Spatial memory in nonhuman primates implanted with the subdural pharmacotherapy device.

This study investigated the possible influence of the Subdural Pharmacotherapy Device (SPD) on spatial memory in 3 adult, male bonnet macaques (Macaca radiata). The device was implanted in and above the subdural/subarachnoid space and cranium overlaying the right parietal/frontal cortex: a circuitry involved in spatial memory processing. A large test chamber, equipped with four baited and four non-baited food-ports at different locations, was used: reaches into empty food ports were counted as spatial memory errors. In this study of within-subject design, before SPD implantation (control) the animals made mean 373.3 ± 114.9 (mean ± SEM) errors in the first spatial memory test session. This value dropped to 47.7 ± 18.4 by the 8th session. After SPD implantation and alternating cycles of transmeningeal saline delivery and local cerebrospinal fluid (CSF) drainage in the implanted cortex the spatial memory error count, with the same port locations, was 33.0 ± 12.2 during the first spatial memory test session, further decreasing to 5.7 ± 3.5 by the 8th post-implantation session (P<0.001 for trend). Replacing transmeningeal saline delivery with similar delivery of the GABAA receptor agonist muscimol (1.0mM) by the SPD did not affect the animals' spatial memory performance, which in fact included at least one completely error-free session per animal over time. The study showed that complication-free implantation and use of the SPD over the parietal and frontal cortices for months leave spatial memory processes intact in nonhuman primates.

Long-term behavioral, electrophysiological, and neurochemical monitoring of the safety of an experimental antiepileptic implant, the muscimol-delivering Subdural Pharmacotherapy Device in monkeys.

OBJECT: The authors evaluated the extent to which the Subdural Pharmacotherapy Device (SPD), chronically implanted over the frontal cortex to perform periodic, localized muscimol-delivery/CSF removal cycles, affects overall behavior, motor performance, electroencephalography (EEG) activity, and blood and CSF neurochemistry in macaque monkeys. METHODS: Two monkeys were used to adjust methodology and 4 monkeys were subjected to comprehensive testing. Prior to surgery, the animals' behavior in a large test chamber was monitored, and the motor skills required to remove food pellets from food ports located on the walls of the chamber were determined. The monkeys underwent implantation of the subdural and extracranial SPD units. The subdural unit, a silicone strip integrating EEG electrodes and fluid-exchange ports, was positioned over the right frontal cortex. The control unit included a battery-powered, microprocessor-regulated dual minipump and radiofrequency module secured to the cranium. After implantation, the SPD automatically performed periodic saline or muscimol (1.0 mM) deliveries at 12-hour intervals, alternating with local CSF removals at 6-hour intervals. The antiepileptic efficacy of this muscimol concentration was verified by demonstrating its ability to prevent focal acetylcholine-induced seizures. During SPD treatment, the monkeys' behavior and motor performance were again monitored, and the power spectrum of their radiofrequency-transmitted EEG recordings was analyzed. Serum and CSF muscimol levels were measured with high-performance liquid chromatography electrochemical detection, and CSF protein levels were measured with turbidimetry. RESULTS: The SPD was well tolerated in all monkeys for up to 11 months. The behavioral study revealed that during both saline and muscimol SPD treatment, the monkeys could achieve the maximum motor performance of 40 food-pellet removals per session, as before surgery. The EEG study showed that local EEG power spectra were not affected by muscimol treatment with SPD. The neurochemical study demonstrated that the administration of 1.0 mM muscimol into the neocortical subarachnoid space led to no detectable levels of this compound in the blood and cisternal CSF, as measured 1-125 minutes after delivery. Total protein levels were within the normal range in the cisternal CSF, but protein levels in the cortical-site CSF were significantly higher than normal: 361 ± 81.6 mg/dl. Abrupt discontinuation of 3-month, periodic, subdural muscimol treatments induced withdrawal seizures, which could be completely prevented by gradually tapering off the subdural muscimol concentration from 1.0 mM to 0.12-0.03 mM over a period of 2 weeks. The monkeys' general health and weight were maintained. Infection occurred only in one monkey 9 months after surgery. CONCLUSIONS: Long-term, periodic, transmeningeal muscimol delivery with the SPD is essentially a safe procedure. If further improved and successfully adapted for use in humans, the SPD can be used for the treatment of intractable focal neocortical epilepsy affecting approximately 150,000 patients in the US.

An implantable triple-function device for local drug delivery, cerebrospinal fluid removal and EEG recording in the cranial subdural/subarachnoid space of primates.

