Analgesic effect of histamine induced by intracerebral injection into mice

Three methods were used to study the analgesic effect of intracerebral injection of histamine (Hi) on mice: the writhing test (acetic acid and phenylquinone), the electrical stimulation of the tail and the hot plate test. At doses higher than 2 g, Hi inhibited the writhing syndrome significantly, and at doses of 10 g or higher, Hi displayed a marked analgesic effect during both the electrical stimulation and hot plate methods. The saline injection produced only a negligible effect.Simultaneous application of Hi and 10 g of diphenhydramine, pyrilamine or promethazine, apparently causing no analgesic effect from a single administration, caused a parallel shift of the dose-response curve of Hi to the right. ED50 of Hi was increased approximately 2, 2.8 and 3.8 times, respectively. However, cimetidine did not reveal any antagonistic effect on Hi-induced analgesia. Subcutaneously administered, 3 mg/kg of morphine augmented the analgesic effect of Hi. In accordance with this, pretreatment of naloxone (0.005 mg/kg) antagonized the analgesic action of Hi almost completely. When 5 mg/kg of leucine-enkephalin, less than the minimum effective dose, was given prior to Hi injection, the analgesic effect of Hi was enhanced. In addition, 10 and 20 g of Hi increased the morphine analgesia markedly and parallel shifted the dose-response curve of morphine to the left.     

Peripheral and central opioid activity in the analgesic potency of morphine

The role of neural histamine in morphine-analgesia and in morphine-induced potentiation of stress analgesia was studied. Pretreatment of rats with -fluoromethylhistidine (-FMH) (200 g i.c.v./rat; daily for five days) increased the analgesic potency of morphine, centrally or peripherally injected, in the tail-flick assay. This increase was significantly blocked by i.c.v. or i.p.-funaltrexamine (-FNA) a mu selective irreversible opioid receptor antagonist, whereas i.c.v injected naltrexone did not block the increased analgesic potency of the i.c.v. morphine. Rats subjected to cold-restrained stress (60 min at 4°C) showed increased tail-flick latency, compared to the unstressed group. The analgesic potency of morphine was significantly greater in rats subjected to restraint with respect to unstressed rats. However, the inhibition of histamine biosynthesis by -FMH significantly reduced cold-restraint analgesia in controls, and also inhibited the analgesic efficacy of the opiate. These results indicate that neural histamine may be responsible for pain response modifications observed in rats subjected to cold-restraint conditions, and of morphine-potentiation of stress analgesia. The data also suggest a close association between increased analgesic potency of morphine and inhibition of histaminergic effects, possibly implying a functional supersensitivity and an increase in opioid receptors.     

Alterations in axons and synapses of olfactory cortex following olfactory bulb lesions in newborn rats

Summary The olfactory cortex of rats is being studied at various survival times following deafferentating olfactory bulb ablation on the day of birth. The neonatal axons and synaptic terminals undergo rapid, flocculent degeneration and fragmentation. Most are not electron-dense and therefore probably not argyrophilic at this particular age of the lesion. The degeneration and removal of debris is far more rapid than in adults, yielding a markedly enlarged extracellular space with a relative absence of glia at the vacated postsynaptic thickenings. Denervated postsynaptic thickenings become occupied by neuronal and nonneuronal profiles and profiles of uncertain origin, singly or in various combinations, or the sites may remain partially vacant. One or more axons with synaptic vesicles often aggregated at the site are commonly involved. Certain terminals form contacts on progressively greater lengths of the thickening until typical synaptic contacts predominate by 14 days survival. The results suggest a competitive reinnervation process and provide a fine structural explanation for the events leading to alterations in this pathway following neonatal deafferentation.This project was supported in part by NIH Research Grants DE 04942, awarded by the National Institute of Dental Research, and Grants NS 09678 and NS 04053 from the National Institute of Neurological and Communicative Disorders and Stroke, PHS/DHEWDr. Westrum is also an affiliate of the Child Development and Mental Retardation Center, University of Washington     

