At-Home Administration of Gantenerumab by Care Partners to People with Early Alzheimer's Disease: Feasibility, Safety and Pharmacodynamic Impact.

BACKGROUND: Monoclonal antibodies that target amyloid-beta and remove amyloid plaques can slow cognitive and functional decline in early Alzheimer's disease. Gantenerumab is a subcutaneously administered fully-human anti-amyloid-beta monoclonal antibody with highest affinity for aggregated amyloid-beta. Since the phase 3 GRADUATE trials did not meet the primary endpoint (change from baseline to Week 116 in Clinical Dementia Rating scale - Sum of Boxes), development of gantenerumab in sporadic Alzheimer's disease was stopped and all ongoing trials were terminated early due to sponsor decision. Subcutaneous administration at the clinic or at home by care partner would be an important option for other therapies in this class in order to increase flexibility and reduce overall burden. The insights obtained from the experience with gantenerumab home administration by care partner in the phase 2 GRADUATION trial will serve to guide the ongoing efforts with other anti-amyloid-beta antibodies. OBJECTIVES: To evaluate the pharmacodynamic effects on brain amyloid load of once weekly subcutaneous administration of gantenerumab and the safety and feasibility of home administration by care partners. DESIGN: Phase 2, open-label, single arm study. SETTING: Multicenter trial conducted in 33 sites in 8 countries from November 2020 to March 2023. PARTICIPANTS: Participants aged 50 to 90 with early symptomatic Alzheimer's disease (mild cognitive impairment/mild dementia due to Alzheimer's disease), and evidence of amyloid positron emission tomography positivity. INTERVENTION: Participants could receive up to 255 mg gantenerumab once-weekly, administered subcutaneously at site or at home by healthcare professionals or non-healthcare-professional care partners. MEASUREMENTS: The primary endpoint was the change from baseline to Week 52 and to Week 104 in brain amyloid load as measured by PET centiloid levels. The secondary endpoints were responses to the home administration questionnaire, plasma concentrations and safety. RESULTS: The overall number of participants enrolled was 192, with a mean (standard deviation) amyloid PET load at baseline of 101.80 (29.80) centiloids. At the time of early study termination by sponsor, 149 participants had valid Week 52 amyloid PET data (primary endpoint), and 12 participants had an early termination PET within the pre-defined time range of Week 104. The mean change in amyloid PET from baseline to Week 52 and Week 104 was -26.19 centiloids (range: -75.6-15.8; n=149) and -35.48 centiloids (range: -63.2--7.0; n=12), respectively. Responses to the home administration questionnaire at Week 52 (n=148) indicated that the majority of care partners (88-97%) considered administration of study drug at home easy (30.4%) or very easy (57.4%), and convenient (25.7%) or very convenient (70.9%). Care partners felt confident (31.1%) or very confident (62.2%) and satisfied (29.7%) or very satisfied (64.9%) with giving the injection at home. Responses by care partners at Week 36 (n=72), Week 76 (n=126) and Week 104 (n=29) and participant (patient) assessment of convenience and satisfaction at these time points were similar. There were no new safety findings associated with gantenerumab administered subcutaneously once weekly at 255 mg or safety issues associated with at-home injections by non-healthcare professional care partners. CONCLUSIONS: Once-weekly subcutaneous home administration of the anti-amyloid-beta antibody gantenerumab by non-healthcare-professional care partners to participants with early Alzheimer's disease was feasible, safe, well tolerated, and considered as a convenient option by both the care partners and participants with Alzheimer's disease. Although gantenerumab's development has been stopped due to lack of efficacy, this approach has the potential to reduce the frequency of hospital/outpatient clinic visits required for treatment with other anti-amyloid-ß antibodies and can increase flexibility of drug administration for people living with Alzheimer's disease and their families.

Establishing Clinically Meaningful Change on Outcome Assessments Frequently Used in Trials of Mild Cognitive Impairment Due to Alzheimer's Disease.

