and WY 26392 to displace [ 3H]yohimbine and [ 3H]idazoxan from their binding sites. These data suggest that [ 3H]idazaxan and [ 3H]yohimbine bind to different sites on rabbit tissue membranes.

The effects of sexual maturation on α-adrenoceptors in female rabbits

α-Adrenoceptor number and function were examined in brain, platelets, and other peripheral tissues of young (2–3 months) and mature (6–8 months) non pregnant female rabbits. α1-Adrenoceptor number was significantly higher in forebrain, hindbrain, spleen and heart of mature rabbits. α2-Adrenoceptor number, on the other hand, was found to be significantly lower in platelets, forebrain and spleen but not changed in hindbrain and kidney of mature animals compared to young females. There was a significant reduction in platelet aggregation with maturation. However, no change in in vivo pressor or depressor responses to α-adrenoceptor agonists was observed in vivo.

Characterization, development, and localization of the deoxycytidine phosphorylating systems in mammalian brain.

The accumulation of deoxycytidine by rabbit and mouse brain was studied in vitro. Brain slices from brain stem, cerebellum, and forebrain of rabbits of various ages (1 day to 2.5 years) and forebrain from adult mice were incubated for various times in artificial CSF containing 6 nM [3H]deoxycytidine at 37 degrees C under 95% O2/5% CO2. Rabbit and mouse brain slices of all ages accumulated [3H]deoxycytidine by a saturable system (IC50 = 4 microM) and converted it to [3H]deoxycytidine phosphates and [3H]DNA. When slices from all brain regions of 1-day-old rabbits were incubated in 6 nM [3H]deoxycytidine for 30 min, tissue-to-medium ratios of 3H were between 1.2 and 2.5 and declined with age, except in cortex; the percentages of total 3H in perchloric acid homogenates of brain slices as [3H]DNA were 10-24% and declined to low levels in middle age. However, at all ages and in all regions tested, 30-85% of the [3H]deoxycytidine within the slices was phosphorylated. After homogenization and subcellular fractionation of the brain slices incubated in [3H]deoxycytidine for 30 min, the highest percentage of [3H]deoxycytidine phosphates plus [3H]DNA was present in the nuclear and mitochondrial fractions of all brain regions. Deoxycytidine phosphates were synthesized from deoxycytidine in all brain regions tested into middle age.

Immunohistochemical localization of choline acetyltransferase in rabbit forebrain

Guinea pig antiserum specific to the purified bovine choline acetyltransferase was used to demonstrate the localization of this enzyme in rabbit forebrain by the peroxidase-antiperoxidase immunohistochemical method. Choline acetyltransferase was localized in olfactory bulb, olfactory tract, olfactory tubercle, piriform cortex, septum, diagonal band, basal ganglia, thalamus, hypothalamus, subthalamus, habenula, cerebral cortex, hippocampal region, corpus callosum, internal capsule, fornix, longitudinal striae and other areas. The findings reflect the distribution of cholinergic axons and, possibly, their terminals. These observations correlate well with biochemical determinations of choline acetyltransferase and with previously proposed cholinergic pathways.