Intraventricular Dose Research Articles

Multicenter Pilot Trial of Intrathecal Liposomal Cytarabine Combined with FAB Chemoimmunotherapy with Reduced Doxorubicin in CAYA with Mature De-Novo B-NHL

Background: Children, adolescents, and young adults (C-AYA) with newly diagnosed advanced Mature B Non-Hodgkin Lymphoma (MB-NHL), specifically Burkitt Lymphoma (BL) and Diffuse Large B Cell Lymphoma (DLBCL), have achieved ≥ 90% overall survival with multi-agent chemotherapy and intrathecal chemotherapy (IT) without central nervous system (CNS) radiation (Cairo et al., Blood 2007; Goldman/Cairo et al., BJH 2014; Frazier/Cairo, et al., BJH 2014; Minard-Colin, et al., NEJM 2020). Standard therapy includes short but intensive courses of multiagent chemotherapy including CNS-penetrating high dose methotrexate and cytarabine for CNS penetration as well as vincristine, prednisone, doxorubicin, and cyclophosphamide with or without etoposide. Patients also receive 9, 10 and 13 IT doses of intrathecal chemotherapy when treated according to FAB Group B, FAB Group C (CNS -) and FAB Group C (CNS +) protocols, respectively. While this approach has effectively eliminated need for CNS radiation for disease control, the need for sedation of patients during these procedures results in the need for repeated episodes of patient fasting, increased healthcare costs, and most importantly, general anesthesia is associated with long-term late effects in cognitive development (Banerjee et al., JAMA Oncol, 2019). Liposomal cytarabine (LC) is a formulation of cytarabine encapsulated in spherical multivesicular, biodegradable particles known as DepoCyt® which has a maximum-tolerated intrathecal dose of 35 mg in patients between the ages of 3 and 21 years (Bomgaars et al., JCO, 2004). This liposomal formulation has a half-life of 100-263 hours compared with only 3.4 hours of standard cytarabine. As an s-phase specific agent, prolonged exposure may increase its efficacy in controlling CNS disease while decreasing the total number of intraventricular doses required for treatment. Objective: To determine the safety and efficacy of reduction of IT therapy and substitution of LC within modified FAB group B and C backbones of systemic immunochemotherapy. Methods: LC was incorporated into the multiagent chemotherapy regimen in a unique manner to mitigate the risk of possible CNS toxicity. A total of 2 doses of LC were administered as part of the prophylaxis IT therapy for Group B and CNS negative group C patients. A total of 4 doses of LC were administered as part of the treatment of Group C CNS + patients (Table 1). The LC was given only in phases of therapy in which no systemic cytarabine was administered. When Methotrexate was given, the LC was only given after clearance. Dexamethasone replaced prednisone for all patients to mitigate potential CNS toxicities from LC. Results: This trial enrolled 33 patients with newly diagnosed MB-NHL (25 Group B, 8 Group C with 7 CNS+). Median age was 12 (Range 3-25). Males comprised 64% of patients and 52% had Burkitt Lymphoma/Leukemia. The CNS was involved in 21% of patients, and a total of 78 doses of LC was given. Twenty-six patients received 2 prophylactic doses (25 Group B and 1 Group C CNS negative). Six of seven CNS + patients received all 4 planned doses of LC. The median days from the start of the induction cycles until LC administration (post methotrexate clearance) was 3 days. Of the 33 patients, only 1 (3%) had a transient Grade 3 adverse event (facial nerve palsy). With dexamethasone prophylaxis, there were minimal adverse events and no toxic deaths reported. There were no other serious adverse events, such as seizure, headaches, nausea, vomiting, fever, somnolence, confusion, or asthenia that have been previously reported. The 2-year EFS and OS of LC when added to an FAB backbone for MB-NHL, was 94.5% and 97.2%, respectively (Figure 1). Conclusions: By utilizing dexamethasone prophylaxis and waiting for systemic methotrexate clearance, we were able to demonstrate that IT LC in C-AYAs with MB-NHL who received FAB chemoimmunotherapy with HD MTX was feasible, safe, and did not compromise event free and overall survival. We were also able to reduce the total number of IT injections without apparent compromise to CNS prophylaxis and treatment.