BACKGROUND: Consensus is lacking on what constitutes a meaningful score change for individual patients on clinical outcome assessments (COAs) that are commonly used in clinical trials of Alzheimer's disease. Such thresholds are one important approach to help contextualize trial results and demonstrate meaningful treatment benefit. OBJECTIVES: To estimate meaningful within-patient change thresholds for the Clinical Dementia Rating Scale - Sum of Boxes (CDR-SB), Alzheimer's Disease Assessment Scale - Cognitive Subscale (ADAS-Cog), and the Mini-Mental State Examination (MMSE) among participants with mild cognitive impairment (MCI). DESIGN: Retrospective anchor- and distribution-based analyses of data from the ADC-008 (NCT00000173) study were used to estimate thresholds for meaningful within-patient change on the target measures. SETTING: Analyses were conducted using data from ADC-008 a Phase III, multicenter, randomized, double-blind, placebo-controlled, parallel-group study among participants with the amnestic subtype of MCI, which was conducted by the Alzheimer's Disease Cooperative Study (ADCS) between March 1999 and January 2004 in the United States and Canada. PARTICIPANTS: Analyses were based on 769 eligible participants who completed the baseline assessment from 69 ADCS sites in the United States and Canada. MEASUREMENTS: The target outcome measures for this analysis included the CDR-SB, the ADAS-Cog, and the MMSE. The anchor measures for this analysis included the Global Deterioration Scale and the MCI-Clinical Global Impression of Change. RESULTS: Focusing on the 12-month time point, within-patient increases of 1-2.5 points in the CDR-SB and increases of 2-5 points on the 11-item ADAS-Cog and 13-item ADAS-Cog, on average, reflect minimal-to-moderate levels of deterioration, respectively. CONCLUSIONS: These thresholds may be useful to aid the interpretation of Alzheimer's disease clinical trial data by illustrating meaningful within-patient progression over the course of a clinical trial via supplementary progressor analyses, which may in turn be informative for treatment decisions. Estimates generated via these methods are specifically intended to evaluate within-patient change and are not intended to assess the magnitude and meaningfulness of differences between group-level changes over time.

Thirty-Six-Month Amyloid Positron Emission Tomography Results Show Continued Reduction in Amyloid Burden with Subcutaneous Gantenerumab.

Previous findings from the positron emission tomography (PET) substudy of the SCarlet RoAD and Marguerite RoAD open-label extension (OLE) showed gantenerumab doses up to 1200 mg every 4 weeks administered subcutaneously resulted in robust beta-amyloid (Aß) plaque removal over 24 months in people with prodromal-to-moderate Alzheimer's disease (AD). In this 36-month update, we demonstrate continued reduction, with mean (standard error) centiloid values at 36 months of -4.3 (7.5), 0.8 (6.7), and 4.7 (8.0) in the SCarlet RoAD (double-blind pooled placebo and active groups), Marguerite RoAD double-blind placebo, and Marguerite RoAD double-blind active groups respectively, representing a change of -57.0 (10.3), -90.3 (9.0), and -74.9 (10.5) centiloids respectively. These results demonstrate that prolonged gantenerumab treatment, at doses up to 1200 mg, reduces amyloid plaque levels below the amyloid positivity threshold. The ongoing GRADUATE Phase III trials will evaluate potential clinical benefits associated with gantenerumab-induced amyloid-lowering in people with early (prodromal-to-mild) AD.

Hippocampal CA1 apical neuropil atrophy in mild Alzheimer disease visualized with 7-T MRI.

OBJECTIVES: In Alzheimer disease (AD), mounting evidence points to a greater role for synaptic loss than neuronal loss. Supporting this notion, multiple postmortem studies have demonstrated that the hippocampal CA1 apical neuropil is one of the earliest sites of pathology, exhibiting tau aggregates and then atrophy before there is substantial loss of the CA1 pyramidal neurons themselves. In this cross-sectional study, we tested whether tissue loss in the CA1 apical neuropil layer can be observed in vivo in patients with mild AD. METHODS: We performed ultra-high-field 7-T MRI on subjects with mild AD (n = 14) and age-matched normal controls (n = 16). With a 2-dimensional T2*-weighted gradient-recalled echo sequence that was easily tolerated by subjects, we obtained cross-sectional slices of the hippocampus at an in-plane resolution of 195 µm. RESULTS: On images revealing the anatomic landmarks of hippocampal subfields and strata, we observed thinning of the CA1 apical neuropil in subjects with mild AD compared to controls. By contrast, the 2 groups exhibited no difference in the thickness of the CA1 cell body layer or of the entire CA1 subfield. Hippocampal volume, measured on a conventional T1-weighted sequence obtained at 3T, also did not differentiate these patients with mild AD from controls. CONCLUSIONS: CA1 apical neuropil atrophy is apparent in patients with mild AD. With its superior spatial resolution, 7-T MRI permits in vivo analysis of a very focal, early site of AD pathology.

