Acute minocycline treatment inhibits microglia activation, reduces infarct volume, and has domain-specific effects on post-ischemic stroke cognition in rats.

Ischemic stroke affects millions of individuals worldwide and a high prevalence of survivors experience cognitive deficits. At present, the underlying mechanisms that drive post-stroke cognitive decline are not well understood. Microglia play a critical role in the post-stroke inflammatory response, but experimental studies show that an accumulation of chronically activated microglia can be harmful and associates with cognitive impairment. This study assessed the effect of acute post-stroke minocycline treatment on chronic microglia and astrocyte expression within the infarct and remote white matter regions, as well as its effect on various domains of cognitive function post-stroke. Nine-month-old male rats received an injection of endothelin-1 into the right dorsal striatum to induce transient focal ischemia, and then were treated with minocycline or saline for 4 days post-stroke. Rats were tested using a series of lever-pressing tasks and the Morris water maze to assess striatal-based learning, cognitive flexibility, and spatial learning and reference memory. We found that minocycline-treated rats had smaller stroke-induced infarcts and less microglia activation in the infarct area and remote white matter regions compared to saline-treated rats at 28 days post-stroke. The behavioural testing results differed according to the cognitive domain; whereas minocycline-treated rats trended towards improved striatal-based learning in a lever-pressing task, but cognitive flexibility was unaffected during the subsequent set-shifting task. Furthermore, minocycline treatment unexpectedly impaired spatial learning, yet it did not alter reference memory. Collectively, we show that post-stroke minocycline treatment can reduce chronic microglia activation even in remote brain regions, with domain-specific effects on cognitive function.

Connectional parameters determine multisensory processing in a spiking network model of multisensory convergence.

For the brain to synthesize information from different sensory modalities, connections from different sensory systems must converge onto individual neurons. However, despite being the definitive, first step in the multisensory process, little is known about multisensory convergence at the neuronal level. This lack of knowledge may be due to the difficulty for biological experiments to manipulate and test the connectional parameters that define convergence. Therefore, the present study used a computational network of spiking neurons to measure the influence of convergence from two separate projection areas on the responses of neurons in a convergent area. Systematic changes in the proportion of extrinsic projections, the proportion of intrinsic connections, or the amount of local inhibitory contacts affected the multisensory properties of neurons in the convergent area by influencing (1) the proportion of multisensory neurons generated, (2) the proportion of neurons that generate integrated multisensory responses, and (3) the magnitude of multisensory integration. These simulations provide insight into the connectional parameters of convergence that contribute to the generation of populations of multisensory neurons in different neural regions as well as indicate that the simple effect of multisensory convergence is sufficient to generate multisensory properties like those of biological multisensory neurons.

Somatosensory and multisensory properties of the medial bank of the ferret rostral suprasylvian sulcus.

In ferret cortex, the rostral portion of the suprasylvian sulcus separates primary somatosensory cortex (SI) from the anterior auditory fields. The boundary of the SI extends to this sulcus, but the adjoining medial sulcal bank has been described as "unresponsive." Given its location between the representations of two different sensory modalities, it seems possible that the medial bank of the rostral suprasylvian sulcus (MRSS) might be multisensory in nature and contains neurons responsive to stimuli not examined by previous studies. The aim of this investigation was to determine if the MRSS contained tactile, auditory and/or multisensory neurons and to evaluate if its anatomical connections were consistent with these properties. The MRSS was found to be primarily responsive to low-threshold cutaneous stimulation, with regions of the head, neck and upper trunk represented somatotopically that were primarily connected with the SI face representation. Unlike the adjoining SI, the MRSS exhibited a different cytoarchitecture, its cutaneous representation was largely bilateral, and it contained a mixture of somatosensory, auditory and multisensory neurons. Despite the presence of multisensory neurons, however, auditory inputs exerted only modest effects on tactile processing in MRSS neurons and showed no influence on the averaged population response. These results identify the MRSS as a distinct, higher order somatosensory region as well as demonstrate that an area containing multisensory neurons may not necessarily exhibit activity indicative of multisensory processing at the population level.

Double deletion of Panx1 and Panx3 affects skin and bone but not hearing.