Abstract 190: Safety, Tolerability, Pharmacokinetics and Efficacy of Intraventricular Sustained Release Nimodipine (EG-1962) for Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is associated with high morbidity and mortality. EG-1962 is a sustained release formulation of nimodipine for intraventricular delivery into the subarachnoid space while avoiding dose-limiting hypotension common with systemic administration. We conducted a phase 1/2a multicenter, controlled, randomized, open label, dose escalation study to determine the maximum tolerated dose (MTD) and assess safety, tolerability, pharmacokinetics and clinical outcome at 90 days on the extended Glasgow outcome scale (GOSE) of a single intraventricular dose of EG-1962 (www.clinicaltrials.gov Identifier: NCT01893190). Subjects with aSAH repaired by clipping or coiling were randomized within 60 hours of aSAH to EG-1962 or oral nimodipine if they were World Federation of Neurological Surgeons grade 2 to 4 and had a ventricular catheter. Cohorts of 12 subjects received 100, 200, 400, 600, 800 or 1200 mg EG-1962 (9 per cohort) or oral nimodipine (3 per cohort). The MTD was 800 mg EG-1962. Plasma nimodipine concentrations after administration of EG-1962 were sustained for 21 days and increased in a dose-dependent fashion. Cerebrospinal fluid nimodipine concentrations with EG-1962 were orders of magnitude higher than in plasma and with oral nimodipine. There was one serious adverse event (possible allergic reaction) related to EG-1962 (400 mg) and two EG-1962 dose limiting toxicities (increased intracranial pressure, 400 and 800 mg); all were without clinical sequelae. There was no EG-1962-related hypotension as compared to hypotension in 17% (3/18) with oral nimodipine. Favorable outcome (GOSE 6-8) was achieved in 27 of 45 (60%) EG-1962 subjects (5 of 9 with 100, 6 of 9 with 200, 7 of 9 with 400, 4 of 9 with 600 and 5 of 9 with 800 mg) and 5 of 18 (28%) oral nimodipine subjects. Improved efficacy was supported by reduction in delayed cerebral ischemia (15/45 [33%] EG-1962 versus 11/18 [61%] oral nimodipine) and rescue therapy (11/45 [24%] versus 10/18 [56%]) in EG-1962 subjects. Intraventricular EG-1962 was safe and tolerable to 800 mg, associated with sustained and dose-dependent nimodipine plasma concentrations,improved clinical outcome and reduced delayed cerebral ischemia and use of rescue therapy after aSAH.

Orexin/Hypocretin and Histamine: Distinct Roles in the Control of Wakefulness Demonstrated Using Knock-Out Mouse Models

To determine the respective role played by orexin/hypocretin and histamine (HA) neurons in maintaining wakefulness (W), we characterized the behavioral and sleep-wake phenotypes of orexin (Ox) knock-out (-/-) mice and compared them with those of histidine-decarboxylase (HDC, HA-synthesizing enzyme)-/- mice. While both mouse strains displayed sleep fragmentation and increased paradoxical sleep (PS), they presented a number of marked differences: (1) the PS increase in HDC(-/-) mice was seen during lightness, whereas that in Ox(-/-) mice occurred during darkness; (2) contrary to HDC(-/-), Ox(-/-) mice had no W deficiency around lights-off, nor an abnormal EEG and responded to a new environment with increased W; (3) only Ox(-/-), but not HDC(-/-) mice, displayed narcolepsy and deficient W when faced with motor challenge. Thus, when placed on a wheel, wild-type (WT), but not littermate Ox(-/-) mice, voluntarily spent their time in turning it and as a result, remained highly awake; this was accompanied by dense c-fos expression in many areas of their brains, including Ox neurons in the dorsolateral hypothalamus. The W and motor deficiency of Ox(-/-) mice was due to the absence of Ox because intraventricular dosing of orexin-A restored their W amount and motor performance whereas SB-334867 (Ox1-receptor antagonist, i.p.) impaired W and locomotion of WT mice during the test. These data indicate that Ox, but not HA, promotes W through enhanced locomotion and suggest that HA and Ox neurons exert a distinct, but complementary and synergistic control of W: the neuropeptide being more involved in its behavioral aspects, whereas the amine is mainly responsible for its qualitative cognitive aspects and cortical EEG activation.