Direct presynaptic regulation of GABA/glycine release by kainate receptors in the dorsal horn: an ionotropic mechanism.

In the spinal cord dorsal horn, excitatory sensory fibers terminate adjacent to interneuron terminals. Here, we show that kainate (KA) receptor activation triggered action potential-independent release of GABA and glycine from dorsal horn interneurons. This release was transient, because KA receptors desensitized, and it required Na+ entry and Ca2+ channel activation. KA modulated evoked inhibitory transmission in a dose-dependent, biphasic manner, with suppression being more prominent. In recordings from isolated neuron pairs, this suppression required GABA(B) receptor activation, suggesting that KA-triggered GABA release activated presynaptic GABA(B) autoreceptors. Finally, glutamate released from sensory fibers caused a KA and GABA(B) receptor-dependent suppression of inhibitory transmission in spinal slices. Thus, we show how presynaptic KA receptors are linked to changes in GABA/glycine release and highlight a novel role for these receptors in regulating sensory transmission.

Genetic enhancement of inflammatory pain by forebrain NR2B overexpression.

N-methyl-D-aspartate (NMDA) receptors contribute to many brain functions. We studied the effect of forebrain-targeted overexpression of the NMDA receptor subunit NR2B on the response of mice to tissue injury and inflammation. Transgenic mice exhibited prominent NR2B expression and enhanced NMDA receptor-mediated synaptic responses in two pain-related forebrain areas, the anterior cingulate cortex and insular cortex, but not in the spinal cord. Although transgenic and wild type mice were indistinguishable in tests of acute pain, transgenic mice exhibited enhanced responsiveness to peripheral injection of two inflammatory stimuli, formalin and complete Freund's adjuvant. Genetic modification of forebrain NMDA receptors can therefore influence pain perception, which suggests that forebrain-selective NMDA receptor antagonists, including NR2B-selective agents, may be useful analgesics for persistent pain.

Presynaptic kainate receptors regulate spinal sensory transmission.

Small diameter dorsal root ganglion (DRG) neurons, which include cells that transmit nociceptive information into the spinal cord, are known to express functional kainate receptors. It is well established that exposure to kainate will depolarize C-fiber afferents arising from these cells. Although the role of kainate receptors on sensory afferents is unknown, it has been hypothesized that presynaptic kainate receptors may regulate glutamate release in the spinal cord. Here we show that kainate, applied at low micromolar concentrations in the presence of the AMPA-selective antagonist (RS)-4-(4-aminophenyl)-1, 2-dihydro-1-methyl-2-propyl-carbamoyl-6,7-methylenedioxyphthalazine++ +, suppressed spontaneous NMDA receptor-mediated EPSCs in cultures of spinal dorsal horn neurons. In addition, kainate suppressed EPSCs in dorsal horn neurons evoked by stimulation of synaptically coupled DRG cells in DRG-dorsal horn neuron cocultures. Interestingly, although the glutamate receptor subunit 5-selective kainate receptor agonist (RS)-2-alpha-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid (ATPA) (2 micrometer) was able to suppress DRG-dorsal horn synaptic transmission to a similar extent as kainate (10 micrometer), it had no effect on excitatory transmission between dorsal horn neurons. Agonist applications revealed a striking difference between kainate receptors expressed by DRG and dorsal horn neurons. Whereas DRG cell kainate receptors were sensitive to both kainate and ATPA, most dorsal horn neurons responded only to kainate. Finally, in recordings from dorsal horn neurons in spinal slices, kainate and ATPA were able to suppress NMDA and AMPA receptor-mediated EPSCs evoked by dorsal root fiber stimulation. Together, these data suggest that kainate receptor agonists, acting at a presynaptic locus, can reduce glutamate release from primary afferent sensory synapses.

Zn2+ current is mediated by voltage-gated Ca2+ channels and enhanced by extracellular acidity in mouse cortical neurones.

