Browsing by Author "Douglas, Rodney J"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Open Access
    The crossed mesostriatal pathway and circling behaviour in rats
    (1987) Van Wageningen, Gerhard Derek; Douglas, Rodney J
    Rats with unilateral 6-OHDA lesions of the nigrostriatal (NS) projection display motor asymmetry in the form of rotational behaviour. The rotation is in the direction ipsilateral with respect to the lesioned side (Ungerstedt 1979). The nett ipsilateral rotations decrease with time, from 1 week to about a month. This decrease has been interpreted as recovery from the lesion-induced motor asymmetry (Glick and Cox 1978). Pritzel et al. (1983) have ascribed the recovery from motor asymmetry to increased activity of a crossed NS projection, which is spared by the ipsilateral lesion. The present study has defined the size and anatomical path of this crossed projection, and has examined its involvement in the behavioural recovery of rats from lesion-induced motor asymmetry. The anatomy of the crossed projection was investigated in male Long-Evans rats using retrograde HRP tract tracing from deposition sites in the striatum.
  • Thumbnail Image
    Item
    Open Access
    Development and implementation of hardware and software for a minicomputer based programmable interval timer for use in point process analysis of neuronal action potentials
    (1980) Willenberg, Keith David; Douglas, Rodney J
    A precision programmable interval timer (PIT) for use in point process analysis of the neutronal action potentials derived from multiple extracellular electrode arrays is described. The PIT is based on a commercially available LSI package, INS8253 and is interfaced to a Data General (DG) microNova 16-bit microcomputer via a DG General Purpose Interface (GPI) board. The programmable clock periods range from 1 μsec to 10 msec in decade multiples, offering a total timing duration of 65 msec to 650 sec. The PIT operates in two Modes : 1. Count-down timer 2. Elapsed time timer (Event resettable timer) Clock-overrun and data lost flags are provided. Testing and applications software have also been developed.
  • Thumbnail Image
    Item
    Open Access
    Pontomedullary reticular formation neurones : a study of microanatomy, transmitter sensitivity and connections from the substantia nigra pars reticulata
    (1990) Kellaway, Lauriston Arthur; Douglas, Rodney J
    This investigation examines certain aspects of the medial pontomedullary reticular formation (PMRF) microanatom y and neurotransmission and also the connections between the substantia nigra pars reticulata (SNr) and the PMRF in the rat. The anatomical distribution of the population of PMRF neurones was determined by combining physiological identification with electrical stimulation and retrograde HRP tract-tracing. A dual stimulating/deposition electrode was used to combine antidromic stimulation of PMRF cells with optimal retrograde labelling. 139 PMRF neurones were identified by means of their stereotaxic location and physiological criteria, namely; spontaneous discharge, polymodal sensory responses and large receptive fields.
  • Thumbnail Image
    Item
    Open Access
    Processing of transient stimuli by the visual system of the rat
    (1993) Kara, Prakash; Douglas, Rodney J
    While three decades of intensive cortical electrophysiology using a variety of sustained visual stimuli has made a significant contribution to many aspects of visual function, it has not supported the existence of intracortical circuit operations in cortical processing. This study investigated cortical processing by a comparison of the response of primary visual cortical neurones to transient electrical and strobe-flash stimulation. Experiments were performed on 74 anaesthetised Long Evans rats. Standard stereotaxic and extracellular electrophysiological techniques were employed. Continuous (on-line) raster plots and peri-stimulus time histograms (PSTHs) of the extracellular spikes from 81 visual cortical and 55 lateral geniculate nucleus (LGN) neurones were compiled. The strobe-flash stimuli (0.05 ms) were applied to the contralateral eye while the monopolar or bipolar electrical stimuli (0.2 ms, 80-400 μA) were applied to the ipsilateral LGN. 60 of the 81 (74%) tested cortical units were found to be responsive to visual stimuli. A distinct and consistent difference in the cortical response to the two types of transient stimuli was found: (a) Electrical stimulation evoked a prolonged period (197 ± 61 ms) of inhibition in all cortical neurones tested (n=20). This was the case even in those cortical units that were completely unresponsive to visual