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Biomedical subjects

C M Richardson

Publications and source records attributed to C M Richardson.

31 records · Page 2Linked to original sources
PubMed1996

Photoperiod effect on bud burst in Prunus is phase dependent: significance for early photosynthetic development.

A 16-h photoperiod stimulated bud burst in mature rooted cuttings of Prunus avium cv. Stella, but not in selfed Stella seedlings. However, in a 12-h photoperiod, bud burst occurred earlier in the seedlings than in the mature cuttings. In the 12-h photoperiod, production of polypeptides involved in carbon dioxide fixation and photosynthetic electron transport was higher in seedlings than in mature cuttings, whereas in the 16-h photoperiod, shoot development and polypeptide production were similar in seedlings and mature cuttings. In both photoperiods, the amount of large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase that was associated with thylakoid membranes in young leaves was higher in seedlings than in mature cuttings. Transcript levels of rbcL mRNA were influenced by photoperiod in mature cuttings but not in seedlings. In seedlings, early bud burst and development of the light harvesting apparatus would be an advantage at the start of the growing season, before the mature tree canopy reduces irradiances near the woodland floor.

Journal Article↗
PubMed1995

Novel pharmacological sensitivity of the presynaptic calcium channels controlling acetylcholine release in skate electric organ.

The presynaptic terminals of skate (Raja montagui) electric organ were tested for their sensitivity to calcium channel antagonists. Acetylcholine (ACh) release and the elevation of intraterminal Ca2+ concentrations triggered by K+ depolarisation were studied. ACh release was measured as 3H efflux from slices of organ prelabelled with [3H]choline. Depolarisation caused a marked, Ca(2+)-dependent increase in 3H efflux that was completely blocked by 100 microM Cd2+ and by 300 nM omega-conotoxin-MVIIC (MVIIC). Inhibition by MVIIC was concentration dependent (IC50 of approximately 20 nM) and reversible. No inhibition was seen with nifedipine (5 microM) or the two other peptide antagonists studied: omega-conotoxin-GVIA (GVIA) at 5 microM and omega-agatoxin-IVA (Aga-IVA) at 1 microM. In a "nerve plate" preparation (a presynaptic plexus of nerve fibres, Schwann cells, and nerve terminals) changes in intraterminal Ca2+ concentrations were measured by microfluorimetry using fluo-3. An increase in fluorescence, indicating a rise in the free [Ca2+], rapidly followed K+ depolarisation, and this change was restricted to the nerve terminals. This response was insensitive to nifedipine (5 microM), GVIA (5 microM), and Aga-IVA (300 nM) but almost completely abolished by MVIIC (1 microM). MVIIC inhibition was concentration dependent and partially reversible. These results show that the nerve terminals in skate electric organ have calcium channels with a pharmacological sensitivity that is markedly different from the established L, N, and P types in other systems but shares some, but not all, of the features of the recently described Q type.

Acetylcholine↗
PubMed1989

Unilateral periarcuate and posterior parietal lesions impair conditional position discrimination learning in the monkey.

Monkeys were trained on a conditional position discrimination in which the conditional cue was a light blinking at two distinct rates and the discriminanda (illuminated buttons) appeared in varying symmetrical positions of eccentricity. Unilateral arcuate, posterior parietal, or principal sulcus lesions were performed at criterion. The monkeys were tested to recovery when a homologous lesion was made contralaterally. The first of two analyses examined a period of 4 weeks following each lesion; the unit of analysis was lesions. The arcuate and parietal lesions produced impairments on both widely eccentric and central discriminanda locations; initially, virtually all responses were deflected to the ipsilateral side. There was significant improvement after the arcuate and parietal lesions from weeks 1 to 4. An analysis of total trials to criterion showed major deficits from the second arcuate and parietal lesions, with the arcuate lesion impairment being particularly severe. These results establish that a spatial concept of left vs right is seriously deranged by unilateral lesions of cortical association areas involved in spatial orientation and discrimination.

Animals↗
PubMed1987

Lateralization of emotionality in right parietal cortex of the rat.

Lesions of right parietal cortex in the rat increase activity in the open field compared with left parietal lesions, especially after section of the corpus callosum. Left or right motor or medial frontal cortex lesions do not have a lateralized effect. This evidence of a localized asymmetry between the cerebral hemispheres strongly implies that right parietal cortex has a role in emotionality in this species. Our findings suggest a functional similarity to right parietal cortex in man.

Animals↗
PubMed1987

Effects of age on nocturnal activity rhythms in rats.