1. Mammalian neuronal voltage-gated Ca2+ channels have been implicated as potential mediators of membrane permeability to Zn2+. We tested directly whether voltage-gated Ca2+ channels can flux Zn2+ in whole-cell voltage-clamp recordings from cultured murine cortical neurones. 2. In the presence of extracellular Zn2+ and no Na+, K+, or other divalent cations, a small, non-inactivating, voltage-gated inward current was observed exhibiting a current-voltage relationship characteristic of high-voltage activated (HVA) Ca2+ channels. Inward current was detectable at Zn2+ levels as low as 50 microM, and both the amplitude and voltage sensitivity of the current depended upon Zn2+ concentration. This Zn2+ current was sensitive to blockade by Gd3+ and nimodipine and, to a lesser extent, by omega-conotoxin GVIA. 3. Zn2+ could permeate Ca2+ channels in the presence of Ca2+ and other physiological cations. Inward currents recorded with 2 mM Ca2+ were attenuated by Zn2+ (IC50 = 210 microM), and currents recorded with Zn2+ were unaffected by up to equimolar Ca2+ concentrations. Furthermore, the Zn2+-selective fluorescent dye Newport Green revealed a depolarisation-activated, nimodipine-sensitive Zn2+ influx into cortical neurones that were bathed in a physiological extracellular solution plus 300 microM ZnCl2. 4. Surprisingly, while lowering extracellular pH suppressed HVA Ca2+ currents, Zn2+ current amplitude was affected oppositely, varying inversely with pH with an apparent pK of 7.4. The acidity-induced enhancement of Zn2+ current was associated with a positive shift in reversal potential but no change in the kinetics or voltage sensitivity of channel activation. 5. These results provide evidence that L- and N-type voltage-gated Ca2+ channels can mediate Zn2+ entry into cortical neurones and that this entry may be enhanced by extracellular acidity.

Zinc-induced neuronal death in cortical neurons.

Although Zn2+ is normally stored and released in the brain, excessive exposure to extracellular Zn2+ can be neurotoxic. The purpose of the present study was to determine the type of neuronal cell death, necrosis versus apoptosis, induced by Zn2+ exposure. Addition of 10-50 microM ZnCl2 to the bathing medium of murine neuronal and glial cell cultures induced, over the next 24 hrs., Zn2+-concentration-dependent neuronal death; some glial death also occurred with Zn2+ concentrations above 30 microM. The neuronal death induced by 20 microM Zn2+ was characterized by coarse chromatin condensation, the formation of apoptotic bodies, and internucleosomal DNA fragmentation. It was attenuated in cortical cell cultures prepared from mice null for the bax gene, and by the caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-CH2F (ZVAD, 100 microM), but not by the NMDA receptor antagonist, D-2-amino-5-phosphonovalerate (D-APV, 200 microM ). In contrast, the neuronal death induced by 50 microM Zn2+ was characterized by plasma membrane disruption and random DNA fragmentation; this death was attenuated by D-APV, but exhibited little sensitivity to ZVAD or deletion of bax. These results suggest that Zn2+ can induce cell death with characteristics of either apoptosis or necrosis, depending on the intensity of the Zn2+ exposure.

AMPA receptor-PDZ interactions in facilitation of spinal sensory synapses.

Silent synapses form between some primary sensory afferents and dorsal horn neurons in the spinal cord. Molecular mechanisms for activation or conversion of silent synapses to conducting synapses are unknown. Serotonin can trigger activation of silent synapses in dorsal horn neurons by recruiting AMPA receptors. AMPA-receptor subunits GluR2 and GluR3 interact via their cytoplasmic C termini with PDZ-domain-containing proteins such as GRIP (glutamate receptor interacting protein), but the functional significance of these interactions is unclear. Here we demonstrate that protein interactions involving the GluR2/3 C terminus are important for serotonin-induced activation of silent synapses in the spinal cord. Furthermore, PKC is a necessary and sufficient trigger for this activation. These results implicate AMPA receptor-PDZ interactions in mechanisms underlying sensory synaptic potentiation and provide insights into the pathogenesis of chronic pain.

Genetic enhancement of learning and memory in mice.