Pyramidal tract of the cat: axon size and morphology

Summary The purpose of this work was to determine the number and morphology of pyramidal tract (PT) axons in the cat, using electron microscopy, modern methods of fixation, and computer-assisted morphometric analysis. Sections taken at the level of the medullary pyramids in three animals were fixed and magnified up to 10,000 x to produce photomicrographs. Morphological data were entered into computer files for analysis by tracing axon perimeters on micrographs mounted on a digitizer tablet. The number of axons per PT averaged 415,000, of which 88% were myelinated and 12% were unmyelinated. 90% of the myelinated axons fell in the diameter range 0.5–4.5 m. Axons larger than 9 m diameter accounted for 1% of the total; the largest were 20–23 m. Myelinated axon mean diameter was 1.98 m; because of the skewed distribution, with many small axons and a few very large axons, median diameter was 1.60 m. Size distribution was relatively uniform throughout the PT cross section, with all sizes represented in all regions. However, the more medial regions had a higher proportion of small fibers than the more lateral regions: mean medial diameter was 1.85 m while mean lateral diameter was 2.09 m. Myelin sheath thickness averaged 7.9% of fiber diameter for axons up to 11 m, but was constant at 0.9 m for larger fibers. Myelinated fibers were distorted from the circular shape in cross section, with a mean circularity index (or form factor) of 0.85, which implies that the fibers could swell about 15% without rupture of the cell membrane. Unmyelinated fibers averaged 0.18 m diameter (range 0.05–0.6 m); the largest unmyelinated axons were larger than the smallest myelinated axons. It is concluded that previous work greatly underestimated the number of axons in the cat pyramidal tract.     

Antibody response inPlasmodium vinckei malaria after treatment with chloroquine and adjuvant interferon-γ

The antibody response of mice infected withPlasmodium vinckei after treatment with chloroquine either alone or in combination with interferon- (IFN-) was determined. Sequential serum samples were drawn from BALB/c mice receiving either 240 g chloroquine on the day of infection or 120 g chloroquine plus 10⁴ units IFN- daily for 11 days beginning on day 3 prior to infection. Mice treated with additional IFN- showed an early induction of IgG2a response and a reduction in IgG1 antibodies as detected by the immunofluorescence technique at between 10 and 16 days after infection as compared with mice treated with chloroquine alone. Thus, IFN- may partly exert its antimalarial activity via the induction of IgG2a antibody formation. At 4–6 weeks after infection, when mice from both groups resisted homologous re-infection, the predominant antibody isotypes found in both groups were IgG1 and IgG2a. Serum samples obtained from mice in both treatment groups at 6 weeks after infection were used for serum transfer experiments. When parasitised erythrocytes were preincubated with such immune serum, a retardation of the course of parasitaemia by 2 days was observed.     

Inhibition of lung colonization of mouse colon 26 adenocarcinoma by recombinant mouse interferon β through a modification of platelet function

Recombinant murine interferon (MuIFN-) given i.v. efficiently inhibited both pulmonary arrest and formation of lung colonies of NL-17, a highly metastatic variant of mouse colon adenocarcinoma 26. NL-17 was rather resistant to MuIFN- in vitro and was highly resistant to natural killer cells of mice even though they were treated in vivo with MuIFN-. Platelets isolated from MuIFN--treated mice showed reduced aggregating activity induced by NL-17. Since lung colonization by NL-17 is influenced by platelet aggregation, the inhibition of colonization by MuIFN- could be partly mediated through modification of platelet function in vivo. The effect of MuIFN- on platelet function and its subsequent inhibition of lung colony formation give new insights into the action of recombinant MuIFN-.     

Chromosomal NOR Activity in Mice Selected for High and Low Swim Stress-Induced Analgesia

Metaphase nucleolar organizer region (NOR) activity was studied in mouse lines selectively bred for high analgesia (HA) and for low analgesia (LA) induced by 3-min swimming in 20°C water. Apart from pain-related traits, HA mice also manifest, as compared to the LA line, higher emotionality in certain behavioral tests and are less capable of coping with the hypothermic challenge of swimming in cold water, in addition to being more susceptible to the mutagenic effect of whole-body -radiation and mitomycin C injection. We here compared NOR activity in HA and LA mice. A statistically significant difference (p .01) was detected in mean silver-stained nucleolar number/cell between the HA and LA lines, being lower for HA mice. We propose that the breeding strategy, along with the differentiation of stress-related phenomena, has altered the activity of genes coding rRNA and that this activity is important in controlling DNA repair in each line. It is concluded that quantitative studies of nucleolar changes may be useful in evaluating the biological reactivity to stress stimuli.     

