The rat ventral tegmentum (containing somata and dendrites of mesolimbic dopaminergic neurones) contained 1.3 mumol/g wet weight of glycine. Slices of ventral tegmentum accumulated exogenous [3H]glycine by an energy-, temperature- and sodium-dependent mechanism. The uptake was medicated by two different transport systems; one system with relatively low affinity for glycine (Km approximately 400 microM) and the other a higher affinity for glycine (Km approximately 10 microM). Small amino acid analogues of glycine inhibited the uptake process, the most potent being taurine and beta-alanine (47% and 44% inhibition, respectively, at 1 mM). Release of exogenous [3H]glycine by elevated potassium and by protoveratrine A was calcium-dependent and tetrodotoxin-sensitive. Glycine (500 microM--2mM) potentiated the protoveratrine A-induced release of exogenous [3H]dopamine from slices of ventral tegmentum; this potentiation was blocked by atrychnine (10 microM). A convulsant dose of strychnine elevated the concentration of 3,4-dihydroxyphenylacetic acid in the ventral tegmentum. Glycine is likely to be a transmitter in the ventral tegmentum and to have a role regulating the activity of somatodendritic regions of mesolimbic dopaminergic neurones.

The subnuclear organization of rat interpeduncular nucleus (IPN) has been examined by light microscopy following staining with Nissl and Holmes methods, 3H-leucine autoradiography, acetylcholinesterase (AChE), and cytochrome oxidase histochemistry on plastic sections stained with toluidine blue, and by electron microscopy. Three unpaired and four paired subnuclei are recognized. The rostral subnucleus is heavily stained for AChE, which clearly delineates its borders. It is distinguished ultrastructurally by two types of synapses on dendrites, and two on perikarya. Of the former, one type is formed by presynaptic processes which contain spherical and dense-cored vesicles and make asymmetrical contacts. Dense-cored vesicles are observed in many of the postsynaptic dendrites. A second type has presynaptic processes containing small, pleomorphic vesicles which make symmetrical contacts. Synapses on perikarya are found in the rostral, central, intermediate, lateral, and interstitial subnuclei. The dorsal subnucleus is continuous with the serotonin-containing B8 cells. The central subnucleus is distinguished by longitudinally oriented medial habenular axons separating palisades of cell bodies. These axons, which also traverse the intermediate subnuclei, form en passant S synapses with small dendrites of the central subnucleus. The intermediate subnuclei react faintly for AChE and intensely for cytochrome oxidase. They contain crest synapses formed by two habenular afferents, one from each medial habenula, which contact a narrow dendritic process en passant. The lateral subnuclei react intensely for AChE and have ultrastructural features similar to the rostral subnuclei. The interstitial subnuclei lie within each fasciculus retroflexus as it enters IPN. The small dorsal lateral subnuclei are evident by light microscopy.

We have investigated the interaction between opioid peptides and dopaminergic A10 (DA-A10) neurones in the ventral tegmental area (VTA). The behavioural consequences of VTA infusion of d-Ala-Met-enkephalinamide (DALA) were analyzed. DALA elicited a dose-dependent increase in locomotor activity measured in photocell cages and the circular corridor. Observations in the open field and in a hole box revealed that DALA-induced behavioural stimulation was characterized by enhancement of locomotion, rearing, and number of hole visits, while grooming time and duration of hole visits were decreased. DALA-induced stimulation was reserved by naloxone, and was completely blocked by 6-OHDA destruction of DA-A10 terminals. d-Amphetamine-induced behavioural activation was potentiated by simultaneous VTA infusion of DALA which indicates that the behavioural response to DALA is dependent on DA-A10 neuronal activity. It is postulated that stimulation of opiate receptors exerts a presynaptic inhibition of an inhibitory input to DA-A10 neurones (eg. GABA or dendritic DA), thus releasing dopaminergic activity. In contrast to the acute effect, the d-amphetamine response was strongly attenuated 4 h, 1 and 6 days after VTA infusion of DALA, and returned to normal only at 14 days. This long-lasting modification may reflect decreased activity of opioid neurones, releasing the inhibition of DA-A10 neurones. Our findings suggest that endogenous opioid peptides may exert a modulatory influence on the dopaminergic mesocorticolimbic system.