Pharmacokinetics and Safety of Intrathecal Liposomal Cytarabine in Children Aged <3 Years

Liposomal cytarabine (DepoCyte) is a slow-release formulation for intrathecal application, ensuring prolonged drug exposure. Although there is an urgent need for new treatment options for infants with leptomeningeal dissemination of a malignant brain tumour, there are no clinical and pharmacokinetic data available on this drug for children aged <3 years. The objective of this pilot study was to determine the feasibility, safety and pharmacokinetics of cytarabine after intrathecal administration of liposomal cytarabine 25 mg in patients aged <3 years. Six male patients with a mean age of 21 months and CNS primitive neuroectodermal tumours (n = 3) or atypical teratoid/rhabdoid tumours (n = 3) were included. Liposomal cytarabine (25 mg) was administered intraventricularly. One patient also received the drug by lumbar puncture. Dexamethasone was used concomitantly for 3-5 days to prevent arachnoiditis. Cerebrospinal fluid (CSF) and plasma samples were collected before administration of liposomal cytarabine and 1 hour, 12 hours, 24 hours, 1 week and 2 weeks post-dosing. Noncompartmental pharmacokinetic analysis of CSF and plasma was performed. Liposomal cytarabine was generally well tolerated; only grade 2 headache occurred in one patient. After intraventricular administration of cytarabine 25 mg, free and encapsulated drug concentrations above the cytotoxic drug level of 0.1 microg/mL were detectable in the CSF for at least 7 days and up to 14 days post-dosing. The average elimination half-lives were 56.7 hours for encapsulated cytarabine and 59.3 hours for free cytarabine. After intralumbar administration, the elimination half-life of free cytarabine, measured in the ventricular CSF during two courses in one patient, was significantly shorter (32.7 hours). Application of liposomal cytarabine with concomitant dexamethasone appears to be safe and well tolerated in children aged <3 years. Drug exposure in infants aged <3 years after an intraventricular dose of 25 mg is comparable to that after administration of 50 mg in adult patients and 35 mg in older children.

Antimicrobial Therapy and Local Toxicity of Intraventricular Administration of Vancomycin in a Neonate With Ventriculitis

Infection is the most common complication and cause of failure of cerebrospinal fluid (CSF) shunt devices used to control hydrocephalus. A male newborn was admitted for treatment of congenital occlusive hydrocephalus by means of a ventriculo-peritoneal shunt. A day later, the skin area around the site of insertion of ventriculo-peritoneal catheter was red and edematous. Intravenous ceftazidime and vancomycin were initiated. The shunt was removed but the external ventricular drain was preserved. Blood and CSF cultures showed Enterococcus faecalis sensitive to vancomycin, ciprofloxacin and gentamicin, but resistant to ampicillin. Intraventricular administration of vancomycin 10 mg/24 h was initiated through the external ventricular drain. Before the first dose of vancomycin intraventricularly, CSF levels were 19 mg/dL as a result of administration. On the third day of intraventricular dosing, vancomycin levels in CSF reached 388 mg/dL and protein levels were 1160 mg/dL. On the fifth day of intraventricular treatment the patient had clinically improved and was bacteriologically cured. However, in CSF, protein levels were 3300 mg/dL and vancomycin levels 201 mg/dL. In an attempt to prevent high and potentially toxic levels in CSF, the intraventricular dose of vancomycin should be individualized according to clinical response, bacteriological cultures, vancomycin levels in CSF, and surrogate markers of neurotoxicity, that is, eosinophilia and high protein levels in CSF.

Dexamethasone dosing, mechanical ventilation and the risk of cerebral palsy

Objective. Risk factors for cerebral palsy (CP) in premature infants include duration of mechanical ventilation and exposure to postnatal dexamethasone (DEX). Since DEX can reduce the duration of mechanical ventilation, limited DEX exposure could be beneficial.Methods. This was a retrospective, cohort study of infants of less than 1500 g birth weight surviving to discharge between 1 January 1996 and 30 June 2001 who received postnatal dexamethasone. DEX administration was based only on the need for O2 and/or mechanical ventilation. CP was diagnosed at over 10 months post-conceptional age. Univariate and multivariate analyses were used to determine significant risk factors and the relative contribution of these factors to overall risk of CP.Results. Of 218 eligible infants 162 were followed-up (74%). The CP rate was 27.3%. Significant risk factors for CP included gestational age, ventilator duration, DEX dose, presence of periventricular leukomalacia (PVL), seizures, diagnosis of retinopathy of prematurity (ROP) and use of vasopressors. By multiple logistic regression, ventilator duration, PVL, grade III/IV intraventricular hemorrhage (IVH) and DEX dose were significantly related to CP. By stepwise multiple regression, grade III/IV IVH and ventilator duration were the strongest risk factors, but DEX dose continued to be a significant risk factor.Conclusions. The risk of CP was significantly related to the total cumulative dose of DEX. This could be due to a smaller exposure to DEX or to a reduced need for mechanical ventilation.