Neuron Activity in the Prefrontal Cortex of the Brain in Rats with Different Typological Characteristics in Conditions of Emotional Stimulation

Male Wistar rats were separated according to the emotional resonance method (groups of animals avoiding (altruists) and not avoiding (egotists) the pain cries of partner rats) and neuron activity in the prefrontal areas of the cortex was studied in the right and left hemispheres. Assessments were made of changes in the frequency of nerve cell spike activity (in relation to the baseline activity of neurons in sated animals) in rats subjected to one day of food deprivation and after electrical stimulation of emotionally positive (lateral hypothalamus) and negative (tegmentum of the midbrain) brain structures and after exposure to the pain cries of partner rats. The results of these experiments revealed a series of differences in the cell activities of the two groups of rats. In conditions of hunger, the discharge frequency in the altruists was higher than that in egotists. Cortical neuron responses to positive stimulation were greater than those to negative stimulation in rats of both groups. Intracerebral stimulation produced significantly greater increases in discharge frequency in neurons of both prefrontal areas of the cortex in altruists than in egotists. In both groups of rats, neurons in the right hemisphere responded to emotionally negative stimulation with significantly greater activation than cells in the left hemisphere, while activity in the left hemisphere was greater in conditions of emotionally positive stimulation. Altruists showed significantly greater neuron responses during exposure to pain cries from victim rats in both the right and left hemispheres. The responses of egotists to victim cries were not significantly different from baseline activity levels.     

On the regulation of the expressed L-type calcium channel by cAMP-dependent phosphorylation

The Ca²⁺ channel subunits _1C-a and _1C-b were stably expressed in Chinese hamster ovary (CHO) and human embryonic kidney (HEK) 293 cells. The peak Ba²⁺ current (I _Ba) of these cells was not affected significantly by internal dialysis with 0.1 mM cAMP-dependent protein kinase inhibitor peptide (mPKI), 25 M cAMP-dependent protein kinase catalytic subunit (PKA), or a combination of 25 M PKA and 1 M okadaic acid. The activity of the _1C-b channel subunit expressed stably in HEK 293 cells was depressed by 1 M H 89 and was not increased by superfusion with 5 M forskolin plus 20 M isobutylmethylxanthine (IBMX). The _1C-a·₂·₂/ complex was transiently expressed in HEK 293 cells; it was inhibited by internal dialysis of the cells with 1 M H 89, but was not affected by internal dialysis with mPKI, PKA or microcystin. Internal dialysis of cells expressing the _1C-a·₂·₂/ channel with 10 M PKA did not induce facilitation after a 150-ms prepulse to +50 mV. The Ca²⁺ current (I _Ca) of cardiac myocytes increased threefold during internal dialysis with 5 M PKA or 25 M microcystin and during external superfusion with 0.1 M isoproterenol or 5 M forskolin plus 50 M IBMX. These results indicate that the L-type Ca²⁺ channel expressed is not modulated by cAMP-dependent phosphorylation to the same extent as in native cardiac myocytes.     