Transmeningeal pharmacotherapy for cerebral cortical disorders requires drug delivery through the subdural/subarachnoid space, ideally with a feedback controlled mechanism. We have developed a device suitable for this function. The first novel component of the apparatus is a silicone rubber strip equipped with (a) fluid-exchange ports for both drug delivery and local cerebrospinal fluid (CSF) removal, and (b) EEG recording electrode contacts. This strip can be positioned between the dura and pia maters. The second novel component is an implantable dual minipump that directs fluid movement to and from the silicone strip and is accessible for refilling and emptying the drug and CSF reservoirs, respectively. This minipump is regulated by a battery-powered microcontroller integrating a bi-directional radiofrequency (RF) communication module. The entire apparatus was implanted in 5 macaque monkeys, with the subdural strip positioned over the frontal cortex and the minipump assembly secured to the cranium under a protective cap. The system was successfully tested for up to 8 months for (1) transmeningeal drug delivery using acetylcholine (ACh) and muscimol as test compounds, (2) RF-transmission of neocortical EEG data to assess the efficacy of drug delivery, and (3) local CSF removal for subsequent diagnostic analyses. The device can be used for (a) monitoring neocortical electrophysiology and neurochemistry in freely behaving nonhuman primates for more than 6 months, (b) determining the neurobiological impact of subdural/subarachnoid drug delivery interfaces, (c) obtaining novel neuropharmacological data on the effects of central nervous system (CNS) drugs, and (d) performing translational studies to develop subdural pharmacotherapy devices.

Transmeningeal muscimol can prevent focal EEG seizures in the rat neocortex without stopping multineuronal activity in the treated area.

Muscimol has potent antiepileptic efficacy after transmeningeal administration in animals. However, it is unknown whether this compound stops local neuronal firing at concentrations that prevent seizures. The purpose of this study was to test the hypothesis that epidurally administered muscimol can prevent acetylcholine (Ach)-induced focal seizures in the rat neocortex without causing cessation of multineuronal activity. Rats were chronically implanted with a modified epidural cup over the right frontal cortex, with microelectrodes positioned underneath the cup. In each postsurgical experimental day, either saline or 0.005-, 0.05-, 0.5- or 5.0-mM muscimol was delivered through the cup, followed by a 20-min monitoring of the multineuronal activity and the subsequent delivery of Ach in the same way. Saline and muscimol pretreatment in the concentration range of 0.005-0.05 mM did not prevent EEG seizures. In contrast, 0.5-mM muscimol reduced the average EEG Seizure Duration Ratio value from 0.30±0.04 to 0. At this muscimol concentration, the average baseline multineuronal firing rate of 10.9±4.4 spikes/s did not change significantly throughout the 20-min pretreatment. Muscimol at 5.0mM also prevented seizures, but decreased significantly the baseline multineuronal firing rate of 7.0±1.8 to 3.7±0.9 spikes/s in the last 10 min of pretreatment. These data indicate that transmeningeal muscimol in a submillimolar concentration range can prevent focal neocortical seizures without stopping multineuronal activity in the treated area, and thus this treatment is unlikely to interrupt local physiological functions.

Comparison of the antiepileptic properties of transmeningeally delivered muscimol, lidocaine, midazolam, pentobarbital and GABA, in rats.

This study compared the potencies of epidurally delivered muscimol, lidocaine, midazolam, pentobarbital and gamma-aminobutyric acid (GABA) to prevent focal neocortical seizures induced by locally applied acetylcholine (Ach), in rats (n=5). An epidural cup was chronically implanted over the right somatosensory cortex in each animal, with epidural EEG electrodes placed posterior to the edge of the cup. After recovery, either artificial cerebrospinal fluid (ACSF; control solution) or one of the five drugs was delivered into epidural cup, followed by Ach administration into the cup to induce seizures. EEG seizure duration ratio was calculated for each drug delivery/seizure induction session to determine the potency of ACSF and the drugs to prevent the focal Ach-seizures. The concentration of all examined drug solutions was 1.0mM. ACSF, lidocaine, midazolam, pentobarbital and GABA all failed to prevent the Ach-induced neocortical EEG seizures, yielding EEG seizure duration ratios ranging from 0.41 to 0.80. In contrast, muscimol pretreatment fully prevented the development of ictal EEG in all animals. These results suggest that when used at low concentration muscimol was the best of the five drugs for transmeningeal pharmacotherapy trials for focal neocortical epilepsy.

Localized transmeningeal muscimol prevents neocortical seizures in rats and nonhuman primates: therapeutic implications.