The greater activity of tyrosine hydroxylase (TH) in substantia nigra and corpus striata of adult BALB/cJ than CBA/J mice, is attributable to differences in the number of dopamine neurons in the ventral midbrain tegmentum. To determine if strain differences in TH activity develop postnatally we have measured the development of TH in the midbrain (SN) and in the corpus striatum (CS). In the midbrain neonatal TH activity was 20% of adult levels. Thereafter, TH activity increased rapidly achieving adult levels by 11 days. A 25%"overshoot' above adult values at 15 days was followed by a gradual decrease to adult activity at 4 weeks. In the CS neonatal activity was about 10% of adult levels and increased slowly to reach adult values at 4 weeks. Striatal choline acetyltransferase (CAT) activity in the neonate was only 3.7% of adult values and at 21 days had only reached 70% of adult activity. Neonatal glutamic acid decarboxylase (GAD) activity was relatively high in both brain regions and increased gradually to adult activity by 4 weeks. Strain differences in TH activity were not present at birth but first appeared at 9 days in SN and 11 days in CS. Once established, the differences were maintained. These results suggest that strain differences in TH are most probably a consequence of differences in postnatal neuron survival, although the possibility that some neurons lose their phenotypic expression of TH cannot be excluded.

1 Drug effects on dopamine catabolism of the mesolimbic dopaminergic pathway have been investigated using a sensitive radioenzymatic assay for 3,4-dihydroxyphenylacetic acid (DOPAC). 2 Turnover of DOPAC was less rapid in the ventral tegmentum (containing somata and dendrites) than in the nucleus accumbens (containing nerve terminals): 9 and 115 ng g-1 min-1 for ventral tegmentum and nucleus accumbens respectively. 3 Reserpine (5 mg/kg, 1 h) elevated DOPAC concentration to a greater extent in ventral tegmentum than in nucleus accumbens. 4 Neuroleptic drugs elevated DOPAC levels in ventral tegmentum and nucleus accumbens. Thioridazine, sulpiride and clozapine, thought to act preferentially on the mesolimbic system, caused a similar elevation in both brain regions. 5 gamma-Butyrolactone (750 mg/kg) caused a significant decrease in the DOPAC concentration in ventral tegmentum after 0.5 and 1 h, while DOPAC levels in nucleus accumbens were not significantly altered at these time intervals. 6 Similarities exist between the dopamine catabolism in somatodendritic and nerve terminal regions of mesolimbic dopaminergic neurones in the response to neuroleptic drugs, but differences in catabolism are evident following certain pharmacological treatments such as reserpine and gamma-butyrolactone. 7 Dopamine release occurs in the somatodendritic region of mesolimbic dopaminergic neurones and release sites may be dendritic as has been found for nigrostriatal dopaminergic neurones.

Using biochemical parameters the present study sought to assess the normal developmental pattern of the dopaminergic innervation of the olfactory tubercle (OT) and how it is affected by olfactory bulbectomy. In rats, the adult pattern of cellular organization is achieved in the OT gradually over the first 7 days after birth. On the other hand, tyrosine hydroxylase (TH) and [3H]dopamine ([3H]DA) uptake, while present at low levels, start to increase rapidly only after the first 7 days reaching adult levels by 40 and 20 days after birth, respectively. TH in dopamine (DA) cell bodies of A10 was already high, 40% of adult value, at birth, reached 150% by day 14 and decreased back to adult values by day 21 after birth. In 10-day-old rats, bulbectomy resulted, 30 days later, in an increase to 123% of control in TH activity and 137% in [3H]DA uptake within the OT. Comparable changes were found following bulbectomy in adults. However, bulbectomy in 1-day-old rats did not produce any significant changes 40 days later. The findings suggest that during postnatal growth TH activity is increased in DA cell bodies, preceding the changes in DA terminals of the OT, resembling the changes occurring during collateral sprouting in adults. In addition, changes indicative of collateral sprouting do not occur in response to deafferentation of the OT in 1-day-olds but do in 10-day-olds or older animals, a phenomenon probably related to a critical development period of the OT.