Integration in trigeminal premotor interneurones in the cat

Summary The profile of integration in a sample of 183 interneurones localized in the subnucleus- of the oral nucleus of the spinal trigeminal tract (NVspo-) has been analyzed. 134 neurones were tested for inputs from primary afferents of the trigeminal, facial and cervical nerves as well as for inputs from the midbrain and from the cervical spinal cord. The remaining 49 neurones were tested for inputs from the primary afferents and for descending convergence from defined sites within the oro-facial primary projections of the cerebral cortex. It was found that the interneurones, mainly recorded in the dorsal and dorsomedial aspect of the NVspo-, receive short latency inputs from the low threshold oral and perioral afferents and longer latency inputs from the high threshold jaw and neck muscle afferents. There was evidence for convergence from the cervical segmental level (29%) and some of the neurones had axon terminals in the superior colliculus. However, the interneurones did not receive a descending tectal input. About 80% of the NVspo- interneurones were activated from the orofacial primary projection fields within cytoarchitectonic areas 3a and 3b of the coronal gyrus. This input was topographically organized and the neurones were activated from the same oral and perioral region of the periphery as the cortical region from which the descending projections themselves originated. Minimum latencies indicated a monosynaptic connection. The convergence profile onto the NVspo- interneurones appeared unique as compared with interneurones located in the intertrigeminal area. Aspects of the possible functional roles of the NVspo- neurones are discussed in relation to ongoing oro-facial (masticatory) movements. The properties of a selected sample of NVspo- interneurones, which were antidromically activated from the digastric subnucleus of the trigeminal motor nucleus, are reported in a companion paper (Olsson and Westberg 1991).Abbreviations AD Antidromic - Alv inf Inferior alveolar nerve - C2 2nd cervical spinal nerve - C2mt Motor nuclei of the 2nd cervical spinal segment - Co Contralateral - Coll sup Colliculus superior - cor Coronal sulcus - D Dorsal - Dig Digastric nerve - FTC Central tegmental field - HRP Horseradish peroxidase - Ip Ipsilateral - Ling Lingual nerve - M Medial - Mass Masseteric nerve - MGP Principal nucleus of the medial geniculate body - Mx Maxillary nerve - Mx-w Infraorbital nerve, branch to whiskers and lip - NintV Intertrigeminal area - NR Nucleus ruber - NVmt Trigeminal motor nucleus - NVsnpr Main sensory trigeminal nucleus - NVspo--- Subnucleus--- of the oral nucleus of the spinal trigeminal tract - OD Orthodromic - orb Orbital sulcus - prsyl Presylvian sulcus - SCS Superior colliculus, superficial layer - SCI Superior colliculus, intermediate layer - SCD Superior colliculus, deep layer - T Threshold stimulus - V Trigeminal nerve/ tract - VII Facial nerve - Vrm Trigeminal motor root - WGA-HRP Wheat germ agglutinin-conjugated horseradish peroxidase     

Synergistic effects of tumour necrosis factor-α and interferon-γ on feline haemopoietic progenitors

Pathogenic mechanisms that underlie feline leukaemia virus subgroup-C (FeLV-C) induced erythroid aplasia are unknown. FeLV-C infection is associated with higher serum levels of interferon- (IFN-) and tumour necrosis factor- (TNF-), which may act synergistically to cause haemopoietic suppression. In the present studies, the synergistic effects of TNF- and IFN- on feline bone marrow progenitors in vitro were evaluated. Bone marrow mononuclear cells from specific-pathogen-free cats were exposed to TNF- (100 and 200 pg/ml) and IFN- (100 or 200 units/ml), alone or in combination, for 2 h before plating for clonal assays of colony forming units. Our results show that TNF- and IFN- in combination caused marked suppression of feline colony forming units-erythroid (CFU-E), burst forming units-erythroid (BFU-E), and colony forming units-fibroblasts (CFU-F), whereas colony forming units-granulocyte/macrophage (CFU-GM) were minimally affected. The same concentrations of TNF- and IFN- alone had minimal effects on CFU-E, BFU-E and CFU-F. These results suggest that TNF- and IFN- may play a significant role in regulating haemopoiesis in cats and may be involved in the pathogenesis of erythroid aplasia in cats infected with feline leukaemia virus.     

Antibodies to β2-Glycoprotein-I: Urea Resistance, Binding Specificity, and Association with Thrombosis

The aim of the present study was to evaluate the urea resistance and binding characteristics of anti-2-glycoprotein I (anti-2GPI) antibodies using standard anticardiolipin (aCL) and anti-2GPI enzyme immunosorbent assays (ELISAs). Sera from patients with antiphospholipid syndrome (APS) (n = 22) and non-APS (n = 24), positive in a standard aCL ELISA, were tested in an anti-2GPI ELISA performed in polystyrene-irradiated ELISA plates. Urea resistance aCL and anti-2GPI ELISAs were performed by measuring the ability of antibodies to recognize antigen in the presence of 2 M urea. The serum dilution after urea treatment (D) expressed as a percentage of the serum dilution without urea treatment (D _o) corresponding to the same optical density was defined as residual activity (RA = 100 D/D _o). The higher the RA, the higher the resistance of the antibodies to urea. APS compared to non-APS sera had higher aCL binding (absorbance values ranging between 0.180 and 1.400; median, 0.717 vs 0.120–1.273; median, 0.250, respectively; P < 0.004). Six APS patients' sera had low aCL levels but they expressed RA 30%. Anti-2GPI antibodies were detected in 15 of 22 APS vs 3 of 24 non-APS patients (P < 0.03); RA 30% was detected in 15 of 22 APS vs 1 of 23 non-APS patients (P < 0.004). Using a CL affinity column, antibodies were purified from three APS anti-2GPI negative and three non-APS anti-2GPI-positive patients and tested in a aCL ELISA, using highly purified bovine serum albumin (BSA) as a blocking agent (modified ELISA); reactivity was not detected in two APS and one non-APS sera. On the contrary, the reactivity of the purified antibodies was high when 2GPI was incubated with CL in the ELISA plates; thus some anti-2GPI negative sera from APS patients recognized the CL/2GPI complex, rather than CL or 2GPI alone. In conclusion, anti- 2GPI antibodies are common in the APS patients, but a number of such patients recognize the CL/2GPI complex and not CL or 2GPI. Antibodies to either 2GPI or the CL/2GPI complex derived from APS sera present a high resistance to urea. Anti-2GPI antibodies of low urea resistance exist in a minority of non-APS patients with autoimmune disease.     