PURPOSE: To determine whether muscimol delivered epidurally or into the subarachnoid space can prevent and/or terminate acetylcholine (Ach)-induced focal neocortical seizures at concentrations not affecting behavior and background electroencephalography (EEG) activity. METHODS: Rats (n = 12) and squirrel monkeys (n = 3) were chronically implanted with an epidural or subarachnoid drug delivery device, respectively, over the right frontal/parietal cortex, with adjacent EEG electrodes. Recordings were performed in behaving rats and chaired monkeys. Via the implants, either a control solution (artificial cerebrospinal fluid, ACSF) or muscimol (0.25-12.5 mm) was delivered locally as a "pretreatment," followed by the similar delivery of a seizure-inducing concentration of Ach. In five additional rats, the quantities of food-pellets consumed during epidural ACSF and muscimol (2.5 mm) exposures were measured. In a last group of four rats, muscimol (0.8-2.5 mm) was delivered epidurally during the ongoing, Ach-induced EEG seizure. RESULTS: In contrast to ACSF pretreatments, epidural muscimol pretreatment in rats completely prevented the seizures at and above 2.5 mm. In the monkeys, subarachnoid muscimol pretreatments at 2.5 mm completely prevented the focal-seizure-inducing effect of Ach, whereas similar deliveries of ACSF did not affect the seizures. Furthermore, 2.5 mm epidural muscimol left the eating behavior of rats intact and caused only slight changes in the EEG power spectra. Finally, muscimol delivery during Ach-induced EEG seizures terminated the seizure activity within 1-3 min. CONCLUSIONS: The results of this study suggest that muscimol is a viable candidate for the transmeningeal pharmacotherapy of intractable focal epilepsy.

Histological evidence for drug diffusion across the cerebral meninges into the underlying neocortex in rats.

Transmeningeal pharmacotherapy has been proposed to treat neurological disorders with localized pathology, such as intractable focal epilepsy. As a step toward understanding the diffusion and intracortical spread of transmeningeally delivered drugs, the present study used histological methods to determine the extent to which a marker compound, N-methyl-D-aspartate (NMDA), can diffuse into the neocortex through the meninges. Rats were implanted with bilateral parietal cortical epidural cups filled with 50 mM NMDA on the right side and artificial cerebrospinal fluid (ACSF) in the contralateral side. After 24 h, the histological effects of these treatments were evaluated using cresyl violet (Nissl) staining. The epidural NMDA exposure caused neuronal loss that in most animals extended from the pial surface through layer V. The area indicated by this neuronal loss was localized to the neocortical region underlying the epidural cup. These results suggest that NMDA-like, water soluble, small molecules can diffuse through the subdural/subarachnoid space into the underlying neocortex and spread in a limited fashion, close to the meningeal penetration site.

Transmeningeal delivery of GABA to control neocortical seizures in rats.

Transmeningeal drug delivery, using an implanted hybrid neuroprosthesis, has been proposed as a novel therapy for intractable focal epilepsy. As part of a systematic effort to identify the optimal compounds and protocols for such a therapy, this study aimed to determine whether transmeningeal gamma-aminobutyric acid (GABA) delivery can terminate and/or prevent neocortical seizures in rats. Rats were chronically implanted with an epidural cup and an adjacent EEG electrode in the right parietal cortex. While the rat was behaving freely, a seizure-inducing concentration of acetylcholine (Ach) was applied into the cup. In a seizure termination study, either artificial cerebrospinal fluid (ACSF) or GABA (0.25, 2.5, 25 or 50mM) was delivered into the exposed neocortical area during an ongoing seizure. In a seizure prevention study, either ACSF or 50mM GABA was delivered into the epidural cup before the application of Ach. Epidural delivery of 50mM GABA completely terminated ongoing Ach-induced EEG seizures and convulsions within 17-437s after its delivery. ACSF and lower concentrations of GABA did not produce this effect, but 25mM GABA reduced seizure severity. However, the used GABA concentration could not prevent the development, or affect the severity, of Ach-induced EEG seizures and convulsions. This study indicates that transmeningeal GABA delivery can be used for terminating neocortical seizures, but to achieve seizure prevention via this route either a more efficient GABA delivery method needs to be developed or other neurotransmitters/pharmaceuticals should be employed for this purpose.

Epidural pentobarbital delivery can prevent locally induced neocortical seizures in rats: the prospect of transmeningeal pharmacotherapy for intractable focal epilepsy.

PURPOSE: To determine whether epidural pentobarbital (PB) delivery can prevent and/or terminate neocortical seizures induced by locally administered acetylcholine (Ach) in freely moving rats. METHODS: Rats were implanted permanently with an epidural cup placed over the right parietal cortex with intact dura mater. Epidural screw-electrodes, secured to the cup, recorded local neocortical EEG activity. In the seizure-termination study, Ach was delivered into the epidural cup, and after the development of electrographic and behavioral seizures, the Ach solution was replaced with either PB or artificial cerebrospinal fluid (aCSF; control solution). In the seizure-prevention study, the epidural Ach delivery was preceded by a 10-min exposure of the delivery site to PB or aCSF. Raw EEG recordings, EEG power spectra, and behavioral events were analyzed. RESULTS: Ach-induced EEG seizures associated with convulsions, which were unaffected by epidural aCSF applications, were terminated by epidurally delivered PB within 2-2.5 min. Epidural deliveries of PB before Ach applications completely prevented the development of electrographic and behavioral seizures, whereas similar deliveries of aCSF exerted no influence on the seizure-generating potential of Ach. CONCLUSIONS: This study showed for the first time that epidural AED delivery can prevent, as well as terminate, locally induced neocortical seizures. The findings support the viability of transmeningeal pharmacotherapy for the treatment of intractable neocortical epilepsy.