Running wheel data were analyzed to examine changes in nocturnal activity rhythms with age in Long Evans rats. Five male animals 30 days of age, the same five rats at 70 days of age, and five older animals at 13 months were given free access to activity wheels in a colony room maintained on an LD12:12 cycle. All subjects demonstrated enhancement of activity during the dark phase of the 24-h cycle. A statistically significant decrease in activity of old rats in comparison with weanling rats was observed only in the dark phase (P less than .0001). The age difference was marginal in the light phase compared to that in the dark phase. However, a marked increase in percentage of time spent active in the light phase was observed in the old animals. This may be a combined result of visual hyposensitivity and insomnia that became apparent with increasing age. Mechanisms that control initiation and maintenance of locomotor behavior may become less responsive with age to periodic alternative of light and dark phases.

Aging↗
PubMed1986

Pineal lesion produces bilateral visual and auditory inattention in the rat.

Unilateral lesions in such brain regions as medial frontal cortex and superior colliculus produce polysensory neglect contralateral to the lesion. Since the pineal gland is an unpaired brain structure, both electrophysiologically and hormonally responsive to visual and auditory stimulation, it may modulate bilateral sensory attention mechanisms. Long-Evans male rats were given pineal or sham lesions and were tested behaviourally. Sensory assessment revealed that in comparison to sham animals rats with pineal lesion exhibited unilateral visual and auditory neglect to stimuli presented on either side of the body. Animals with pineal lesions were more likely than sham-lesioned animals to demonstrate visual allesthesis and, compared to sham-lesioned rats, showed extinction on the left side to bilateral simultaneous visual stimulation. This is the first report that midline neuroendocrine damage can produce bilateral sensory inattention.

Animals↗
PubMed1986

Parietal and frontal eye field neglect in the rat.

Rats were given unilateral aspiration lesions of parietal, medial frontal, or dorsolateral frontal (motor) cortex and then tested for visual, auditory and tactile neglect, and for circling. All medial frontal lesion animals showed contralateral neglect in each modality and circled ipsiversively. The parietal lesion rats initially displayed contralateral visual and auditory neglect as severe as that in the medial frontal group. Three weeks after the lesions, the parietal group had a smaller residual deficit on the visual test than the medial frontal group. In the first week, parietal animals responded less than the medial frontals to stroking the vibrissae but were more responsive to mild pinching of a toe contralateral to the lesion side. In striking contrast to the medial frontal animals, the parietal group circled strongly to the contralateral side. No rat with a motor cortex lesion neglected or circled preferentially. Like medial frontal cortex, unilateral parietal lesions also produce neglect and circling, but there are important features distinguishing unilateral lesion effects in these two regions.

Acoustic Stimulation↗
PubMed1985

A method to section the corpus callosum in the rat.

A simply constructed instrument and a surgical procedure are described for transecting the corpus callosum in the rat. The callosum can be cut in its entirety, or the cut can be limited to anterior or posterior halves. The procedure obviates lateralized incidental damage.

Animals↗
PubMed1984

Evidence for biological activity of two N-terminal fragments of neurotensin, neurotensin1-8 and neurotensin1-10.

Intracisternal (i.c.) administration of the endogenous tridecapeptide neurotensin (NT) has been previously shown to significantly reduce the incidence of cold-restraint stress (CRS)-induced gastric ulcers in rats. In this study we confirm the cytoprotective activity of central NT, and document structure-activity relationships for this effect of NT. When tested in a dose equimolar to 17.9 nmol of NT the NT analogs [Gln4]NT, D-Trp11-NT, and D-Arg8-NT were cytoprotective, whereas D-Arg9-NT was not. Gonadotropin-releasing hormone (Gn-RH) and melanocyte-stimulating hormone-release inhibiting factor (MIF-1), two oligopeptides structurally unrelated to NT exhibited no cytoprotective efficacy in this paradigm. The C-terminal fragments of NT, xenopsin and NT8-13, and the N-terminal fragment NT1-6 were completely ineffective. Finally, NT1-8 and NT1-10, two N-terminal fragments of NT produced significant cytoprotective activity at this dose level. The cytoprotection afforded by NT1-8 and NT1-10, like that of NT, was dose-dependent with ED50's similar to that of NT (NT = 16.2 nmol, NT1-8 = 17.8 nmol and NT1-10 = 19.9 nmol). In conclusion, we demonstrate that smaller molecular weight forms of NT thought to be degradation products of NT can effectively exert biological effects.

Animals↗
PubMed1983

Brief deprivation of vision after unilateral lesions of the frontal eye field prevents contralateral inattention.

Brief deprivation of vision after unilateral lesions of the frontal eye field prevents the appearance of contralateral inattention to visual, auditory, and somatosensory stimuli. The forced circling that accompanies inattention, however, is not affected. An equivalent preoperative period in the dark only partly reduces inattention symptoms. Visual deprivation does not reduce or prevent inattention resulting from lesions of the superior colliculus.

Animals↗