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  • 1
    Electronic Resource
    Electronic Resource
    Possible intermixing of neurons from the subthalamic nucleus and substantia nigra pars compacta in the guinea-pig (1995)
    Springer
    Experimental brain research 107 (1995), S. 151-165 
    Details
    ISSN: 1432-1106
    Keywords: Intracellular recording ; Subthalamic nucleus ; Substantia nigra pars compacta ; Cyanide ; Apomorphine ; Guinea-pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A population of cells in the anterior substantia nigra pars compacta (SNPc) of the guinea-pig have been reported previously that differ from classical dopaminergic neurons in terms of their active and passive membrane properties. To investigate this population further, anterior nigral neurons (n=17) were compared with neurons in the adjacent subthalamic nucleus (STN; n=26). The anterior nigral neurons were found to be indistinguishable from STN neurons in their action potential characteristics, firing rate, resting membrane potential and input resistance. A low-threshold calcium conductance and anomalous rectification could be demonstated in cells from both groups. Furthermore, the gross morphological characteristics of anterior nigral neurons and STN neurons were very similar, as assessed following the intracellular injection of biocytin. A further similarity was seen in the response of the two cell groups to cyanide (200 μM) and apomorphine (500 μM). Cyanide hyperpolarised the membrane potential of all STN neurons and the majority (77.8%) of anterior nigral neurons, in both cases producing a concomitant reduction in firing rate. These changes were accompanied by an increase in membrane conductance for potassium ions. Apomorphine depolarised the membrane potential of all STN neurons and anterior nigral neurons, in most cases increasing the input resistance (83.3% of STN neurons and 100% of anterior nigral neurons). In both groups of cells, when firing rate was affected, an increase was usually seen. Given the physiological, morphological and pharmacological similarities of STN and anterior nigral neurons, the most parsimonious interpretation is that the anterior nigral neurons belong to the STN. However, the anterior nigral neurons were found in slices that, when resectioned, contained tyrosine hydroxylase (TH)-immunoreactive cell bodies in every section, in a location corresponding to the SNPc. The implication is that in the guinea pig the SNPc and STN (usually considered to be anatomically distinct nuclei) intermix at this level for several hundred microns. This close association of the STN and the compacta was further demonstrated by the presence of TH-positive varicose and non-varicose neuronal processes within the STN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230038
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  • 2
    Electronic Resource
    Electronic Resource
    Do non-dopaminergic neurons in the ventral tegmental area play a role in the responses elicited in A10 dopaminergic neurons by electrical stimulation of the prefrontal cortex? (1998)
    Springer
    Experimental brain research 118 (1998), S. 466-476 
    Details
    ISSN: 1432-1106
    Keywords: Key words Extracellular recording ; Cortical efferents ; A10 cell group ; Non-dopaminergic neurons ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  It is rapidly becoming apparent that the prefrontal cortex (PFC) plays a major role in controlling the activity of midbrain dopaminergic (DA) neurons. We have previously demonstrated that electrical stimulation of the PFC elicits inhibition-excitation (IE) and excitation (E) activity patterns in DA neurons in the ventral tegmental area (VTA; A10 cell group). Since non-DA neurons in the VTA are cortically innervated, synapse upon DA neurons and appear to have an inhibitory impact, we determined the extent to which the responses of these neurons to stimulation of the PFC could account for the responses seen in DA neurons upon cortical stimulation. Stimulation of the PFC (0.25 mA and 1.0 mA) elicited three categories of response in the majority of VTA non-DA neurons. Types I and II were characterised by a short-to-moderate latency excitation (referred to as “early excitations”), in the latter case preceded by inhibition. Type III responses consisted of inhibition in the absence of an early excitation. Elements of these responses were compared with the temporal characteristics of key elements of responses elicited in DA neurons by PFC stimulation. Although the early excitations in non-DA neurons preceded the inhibitions in DA neurons exhibiting IE responses, the early excitations began approximately 100 ms before the inhibitions in DA neurons and often ended several tens of milliseconds before the inhibitions began, making a causal relationship between these events unlikely. The inhibitions in Type III responses, combined with the inhibitions which followed the early excitations in many Type I and II responses, showed temporal characteristics that suggested a possible causal relationship with the excitations in DA neurons exhibiting E responses, but not those exhibiting IE responses. However, since the excitatory phases of E and IE responses appear to be homologous, the lack of involvement of non-DA neurons in the excitatory phase of IE responses tends to cast doubt on the involvement of non-DA neurons in the excitation during E responses. In fact, the most coherent impression that emerges is that non-DA neurons in the VTA do not influence the activity of A10 DA neurons on a short time-scale (i.e. phasically), but instead may influence activity on a longer time-scale (i.e. tonically).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050303
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  • 3
    Electronic Resource
    Electronic Resource
    A pharmacological analysis of the burst events induced in midbrain dopaminergic neurons by electrical stimulation of the prefrontal cortex in the rat (1996)
    Springer
    Journal of neural transmission 103 (1996), S. 523-540 
    Details
    ISSN: 1435-1463