P.3.d.018 Estimating extrapyramidal syndrome-inducing liability of antipsychotics in rodent behavioural models

Intraventricular administration of haloperidol or chlorpromazine produces catalepsy and blocks apomorphine-induced stereotypic behavior. Low intraventricular doses of domperidone, sulpiride and spiperone, equally cataleptogenic as haloperidol or chlorpromazine, augment rather than diminish stereotypic behavior produced by subsequent apomorphine treatment. The resultant stereotypic behavior continues even while the animal is in a rigid cataleptic posture and is marked by persistent gnawing and licking. Prior to the induction of catalepsy and after recovery from it, mice display the entire range of typical apomorphine-induced behavior including sniffing, climbing, gnawing, and licking. This animal model may be related to the clinical observation of the coexistence of tardive dyskinesia and drug-induced Parkinsonism in individual patients.

Intrathecal Mafosfamide: A Preclinical Pharmacology and Phase I Trial

Preclinical studies of mafosfamide, a preactivated cyclophosphamide analog, were performed to define a tolerable and potentially active target concentration for intrathecal (IT) administration. A phase I and pharmacokinetic study of IT mafosfamide was performed to determine a dose for subsequent phase II trials. In vitro cytotoxicity studies were performed in MCF-7, Molt-4, and rhabdomyosarcoma cell lines. Feasibility and pharmacokinetic studies were performed in nonhuman primates. These preclinical studies were followed by a phase I trial in patients with neoplastic meningitis. There were five dose levels ranging from 1 mg to 6.5 mg. Serial CSF samples were obtained for pharmacokinetic studies in a subset of patients with Ommaya reservoirs. The cytotoxic target exposure for mafosfamide was 10 micromol/L. Preclinical studies demonstrated that this concentration could be easily achieved in ventricular CSF after intraventricular dosing. In the phase I clinical trial, headache was the dose-limiting toxicity. Headache was ameliorated at 5 mg by prolonging the infusion rate to 20 minutes, but dose-limiting headache occurred at 6.5 mg dose with prolonged infusion. Ventricular CSF mafosfamide concentrations at 5 mg exceeded target cytotoxic concentrations after an intraventricular dose, but lumbar CSF concentrations 2 hours after the dose were less than 10 micromol/L. Therefore, a strategy to alternate dosing between the intralumbar and intraventricular routes was tested. Seven of 30 registrants who were assessable for response had a partial response, and six had stable disease. The recommended phase II dose for IT mafosfamide, administered without concomitant analgesia, is 5 mg over 20 minutes.

Pharmacokinetics and Effects of Ribavirin following Intraventricular Administration for Treatment of Subacute Sclerosing Panencephalitis

Ribavirin is a broad-spectrum antiviral drug with inhibitory activity against many RNA viruses, including measles virus. Five patients with subacute sclerosing panencephalitis (SSPE) were treated with ribavirin by intraventricular administration. Although there were transient side effects attributed to ribavirin, such as drowsiness, headache, lip and gingival swelling, and conjunctival hyperemia, intraventricular ribavirin therapy was generally safe and well tolerated. The cerebrospinal fluid (CSF) ribavirin concentration decreased, as described by a monoexponential function, after a single intraventricular dose. There was considerable interindividual variability, however, in the peak level and half-life. We aimed to adjust the individual dose and frequency of intraventricular administration based on the peak level and half-life of ribavirin in the CSF in order to maintain the CSF ribavirin concentration at the target level. Clinical effectiveness (significant neurologic improvement and/or a significant decrease in titers of hemagglutination inhibition antibodies against measles virus in CSF) was observed for four of five patients. For these four patients, CSF ribavirin concentrations were maintained at a level at which SSPE virus replication was almost completely inhibited in vitro and in vivo, whereas the concentration was lower in the patient without clinical improvement. These results suggest that intraventricular administration of ribavirin is effective against SSPE if the CSF ribavirin concentration is maintained at a high level. Intraventricular ribavirin therapy should be pursued further for its potential use for patients with SSPE and might be applied in the treatment of patients with encephalitis caused by other RNA viruses.