stimulation. The protracted inhibition was usually followed by a 100-200 ms phase of rebound excitation. (b) Flash stimulation evoked a prominent excitatory discharge (5-30 ms duration) after a latency of 30-60 ms from the onset of the stimulus (n = 59). This was followed by either moderate inhibition or return to a firing rate similar to control activity, for a maximum of 40 ms. Thereafter, cortical neurones showed a sustained increased level of activity with superimposed secondary excitatory phases. The duration of this late re-excitatory phase was 200-300 ms. In 17 of 20 (85%) tested units, the temporal profile of the cortical response to flash stimulation was modulated by small changes in the level of background illumination. In 16 of the 17 units, this sensitivity was reflected primarily as an emergence of a brief secondary inhibitory phase at the lowest level of background illumination (0 lux). Only 1 of the 17 cortical units displayed a flash-evoked primary inhibitory phase at O lux. We explored the possibility that neurones in the lateral geniculate nucleus (LGN) of the thalamus were responsible for the late phase of cortical reexcitation. 49 of the 55 (89%) LGN neurones could be classified as either of the "ON type" i.e. excited by visual stimuli, or the "OFF type" i.e. inhibited by visual stimuli. The response of ON-like LGN neurones to strobe-flash stimulation of the contralateral eye was characterised by a primary excitatory or early discharge (ED) phase after a latency of 25-40 ms. Thereafter, a 200- 400 ms period of inhibition was observed. In 57% of the sample, a rebound excitatory or late discharge (LD) phase completed the response. OFF-like LGN neurones were inhibited by the strobe-flash stimuli after a latency of 30- 35 ms. This flash-evoked inhibition was maintained for 200-400 ms. The sensitivity of the flash-evoked LGN response to the level of background illumination was tested in 11 ON-like and 10 OFF-like neurones. No sustained secondary excitatory events, as observed in visual cortical neurones, were found in any of the ON- and OFF-like LGN neurones, irrespective of the level of background illumination. In conclusion, the data show that the late re-excitatory phase evoked in cortical neurones upon strobe-flash stimulation, is not due to sustained LGN (thalamic) input. Rather, it suggests that these re-excitatory phases are due to intracortical processing of the transient stimuli. These findings emphasize the independent role of the cortex in computing the response to visual stimuli, and cast doubt on traditional theories that have emphasised the role of the thalamus in shaping cortical responses. The difference in the flash and electrically evoked cortical response suggests that even though substantial inhibition is available to the cortex, only a small fraction of this inhibitory capacity is utilised during natural stimulation.
  • Thumbnail Image
    Item
    Open Access
    Somatosensory processing by rat medial pontomedullary reticular formation neurones : responses to innocuous and noxious thermal and mechanical stimuli
    (1991) Farham, Craig Jeffrey; Douglas, Rodney J
    This work examines somatosensory processing in "giant" neurones of the medial pontomedullary reticular formation (PMRF) in the rat, with particular emphasis on the response to cutaneous thermal stimuli. Thermal test stimuli were employed as these were deemed to be more precisely quantifiable than other forms of cutaneous stimulation. Activity was recorded from 235 PMRF neurones in 94 female Long Evans rats (270 to 320 g) anaesthetised with urethane (1,25g/kg, i.p.). Rectal temperature was closely controlled at 38 ± 0,5°C. Standard stereotactic and extracellular recording techniques were employed. PMRF giant neurones were identified by their stereotactic location, large, stable spike amplitudes of long duration, responses to cutaneous mechanical stimuli and receptive field properties, and spontaneous discharge characteristics. Ramp, step and sine wave cutaneous thermal stimuli (35-48 °C) were applied to the glabrous skin on the hindpaw by means of a computer-controlled Peltier device. The location of the units was confirmed by subsequent histology. One hundred and eleven neurones were located in nucleus reticularis pontis caudalis (NPC), and 124 in nucleus reticularis gigantocellularis (NGC). Mechanical stimulation excited 188 of 235 (80%) PMRF neurones (ON-m cells), and inhibited 40 (17%, OFF-m cells). Seven cells (3%) had mosaic receptive fields of excitation and inhibition (complex responses, CX-m). Twenty-eight percent of neurones were responsive to both weak and intense stimuli (mixed neurones). The