    Keywords: Substantia nigra pars compacta ; ventral tegmental area ; extracellular recording ; picrotoxin ; apomorphine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Electrical stimulation of the prefrontal cortex produces an inhibition-excitation (IE) activity pattern in the majority of responsive midbrain dopaminergic neurons. The excitatory phase often contains events, time-locked to the stimulation, which resemble natural bursts. The present study investigated the relationship between the inhibition and time-locked bursts by reducing the impact of the inhibition through membrane hyperpolarisation with the dopamine agonist apomorphine (i.v.) or antagonism with the GABAA antagonist picrotoxin (i.v. and iontophoretic). Apomorphine abolished or reduced time-locked bursting in all IE cells. Picrotoxin reduced the initial inhibition in the majority of IE cells, and abolished or reduced time-locked bursting at the highest intravenous dose. However, reductions in the initial inhibition were not systematically related to reductions in time-locked bursting. Hence, the phenomena do not appear to be causally related. Instead, time-locked bursts appear to be based on a straightforward excitation, which makes them closely analogous to natural bursts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01273151
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  • 4
    Electronic Resource
    Electronic Resource
    Antagonism of NMDA receptors but not AMPA/kainate receptors blocks bursting in dopaminergic neurons induced by electrical stimulation of the prefrontal cortex (1996)
    Springer
    Journal of neural transmission 103 (1996), S. 889-904 
    Details
    ISSN: 1435-1463
    Keywords: Ventral tegmental area ; substantia nigra pars compacta ; extracellular recording ; excitatory amino acids ; rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Evidence suggests that the prefrontal cortex (PFC) plays an important role in the burst activity of midbrain dopaminergic (DA) neurons. In particular, electrical stimulation of the PFC elicits patterns of activity in DA neurons, closely time-locked to the stimulation, which resemble natural bursts. Given that natural bursts are produced by the activity of excitatory amino acid (EAA)-ergic afferents, if PFC-induced time-locked bursts are homologues of natural bursts, EAA antagonists should attenuate them. Hence, the NMDA (N-methy1-D-aspartate) antagonist CPP (3-((±)-2-carboxypiperazin-4-yl)propyl-1-phosphonic acid) and the AMPA (D,L-α-amino-3-hydroxy-5-methyl-4-isoxalone propionic acid)/kainate antagonist CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) were applied by iontophoresis to DA neurons exhibiting time-locked bursts during PFC stimulation. CPP produced a significant reduction in time-locked bursting. In contrast, CNQX (at currents which antagonised AMPA responses) did not. These effects of CPP and CNQX on time-locked bursting mirror the effects previously reported for these drugs on natural bursting. Since natural bursting and bursting induced by PFC stimulation are both blocked selectively by CPP, the present results increase the degree of analogy between the two burst phenomena, thereby adding extra support to the contention that the cortex is involved in producing the natural bursting in DA neurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01291780
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  • 5
    Electronic Resource
    Electronic Resource
    D-Amphetamine potentiates muscimol-induced disinhibition of A10 dopaminergic neurons in the rat (2000)
    Springer
    Journal of neural transmission 107 (2000), S. 1381-1391 
    Details
    ISSN: 1435-1463
    Keywords: Keywords: Ventral tegmental area ; excitatory amino acids ; medial prefrontal cortex ; non-DA neurons ; synaptic plasticity ; behavioural sensitisation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary. Evidence suggests that sensitisation to the behavioural effects of d-amphetamine involves a late-onset (〉3 hrs), long-term potentiation (LTP)-like change at medial prefrontal cortex (mPFC)-regulated synapses on A10 dopaminergic (DA) neurons. Since muscimol-induced excitation of A10 DA neurons is dependent on mPFC-regulated afferents, this assay was used to assess whether d-amphetamine enhances the driving of A10 DA neurons by the mPFC, as would be predicted if it resulted in the conditions necessary for LTP. Animals were administered d-amphetamine or saline, 3–4.5 hrs prior to recording. In the acute condition, animals were drug-naïve prior to d-amphetamine, whilst in the challenge condition, animals had previously received d-amphetamine (or saline) each day for 6 days. Recording took place on withdrawal day 2. Muscimol produced significantly less inhibition of A10 DA neurons from animals administered d-amphetamine (rather than saline), but only when d-amphetamine had been chronically administered beforehand (i.e. in the challenge condition). Hence, although the studies fail to provide evidence that acute d-amphetamine administration produces the conditions necessary for LTP, chronic d-amphetamine administration appears to potentiate the impact on A10 DA neurons of mPFC-regulated excitatory activity, thus strengthening the link between this potentiation and the sensitisation process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007020070002
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  • 6
    Electronic Resource
    Electronic Resource
    Determinants of neuronal firing pattern in the guinea-pig subthalamic nucleus: Anin vivo andin vitro comparison (1995)
    Springer
    Journal of neural transmission 10 (1995), S. 41-54 
    Details
    ISSN: 1435-1463
    Keywords: Extracellular recording ; intracellular recording ; electrical stimulation ; striatopallidal complex ; burst firing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To ascertain the extent to which neuronal firing pattern in the subthalamic nucleus (STN) is determined by afferent inputs, a comparison was made between STN neurons recordedin vivo andin vitro (a largely denervated preparation).In vivo, the majority of cells exhibited an irregular firing pattern, although some showed evidence of burst firing. In contrast, all cells had a regular firing patternin vitro. Electrical stimulation of the striatopallidal complexin vivo induced a short latency inhibition in STN neurons, followed by a burst of spikes. These effects could be reproducedin vitro; hyperpolarising pulses gave rist to a slow depolarising potential upon termination, which was accompanied by a burst of action potentials. Hence, the evidence suggests that afferents play an important role in determining the firing pattern of STN neurons. Howerver, the cells also possess intrinsic membrane properties which allow inputs to trigger either single spikes or bursts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02256628
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