1. We have investigated the electrical properties of neurons acutely dissociated from the substantia nigra zona compacta (SNZC) of the postnatal rat with whole cell patch-clamp recordings. Retrogradely labeled nigrostriatal neurons were identified with the use of rhodamine-labeled fluorescent latex microspheres. Over 90% of the rhodamine-labeled neurons in the SNZC demonstrated formaldehyde/glutaraldehyde-induced catecholamine fluorescence, indicating that they were dopaminergic (DA) neurons. 2. DA neurons had 15-20 microns ovoid or fusiform-shaped cell bodies with 2-3 thick proximal processes. Labeled neurons generated spontaneous action-potential activity in both regular and irregular patterns. These cells exhibited input resistances of 300-600 M omega and action-potential amplitudes of 60-80 mV. Locally applied dopamine inhibited the spontaneous activity of these neurons by hyperpolarizing the cells. 3. Outward currents were examined with voltage-clamp recordings using a tetrodotoxin (TTX)-containing medium. In all DA cells, depolarizing voltage commands activated several components of outward current depending on the holding potential of the cell. When cells were held at -40 mV (or more positive), voltage steps activated a sustained outward current. If the membrane potential was held more negative than -50 mV, a rapidly activating and inactivating component of outward current response could also be detected. 4. From a hyperpolarized holding potential (-90 mV) the transient outward current activated with depolarizing commands to -55 mV, peaking within 5 ms. The current inactivated with a monoexponential time constant of 53 +/- 4 (SE) ms. At more positive holding potentials (-40 mV) the steady-state inactivation of the current could be removed by applying a conditioning hyperpolarizing prepulse. In response to a fixed depolarizing voltage step, half-maximal inactivation occurred at about -65 mV. The transient current was blocked by 4-aminopyridine (4-AP). 5. The sustained outward currents were isolated by holding the cells at -40 mV. Two components of sustained outward current were distinguished by their sensitivity to the calcium channel blockers Co2+ (5 mM) and/or Cd2+ (200 microM). The current remaining in the presence of Co2+/Cd2+ was activated by depolarizing voltage commands more positive than -40 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

The preoptic area contains thermosensitive, osmosensitive, and glucosensitive neurons, which have been implicated in thermal, osmotic, and metabolite regulations, respectively. In this study, rat preoptic tissue slices are used to examine the specificity of these neurons by determining their individual firing rate responses to thermal, osmotic, and glucose stimuli. Of the neurons classified according to thermosensitivity, 35% were warm sensitive, 10% were cold sensitive, and 55% were temperature insensitive. Of these, 107 neurons were also tested for their responses to tissue slice perfusions of low-glucose and/or hyperosmotic media. These experimental perfusions affected one-third of the temperature-insensitive neurons and nearly half of the thermosensitive neurons and generally excited warm-sensitive neurons and inhibited cold-sensitive neurons. A lack of specificity was also observed between the groups of osmosensitive and glucosensitive neurons, since most of the responsive neurons were affected by both hyperosmotic and low-glucose media. Although these findings do not suggest a strong functional specificity for preoptic neurons, they do support previous studies that emphasize interactions between regulatory systems.