Beneficial effects of intraventricularly administered BMP-7 following a striatal 6-hydroxydopamine lesion

The present study was undertaken to investigate the effects of bone morphogenetic protein-7 (BMP-7), also named osteogenic protein-1 (OP-1), on the progression of a striatal 6-hydroxydopamine (6-OHDA) lesion. BMP-7, a member of the transforming growth factor-β (TGF-β) superfamily of proteins, has been shown to have protective effects in other animal models of neuronal damage. In this study, male Fischer 344 rats received striatal 6-OHDA lesions followed 1 week later by an intraventricular dose of BMP-7. No significant effect of BMP-7 treatment on spontaneous locomotor activity was observed, however BMP-7 significantly increased the density of tyrosine hydroxylase (TH) immunoreactivity (TH-ir) in the substantia nigra (SN) pars compacta, in the lesioned hemisphere [31.7±5.2 (optical density (O.D.) arbitrary units) control vs. 50.2±4.3 O.D. BMP-7-treated; p<0.05]. Interestingly, BMP-7 significantly increased TH-ir in the SN of the non-lesioned hemisphere (pars reticulata: 14.8±1.19 O.D. control vs. 36±2.6 O.D. BMP-7-treated, p<0.05; pars compacta: 29.0±4.9 O.D. control vs. 64.4±6.9 O.D. BMP-7-treated, p<0.001). A significant increase in DA concentration in the contralateral, non-lesioned hemisphere was also noted (113.2 ng/g control vs. 198.2 ng/g BMP-7-treated, p<0.01). In contrast to other intraventricularly administered neurotrophic factors, BMP-7 was not associated with an increase in the sensitivity to pain. These results suggest that BMP-7 is able to act as a dopaminotrophic agent without unwanted side effects and as such may be a useful pharmacological tool in the treatment of Parkinson's disease in humans.

Successful treatment of ventriculostomy-related meningitis caused by vancomycin-resistant Enterococcus with intravenous and intraventricular quinupristin/dalfopristin

We report a case of ventriculostomy-related meningitis caused by vancomycin-resistant Enterococcus faecium (VRE). The patient was successfully treated with administration of quinupristin/dalfopristin by both intravenous and intraventricular routes. A brief review of the literature is provided, which indicates that optimal management with quinupristin/dalfopristin should include daily intraventricular doses of at least 2 mg.

Brain alpha 1-adrenergic neurotransmission is necessary for behavioral activation to environmental change in mice

Terazosin, a water-soluble alpha 1 antagonist that can be administered in high doses intraventricularly was used to study the relationship between brain alpha 1 adrenoceptor neurotransmission and behavioral activation in the mouse. The antagonist was found to produce a dose-dependent, complete inhibition of motor activity and catalepsy which were reversed preferentially by coinfusion of an alpha 1 agonist (phenylephrine) compared to a D1 (SKF38393) or a D2 agonist, (quinpirole). Blockade of central beta-1 (betaxolol), alpha-2 (RX821002) or beta-2 (ICI118551) adrenoceptors had smaller or non-significant effects. Terazosin's selectivity for alpha 1 receptors versus dopaminergic receptors was verified under the present conditions by showing that the intraventricularly administered antagonist protected striatal and cerebral cortical alpha 1 receptors but not striatal or cortical D1 receptors from in vivo alkylation by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroxyquinoline. That its effect was due to blockade of brain rather than peripheral receptors was shown by the finding that intraperitoneal doses of terazosin three to 66 times greater than the maximal intraventricular dose produced less behavioral inhibition. Intraventricular terazosin also produced hypothermia and a reduced respiratory rate suggestive of a reduced sympathetic outflow. However, external heat did not affect the inactivity, and captopril, a hypotensive agent, did not mimic it. Terazosin did not impair performance on a horizontal wire test or the ability to make co-ordinated movements in a swim test suggesting that its activity-reducing effect was not due to sedation and may have a motivational or sensory gating component. It is concluded that central alpha 1-noradrenergic neurotransmission is required for behavioral activation to environmental change in the mouse and may operate on sensorimotor and motivational processes.

The involvement of bulbospinal pathways in fentanyl-induced inhibition of spinal withdrawal reflexes in the decerebrated rabbit.

