Book of abstracts - British Neuroscience Association

52.04
Stress and adult neurogenesis
Glasper E
Department of Psychology, Program in Neuroscience, Princeton
University, Princeton NJ 08544
The hippocampus of adult mammals continues to add new granule
neurons throughout life. Adult neurogenesis in the hippocampus is
modulated by hormones and experience. Several studies indicate that
stress, during development or in adulthood, decreases cell
proliferation and immature neuron in the dentate gyrus of adult rodents
and primates. Some evidence links these effects to stress-induced
elevations in glucocorticoids. However, other studies suggest that the
motivational valence of the stressor is important for mediating stress
effects on neurogenesis – positive stressors like running and sexual
experience do not inhibit adult neurogenesis and indeed, can increase
the number of new neurons. The mechanisms which serve to buffer
the brain from high levels of glucocorticoids under conditions of
“positive stress” remain unexplored.
53.01
Subcortical loops through the basal ganglia.
Redgrave P
The architecture of cortico-basal ganglia-cortical connections is
characterised by parallel, largely segregated, closed-loop projections.
Evidence will be considered suggesting that such loops involving the
neocortex are neither novel nor the first evolutionary example of closedloop
architecture involving the basal ganglia. The specific proposal will be
that a phylogenetically older, closed-loop series of subcortical connections
exist between the basal ganglia and brainstem sensorimotor structures, a
good example of which is the midbrain superior colliculus. Insofar as this
organisation represents a general feature of brain architecture, cortical and
subcortical inputs to the basal ganglia may act independently, cooperatively,
or competitively to influence the mechanisms of action
selection.
53.02
Behavioural roles of the pedunculopontine tegmental nucleus
Winn P
School of Psychology, St Andrews University, St Andrews, Fife KY16
9JP
The pedunculopontine tegmental nucleus (PPTg), in the mesopontine
tegmentum, has a structure and pattern of connectivity consistent
across vertebrate species. It has intimate connections with the basal
ganglia, both ascending and descending. It is a target of outflow from
pallidum, subthalamic nucleus (STn) and substantia nigra reticulata,
while PPTg neurons innervate pallidum, STn and provide excitatory
input to dopamine containing neurons in substantia nigra compacta
and the ventral tegmental area. Growing recognition that the PPTg
can be considered as part of the basal ganglia family has been
accompanied by re-assessment of its behavioural functions. An older
literature emphasizes roles for the PPTg in locomotion and
behavioural state control, but recent research has played down the
importance of the PPTg in regard to these and instead emphasized
roles in other processes. We have conducted research over the last
several years using excitotoxins to lesion the whole PPTg. In rats,
bilateral lesions of the entire PPTg produce no deficits in locomotion,
sleep regulation (in non-deprived conditions), or "emotional"
behaviour. There are however, profound disturbances in tests of
learning, memory and attention, higher-order functions associated with
corticostriatal systems. These studies show that the PPTg has more
complex functions than previously suspected. Having established this,
the key tasks now are (i) to better characterize the behavioural deficits
– are they all related to a core dysfunction, perhaps in association
learning (ii) To define better the internal structure of the PPTg such
that specific functions of component parts (identified neurochemically
and hodologically) can be identified.
53.03
Physiological analyses of cholinergic and non-cholinergic neurons in
the PPN that innervate the basal ganglia
Mena-Segovia J, Sims H M, Magill P J, Bolam J P.
MRC Anatomical Neuropharmacology Unit, Mansfield Road, , Oxford OX1
3TH, United Kingdom,
Previous studies have shown that neurons of the pedunculopontine nucleus
(PPN) are highly interconnected with the basal ganglia. The PPN, once
considered a predominantly cholinergic structure, is now recognised as a
neurochemically heterogeneous nucleus, with populations of GABAergic
and glutamatergic neurons. Electrophysiological studies show a high
degree of heterogeneity among PPN neurons. To define the characteristics
of the neurons that innervate the basal ganglia, we recorded the activity of
single cells in vivo and then labelled them by the juxtacellular method to
define their location within the PPN and define their morphological and
neurochemical properties. Identified cholinergic neurons fired in association
with the cortical gamma oscillations during both slow wave activity, and the
activated state. Their axons projected to the basal ganglia (substantia nigra
pars compacta and reticulata, and subthalamic nucleus), and they also had
ascending and descending collaterals (towards the thalamus and colliculi,
and lower brainstem, respectively). In contrast, identified non-cholinergic
neurons showed more heterogeneous electrophysiological characteristics:
their firing was correlated with cortical activity or independent of it, in which
case the pattern of firing was tonic, bursty or nearly silent. Non-cholinergic
neurons also have differences in their branching pattern: they have a single
collateral projecting towards the basal ganglia, a single ascending collateral
projecting towards the inferior and superior colliculi, or two collaterals
projecting to basal ganglia and thalamus. The PPN thus contains
neurochemically distinct populations of neurons that have distinct
electrophysiological properties and distinct connections with the basal
ganglia.
Supported by the Parkinson’s Disease Society and MRC.
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