Hebb's rule (1949) states that learning and memory are based on modifications of synaptic strength among neurons that are simultaneously active. This implies that enhanced synaptic coincidence detection would lead to better learning and memory. If the NMDA (N-methyl-D-aspartate) receptor, a synaptic coincidence detector, acts as a graded switch for memory formation, enhanced signal detection by NMDA receptors should enhance learning and memory. Here we show that overexpression of NMDA receptor 2B (NR2B) in the forebrains of transgenic mice leads to enhanced activation of NMDA receptors, facilitating synaptic potentiation in response to stimulation at 10-100 Hz. These mice exhibit superior ability in learning and memory in various behavioural tasks, showing that NR2B is critical in gating the age-dependent threshold for plasticity and memory formation. NMDA-receptor-dependent modifications of synaptic efficacy, therefore, represent a unifying mechanism for associative learning and memory. Our results suggest that genetic enhancement of mental and cognitive attributes such as intelligence and memory in mammals is feasible.

Speaking out of turn: a role for silent synapses in pain.

Severe tissue or nerve injury can result in a chronic and inappropriate sensation of pain, mediated in part by the sensitization of spinal dorsal horn neurons to input from primary afferent fibers. Synaptic transmission at primary afferent synapses is mainly glutamatergic. Although a functioning excitatory synapse contains both alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors in the postsynaptic membrane, recent evidence suggests that dorsal horn neurons contain some "silent" synapses, which exhibit purely NMDA receptor-mediated evoked postsynaptic currents and do not conduct signals at resting membrane potential. Serotonin, which is released onto dorsal horn neurons by descending fibers from the rostroventral medulla, potentiates sensory transmission by activating silent synapses on those neurons, i.e., by recruiting functional AMPA receptors to the postsynaptic membrane. This phenomenon may contribute to the hyperexcitability of dorsal horn neurons seen in chronic pain conditions.

Endogenous voltage-gated potassium channels in human embryonic kidney (HEK293) cells.

Endogenous voltage-gated potassium currents were investigated in human embryonic kidney (HEK293) and Chinese hamster ovary (CHO) cells using whole-cell voltage clamp recording. Depolarizing voltage steps from -70 mV triggered an outwardly rectified current in nontransfected HEK293 cells. This current had an amplitude of 296 pA at +40 mV and a current density of 19.2 pA/pF. The outward current was eliminated by replacing internal K+ with Cs+ and suppressed by the K+ channel blockers tetraethylammonium and 4-aminopyridine. Raising external K+ attenuated the outward current and shifted the reversal potential towards positive potentials as predicted by the Nernst equation. The current had a fast activation phase but inactivated slowly. These features implicate delayed rectifier (I(K))-like channels as mediators of the observed current, which was comparable in size to I(K) currents in many other cells. A small native inward rectifier current but no transient outward current I(A), the M current I(M), or Ca2+-dependent K+ currents were detected in HEK293 cells. In contrast to these findings in HEK293 cells, little or no I(K)-like current was detected in CHO cells. The difference in endogenous voltage-activated currents in HEK293 and CHO cells suggest that CHO cell lines are a preferred system for exogenous K+ channel expression.

Measurement of intracellular free zinc in living cortical neurons: routes of entry.

We used the ratioable fluorescent dye mag-fura-5 to measure intracellular free Zn2+ ([Zn2+]i) in cultured neocortical neurons exposed to neurotoxic concentrations of Zn2+ in concert with depolarization or glutamate receptor activation and identified four routes of Zn2+ entry. Neurons exposed to extracellular Zn2+ plus high K+ responded with a peak cell body signal corresponding to a [Zn2+]i of 35-45 nM. This increase in [Zn2+]i was attenuated by concurrent addition of Gd3+, verapamil, omega-conotoxin GVIA, or nimodipine, consistent with Zn2+ entry through voltage-gated Ca2+channels. Furthermore, under conditions favoring reverse operation of the Na+-Ca2+ exchanger, Zn2+ application induced a slow increase in [Zn2+]i and outward whole-cell current sensitive to benzamil-amiloride. Thus, a second route of Zn2+ entry into neurons may be via transporter-mediated exchange with intracellular Na+. Both NMDA and kainate also induced rapid increases in neuronal [Zn2+]i. The NMDA-induced increase was only partly sensitive to Gd3+ or to removal of extracellular Na+, consistent with a third route of entry directly through NMDA receptor-gated channels. The kainate-induced increase was highly sensitive to Gd3+ or Na+ removal in most neurons but insensitive in a minority subpopulation ("cobalt-positive cells"), suggesting that a fourth route of neuronal Zn2+ entry is through the Ca2+-permeable channels gated by certain subtypes of AMPA or kainate receptors.