The selective opioid OP3(mu)-receptor agonist fentanyl was administered via the intravenous, intrathecal and intraventricular routes to decerebrated rabbits in doses from 1-30 microg/kg. Reflexes evoked in medial gastrocnemius motoneurones by electrical stimulation of the sural nerve were depressed by fentanyl given by all three routes. The opioid was most potent when given intrathecally and least potent when given into the fourth ventricle. Blockade of spinal alpha2-adrenoceptors by intrathecal RX 821002 (100 microg) reduced the effectiveness of intrathecal and low (<3 microg/kg) intravenous doses of fentanyl, but did not affect or enhanced responses to high intraventricular and intravenous doses. Spinalization reduced the effectiveness of intrathecal and intravenous fentanyl and abolished inhibition from intraventricular dosing. These data show that fentanyl acts in the spinal cord and in the brain stem to suppress spinal reflexes, although very high doses were required for effects from the latter site. It appears that low intravenous doses of fentanyl act mainly in the spinal cord and that increasing the dosage recruits descending inhibition. The results of alpha2-adrenoceptor blockade indicate that the spinal inhibitory effects of opioids are enhanced by an interaction with endogenous noradrenaline in the spinal cord. Thus, the full expression of the spinal inhibitory effects of fentanyl is dependent on brain stem cell groups, either as a source of noradrenaline input to the spinal cord, or as a site from which opioids can activate descending inhibitory systems.

Neurotoxicity of (2S,1'R,2'R,3'R)-2-(2,3-dicarboxycyclopropyl)glycine, a potent agonist for class II metabotropic glutamate receptors, in the rat.

Neurotoxicity of (2S,1'R,2'R,3'R)-2-(2,3-dicarboxycyclopropyl)glycine (DCG-IV), a potent agonist for metabotropic glutamate receptors negatively coupled to adenylyl cyclase, was investigated in vivo by the intraventricular administration in the rat, compared with that of (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine (L-CCG-I) and (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD]. Neither L-CCG-I nor (1S,3R)-ACPD caused any apparent pathological change in the brain at an intraventricular dose of 1 mumol, whereas DCG-IV induced selective neuronal damage in some rats at higher doses than 3 nmol. The neurotoxicity was intensified in a dose-dependent manner, and at a dose of 50 nmol DCG-IV caused repetitive seizures and selective neuronal damage in all cases. Neuronal damage was pronounced in the cingulate cortex, lateral septum and hippocampus, and a few degenerating neurons were observed also in other brain areas, such as the striatum, thalamus or neocortex. Since DCG-IV activates N-methyl-D-aspartate-type receptors as well at relatively high concentrations, the protective effect of a competitive antagonist for N-methyl-D-aspartate receptors, 3-[(RS)-2-carboxypiperazin-4-yl]propyl-1-phosphonic acid (CPP), was examined on the neurotoxicity of DCG-IV. Although a combined treatment with CPP (0.1 nmol) completely blocked the neurotoxicity of N-methyl-D-aspartate (100 nmol), at least 3 nmol of CPP was necessary to decrease the neurotoxicity of DCG-IV (50 nmol) to a considerable extent. The synergistic activation of metabotropic glutamate receptors and N-methyl-D-aspartate receptors is suggested as a possible mechanism underlying the selective neuronal damage induced by DCG-IV, although a direct participation of metabotropic glutamate receptors in glutamate neurotoxicity is not deniable.

DNQX inhibits phencyclidine (PCP) and ketamine induction of the hsp70 heat shock gene in the rat cingulate and retrosplenial cortex

Phencyclidine (PCP) and ketamine are known to block NMDA receptor mediated excitotoxicity by non-competitively blocking the NMDA receptor calcium channel. PCP and ketamine have the paradoxical effect of also inducing the heat shock gene, hsp70, in the cingulate and retrosplenial cortex of the rat. The present study shows that DNQX, a specific AMPA receptor antagonist, given as either a 5 mg/kg or 10 mg/kg intraperitoneal dose or into the lateral cerebral ventricle (5 μl of 0.5 mg/ml) significantly diminished PCP (40 mg/kg) and ketamine (80, 100, 120 mg/kg) hsp70 induction in the posterior cingulate and retrosplenial cortex. The most dramatic decrease of hsp70 induction was seen with the intraventricular dose of DNQX. Present findings show that the AMPA receptor has a role in PCP/ketamine induction of hsp70 in the cortex. DNQX inhibition of PCP/ketamine hsp70 induction was likely related to AMPA receptor antagonism which prevented excess calcium influx via voltage-gated calcium channels.