Pannexins (Panxs), large-pore channel forming glycoproteins, are expressed in a wide variety of tissues including the skin, bone, and cochlea. To date, the use of single knock-out mouse models of both Panx1 and Panx3 have demonstrated their roles in skin development, bone formation, and auditory phenotypes. Due to sequence homology between Panx1 and Panx3, when one Panx is ablated from germline, the other may be upregulated in a compensatory mechanism to maintain tissue homeostasis and function. To evaluate the roles of Panx1 and Panx3 in the skin, bone, and cochlea, we created the first Panx1/Panx3 double knock-out mouse model (dKO). These mice had smaller litters and reduced body weight compared to wildtype controls. The dKO dorsal skin had decreased epidermal and dermal area as well as decreased hypodermal area in neonatal but not in older mice. In addition, mouse skull shape and size were altered, and long bone length was decreased in neonatal dKO mice. Finally, auditory tests revealed that dKO mice did not exhibit hearing loss and were even slightly protected against noise-induced hearing damage at mid-frequency regions. Taken together, our findings suggest that Panx1 and Panx3 are important at early stages of development in the skin and bone but may be redundant in the auditory system. KEY MESSAGES: Panx double KO mice had smaller litters and reduced body weight. dKO skin had decreased epidermal and dermal area in neonatal mice. Skull shape and size changed plus long bone length decreased in neonatal dKO mice. dKO had no hearing loss and were slightly protected against noise-induced damage.

Muscle size, strength, and bone geometry in the upper limbs of young and old men.

BACKGROUND: Bone loss in old men is associated with a decrease in muscle mass and strength. However, the influence of muscle size and strength on age-related changes in bone geometry has not been comprehensively described. Methods. Men in their third (group I, 23 +/- 3 y, n = 20), eighth (group II, 77 +/- 1 y, n = 10), and ninth (group III, 86 +/- 4 y, n = 13) decades of age were studied. The cross-sectional area (CSA) of the elbow flexors, elbow extensors, and forearm muscles, the total area (TA), cortical area (CA), and medullary area (MA) of the midhumerus, and distal third of the radius and ulna (n = 7 group II; n = 6 group III) were measured with magnetic resonance imaging. The maximal isometric strength (MVC) of the elbow flexors and elbow extensors was also determined. RESULTS: The CSA and MVC of the arm muscles (elbow flexors plus elbow extensors) were less in group II (-17% and -22%) and III (-32% and -39%), respectively, compared to group I. However, forearm CSA was less (-21%) in group III only. The TA and MA of all bones were greater in the older groups. The CA of the humerus (-14%) and ulna (-10%), but not the radius, was less in group III compared to group I, whereas CA was unchanged in group II. Stepwise multiple linear regression determined that arm muscle CSA (r = 0.52, p <.01) and forearm muscle CSA (r = 0.41, p <.05) provided the best prediction of CA in the humerus and forearm, respectively. CONCLUSIONS: Muscle size and strength are important determinants of CA in the humerus and forearm. The lower CA in the ninth decade may be explained, in part, by reduced bone strains due to a smaller muscle mass.

Multisensory dysfunction accompanies crossmodal plasticity following adult hearing impairment.

Until now, cortical crossmodal plasticity has largely been regarded as the effect of early and complete sensory loss. Recently, massive crossmodal cortical reorganization was demonstrated to result from profound hearing loss in adult ferrets (Allman et al., 2009a). Moderate adult hearing loss, on the other hand, induced not just crossmodal reorganization, but also merged new crossmodal inputs with residual auditory function to generate multisensory neurons. Because multisensory convergence can lead to dramatic levels of response integration when stimuli from more than one modality are present (and thereby potentially interfere with residual auditory processing), the present investigation sought to evaluate the multisensory properties of auditory cortical neurons in partially deafened adult ferrets. When compared with hearing controls, partially-deaf animals revealed elevated spontaneous levels and a dramatic increase (∼2 times) in the proportion of multisensory cortical neurons, but few of which showed multisensory integration. Moreover, a large proportion (68%) of neurons with somatosensory and/or visual inputs was vigorously active in core auditory cortex in the absence of auditory stimulation. Collectively, these results not only demonstrate multisensory dysfunction in core auditory cortical neurons from hearing impaired adults but also reveal a potential cortical substrate for maladaptive perceptual effects such as tinnitus.

Salicylate-induced peripheral auditory changes and tonotopic reorganization of auditory cortex.