remainder (72%) responded only to intense mechanical stimulation of the skin (high threshold neurones). The (excitatory or inhibitory) response of the mixed neurones to intense stimuli was generally greater than to mild stimuli, Receptive fields ranged in size from restricted (hindlimbs only) to very extensive (covering the entire body surface). Neurones with small receptive fields were almost exclusively of the high threshold type, and tended to be located in NGC, while mixed neurones tended to have larger receptive fields, and were located predominantly in NPC. Some portion of the hind limbs were represented in the receptive fields of all but one of the neurones studied, while the tail and/ or trunk were represented in 77%, and the forelimbs and face in 28% of receptive fields. Most of the cells responding to cutaneous mechanical stimulation had bilateral (usually symmetric) receptive fields. Spontaneous (background) activity occurred in the absence of any deliberate sensory stimulation in 72% of PMRF neurones. The frequency of spontaneous discharge rates ranged from O to 47 spikes/ s. The coefficient of variation of the spontaneous discharge rate of a given neurone was generally less than 20% (range O to 85%). Of the 235 identified mechanosensitive PMRF neurones, 203 (86%) also responded to cutaneous thermal stimulation (43-48 °C) of the ipsilateral hind paw. Eighty percent of these responded with increased discharge rates (ON-t cells), and 20% were inhibited (OFF-t cells). The polarities of response of individual PMRF neurones to mechanical and thermal stimuli, and to repeated ipsilateral and contralateral thermal stimuli, did not differ significantly. Following transient thermal stimulation, spontaneous discharge rates largely returned to pre-stimulus levels. The thresholds of response to slow ramp (0,15°C/s) and stepped (2°C/s) thermal stimuli occurred both in the innocuous and noxious temperature ranges (below and above 42°C, respectively). The threshold temperatures showed large variability to repeated identical thermal stimuli. Despite the poor reproducibility of the threshold responses, the distribution of thresholds to thermal ramp stimuli was consistently bimodal, with peaks occurring at 39 and 43°C. The bimodality persisted even when the ipsilateral and contralateral data were pooled. The modes of these threshold distributions conform to the maximum discharge ranges for warm and noxious cutaneous receptors. Thus, it is likely that thermal input to individual PMRF neurones is derived from both types of receptors. The responses of PMRF neurones to repeated thermal stimuli were stable and reproducible with respect to magnitude and time course. The average (static) and maximum (dynamic) responses to thermal stimuli were generally small: for example, the mean of the average responses to ramp stimuli was 5,9 spikes/s ± 11,0 SD, (range -28 to 40 spikes/s), and the mean of the maximum responses was 9,3 spikes/s ± 16,1 SD, (range -46 to 65 spikes/s). The absolute change in firing rate of individual PMRF neurones, and of the population, increased monotonically as a function of the intensity of stepped cutaneous thermal stimuli in the range 40 to 48 °C. However, their resolution, based on their average and maximum responses, was poor. Incorporating the post-stimulus responses into the comparisons between different stimulus intensities marginally increased the resolution of these neurones. Thus, while the majority of PMRF neurones are able to distinguish innocuous from noxious stimuli, few are capable of encoding stimulus intensity within the noxious range (above 43 °C). The majority (70%) of PMRF neurones responded to sustained thermal stimuli with a slow increase or decrease to a new static discharge rate which was maintained with little or no adaptation. Latency to onset of response to stepped thermal stimuli varied from 1 to 50 seconds, and the time to maximal response between 5-60 seconds. Many PMRF neurones also showed marked after-discharge for periods of up to 5 minutes after removal of the stimulus. The thermal receptive fields of over 90% of PMRF neurones were large, incorporating at least both hindlimbs. The extensive receptive field sizes of individual PMRF neurones provides evidence against them having a role in stimulus location. The large number of PMRF neurones showing multimodal convergence, their small magnitude responses, their slow response times, and their large receptive fields strongly suggest that these neurones are not participating in classical sensory discrimination. Rather, they may function as stimulus detectors or alternatively play a role in associative processes.