192 immunoglobulin G-saporin produces graded behavioral and biochemical changes accompanying the loss of cholinergic neurons of the basal forebrain and cerebellar Purkinje cells

Immunolesions of the cholinergic basal forebrain were produced in rats using various intraventricular doses of the immunotoxin 192 immunoglobulin G-saporin: 0.34, 1.34, 2.0, 2.7 and 4.0 micrograms/rat. A battery of behavioral tests, chosen on the basis of reported sensitivity to conventional medial septal or nucleus basalis lesions, was administered. Dose-dependent impairments were found in acquisition, spatial acuity and working memory in the water maze. Dose-dependent hyperactivity in the open field and in swimming speed was observed. The highest dose group (4.0 micrograms) exhibited motoric disturbances which were particularly apparent in swimming and in clinging to an inclined screen. Response and habituation to acoustic startle were diminished in the three higher dose groups. Histological results from acetylcholinesterase and low-affinity nerve growth factor receptor staining showed that the lesion was selective for cholinergic neurons bearing p75 nerve growth factor receptors in the basal forebrain nuclei. However, some Purkinje cells in the superficial layers of the cerebellum were also destroyed at the higher doses of immunotoxin. The activity of choline acetyltransferase, used as a marker of cholinergic deafferentation in regions innervated by the basal forebrain nuclei, was decreased with increasing doses to a plateau level of about 90% (average depletion) for the two highest dose groups. These two groups were the only ones to exhibit consistent and severe behavioral impairments on all behavioral tests performed. Thus, for a relatively selective cholinergic basal forebrain lesion, almost a 90% reduction in choline acetyltransferase activity is needed to produce substantial behavioral deficits. It appears that either a considerable safety factor exists or robust compensatory mechanisms can ameliorate behavioral deficits from a major, but incomplete loss of cholinergic basal forebrain innervation.

Evaluation of the hypothesis that hippocampal interictal spikes are caused by long-term potentiation.

Hippocampal spontaneous interictal spikes (SISs) occur in the EEG after repeated afterdischarges (ADs) induced by high-frequency (200 Hz) stimulation trains. Because SISs resemble population excitatory postsynaptic potentials (EPSPs), and SISs persist for several days like some types of hippocampal long-term potentiation (LTP), LTP has been suggested as a mechanism for SISs. We specifically examined the hypothesis that SISs are caused by basal-dendritic LTP in CA1. Rats were chronically implanted with bilateral electrodes in the hippocampal CA1 region. In the first experiment, 10-18 patterned primed burst (PB) stimulations were delivered hourly for 2-3 days to activate the commissural basal-dendritic EPSP in CA1. Robust LTP of the basal-dendritic CA1 synapse was detected, typically saturating at 100% enhancement after five stimulations. However, few SISs were detected if ADs were not elicited. In the second experiment, repeated commissurally evoked ADs induced a high rate of SISs, together with LTP of the basal-dendritic and apical-dendritic EPSP in CA1, but the SIS rate was not necessarily related to the level of LTP. In the third experiment, an intraventricular dose (20 micrograms) of an N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovalerate (APV) was used to block the basal-dendritic LTP in CA1. The increase in SISs induced by a single AD was not blocked, however, suggesting that NMDA receptors were not critical in generation of SISs. In the fourth experiment, PBs (that induced LTP but no ADs) were able to increase the rate of SISs marginally when SISs were already present. In all, the experiments suggest that LTP at the basal dendrites of CA1 is not critical in generation of hippocampal SISs, although an increase in LTP may increase the rate of SISs marginally when SISs are already present.

Evidence for an involvement of the μ-type of opioid receptor in the modulation of learning