The neuronal mechanism underlying the phantom auditory perception of tinnitus remains elusive at present. For over 25 years, temporary tinnitus following acute salicylate intoxication in rats has been used as a model to understand how a phantom sound can be generated. Behavioral studies have indicated that the pitch of salicylate-induced tinnitus in the rat is approximately 16 kHz. In order to better understand the origin of the tinnitus pitch measurements were made at the levels of auditory input and output; both cochlear and cortical physiological recordings were performed in ketamine/xylazine anesthetized rats. Both compound action potentials and distortion product otoacoustic emission measurements revealed a salicylate-induced band-pass-like cochlear deficit in which the reduction of cochlear input was least at 16 kHz and significantly greater at high and low frequencies. In a separate group of rats, frequency receptive fields of primary auditory cortex neurons were tracked using multichannel microelectrodes before and after systemic salicylate treatment. Tracking frequency receptive fields following salicylate revealed a population of neurons that shifted their frequency of maximum sensitivity (i.e. characteristic frequency) towards the tinnitus frequency region of the tonotopic axis (∼16 kHz). The data presented here supports the hypothesis that salicylate-induced tinnitus results from an expanded cortical representation of the tinnitus pitch determined by an altered profile of input from the cochlea. Moreover, the pliability of cortical frequency receptive fields during salicylate-induced tinnitus is likely due to salicylate's direct action on intracortical inhibitory networks. Such a disproportionate representation of middle frequencies in the auditory cortex following salicylate may result in a finer analysis of signals within this region which may pathologically enhance the functional importance of spurious neuronal activity concentrated at tinnitus frequencies.

Differential age-related changes in motor unit properties between elbow flexors and extensors.

AIM: Healthy adult ageing of the human neuromuscular system is comprised of changes that include atrophy, weakness and slowed movements with reduced spinal motor neurone output expressed by lower motor unit discharge rates (MUDRs). The latter observation has been obtained mostly from hand and lower limb muscles. The purpose was to determine the extent to which elbow flexor and extensor contractile properties, and MUDRs in six old (83 +/- 4 years) and six young (24 +/- 1 years) men were affected by age, and whether any adaptations were similar for both muscle groups. METHODS: Maximal isometric voluntary contraction (MVC), voluntary activation, twitch contractile properties, force-frequency relationship and MUDRs from sub-maximal to maximal intensities were assessed in the elbow flexors and extensors. RESULTS: Both flexor and extensor MVCs were significantly (P < 0.05) less (approximately 42% and approximately 46% respectively) in the old than in the young. Contractile speeds and the force-frequency relationship did not show any age-related differences (P > 0.05). For the elbow flexors contraction duration was approximately 139 ms and for the extensors it was approximately 127 ms for both age groups (P > 0.05). The mean MUDRs from 25% MVC to maximum were lower (approximately 10% to approximately 36%) in the old than in the young (P < 0.01). These age-related differences were larger for biceps (Cohen's d = 8.25) than triceps (Cohen's d = 4.79) brachii. CONCLUSION: Thus, at least for proximal upper limb muscles, mean maximal MUDR reductions with healthy adult ageing are muscle specific and not strongly related to contractile speed.

Incomplete recovery of voluntary isometric force after fatigue is not affected by old age.

The 60-min recovery profiles of voluntary and electrically stimulated force, contractile speed, surface electromyography, muscle activation via twitch interpolation, and muscle compound action potentials (M-waves) in the elbow flexors of seven young men (24 +/- 2 years) and seven men over 80 years of age (84 +/- 2 years) were compared following intermittent (3 s on, 2 s off) contractions at 60% of each subject's maximum voluntary contraction (MVC) force. There was no age-related difference between groups in the average time to fatigue or the rate of voluntary force loss; both groups lost 40% of their force within approximately 5 min. Despite a rapid increase to approximately 83% of the prefatigue MVC by the third minute of recovery for both groups, MVC force did not return to the prefatigue value within 60 min (94 +/- 4% young, 91 +/- 3% old). These results suggest that the incomplete recovery of voluntary force was likely due to a peripheral limitation in the muscle at the level of excitation--contraction coupling, and was not affected by age. Delayed recovery of voluntary force and a greater degree of low-frequency fatigue in the old men were not observed and there were no age-related impairments in any parameter normalized to the prefatigue value during fatigue or recovery. We suggest that the specific fatigue task may be more important to recovery than proposed alterations in the aged neuromuscular system when normalization and matching of the fatigue task criteria occurs.

Fluoroimmunoassay of progesterone in human serum or plasma.

We describe a fluoroimmunoassay for progesterone in serum or plasma. The assay involves use of an antiserum to progesterone-11-hemisuccinate and a labeled antigen prepared by linking fluoresceinamine to progesterone-3-carboxymethyloxime by use of a mixed-anhydride procedure. Serum or plasma samples are extracted with hexane. After incubation of a portion of the evaporated extract with antiserum and labeled antigen, antibody-bound and free antigen are separated and the fluorescence of the bound fraction is measured. Separation is effected either by using ammonium sulfate to precipitate liquid-phase antiserum or by using a solid-phase antiserum: antiserum covalently linked to magnetizable cellulose particles, which are separated with a magnet. With either separation technique, analytical recovery, linearity, and precision were acceptable and results compared satisfactorily with those obtained with a conventional radioimmunoassay. The solid-phase assay is more precise and more technically convenient, but the performance of both fluoroimmunoassays was adequate for clinical use in the detection of ovulation.