The specific activity of angiotensin converting enzyme (ACE) was studied in eight brain regions in rats 2--65 days of age. At 65 days of age the activities in various regions relative to the cortex were: neostriatum, 1,200%; hippocampus/amygdala, 430%; hypothalamus, 190%; cerebellum, 140%; and midbrain, thalamus and pons/medulla, 110%. Significant linear increases were found in the neostriatum, hippocampus/amygdala and cortex at 2--65 days of age, in the pons/medulla and thalamus at 2--42 days of age and in the midbrain at 2--21 days of age. The increase with age was greatest in the neostriatum and the data are consistent with the occurrence of ACE in neurons in this area.

Postmortem studies have revealed a state of chronic inflammation in affected regions of the brain in Alzheimer's disease (AD). Chronic inflammation can be damaging to host cells and the brain may be particularly vulnerable as neurons are not replaced. Evidence suggests that the inflammation is killing neurons in AD brain, so anti-inflammatory agents might slow the process of the disease. More than 20 epidemiological studies have shown that persons taking nonsteroidal anti-inflammatory drugs (NSAIDs) have a greatly reduced incidence of AD. In one clinical trial, indomethacin appeared to halt the progression of memory loss in AD patients. NSAIDs inhibit synthesis of prostaglandins, which are fringe players in the inflammatory process. Agents that would block the more important actors, such as the complement system, activated microglia and inflammatory cytokines, might have important therapeutic benefits in AD as well as in other conditions, such as heart disease and stroke, where inflammation also plays a deleterious role.

It has been established that neuroinflammation is present in the substantia nigra (SN) of Parkinson disease (PD) cases but the factors responsible are as yet unknown. One contributing protein may be the intercellular adhesion molecule-1 (ICAM-1, CD54). ICAM-1 with its counter receptor, the lymphocyte function-associated antigen 1 (LFA-1) is known to play a key role in inflammatory processes and in T-cell mediated host defense mechanisms. We detected large numbers of ICAM-1-positive reactive astrocytes in the SN of a series of 14 patients with neuropathologically confirmed PD, including 3 of familial origin, compared with 11 age-matched controls. In PD SN, these ICAM-1-positive reactive astrocytes were particularly concentrated around many residual neurons in areas of heavy neuronal loss and extracellular melanin accumulation. LFA-1-positive reactive microglia gathered in areas of intense ICAM-1 expression, and LFA-1-positive leukocytes were identified infiltrating the tissue. Double immunostaining for ICAM-1 and LFA-1 revealed aggregates of reactive microglia embedded in areas of diffuse ICAM-1. Leukocyte counts were 5 fold higher in PD SN compared to controls (P < 0.001). Similar over-expression of ICAM-1 was found in monkeys that had been exposed to MPTP from 5.5 to 14 years previously compared with control monkeys. The presence of ICAM-1-positive reactive astrocytes in Parkinson disease and MPTP-treated monkeys is indicative of a sustained inflammatory process and suggests that antiinflammatory agents may have a place in PD therapy.

Over the past fifteen years, evidence has been accumulating that there is a chronic inflammatory reaction in areas of the brain affected by Alzheimer's disease. Chronic inflammation, which arises in reaction to an underlying pathology, represents a threat in its own right, wherever it may occur, and can in fact surpass primary affronts upon tissues. The brain, however, is particularly vulnerable because neurons are generally irreplaceable. In the case of Alzheimer's disease, inflammatory processes thus have the potential for turning a relatively slowly progressing condition into one characterized by rapid neurodegeneration.