Pavlovian conditioning of the rabbit's nictitating membrane response was used to determine whether the retardation of learning produced by enkephalin derivatives was mediated through an action on μ- or δ-opioid receptors. Intraventricular injection of the highly selective μ-agonist, [D-Ala 2, MePhe 4, Gly-ol 5] enkephalin (DAMGO) significantly retarded (2 nmol) or completely blocked (20 nmol) the acquisition of conditioned responses. The retarded or blocked acquisition of conditioned responses produced by DAMGO could still be detected when the rabbits were tested two days after cessation of drug injections, suggesting that DAMGO had affected learning and not simply performance of conditioned responses. Intraventricular injection of a comparable dose (20 nmol) of the highly selective δ-agonist, [D-Pen 2.5] enkephalin (DPDPE) did not retard learning. A higher dose of DPDPE (200 nmol), which would be expected to act at both μ- and δ-receptors, did produce a retardation of acquisition that was comparable to the effects of a 2-nmol dose of DAMGO. However, unlike DAMGO, the retardation of learning produced by this dose of DPDPE appeared to be due, at least in part, to a reduction in the aversive properties of the unconditioned stimulus. The retardation of learning produced by 2 nmol of DAMGO and 200 nmol of DPDPE was due to an action on an opioid receptor because this effect was blocked by a subcutaneous injection of naloxone (2.5 μmol/kg), a specific opioid antagonist. The stereoselective effects of the μ-opioid agonist levorphanol further confirmed that the retarded learning was mediated through actions at the μ-opioid receptor. Autoradiographic studies indicated that a 2-nmol, intraventricular dose of DAMGO achieved contents greater than 1 pmol/mg in tissue lying within 2 mm of the lateral ventricle, third ventricle and cerebral aqueduct. These data suggest that enkephalins produce a retardation of learning through an effect on the μ-type of opioid receptor and that at least one locus of their actions is produced at periventricular sites lying within 2 mm of the ventricles. It was concluded that the μ-type of opioid receptor was normally involved in the modulation of learning and that such modulation would be expected to be most prominent during environmental conditions that have been demonstrated to produce a large release of endogenous enkephalins.

Cerebrospinal fluid pharmacokinetics and toxicology of intraventricular and intrathecal arabinosyl-5-azacytosine (fazarabine, NSC 281272) in the nonhuman primate.

Arabinosyl-5-azacytosine (AAC), a new nucleoside antimetabolite, is broadly active in preclinical tumor screening evaluations. To assess the potential for intrathecal use of this drug, we studied the toxicity and pharmacokinetics of intrathecal and intraventricular administration in nonhuman primates. Four adult male rhesus monkeys were given single 10 mg intrathecal (n = 1) or intraventricular (n = 3) doses of AAC to determine its acute toxicity and pharmacokinetic parameters. An additional 3 animals were given four weekly 10 mg intrathecal doses to assess the systemic and neurologic toxicity associated with chronic administration. Disappearance from the cerebrospinal fluid (CSF) was biexponential, and CSF clearance was 0.2 ml/min, which exceeds the rate of CSF bulk flow by 5-fold. The peak CSF concentration and area under the concentration x time curve achieved with the intraventricular administration of 10 mg were one hundred, and fifty fold greater, respectively, than those achieved after an intravenous dose of 200 mg/kg (1500-2400 mg) in prior experiments. No clinically evident neurotoxicity was observed in either the single or the weekly x 4 dose groups. A slight, transient CSF pleocytosis and increased CSF protein was observed. Systemic toxicity was limited to one animal in the weekly x 4 dose group who demonstrated a mild and transient decrease in his peripheral leukocyte count unassociated with a change in his hematocrit or platelet count. These studies in nonhuman primates demonstrate a clear pharmacokinetic advantage for intrathecal vs systemic administration of AAC. This is demonstrated by a 50-fold greater CSF drug exposure with an intrathecal or intraventricular dose 1/200th of that which can be given systemically.(ABSTRACT TRUNCATED AT 250 WORDS)

Neural and behavioural effects of domoic acid, an amnesic shellfish toxin, in the rat.

To examine the neurotoxic effects of domoic acid, an amnesic shellfish toxin, electroencephalographic and behavioural experiments were conducted on 38 rats. Injection of domoic acid (0.5-1.0 mg/kg intravenously, or 0.04-0.08 microgram intraventricularly) caused seizure discharges in the hippocampus, tonic-clonic convulsions, and death within a few days. Convulsions and ensuing death were prevented by diazepam. Animals pretreated with diazepam (5 mg/kg, ip) tolerated intraventricular dose of domoic acid 0.4 microgram, but showed a loss of pyramidal neurons mainly in the CA3, CA4, and a part of CA1 areas of the dorsal hippocampus. Learning of a radial maze task was severely impaired in naive rats after intraventricular injection of domoic acid (and diazepam, ip). In the animals previously trained on the maze task, domoic acid interfered with relearning of the same task. These effects appear similar to those of kainic acid and are analogous to the symptoms observed in humans who ingested mussels tainted with domoic acid.