A Proposed Heuristic for Communicating Heritability Estimates to the General Public, with Obesity as an Example

It is well established that many continuously distributed traits have a heritable component. However, it is often difficult to communicate to the general public the meaning of quantitative estimates of heritability. To address this problem, the present paper introduces a heuristic for communicating heritability to nonscientific audiences. This heuristic involves adopting an extremely simplified model of inheritance and artificially (and somewhat arbitrarily) defining a cutoffs of low environmental risk and affectation status. Using body weight and obesity as an example, we present a table which gives estimates of the proportion of obese persons who are genetically obese assuming varying levels of environmental risk for obesity and relative body weight scores for defining obesity. The resulting statistic may prove useful for lay audiences in understanding a heritability estimate.     

Disturbance of delayed match-to-sample in macaques by tetanization of anterior commissure versus limbic system or basal ganglia

Summary Three pig-tailed macaques were trained to select (match) from a pair of colored images that which they had seen (sample) and responded to 5–15 s previously. The anterior commissure (AC) and/or its radiation, various loci in basal ganglia, hippocampal formation and control areas, (splenium of corpus callosum, precentral gyrus, insular cortex), totalling 40 loci, were each tetanized for 4 s during presentation of the sample image, during the delay period, or when the monkey was required to select the matching image. For several loci in the hippocampal formation tetanization at any phase of the task reduced matching to chance levels and gave evidence of electrical after-discharge; but other comparable hippocampal loci had little or no effect. Response to sample or match stimuli were absent during tetanization of basal ganglia or anterior commissure. When finally made, upon cessation of tetanization, responses were equally correct for basal ganglia and control sites, but for AC were at chance levels.     

Evidence for a direct relationship between mitochondrial genome organization and regeneration ability in hexaploid wheat somatic tissue cultures

Summary Embryogenic and non-embryogenic long-term callus cultures of hexaploid wheat exhibit differences in the organization of their mitochondrial genome. Embryogenic and non-embryogenic fractions of callus cultures initiated from immature embryos of the wheat cultivar Chinese Spring have been isolated and subsequently subcultured. DNA-DNA hybridization experiments using labelled cloned wheat mitochondrial DNA fragments have shown that the mitochondrial DNA organization of embryogenic subcultures derived from embryogenic parts of Chinese Spring calli is closely related to that of the initial Chinese Spring calli, while non-embryogenic subcultures derived from non-embryogenic fragments of Chinese Spring calli exhibit a mitochondrial DNA organization similar to that found in non-embryogenic calli derived from cultivar Aquila. In addition, somatic tissue cultures initiated from three other non-embryogenic wheat cultivars (Talent, Thésée and Capitole) display mitochondrial DNA arrangements similar to those found in cultivar Aquila. These results strongly suggest that, in wheat callus cultures, a particular mitochondrial genome organization is correlated with the ability of cultured cells to regenerate whole plants.Abbreviations mtDNA mitochondrial DNA - ctDNA chloroplast DNA - rRNA ribosomal RNA - kb kilobase pair - cv cultivar - 2,4-D 2,4-dichlorophenoxyacetic acid     