Autoradiographic localization of insulin-like growth factor II receptors in cerebellar cortex of weaver and Purkinje cell degeneration mutant mice.

Autoradiography was used to visualize insulin-like growth factor II (IGF-II) receptors in the cerebellar cortex of weaver and Purkinje cell degeneration (pcd) mice. These mutants were selected for their respective absence of granule or Purkinje cells. Histological preparations confirmed a severe loss of granule cells in the cerebella of weaver mutants and an absence of Purkinje cells in those of pcd mutants. Autoradiographs showed specific IGF-II binding to the granule cell layer of the cerebellar cortex in control mice, and in pcd mutants. No specific [125I]human IGF-II binding was observed in the cerebellar cortex of weaver mutants. These studies suggest that specific IGF-II receptor sites are located on the granule cells of the cerebellum.

The insulin-like growth factor-II (IGF-II) receptor of rat brain: regional distribution visualized by autoradiography.

The presence of insulin-like growth factor-II (IGF-II) in brain and cerebral spinal fluid prompted us to investigate the distribution of receptors for this peptide in rat brain slices. Human 125I-IGF-II (10 pM) was incubated for 16 h at 4 degrees C with thaw-mounted slices of rat brain from 11 different brain regions. Incubations in the absence or presence of excess unlabeled human IGF-II or insulin were performed and the labeled tissues were exposed to X-ray film for 4-7 days. Autoradiographs showed dense labeling in the granule layers of the olfactory bulbs, deep layers of the cerebral cortex, pineal gland, anterior pituitary, hippocampus (CA1-CA4, and dentate gyrus), and the granule cell layers of the cerebellum. Unlabeled IGF-II eliminated most of the binding in these brain regions while insulin produced only a minimal reduction in the amount of 125I-IGF-II bound. These results indicate that a neural receptor for IGF-II is uniquely distributed in rat brain tissue supporting the notion that this peptide might play an important role in neuronal functioning.

Sigma opioid receptor: characterization and co-identity with the phencyclidine receptor.

The properties of the sigma opioid receptor of rat brain cortex have been characterized using the prototypic ligand (+)-[3H] SKF 10,047. Binding to this receptor was rapid, and equilibrium was obtained within 30 min at 37 degrees C. Specific binding was linear with protein concentration up to 500 micrograms/2 ml and was dependent upon protein integrity. Denaturation by boiling destroyed over 95% of the specific binding. A high-affinity binding site with a KD of 150 +/- 40 nM and a maximum binding of 2.91 +/- 0.84 pmol/mg of protein was determined from a Scatchard plot of the binding data. The addition of salt, either NaCl or CaCl2, to the buffers markedly decreased binding, with CaCl2 being more potent than NaCl. A broad pH optimum for specific binding was observed; maximum binding was at pH 9.0. The affinity of a number of ligands for the sigma site and the phencyclidine receptor were compared. The binding (IC50) of 13 ligands to the sigma site showed a correlation of 0.86 (P less than .01) with binding to the phencyclidine site. The data demonstrate that the biochemical properties of the sigma and phencyclidine receptors are similar and support the view that these receptors are one and the same site.

Nasal delivery of polypeptides I: nasal absorption of enkephalins in rats.

The serum levels of two enkephalins after various routes of administration were compared in rats. The results indicated that serum levels of metkephamid after nasal administration were not significantly different than levels after intravenous injection. The oral administration of metkephamid resulted in undetectable serum levels. The effects of a promoter and variations in the peptide dose on nasal absorption were studied. Depending on the stability of the polypeptide and its susceptibility to enzymatic degradation, nasal absorption of peptides can be influenced by the presence of a promoting agent in the formulation. A linear relationship between the dose and the AUC was observed in the range of concentrations studied. The absorption mechanism appears to be passive diffusion. Microscopic examinations of nasal mucosa in rats revealed degrees of irritation which, considering the experimental exposure, were slight and probably repairable. The data indicate that enkephalins can be absorbed through the nasal mucosa into the systemic circulation, and the onset of absorption was rapid. Nasal administration may offer an attractive alternative for the delivery of proteins and/or polypeptides which are, in general, absorbed poorly when given orally.