The ultrastructure of retinula cell endings in the compound eye of the crayfish

Summary The retinula cell axons entering the synaptic region of the optic lamina in the crayfish form large expanded bag-like terminals which are organized with other neural elements into structural units called cartridges. The cytoplasm of the terminals contains synaptic and coated vesicles, ER cisternae, clusters of tubular elements, and mitochondria. Several mitochondria are often found associated with a single large rod-shaped inclusion present within each terminal. The rod-like formation could be demonstrated in both light and EM material, it is composed of 85–95 Å filaments and averages I m in width and 6.5 m in length.The terminal synaptic contacts are characterized by a bar-shaped presynaptic density and three postsynaptic elements. Some synaptic vesicles appear aligned along the bar density which measures approximately 800 Å in width and 0.75 m in length. Each terminal synapse has three postsynaptic elements which have an electron-dense fringe along their membrane bordering the synaptic cleft. From the planes of section through this contact a composite reconstruction is presented.Also present along the central border of the terminals are numerous small invaginated processes, some of which extend almost to the middle of the terminal. No membrane specializations were found along these processes and they have been tentatively identified as neuronal.     

On the terms “reticulosis” and “reticulum cell sarcoma” with regard to the modern concept of the monocyte macrophage system

Summary The terms reticulosis and reticulum cell sarcoma (= malignant lymphoma, histiocytic type) are discussed regarding the modern concept of the monocyte macrophage system which today has replaced the ancient theory of the reticuloendothelial system. The monocyte macrophage system is not independent, but closely related to the myeloid system. Thus, a third blood forming system as was believed in the case of RES does not exist. Phagocytic reticulum cells of the various hematopoietic organs are highly activated monocyte-derived macrophages. All those conditions formerly termed reticuloses have been found to belong either to the myeloid or to the lymphatic system. Considering the reticulum cell sarcomas or malignant histiocytic lymphomas, most of them seem to be of lymphatic rather than of macrophage origin, representing highgrade malignant lymphomas, possibly immunoblastic sarcomas. No relationship between these tumours and the monocyte macrophage system has been established, so far. Therefore, the terms reticulosis and reticulum cell sarcoma should be no longer used in order to avoid confusion, in order to stimulate sufficient diagnostic efforts which will really clarify such cases, and in order to give full credit to modern results of hematopathology.     

Regional localization of aβ-galactosidase locus on human chromosome 22

Human white blood cells with an X/22 translocation [46, XX, t(X; 22)(q23; q13)] were fused with Chinese hamster cells. The isolated hybrids were analyzed for human chromosomes and 21 enzyme markers. An electrophoretic technique for studying the -galactosidase isoenzymes in man-Chinese hamster hybrid cells was developed. Immunological studies showed that the -galactosidase marker studied in these hybrids did contain immunological determinants of human origin. Furthermore the results provided evidence that a locus for -galactosidase is situated on chromosome 22 distal to the breakpoint in q13.     

Ribonuclease activity of the “myofibrillary” fraction of normal and autolyzed muscle tissue

The separation in a sucrose gradient of the myofibrillary fraction of normal and autolyzed muscle tissue gave 4 components. During post-mortem destruction of the tissue there was observed a slight decrease of the myofibrillary fraction yield and also certain changes in the distribution of protein between different components. Under the selected conditions RNase activity was found in all 4 components. During the course of autolysis enzymatic activity increased in the whole myofibrillary fraction, as well as in the lysosomal-mitochondrial components of myofibrils.Research Laboratory, Ministry of Health of the USSR, Moscow. Translated from Buylleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 5, pp. 533–537, May, 1978.     

Interaction of the novel penem CGP 31 608 and Its enantiomer with type Id beta-lactamase and penicillin-binding proteins

The novel penem CGP 31 608 (5R, 6S, 8R) and its enantiomer CGP 32 879 (5S, 6R, 8S) were shown to be essentially stable against hydrolysis by type Id -lactamase isolated from Pseudomonas aeruginosa 18S/H. CGP 31 608 was a potent progressive inhibitor of this enzyme (I50=32 M), which was only weakly inhibited by CGP 32 879 (I50=460 M). CGP 31 608 had the highest affinity for penicillin-binding protein (PBP) 4 from Escherichia coli K-12 (I50= 1 g/ml), followed by PBPs 2 (10 g/ml) and 1A/1Bs (100 g/ml); CGP 32 879 did not inhibit binding of ¹⁴ C-benzylpenicillin to the PBPs. The steric configuration of the -lactam nucleus of penems appears to strongly influence their affinity for -Iactamases and target PBPs. The balanced spectrum of CGP 31 608 may be explained by its -lactamase stability and affinity for several vital PBPs.